U. S. Coast Guard Research and Development Center

1082 Shennecossett Road, Groton, CT 06340-6096

Report No. CG-D-01-03 

CREW ENDURANCE MANAGEMENT PRACTICES 

A Guide for Maritime Operations 

Final Report 

January 2003 

This document is available to the U.S. public through the 

National Technical Information Service, Springfield, VA 22161 

Prepared for 

U.S. Department of Transportation 

United States Coast Guard 

Marine Safety and Environmental Protection (G-M) 

Washington, DC 20593-0001 
 iii 

 

N O T I C E 

This document is disseminated under the sponsorship of the 

Department of Transportation in the interest of information 

exchange. The United States Government assumes no liability 

for its contents or use thereof. 

The United States Government does not endorse products or 

manufacturers. Trade or manufacturers’ names appear herein 

solely because they are considered essential to the object of 

this report. 

This report does not constitute a standard, specification, or 

regulation. 

 

 Marc B. Mandler, Ph.D. 

 Technical Director 

 United States Coast Guard 

 Research & Development Center 

 1082 Shennecossett Road 

 Groton, CT 06340-6096 
 iv 

 

Technical Report Documentation Page 

1. Report No. 

CG-D-01-03 

2. Government Accession Number 3. Recipient’s Catalog No. 

4. Title and Subtitle 

CREW ENDURANCE MANAGEMENT PRACTICES: 

A GUIDE FOR MARITIME OPERATIONS

5. Report Date 

January 2003 

6. Performing Organization Code 

Project No 3302.7.1

7. Author(s): 

Carlos A. Comperatore, PhD; Pik Kwan Rivera

8. Performing Organization Report No. 

R&DC 209 

9. Performing Organization Name and Address 

U.S. Coast Guard 

Research and Development Center 

1082 Shennecossett Road 

Groton, CT 06340-6096

10. Work Unit No. (TRAIS) 

11. Contract or Grant No. 

12. Sponsoring Organization Name and Address 

U.S. Department of Transportation 

United States Coast Guard 

Marine Safety and Environmental Protection (G-M) 

Washington, DC 20593-0001 

13. Type of Report & Period Covered 

Final Report 

14. Sponsoring Agency Code 

Commandant (G-MSE) 

U.S. Coast Guard Headquarters 

Washington, DC 20593-0001 

15. Supplementary Notes 

The U.S. Coast Guard Headquarters point of contact is CDR Bryan Emond (G-MSE-1), 202-267-0177. The U.S. Coast 

Guard Research & Development Center’s point of contact is Dr. Carlos Comperatore, 860-441-2751. 

16. Abstract (MAXIMUM 200 WORDS) 

This guide presents a formal program of practices (the Crew Endurance Management System) for 

controlling risk factors that affect crewmember performance and shipboard safety in the commercial 

maritime industry. The CEMS program is overviewed; a real-world example is provided; techniques for 

managing crewmember energy and performance levels are provided; operational risk factors affecting 

crewmember energy and performance levels are addressed; procedures for implementing a CEMS program 

are described; and supplementary materials are provided. 

17. Key Words 

endurance, crew endurance, fatigue, stress, extreme 

environments, environmental stress factors, deep draft, 

shipping, commercial maritime, risk factors 

18. Distribution Statement 

This document is available to the U.S. public through the 

National Technical Information Service, Springfield, VA 

22161. 

19. Security Class (This Report) 

UNCLASSIFIED 

20. Security Class (This Page) 

UNCLASSIFIED 

21. No of Pages 

126 

22. Price 

Form DOT F 1700.7 (8/72) Reproduction of form and completed page is authorized.
 v 

 

FOREWORD 

In maritime operations, professional mariners are exposed to a variety of 

operational risk factors, including erratic work schedules, extreme 

temperatures, frequent separation from loved ones, and heavy workloads. 

These risk factors can have a negative impact on productivity and safety. 

The ability of crewmembers to cope with operational risk factors depends 

on their level of endurance. The responsibility for maintaining a high level of 

crew endurance rests with company officers, operation managers, safety 

and human resource managers, vessel captains, department heads, 

mates, as well as with crewmembers. 

This guide is specifically designed to help maritime companies ensure the 

highest possible levels of performance and safety. Users of this guide will 

be able to (1) identify specific factors affecting crew endurance in their 

particular operations, and (2) manage these factors toward optimizing 

crewmember endurance. 
 vi 

 

EXECUTIVE SUMMARY 

Normal maritime operations expose crewmembers to a variety of 

operational risk factors, such as irregular work periods, temperature 

extremes, heavy workloads, and extended separations from family 

members. Left unmanaged, these risk factors can degrade crewmember 

endurance, and thereby both performance and safety levels. 

In response to this situation, the U. S. Coast Guard has developed the 

Crew Endurance Management System (CEMS), a set of tools and 

practices maritime operators can use to manage productivity and safety 

levels in their operations. CEMS specifically helps operators identify the 

operational risk factors affecting crew endurance in particular situations, 

and to control these risk factors by means of proven practices and 

procedures. 

These proven practices and procedures apply to the full scope of 

endurance management, not simply to sleep management. In other words, 

crew endurance management encompasses the full range of 

environmental, physiological, operational, and psychological risk factors 

affecting performance and safety in normal maritime operations. 

Section I introduces the concept of Crew Endurance Management; Section 

II provides a quick, real-world example of a CEMS implementation; Section 

III describes how to use light-management techniques to match energy 

level with time-of-day workload; Section IV provides practical 

recommendations for controlling operational risk factors such as 

temperature extremes, stress, and caffeine use; and Section V describes 

how to design, implement, and evaluate CEM plans aboard maritime 

vessels. 
 vii 

 

CONTENTS 

 Page 

FOREWORD ........................................................................................... v

EXECUTIVE SUMMARY ........................................................................ vi

ACKNOWLEDGMENTS ........................................................................xiii

GLOSSARY........................................................................................... xv

About This Guide...................................................................................xix

Purpose.................................................................................................xix

Audience ...............................................................................................xix

Contents................................................................................................ xx

How to Use This Guide.......................................................................... xx

I. Managing Crew Endurance: A Quick Overview..................................3

Crew Endurance in Maritime Operations .................................................3

Crew Endurance Management ................................................................4

Managing the Red Zone .......................................................................4

Managing Endurance Risk Factors.......................................................7

CEM Implementation ...............................................................................8

Setting Up a Crew Endurance Working Group......................................8

Setting Up and Maintaining a Final Common Path ...............................9

II. Quick Example....................................................................................13

Phase I: Program Development.............................................................13

Setting Up a Working Group...............................................................13

Training the Working Group................................................................14

The Science of Crew Endurance Management................................14

The Process of Crew Endurance Management ...............................15

Analyzing the Current Situation ..........................................................15

Drawing Up a Crew Endurance Plan ..................................................19

Operational Recommendations .......................................................19

Environmental Recommendations ...................................................22

Phase II: Program Deployment..............................................................25

Training the Crew ...............................................................................25

Implementing the Plan........................................................................25

Enlisting the Support of the Crew ....................................................25

Making the Recommended System Modifications ...........................26
 viii 

 

Coaching the Crew..........................................................................26

Phase III: Program Assessment ............................................................26

Diet & Endurance Tips from the Captain................................................27

III. Managing the Red Zone ....................................................................31

The Red Zone........................................................................................31

The Red Zone and Energy ....................................................................32

What Energy Is and How It Is Produced .............................................32

How the Body Turns Food into Energy ...............................................34

When Energy Demands Outweigh Normal Production .......................34

Controlling Your Own Energy Level....................................................35

Controlling the Red Zone.......................................................................35

Managing the Biological Clock............................................................36

Optimizing Work Schedules................................................................37

Using Light Management Techniques.................................................39

General Recommendations .............................................................42

Watch Schedules.............................................................................43

Controlling Shiftwork Adaptation.........................................................44

Optimizing Adaptation to Shiftwork ..................................................45

IV. Controlling Performance Stressors in Maritime Operations..........49

Cold-Related Illness...............................................................................50

Causes ...............................................................................................51

Endurance Tips ..................................................................................51

Heat-Related Illness ..............................................................................53

Endurance Tips ..................................................................................55

Motion Sickness ....................................................................................57

Causes ...............................................................................................57

Endurance Tips ..................................................................................58

Stress ....................................................................................................59

Consequences....................................................................................60

Endurance Tips ..................................................................................60

Caffeine.................................................................................................63

Consequences....................................................................................63

Endurance Tips ..................................................................................63

V. Implementing a CEM Program...........................................................67

Phase I: Program Development.............................................................67

Setting Up a Working Group...............................................................67

Analyzing the Current Situation ..........................................................69
 ix 

 

1st Step: Receive Training in CEM Principles and Practices ............69

2nd Step: Identify System Areas of Risk ...........................................69

3rd Step: Identify Specific Risk Factors ............................................72

4th Step: Propose Modifications .......................................................74

Drawing Up a CEM Plan.....................................................................74

Agreeing on and Prioritizing Modifications .......................................75

Setting Up a Crew-Management Final Common Path .....................75

Phase II: Program Deployment..............................................................77

Phase III: Program Assessment ............................................................79

Summary ...............................................................................................80

A-1: Sleep Management ....................................................................... A-3

Sleep cycle.................................................................................... A-3

Everyday Sleep Management........................................................ A-4

A-2: Napping ......................................................................................... A-7

Pre-existing sleep loss................................................................... A-7

Nap length..................................................................................... A-7

Timing of the nap........................................................................... A-8

Length of time between end of nap and work period ..................... A-8

A-3: Circadian Rhythms ....................................................................... A-9

Physiology..................................................................................... A-9

Consequences of Desynchronosis ................................................ A-9

Desynchronosis Controls............................................................. A-10

A-4: Shiftwork, Sleep, and Biological Clock Management .............. A-15

Shiftwork Maladaptation .............................................................. A-15

Inconsistent sleep and daylight exposure reduce safety.............. A-16

Shiftwork maladaptation prevention............................................. A-18

B-1: References .................................................................................... B-3
 x 

 

LIST OF FIGURES

Figure 1. The Red Zone of energy and performance.................................5

Figure 2. Shifting the Red Zone fully into daylight hours ............................6

Figure 3. Operational components aboard example vessel......................16

Figure 4. The Red Zone of energy and performance...............................31

Figure 5. Food is broken down into energy substrates.............................34

Figure 6. Daily energy cycle as a function of time of day..........................37

Figure 7. Shifting the Red Zone toward daylight hours.............................40

Figure 8. Shifting the Red Zone into daylight hours..................................41

Figure 9. Fully-shifted Red Zone..............................................................42

Figure 10. Operational analysis ...............................................................70

Figure 11. Sleep cycle ........................................................................... A-4
 xi 

 

LIST OF TABLES

Table 1. Medications Used for Motion Sickness ...................................58

Table 2. Analyzing the Current Situation ..............................................69
 xii 

 

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 xiii 

 

ACKNOWLEDGMENTS

The authors wish to express their sincere appreciation to the 

organizations and colleagues listed below. These individuals and their 

organizations assisted in coordinating and performing activities that 

contributed to successful implementations of Crew Endurance practices in 

maritime environments, and to the production of this guide. 

Commercial Maritime 

American Commercial Line Washington State Ferries 

Kirby Inland Marine Keystone Shipping Company 

Ingram Barge Line Seabulk International, Inc. 

USCG Headquarters Office of Human Element and Ship Design 

(G-MSE-1)

CAPT Jeffrey Lantz 

Sponsor 

LT Scott Calhoun 

Sponsor/HQ Industry Liaison 

CDR Timothy Close 

Sponsor 

LT Sam Stevens 

Sponsor 

CDR Bryan Emond 

Sponsor 

USCG Headquarters Office of Safety and Environmental Health 

(G-WKS-3) 

Dr. Antonio Carvalhais 

Human Factors Expert 

CAPT Mario Fajardo, M.D. 

Medical Expert 
 xiv 

 

USCG Marine Safety Office Puget Sound 

CAPT Mike Moore LCDR Thomas Miller 

CAPT John Dwyer LT Vivianne Louie 

USCG Research & Development Center 

Jim Hazlin 

Coordinating Contract Officer 

Technical Representative 

Joy Simmons 

Chief, Contracting Office 

Leonard Kingsley 

Project Mgr. 

Susan Stevens 

Supply & Property Officer

Dinah Mulligan 

Contract Specialist 

Vonnie Summers 

Alternate Coordinating Contract Officer 

Technical Representative 

Contractors 

Tom Fitzgerald (PMG) 

Editor 

Luke Jadamec (Anteon) 

Field Technician 
 xv 

 

GLOSSARY 

Biological clock 

The ‘mechanism’ within the brain that regulates physiological and 

cognitive resources throughout the day. See also Circadian rhythms. 

CEM – see Crew Endurance Management 

CEM coach 

Person responsible for monitoring crewmember adherence to CEM 

practices, and for providing guidance and training when necessary. 

Circadian desynchronosis 

A syndrome characterized by jet lag-like symptoms induced by 

seeing light (natural or artificial) at inappropriate times of the day. 

Circadian dip 

A low point in the normal daily rhythm (cycle) of body energy and 

wakefulness. See also Circadian rhythm. 

Circadian rhythms 

The daily ebb and flow of body energy and alertness over the course 

of a 24-hour period. See also Biological clock. 

Coach – see CEM coach 

Crew Endurance 

The ability to maintain performance within safety limits while enduring 

job-related physical, psychological, and environmental challenges. 
 xvi 

 

Crew Endurance Management 

A system for managing the risk factors that can lead to human error 

and performance degradation in maritime work environments. 

Desynchronosis – see circadian desynchronosis 

Endurance risk factors 

Factors such as heavy workloads sleep debt, and caffeine addiction 

that can threaten operational safety and crewmember efficiency in the 

maritime industry. See also Performance stressors. 

Endurance – see Crew Endurance 

Final Common Path 

A CEM deployment strategy in which a team of onboard coaches 

monitors crewmember adherence to implemented CEM practices, 

and provided guidance and training when necessary. See also CEM 

coach. 

Insomnia 

Chronic inability to get to sleep and/or to remain asleep. 

Light management 

The practice of using a regimen of controlled light exposures to adapt 

the body clock for a new sleep-work schedule; that is, to shift the Red 

Zone. See also Red Zone. 

Lux 

Standard measurement for light intensity: one lumen per square 

meter. 
 xvii 

 

Maladaptation 

Shifting into a new sleep-work schedule without adjusting the 

biological clock. 

Performance stressors 

Factors such as motion sickness, psychological stress, and caffeine 

addiction that can individually or collectively have a severe impact on 

safety and endurance in maritime operations. See also Endurance 

risk factors. 

Protocol 

The plan or design for a scientific experiment or treatment. 

Red Zone 

The daily period of lowest energy and alertness, normally occurring 

between bedtime and sunrise. 

Risk factors – see endurance risk factors 

Sleep inertia 

The tendency, after awakening, to feel sleepy and sluggish. 

Synergistic 

Characterized by synergism, or the ability of two agents to create an 

effect neither agent is capable of creating on its own. 

Stamina 

Synonym for endurance. 

Stressors – see performance stressors 
 xviii 

 

Working Group 

A committee charged with the responsibility for implementing all 

aspects of a CEM program. 
 xix 

 

About This Guide

Purpose 

This guide is specifically intended to help maritime operators maximize 

crew performance and safety by identifying and controlling factors affecting 

crew endurance in normal operations. 

Audience 

This guide is intended for: 

• Boat captains, pilots, engineers, mates, and all crewmembers 

interested in safety and health 

• Dispatchers charged with distributing workload and assignment of 

personnel to fulfill operational demands 

• Trainers charged with teaching crewmembers about: (1) the harmful 

effects of normal operational risk factors on crewmember 

performance, and (2) how to control these risk factors 

• Company port captains and operations managers charged with 

maintaining operational safety 

• Coast Guard Marine Safety Offices 

PURPOSE: This guide provides proven practices for managing 

endurance risk factors (sleep loss, stress, heat, cold, etc.) that 

affect operational safety and crewmember efficiency in the 

maritime industry. 
 xx 

 

Contents 

Section I of this guide introduces the concept of Crew Endurance 

Management (CEM) and the factors (including the Red Zone, defined later) 

that degrade crew endurance. 

Section II provides a real-world example of a CEM program implemented 

on a maritime vessel. 

Section III describes and illustrates how to manage the Red Zone (daily 

period of least energy and alertness) toward optimizing crew endurance in 

maritime operations. 

Section IV provides specific guidance on how to control operational risk 

factors that can degrade crew performance and compromise shipboard 

safety. 

Section V provides practical recommendations on how to implement crewendurance management practices. 

How to Use This Guide 

Key concepts are highlighted in boxes. The information contained in these 

boxes is supported by the surrounding text. (Additional supporting 

information is available in the Appendices.) 

Of particular interest are the boxes labeled Management Nuggets, which 

contain key concepts for leaders and managers to use toward making 

immediate improvements in crew endurance. 

It is recommended you approach using this guide as follows: 

• First, scan the guide and read the key information in the boxes 

• Next, read the entirety of Sections I and II (Overview and Quick 

Example) 

• Finally, read the remainder of the guide 
 xxi 

 

This guide is not intended to replace guidelines currently in Oil Pollution Act 

of 1990 (OPA 90) or Standards of Training, Certification and Watchkeeping 

for Seafarers (STCW) regarding hours of work and rest. The fundamental 

purpose of this guide is to provide managers, captains, department heads, 

and officers with tools to manage normal operational risk factors that can 

degrade crew performance and compromise shipboard safety. 

Leaders should use this information, along with the guidelines provided in 

OPA 90 and STCW: 

• To identify risk factors affecting crew endurance in specific operations 

• To implement proven CEMS practices to control these risk factors 

The Crew Endurance Management practices provided in this guide, 

particularly those involving adaptation to nighttime work hours, work 

schedules, policy modifications, and vessel environmental improvements, 

were implemented during normal operations aboard vessels graciously 

made available to us by our partners in the Inland Towing Industry (refer to 

Acknowledgments). 
 xxii 

 

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1 

SECTION I 

Managing Crew 

Endurance: 

A Quick Overview 
2 

[This page left intentionally blank.] 
3 

I. Managing Crew Endurance: 

A Quick Overview 

This section (I) outlines how maritime operators can optimize performance 

and safety by managing risk factors affecting Crew Endurance. 

Crew Endurance in Maritime Operations

The 24-by-7 nature of the maritime industry exposes crewmembers to a 

number of risk factors (sustained wakefulness, temperature extremes, and 

unpredictable workloads, for example) that can degrade crew endurance –

that is, the physical stamina and mental alertness of the crew – and thereby 

performance and safety. 

Optimizing crew endurance on a 24-hour basis is a paramount goal within 

the maritime industry. 

While vessel endurance is a function of how long a vessel can support 

operations without replenishment or maintenance, crew endurance is a 

function of operational risk factors. These factors include the psychological 

state of crewmembers, their level of physical conditioning, their threshold of 

motion discomfort, the quality and duration of their sleep, their diet, and the 

stability of their internal timing system (biological clock). 

Each of these factors can degrade crew endurance by depleting 

crewmember energy stores or by reducing the level of crewmember 

alertness. The overall level of shipboard productivity and safety, therefore, 

depends on the overall level of crewmember endurance. 

BASICS: Crew Endurance refers to the ability to maintain 

performance within safety limits while enduring job-related 

physiological, psychological, and environmental challenges. 
4 

The Crew Endurance Management (CEM) practices provided in this guide 

are intended to help maritime operators optimize crew endurance by 

helping them identify and manage specific risk factors, such as stress and 

temperature extremes, affecting their operations (see Section IV). 

Crew Endurance Management 

Crew Endurance Management is a formal program of proven practices for 

optimizing crewmember productivity and safety by means of: 

• Managing the Red Zone (daily period of lowest energy) of 

crewmembers 

• Controlling endurance risk factors 

Managing the Red Zone

The human body is naturally oriented toward expending energy during 

daylight hours and resting (restoring energy) during nighttime hours. The 

amount of energy available over a 24-hour period, therefore, normally 

peaks in daylight and bottoms out in darkness. Because performance tends 

to correlate with available energy, the human body tends to function most 

efficiently in daylight, when the energy level is highest, and least efficiently 

in darkness, when the energy level is lowest. 

In this guide, the daily period of lowest energy and performance is referred 

to as the Red Zone. See Figure 1. 

Basics: Ambient temperature, humidity, light, noise, and 

vibration are examples of environmental risk factors that can 

degrade stamina and alertness, and thereby both productivity 

and the safety of operations. Another category of risk factors 

includes company policies and shipboard practices. A third 

category includes work-related stress, irregular sleep periods, 

and adverse working conditions. 
5 

 

 

Figure 1. The Red Zone of energy and performance 

For crewmembers accustomed to sleeping at night (typically 2300-0700), 

energy and alertness increase steadily throughout the early morning hours, 

reach a daily peak near mid-morning (1000), dip in the afternoon (1300-

1600), increase again to another daily peak in the early evening (around 

1800), and then decrease steadily during the night, reaching a daily low in 

the early morning hours (approximately between 0300 to 0500). 

The Red Zone is defined as the daily period when energy and alertness 

are at their lowest levels, typically spanning from bedtime to sunrise, with 

the most-critical period spanning from 0300 to sunrise. In the case 

illustrated in Figure 1, the full Red Zone spans from 2100 until 07001

. 

Several factors can influence the duration as well as the intensity of 

individual Red Zones, including crewmember sleep, social, and dietary 

habits; the current period of sustained wakefulness; and accumulated sleep 

debt. 

 

1

 Red Zone time frames tend to vary with the chronotype of the individual, with some individuals being 

prone to sleep late into morning hours; others, to wake up with the birds. 

 Time of Day 

E

n

e

r

g

y

 1200 2100 0700 

 Daylight Daylight 
6 

Although nighttime is usually considered a period of increased operational 

risk, proven light-management techniques can be used to cause 

crewmember energy and alertness levels to peak during nighttime hours 

instead of during daylight hours. In other words, the Red Zone of individual 

crewmembers can be shifted, as needed, to accommodate 24-by-7 watch 

and workload schedules. See Figure 2. 

Figure 2. Shifting the Red Zone fully into daylight hours 

Figure 2 shows the Red Zone being shifted into full daylight hours to 

accommodate sleeping during the day versus at night. The three 

bars/arrows indicate the amount of relative shift realized by applying lightmanagement techniques (discussed in Section III) over three different 

periods of time. (Note: If sunrise occurs prior to 0700, daylight may be 

used for light management once it is of sufficient intensity.) 

Time of Day 

Days 1-2 

Days 3-4 

Days 5-6 

Artificial (or Natural) Light

E

n

e

r

g

y

1200 2100 0200 0700 1200 

1200 2100 0200 0700 1200 
7 

Managing Endurance Risk Factors

As previously mentioned, risk factors encountered in normal maritime 

operations can degrade crew endurance. The following endurance risk 

factors are discussed in detail in Section IV of this guide: 

• Cold-related illness 

Heat & energy loss, hypothermia, frostbite 

• Heat illness 

Dehydration, loss of the minerals needed to maintain normal body 

function 

• Motion sickness 

Dizziness, performance degradation, headaches, nausea, vomiting, 

sleep loss, and fatigue 

• Psychological stress 

Flight-or-fight anxiety, burnout 

• Excessive caffeine use 

Energy drain, anxiety, sleep loss 

• Improper use of over-the-counter medications 

Drowsiness, reduced alertness, reduced performance 

CAUTION! Light Management involves being exposed to 

measured amounts of ambient light of a specific intensity and 

wavelength (color). Light Management does not involve staring 

into naked light bulbs. 
8 

CEM Implementation 

A CEM program can be applied to a particular vessel, a particular 

operation, or a particular industry. In all cases, however, implementing a 

CEM program requires: 

• Setting up a Crew Endurance Working Group (CEWG) 

• Setting up and maintaining a crew-management Final Common 

Path

Setting Up a Crew Endurance Working Group

The Crew Endurance Working Group (CEWG) is responsible for all aspects 

of implementing a CEM program, including: 

• Identifying the relevant endurance risk factors 

• Creating a collaborative network of participants 

• Devising and deploying a specific CEM plan 

To be effective, a Crew Endurance Working Group must include or 

represent all those individuals who stand to be affected by the 

implementation of a CEM program. A CEWG typically consists of the 

following individuals: 

• One or two company officers 

• The company operations manager 

• The captain of the vessel 

• The pilot, the bridge personnel, or both 

• The department chiefs 

• The first mate, the engineer, or both 

• One or more deckhands 
9 

Setting Up and Maintaining a Final Common Path

In order for a CEM program to succeed, a CEM Final Common Path must 

be established and maintained. A Final Common Path consists of the 

following key elements: 

• Setting up a team of onboard coaches to train crewmembers on the 

science and practices of CEM, and to serve as program models and 

monitors 

The team of coaches must include the captain, the pilot or bridge 

personnel, and the first mate. Where available, it should also include 

the department chiefs. 

• Training the coaches in the science and practices of CEM 

Training for coaches is provided by company management, typically 

using resources available from the U.S. Coast Guard Human Element 

and Ship Design Division (202-267-2997). 

• The coaches train the crewmembers in the science and practices of 

CEM, model the required practices, and monitor crew adherence to 

these practices 

Experience has demonstrated that, to implement a CEM program 

successfully, it is not sufficient simply to add more personnel or to modify 

watch schedules. CEM implementation will invariably fail if a crewmanagement Final Common Path has not been set up and practiced 

in the prescribed order: (1) to teach crewmembers how to take 

advantage of working conditions, as well as how to use lightmanagement techniques, and (2) to ensure that appropriate 

environmental changes have been made (for example, to control 

noise and light in sleeping quarters). 

Engrained habits used to cope with work and life aboard a maritime vessel 

will not change unless individual crewmembers are: (1) given a realistic 

opportunity to change their habits, and (2) make daily efforts to change 

their habits and take advantage of improved shipboard working conditions. 

Old habits die hard! 

Section V discusses CEM implementation in detail. 
10 

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 11 

SECTION II 

Quick Example 

 
12 

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13 

II. Quick Example 

This section (II) provides an example of a Crew Endurance Management 

(CEM) program implemented on a commercial maritime vessel. 

The operators and crew of the example vessel implemented their tailormade CEM program in three phases: 

Phase I: Development 

Phase II: Deployment 

Phase III: Assessment 

This section describes these three phases in detail. 

Phase I: Program Development 

The process of developing a tailor-made CEM program for the example 

maritime operation consisted of three critical tasks: 

• Setting up and training a Working Group 

• Analyzing the current situation 

• Drawing up a CEM plan 

Setting Up a Working Group

A Working Group was set up: (1) to identify and assess the risk factors 

currently affecting crew endurance on the example vessel; and (2) to make 

appropriate recommendations concerning controlling these risk factors. 

Members of the Working Group were selected by the operating company 

and consisted of personnel who would be directly or indirectly affected by a 

CEM program implemented aboard the example vessel: 

• The Company Safety Manager 
14 

• The Company Operations Manager 

• The Vessel Captain 

• The Vessel Pilot 

• The Vessel First Mate 

• The Vessel Deckhands 

Note: Because the Head Cook is likely to be considered unbiased, in being 

outside the chain of command, he or she is often a good choice for the 

CEWG, as is the Chief Engineer, who would likely be responsible for 

implementing any environmental changes decided on. 

Training the Working Group

Before beginning their work, the Working Group members received 

professional training on the following: 

• The science of Crew Endurance Management: The major 

environmental, operational, psychological, and physiological factors 

that affect crew endurance (physical stamina and mental alertness). 

• The process of Crew Endurance Management: The procedures 

and tools commonly used for assessment and implementation. 

The Science of Crew Endurance Management 

The USCG R&D Center CEM team provided the Working Group with 

training on the following crew endurance topics: 

• Sleep and shiftwork 

• Light management and the body clock 

• The Red Zone and its impact on performance 

• Stress 

• Caffeine and the use of over-the-counter medications 
15 

• Diet 

• Cold-related illness 

• Heat-related illness 

• Motion sickness 

The Process of Crew Endurance Management 

The USCG CEM team trained members of the Working Group on how to 

deal with cultural barriers (‘This is the way we’ve always done it’; ‘Don’t fix it 

if it ain’t broke’), and how to identify and assess the risk factors affecting 

crew endurance. 

In addition, the CEM team trained crewmembers in the use of riskassessment tools to determine which endurance risk factors were present 

in daily operations. 

Analyzing the Current Situation

The Working Group studied the example vessel’s operational system and 

broke it down into its major components; identified the relationships 

between these major components; and isolated specific elements within 

each component that were currently affecting crewmember endurance. See 

Figure 3 and the following legend and table. 
16 

Figure 3. Operational components aboard example vessel 

Figure Legend:

Company 

Workload 

The accepted number of jobs at the company level. 

Weather Inclement weather can delay or stop operations. 

Workload Heavy workloads require more energy per hour 

from crewmembers. 

Individual 

Choices

Workload

Work Schedule Diet

Company 

Workload

Route

Workforce 

Weather 

Company Policies

Regulatory 

ENDURANCE

Shipboard 

Environment Training
17 

Company 

Policies 

Company policies can affect efforts by 

crewmembers to maintain endurance. 

Shipboard 

Environment 

Factors such as noisy, fumy, and light-porous 

quarters can disrupt sleep. 

Training The amount and focus of crew training can affect 

stamina and alertness factors. 

Work Schedule Long or erratic work schedules can leave 

inadequate time for sufficient sleep. 

Diet How much, what, and when crewmembers eat 

affects energy, mood, stamina, and sleep. 

Individual 

Choices 

Individual choices (for example, watching TV during 

a sleep period) can affect stamina and alertness. 

Route Routing can determine the type of work and the 

work schedule. 

Workforce The number of personnel allotted to each vessel 

can affect the watch regime used. 

Regulatory Coast Guard regulations determine the maximum 

number of work hours per 24-hour day. 

 

The Working Group identified the following specific factors (grouped by 

operational component) that appeared to be affecting crew endurance 

aboard the example vessel: 

Work Schedule The current watch schedule was not 

allowing crewmembers sufficient 

opportunity to obtain the 7-8 hours of 

daily uninterrupted sleep required to 

maintain endurance. 
18 

Diet Crewmembers were eating large 

meals immediately before going to 

bed after watch. Crewmembers were 

consuming large quantities of caffeine 

throughout the day, even close to 

bedtime. 

Individual Choices Crewmembers were consuming 

coffee throughout watches; staying up 

to watch TV, play games, or make 

lengthy phone calls; asking to be 

awakened an hour or more before a 

watch change. 

Crewmembers were being kept 

awake by noises associated with 

crews handling rigging near the 

vessel; slamming doors or banging 

manhole covers; and using 

televisions, radios, hand-held VHF 

radios, etc. at high-volume levels. 

Vessel Environment Crewmembers were being awakened 

by sudden movements of the vessel. 

Crewmembers were being kept 

awake by light entering crew quarters 

through windows and door louvers, 

and by engine-room noise. 

Crew-quarters lights were not 

sufficiently bright for crewmembers to 

adapt to day or night work hours or to 

become alert quickly upon waking. 

Fumes from the diesel engines were 

sometimes entering into staterooms, 

causing discomfort. 
19 

Company Policies Crewmembers were accumulating 

sleep debt because of the ‘no 

napping’ policy. 

Crewmembers were being delayed 

from sleep time by not being able to 

take meals or showers until after 

watch change. 

Drawing Up a Crew Endurance Plan

On the basis of their analysis, the Working Group drew up a list of specific 

recommendations. These recommendations fell into two major categories: 

• Operational recommendations 

• Environmental recommendations

Operational Recommendations 

The Working Group recommended the following operational changes: 

New watch schedule: 

A new watch schedule was designed to meet the following criteria: 

- Crewmembers should have enough time off to obtain 7-8 hours of 

uninterrupted sleep per 24-hour period 

- If unable to obtain 7-8 hours of uninterrupted sleep per 24-hour 

period, crewmembers should have enough time off to obtain at 

least 61⁄2 hours of uninterrupted sleep, as well as a nap of no less 

than two hours, per 24-hour period 

- Crewmembers working at night should be able to maintain the 

same work-rest schedule for at least two continuous weeks 

- Schedule rotations from day to night, or from night to day, should 

be minimized in order to avoid body clock and sleep cycle 

desynchronization (a condition similar to jet lag) 
20 

- Work periods should be no greater than eight continuous hours, 

particularly when prolonged exposures to extreme temperature or 

humidity levels (see Section IV) are involved 

- Environmental light-management techniques should be used to 

adapt crewmembers to night watch (see Section III) 

The major rationale for the new watch schedule was that it allowed 

crewmembers to get up to 61⁄2 hours of uninterrupted sleep during the 

long off-periods, plus a 2- to 3-hour nap during the short off-periods. 

The Working Group members had learned in their CEM training that 

the average adult requires approximately 7 to 8 hours of 

uninterrupted sleep per 24-hour period, and that overall sleep quality 

is best when the daily sleep periods are uninterrupted and extended 

over long stretches. 

The Working Group members also learned in their CEM training that 

it is critically important to use light-management practices in 

conjunction with implementing a new watch schedule, particularly 

when night work is involved. 

New light-management policies 

New light-management polices were implemented to help Night 

Watch and Day Watch crewmembers manage their Red Zone (period 

of lowest energy and alertness). These policies included: 

Basics: Daily sleep requirements vary: While elementary 

students normally require 10-12 hours/day, pre-teens 9-11 

hours, teens 81⁄2-10 hours, most adults normally require 7-8 

hours/day. The operational rule is: If following your 

customary sleep period you feel sleepy during the 

subsequent afternoon period, then you need more sleep. 
21 

- Crewmembers on Night Watch were asked to go to sleep in a 

totally dark environment after getting off watch in the morning, and 

to avoid light until they were called to report for their first watch of 

the day. 

- Day-watch personnel were asked to sleep in a darkened 

environment and to avoid lighted common areas immediately 

preceding bedtime and throughout their sleep period. 

New time-management policies 

The following new meal and shower policies allowed the crew to take 

maximum advantage of their sleep opportunity: 

Policy: Out-of-schedule showers will be allowed. However, 

crewmembers will be expected to discuss any work to be completed 

before taking early showers. An early shower does not relieve anyone 

of any duties to be performed on watch. 

Policy: Out-of-schedule meals will be allowed, provided they do not 

interfere with the cook’s schedule. 

Policy: Crewmembers coming on watch will be given priority seating 

at meal times. 

New watch policies 

The following new watch policies helped prevent crewmember sleep 

debt. 

Policy: On-watch napping will be allowed when prudent and 

practical. 

Policy: On-watch napping will be allowed between 2300 and 0400, 

and between 0530 and daylight. Exceptions can be made when 

circumstances warrant; for example, following strenuous or lengthy 

duties, or recent travel. 

Policy: No napping will be allowed until all necessary work is 

completed. 
22 

Policy: On-watch napping will be used to supplement, not substitute 

for, normal off-watch sleep periods. 

Policy: On-watch napping will be limited to approximately one-half 

(1⁄2) hour per crewmember, per night. 

Policy: During watch, at least one crewmember must be awake at all 

times. 

Policy: Before on-watch napping, a crewmember must inform the 

remaining crew of his or her location. 

Policy: Usual and standard on-watch practices will be maintained. 

Environmental Recommendations 

The Working Group recommended a set of boat policies and physical 

alterations toward enhancing sleep quality: 

New shipboard policies 

Policy: Common courtesy by crewmembers on duty will be exercised 

at all times toward crewmembers off duty. 

Policy: Pilothouse personnel will actively avoid rapid changes in 

throttle settings to the extent possible. 

Policy: Deck crew will actively minimize noise associated with the 

performance of their duties. This will include handling rigging with 

care near the vessel. 

Policy: Crewmembers will avoid slamming doors or banging manhole 

covers, and will keep televisions, radios, hand-held VHF radios, etc. 

to mutually acceptable volume levels. 

Physical changes 

Problem: Stateroom doors have louvers to accommodate return 

airflow for HVAC. These louvers also allow an 

unacceptable level of noise and light to enter the room. 

Recommendation: Install baffles that allow airflow while restricting 

noise and light, on all stateroom doors. 
23 

Problem: Blinds over exterior windows in staterooms do not 

adequately restrict light. 

Recommendation: Install slide panels in all staterooms to replace 

blinds. 

Problem: Stateroom lighting may be inadequate for entraining and 

adapting the body clock. Brighter lights can help 

crewmembers become alert more quickly after waking. 
24 

Recommendation: Install 48”, 4-tube, fluorescent fixtures using 

“daylight” bulbs. 

Problem: Interior entry from living quarters to engine room is a 

single door, allowing noise to enter living quarters. 

Recommendation: Install a second door to create a better sound 

barrier. 

Problem: Smoke from the diesel engines sometimes penetrates 

into staterooms causing discomfort. 

Recommendation: 

- Replace the plywood sealing the exterior HVAC fan enclosure with 

electrostatic air filters. 

- Install reusable electrostatic filters in 1st and 2nd deck return-air 

vents. 

- Install HEPA/HEGA or ionizing air purifiers, or both, in staterooms. 

- Seal all leaks currently allowing exhaust smoke to enter living 

quarters.
25 

Phase II: Program Deployment 

The process of deploying the CEM program on the example vessel 

consisted of the following: 

• Training the full crew 

• Implementing the final CEM plan 

Training the Crew

A USCG CEM team trained the crew of the example vessel in sleep and 

body-clock management, stress management, time management, and 

other crew-endurance practices during a day-and-a-half workshop. 

The example vessel’s CEM coaches reinforced this initial training with 

ongoing training during normal operations. 

Implementing the Plan

The process of implementing a CEM program consisted of the following: 

• Enlisting the support of the full crew 

• Making the recommended system modifications 

• Coaching the crew toward consistency 

Enlisting the Support of the Crew 

The crewmembers were provided key information and training on CEM 

(benefits, factors, procedures, options, etc.), and were presented with the 

Working Group’s CEM plan and the underlying rationale for each of its 

features. It was emphasized that changes were not being recommended 

merely for the sake of making changes, and that legacy systems were not 

necessarily the best possible systems simply because they had been in 

place for a long period of time. 

Crewmembers were encouraged to suggest improvements to the Working 

Group’s CEM plan and to support the final plan. 
26 

Making the Recommended System Modifications 

The working group, together with company management and the example 

vessel’s own endurance coaches (Captain, Pilot, and Mate), ensured that 

all of the system modifications recommended in the final CEM plan were 

made. 

These modifications involved changes in watch schedule, physical changes 

to crewmember quarters, dissemination of new onboard policies, and 

requests to the crew for changes in personal choices (relative to the use of 

caffeine and over-the-counter drugs, for example). 

Coaching the Crew 

The captain, pilot, and first mate of the example vessel were enlisted and 

trained to serve as onboard CEM coaches. The responsibilities of the 

coaches included: 

• Training individual crewmembers in CEM practices 

• Serving as models of CEM practice for crew emulation 

• Actively encouraging crewmembers to follow CEM practices 

• Monitoring and enforcing adherence to the policies and procedures of 

the CEM plan 

Note: The Working Group consistently supported all aspects of crewendurance management aboard the example vessel. 

Phase III: Program Assessment 

At various times during the implementation phase, the program was 

assessed as follows: 

Caution! Crewmember buy-in is as critical to the success of a 

CEM program as is management buy-in. No buy-in, no success. 
27 

• Crewmembers on the After Watch provided saliva specimens to 

measure adaptation to nighttime watch hours 

• Crewmembers performed vigilance tasks to measure alertness 

• Crewmembers completed computerized subjective questionnaires 

Crewmembers who used light management consistently showed hormone 

(melatonin) levels typical of a well-adapted body clock, and experienced 

minimal lapses in alertness during the work hours following the long offperiod. 

Diet & Endurance Tips from the Captain 

Here, in brief, is what the Captain of the example vessel, in his words, 

“preaches to his crew” concerning diet and endurance: 

“The common diet aboard our vessels is extremely high in salt. This is due 

to a generalized use of canned and processed foods, and of condiments; 

crew preference; and the background of the cooks. Except in extreme 

cases, therefore, supplementing dietary salt requirements with salt tablets 

or the like is not necessary. 

Water. There is no substitute. The amount of water absorbed from many 

flavored drinks, tea, carbonated drinks, and the like is diminished because 

the body uses a percentage of the water in the drink to flush the artificial 

flavors, artificial colors, et cetera out of the body. Some of the drinks 

themselves act as a diuretic. High sugar content can reduce magnesium 

absorption and thereby prevent calcium from being used efficiently. 

 I strongly recommend improving on the intake of potassium. The published 

recommended allowance for potassium is 1600 to 3500 mg/day. 

Crewmembers doing heavy work in heat, and sweating, require much more 

than this recommended allowance. I do not believe in the hyped benefit of 

most commercial sports drinks. As an example, the potassium content in 

Gatorade is about 25 mg/8oz., in Sqincher mix, about 50 mg/8oz., whereas 

grapefruit juice contains nearly 300 mg/8oz., orange juice about 450 

mg/8oz.; V-8 Splash, 80 to 140 mg/8oz.; V-8 vegetable juice, over 500 

mg/8oz.; and bananas, about 480 mg each. 
28 

 By advising that my crewmembers actively increase their intake of water 

and juices, in addition to whatever other drinks they choose, I hear of fewer 

complaints of heat-related problems such as leg cramps, heat chills, 

muscle tremors, or heat-caused weakness.” 
 29 

SECTION III 

Managing the 

Red Zone 
30 

[This page left intentionally blank.] 
31 

III. Managing the Red Zone 

This section (III) describes and illustrates how to manage the Red Zone 

toward optimizing crew endurance in maritime operations. 

The Red Zone 

Performance (endurance) varies with the level of available energy, which 

itself, because of natural body rhythms, normally varies in a predictable 

pattern over the course of each 24-hour period. See Figure 4. 

 

 

Figure 4. The Red Zone of energy and performance

For crewmembers working days and sleeping nights, energy and 

performance tend to peak during the daylight hours, and to bottom out 

during the dark nighttime hours. 

 Time of Day 

E

n

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g

y 

 1200 2100 0700 1200

 Daylight Daylight 
32 

The term Red Zone is often applied to the nighttime period of lowest 

energy and performance, because this is the portion of each day during 

which degraded endurance is most likely to have a negative impact. For a 

person who sleeps 7 to 8 hours per night, the Red Zone typically begins at 

about bedtime (2100 hours in our example) and lasts through the nighttime 

hours (until about 0700 in the example), with the most-critical period 

spanning from 0300 to sunrise. See Figure 4. 

Several factors can influence the duration as well as the intensity of 

individual Red Zones, including crewmember sleep, social, and dietary 

habits; the current period of sustained wakefulness; and accumulated sleep 

debt. 

 

The Red Zone and Energy 

The Red Zone is a function of energy level. It is important, therefore, to 

understand how energy is produced, how it affects endurance, and how it 

can be increased or decreased in certain situations. 

What Energy Is and How It Is Produced

Production of molecules called adenosine tri-phosphate (ATP), found in all 

cells of the body, plays a key role in the production of energy. The amount 

of ATP produced by the body depends on good nutrition, adequate 

FACT: Energy comes from the Greek word energia, or ‘in-work’; 

it refers to the capacity to do work. 

BASICS: As sleep debt (getting less than 7-8 hours of sleep per 

day) increases over consecutive days, the Red Zone can 

expand into the morning, afternoon, and evening hours. 
33 

hydration (water intake), oxygen, and (perhaps most important of all) 

sufficient sleep. 

Studies of brain function have shown that seven to eight hours of 

continuous sleep are necessary for the body to produce a sufficient 

amount of ATP to restore depleted energy supplies. If the body does not 

produce sufficient ATP, and thereby sufficient energy, the brain and the 

nervous system cannot function efficiently, causing crewmembers to: 

• Think less clearly 

• Make poor decisions 

• Become irritable 

• Have problems communicating with others 

• Experience degraded endurance throughout work and leisure hours 

• Become withdrawn and less willing to resolve issues and problems 

• Have less ability to fight disease 

Unfortunately, ATP cannot be consumed as a dietary supplement; it must 

be produced within cells in the body. Regardless of how hard people might 

try to compensate for lack of energy, their ability to carry out both physical 

and mental tasks is reduced. This reduction in energy compromises their 

safety as well as the safety of those around them. 

 Adenosine Tri-Phosphate molecules: 

 ATP = ENERGY 
34 

How the Body Turns Food into Energy

The digestive system breaks food down into carbohydrates, proteins, and 

fats, which are then converted, by enzymes, into energy substrates: 

glucose (sugar), amino acids, and fatty acids. These substrates are then 

processed within individual cells into ATP (= energy). See Figure 5. 

Figure 5. Food is broken down into energy substrates 

When Energy Demands Outweigh Normal Production

Chronic stress and sleep disruption tend to deplete energy resources and 

to degrade endurance. This depletion of energy and endurance is harmful 

to crew health and safety in its own right; it can also cause crewmembers 

to make a bad situation worse by inclining them toward using artificial 

means to increase alertness. 

The most common of these artificial means to increase alertness is the use 

of stimulants such as caffeine (found in coffee, soft drinks, and chocolate) 

and pseudoephedrine (found in cold and allergy medications). 

High doses of caffeine, however, can result in increased anxiety, lack of 

concentration, and digestive disorders; frequent use can lead to addiction 

Carbohydrates

Proteins

Fats

Glucose

Amino Acids

Fatty Acids

Substrates 

+ 

Oxygen 

ATP

Caution! Be cautious of products that claim to boost energy 

resources. These products can provide dietary input to the 

energy-producing machinery, but they cannot produce energy. 

The only way to produce energy is through sufficient sleep, 

adequate water intake, a balanced diet, a stable body clock, and 

regular exercise. 

Food 
35 

as well as an even further depletion of energy resources. And, while drugs 

such as pseudoephedrine and ephedrine can maintain alertness, they can 

also become addictive, and they can have adverse side effects as well. 

There are ways of controlling our energy level that do not rely on caffeine 

or drugs. Some of these ways are suggested in the next section. 

Controlling Your Own Energy Level

Here are a few tips on how to control your daily energy level: 

• Exercise daily; any simple form of regular exercise helps: a 20-minute 

walk, running, weight lifting, 10-minute aerobic workouts, etc. 

• Consume a balanced diet: low sugar, low fat, low starch, high in 

green and yellow vegetables, high in chicken, turkey, and fish (no 

turkey before watch, however, as it can cause sleepiness) 

• Get sufficient sleep: 7-8 hours of uninterrupted sleep daily 

• Use relaxation methods to reduce stress at the individual level 

• And remember...ATP = ENERGY 

Controlling the Red Zone 

The human brain requires approximately seven to eight hours of 

uninterrupted sleep daily in order to replenish mental and physiological 

resources. 

CAUTION! All medications containing pseudoephedrine warn 

against chronic use. In fact, most recommend discontinuation 

after three days of continuous use, and always recommend 

supervision by a physician. Be sure to read the label to see if your 

medication contains pseudoephedrine. 
36 

During sleep, the brain cycles through successive periods of light sleep, 

deep sleep, and dream sleep. These cycles require approximately 90-120 

minutes to complete, and are repeated throughout the night. Any 

interruption to these cycles by noise, bright lights, or sudden movements 

causes the brain to spend more time in light sleep, less time in deep and 

dream sleep. 

Sleep disruption reduces the effectiveness of energy restoration processes 

and ultimately results in degraded endurance. A disruption resulting in full 

wakefulness will cause the brain to start the sleep cycle from the beginning, 

such that the entire cycle may not be completed. 

Managing the Biological Clock

Optimally, sleep must take place during a period of time established by our 

internal biological clock. This clock is a physiological mechanism – 

composed of neural networks and hormonal outputs – that regulates the 

timing of sleep onset and wake-up, as well as the availability of energy 

resources (see Appendix A for details). The body’s biological clock 

maintains a sleep/wake schedule in synchronization with local sunrise, 

sunset, and daylight duration. Because we are naturally inclined to sleep 

CAUTION! Energy is restored optimally during uninterrupted 

sleep periods of 7 to 8 hours, with the sleeper reclined on a 

comfortable mattress in dark and quiet room at 65 - 70 F and 60 -

70% humidity. 

BASICS: Daily sleep requirements vary: While elementary 

students normally require 10-12 hours per day, pre-teens 9-

11 hours, teens 81⁄2-10 hours, most adults normally require 

7-8 hours per day. The operational rule is: If following your 

customary sleep period you feel sleepy during the 

subsequent afternoon period, then you need more sleep.
37 

during nighttime hours, and to expend energy during daylight hours, the 

human biological clock reflects this same cycle. 

The biological clock regulates energy cycles so that alertness increases 

after wake-up time, peaks in the mid-morning hours, dips through the latemorning and early-afternoon hours, peaks again in the early-evening hours, 

and then decreases throughout the late-evening and early-night hours, 

reaching a daily low in the middle of the night (see Figure 6 below). The 

exact times of these peaks and valleys depend on specific inputs to the 

biological clock system, namely wake-up times, bedtimes, and daily interval 

of daylight (or artificial bright light) exposure. 

Figure 6. Daily energy cycle as a function of time of day 

Optimizing Work Schedules

Work schedules that impose frequent changes from daytime to nighttime 

duty hours tend to disrupt energy restorative processes and to degrade 

100%

 50%

0%

FACT: Personnel adhering to regular work schedules that 

provide day-to-day consistency enjoy the benefits of a welladapted biological clock. A well-adapted clock ensures that daily 

energy restorative activities occur on a regular basis. 

E

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1200 2100 0700 1200 

Daylight Daylight 
38 

endurance. The same is true of work shifts greater than 12 hours within a 

24-hour period. 

Disruptions to the established rhythm of the biological clock can also 

degrade alertness and performance. For instance, if a person wakes up for 

work at 0600 over a period of five consecutive days, the biological clock will 

adjust itself to waking up at 0600. If this person then sleeps in on the 

weekend, say to 0830 each day, a conflicting signal will be sent to the 

biological clock, because the person is now sleeping past the previously set 

wake-up time of 0600. The biological clock will actually begin to adjust to 

the 0830 wake-up time, thereby disrupting the previously set rhythm, and 

degrading the level of wake-up alertness and performance. 

Changes in the body’s timing mechanism affect the normal regulation of 

physiological functions such as core body temperature, cellular 

metabolism, and production and release of hormones and neurotransmitters. 

In general, the biological clock system requires approximately two to three 

days to fully adjust to a new sleep schedule (e.g., a wake-up time that is 

two hours later). This readjustment will take place most efficiently if the new 

sleep schedule is consistent from day to day. If the changes are 

inconsistent, however, the clock’s timing can become disorganized in such 

a way that the physiological functions under its control no longer occur in a 

predictable pattern. 

 

Inconsistent inputs to the biological clock are common when personnel 

work night shifts. Night personnel typically work in normal or dim (artificial) 

light environments during most of their shift (e.g., on the bridge). Instead of 

being protected from bright natural light after sunrise, however, they are 

fully exposed to it. Hence, rather than their biological clock receiving a 

FACT: Inconsistent inputs to the body clock can result in: 

 Sleepiness during work hours 

 Paradoxical feelings of fatigue: feeling too tired to rest 

 Lack of mental clarity 

 Degraded physical ability 
39 

sleep signal following their shift, it receives the opposite signal and 

responds accordingly, often producing jet-lag-like symptoms. 

Personnel accustomed to waking up and seeing daylight at approximately 

the same time each day (e.g., at 0700) will be more likely to work during 

daylight duty hours and to sleep during nighttime hours. Their biological 

clock will be day-oriented, that is, synchronized to provide energy and 

cognitive resources during daylight and evening hours. 

As illustrated in Figure 6, two peaks of alertness and energy availability will 

take place throughout the day – one in the morning, and one in the early 

evening – with dips in energy and alertness immediately upon awakening, 

sometime in the mid-afternoon, and prior to sleep between sunset and 

bedtime. This pattern of energy availability will be maintained consistently if 

personnel obtain good-quality sleep during daily rest periods of seven to 

eight hours. Good-quality sleep consists of uninterrupted sleep in quiet and 

dark environments. 

Interrupted sleep, and reductions in sleep duration to less than seven to 

eight hours per day, will result in an accumulation of daily sleep debt. The 

consequences of this sleep debt will be experienced as degradations in 

alertness, in decision-making ability, and in mental functions requiring 

logical ability. Persistent sleep debt throughout a week will result in 

increased daytime sleepiness and in an overall degradation in 

performance. 

Using Light Management Techniques

A strategic use of light management can help adapt crewmembers to 

function optimally during nighttime rather than daytime hours. For example, 

exposing the human eye to artificial light during the period between sunset 

and 0200 can shift the Red Zone for Nighttime duty. See Figure 7. 

CAUTION! Inconsistent inputs to the biological clock are 

common when personnel work during nighttime and/or earlymorning hours. This is especially true for crewmembers on night 

watch, who are often exposed to full daylight after sunrise. Such 

inconsistencies can result in a degradation of sleep during the 

day, and of performance during the following night. 
40 

Figure 7. Shifting the Red Zone toward daylight hours 

Light management involves the strategic use of artificial light to shift the 

Red Zone out of its normal nighttime range. See Figure 8. 

Figure 8 shows the Red Zone being shifted into full daylight hours. The 

three arrows indicate the amount of relative shift realized by applying lightmanagement techniques over three different periods of time. (Note that if 

sunrise occurs prior to 0700, natural light may be used for light 

management once daylight is of sufficient intensity.) 

Note that it takes about five or six days of consistent light management to 

shift the Red Zone fully from a nighttime orientation over to a daylight 

(morning) orientation. 

1200 2100 0200 0700 1200 

Time of Day 

E

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Days 1-2 
41 

Figure 8. Shifting the Red Zone into daylight hours 

Light management in this case would consist of closely replicating a 

daylight environment during nighttime hours, and a nighttime environment 

during morning hours. The result of this regimen is illustrated in Figure 9. 

Details on how to implement a light-management regimen are provided in 

the following subsections. 

Time of Day 

E

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1200 2100 0200 0700 1200 

1200 2100 0200 0700 1200 

Days 1-2 

Days 3-4

Days 5-6 

Exposures to Light 
42 

Figure 9. Fully-shifted Red Zone 

General Recommendations 

• Obtain 7-8 hours of uninterrupted sleep per 24-hour period.

• Compensate for any sleep loss with daily naps.

• Eat meals rich in lean protein sources (for example, chicken, fish, 

eggs, peanut butter) and vegetables (spinach, Brussels sprouts, 

zucchini, etc), but low in sugar, white flour, and fatty foods 

• Consume the heaviest meal after waking up from the longest sleep 

period of the day 

1200 2100 0200 0700 1200 

Time of Day 

E

n

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y

Artificial light Sleep in dark room

Night 

1200 2100 0200 0700 1200 
43 

• Eat small light meals within 4 hours of the sleep period 

• Reset the biological clock by using light management 

Exposure times may be as short as 30 minutes per hour; however, 

frequent exposures during the duration of the transition period are 

recommended. (Note: Do not stare directly into the light sources 

being used to replicate daylight.) It is recommended that normal 

activities be conducted while light management is being used. 

• Avoid sunlight and bright artificial light during the sleep period 

Watch Schedules 

There is no ‘one size fits all’ watch schedule; different circumstances 

require different schedules. However, all watch schedules should be based 

on the following fundamental criteria: 

• Crewmembers should have enough time off to obtain 7-8 hours of 

uninterrupted sleep per 24-hour period 

• Crewmembers working at night should be able to maintain the same 

work-rest schedule for at least two continuous weeks 

• Changes in work schedule from day to night, or from night to day, 

should be minimized in order to avoid sleep-cycle desynchronization 

(a condition similar to jet lag) 

• Work periods should be no longer than eight (8) continuous hours, 

particularly when prolonged exposures to extreme temperature or 

humidity levels (see Section III) are involved 

• Environmental light-management techniques should be used to adapt 

crewmembers to night watch (see next section) 

The single most-important consideration is the human requirement 

for 7 to 8 hours of quality sleep per day. 
44 

Note: A CEM software tool is available for optimizing watch schedules for 

particular situations. 

Controlling Shiftwork Adaptation

Adapting to nighttime or daytime work requires synchronization of the 

biological clock to the work schedule. Maladaptation results if the biological 

clock is not adjusted to the work schedule. To adapt the biological clock, 

crewmembers must be exposed to daylight (or bright artificial light of 1,000 

lux or more) both upon awakening and throughout their active periods (for 

example, during work hours). Also, crewmembers must avoid bright light 

from approximately three hours prior to the end of their long sleep period. 

Maladaptation to shiftwork schedules and lack of energy-restoration sleep 

can result in persistent sleepiness, low energy, lack of motivation, and 

depression; in performance degradation during duty hours; and in 

increased safety risk. 

Other health effects such as increased incidence of cardiovascular disease, 

gastrointestinal disorders, and sleep disorders have been historically 

documented in populations subjected to shiftwork maladaptation. The 

MANAGEMENT NUGGET: The only way to fully adapt to night 

watch schedules is to reset the biological clock so that energy 

peaks during nighttime. Work must take place under artificial 

light (of at least 1000 lux) that mimics daylight. Sleep must take 

place in a dark and noise-free environment for approximately 

seven to eight hours. Lacking control of daylight and/or light 

exposure is a significant contributor to fatigue and shiftwork 

maladaptation. 

NOTE: Light management is a critical part of the process of 

adapting to new watch schedules. 
45 

combined effects of disrupted sleep and biological clock disorganization 

can lead to endurance degradation, jet-lag-like symptoms, irritability, 

depression, and, in extreme cases, psychosis. 

Optimizing Adaptation to Shiftwork 

Optimizing crew rest, while preventing shift lag (inadequate adjustment to 

shiftwork schedules), can contribute significantly to crewmember 

adaptation to work and life aboard a maritime vessel. Listed below are 

some critical recommendations that can prevent watch schedules from 

inducing short and disrupted sleep periods and shift lag. 

Total Adaptation to Night Work

• Provide bright-light exposure (e.g., fluorescent bulbs of at least 1000 

lux) during the work period (see Appendix A-4: Shiftwork, Sleep, and 

Biological Clock Management). Note: This artificial-light exposure 

can only be implemented in environments where night vision is not 

required for performing normal duties (e.g., in engineering). 

• Provide nighttime personnel with small-size meals that promote 

energy and alertness (high protein, low fat, low sugar, low starch, no

dairy products or turkey). 

• Adjust meal times so that midnight watch personnel can eat a brunch 

on waking (at approximately 1300), including brewed coffee and 

breakfast foods, if desired. 

• Adapt the mess services to accommodate crewmember needs. This 

accommodation supports both safety and crew morale. 

MANAGEMENT NUGGET: Avoid allowing personnel to work more 

than 12 hours in a 24-hour period. Count these 24 hours from the 

time crewmembers wake up from their longest daily sleep period 

(not naps). 
46 

Partial Adaptation to Night Watch or Work Schedules

When bright lights cannot be used in the work environment, adhere to the 

following recommendations:

• Reduce the duration of the watch in order to minimize the impact of 

endurance degradation on safety. Promote exercise in the evening 

hours. 

• Allow crewmembers in any watch ending in the morning hours to 

retire prior to sunrise, and to sleep at least seven to eight hours free 

of noise and with absolutely no interruptions. Overtime should be 

scheduled to occur after wake-up time (e.g., from 1400-1800), 

whereas leisure activities should be scheduled for the evening hours. 

• A second approach to reducing endurance degradation in the 

Midnight Watch is to allow one watch section to work most of the 

night by extending the watch duration to five or six hours. For this 

approach to work, however, the night watchstanders must be allowed 

to retire before sunset, and to sleep seven to eight uninterrupted 

hours in a dark and quiet environment with absolutely no 

interruptions. Allowing one watch section to cover the entire watch 

avoids the need to adapt other crewmembers physiologically to night 

work. 

These crewmembers must see daylight or sufficiently bright artificial 

light (of at least 1000 lux) after they awaken from their uninterrupted 

sleep period, and throughout their work period. Exposure to daylight 

provides a critical input that facilitates the biological clock’s 

adjustment to the sleep-work schedule.
 47 

SECTION IV 

Controlling Performance 

Stressors in Maritime 

Operations 
 48 

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 49 

IV. Controlling Performance Stressors in 

Maritime Operations 

This section (IV) tells you how to control performance stressors commonly 

experienced in the maritime industry. The following performance stressors 

are covered: 

• Cold-related illness 

• Heat illness 

• Motion sickness 

• Physical and mental stress 

• Caffeine 

• Over-the-counter drugs and prescription medications 
 50 

Cold-Related Illness 

This section describes cold-related illnesses, and provides tips on 

controlling them. 

• Hypothermia 

Hypothermia results when heat loss exceeds heat production. 

Accidental hypothermia results from total or partial immersion in cold 

water, or from exposure to cold air temperatures. Immersion in cold 

water differs from exposure to cold air because of two primary 

physical factors: 

- Water conducts heat away from the body approximately 26 times 

faster than air. 

- Water has a specific heat approximately 1000 times that of air, 

which means each cubic centimeter of water that contacts the skin 

extracts heat 1000 times faster than air. 

Symptoms involve shivering uncontrollably, confusion, carelessness, 

and disorientation. If left untreated, this condition can result in death. 

Management: Remove from cold (water/air); provide shelter; keep 

warm with blankets; remove wet clothing; place heated items 

(rocks/pads) near the skin, but not in direct contact; institute body-tobody rewarming. Do not heat oral fluids, and do not rub cold skin. 

• Frostbite (skin tissue freezes at 30° F) 

Fingers, cheeks, nose, and ears are most at risk of frostbite. 

Symptoms include sensation of coldness, tingling, stinging, aching, 

and numbness. If left untreated, this condition can result in 

amputation or loss of function of the affected area. First aid requires 

treating tissue with warm water (102-110° F) as long as there is no 

chance for re-freezing tissue. Bed rest and medical attention must 

follow first aid. 
 51 

• Trench foot (long exposure to wet and cold) 

Symptoms include tingling, itching, swelling, and pain. If left 

untreated, this condition can result in the death of skin tissue and 

ulceration, as well as in damage to the circulatory system. First aid 

requires moving crewmembers to a warm area, and treating the foot 

with warm water (102-110° F) or warm packs. Bed rest and medical 

attention must follow first aid. 

Causes

Specific factors that can lead to cold-related illness include: 

• Wet clothing 

• Insufficient insulation of body, head, hands, and feet from wind, 

spray, and cold temperature 

• Use of medication that disrupts the body’s ability to regulate core 

body temperature 

• Physical exhaustion 

• Prolonged work-related exposure to cold, windy, and wet 

environments, allowing numbness of fingers and toes to set in 

Endurance Tips

Train crewmembers to:

• Wear 3-layered warm clothing 

- The outside layer serves as a weatherproof, breathable barrier 

that breaks the effects of wind chill. Gortex and nylon materials are 

best for this use. 

CAUTION! Winter months threaten crewmember health and 

endurance; working in unprotected deck areas exposed to the 

cold can result in an extreme reduction of body temperature 

(hypothermia) and in severe frostbite of hands and feet. 
 52 

- The middle layer absorbs sweat, retains vital body heat, and 

insulates the body from the external cold. Wool and synthetic-pile 

are recommended for this use. 

- The innermost layer provides ventilation and allows perspiration to 

vent, keeping the skin dry. Synthetic fibers are best for this use. 

• Bring a change of clothing to prevent having to work in wet garments; 

take a hot shower before changing. 

• Keep the head covered at all times. Most body heat is lost when the 

head is left unprotected. 

• Keep hands, feet, and face covered and warm. Fingers and hands 

cannot function properly below 59° F. 

• Keep feet well insulated from cold and dampness. Layered socks and 

insulated boots are recommended. 

• Keep garments clean. Soiled clothing loses its insulating properties. 

• Drink plenty of water and maintain electrolyte balance (see Heat 

Illness). 

Provide Crewmembers with: 

• A heated shelter 

• Local radiant heaters 

• Thermal insulating materials placed over tool handles at 

environmental temperatures below 30° F 

• Extra breaks in cold environments (deck personnel in particular) 

• Reduced work pace 

• Training session on how to endure cold-related risk factors 
 53 

Heat-Related Illness

This section describes heat-related illnesses and provides prevention tips. 

Exposure to high ambient temperatures is common during the summer 

months. However, this kind of exposure is always present in engineering 

spaces. 

There are six major types of heat illness: 

• Heat stroke 

• Heat exhaustion 

• Heat cramps 

• Heat rash 

• Heat syncope 

• Heat fatigue 

Heat stroke (hyperthermia) is a life-threatening disorder associated with 

working under very hot conditions. It results from a breakdown in the body’s 

ability to regulate its temperature, leading to a rise in core temperature to 

over 107° F. Heat stroke is manifested by hot, dry skin; mental confusion; 

convulsions; and unconsciousness. Death frequently occurs, with a fatality 

rate of nearly 50 percent. Temperature-lowering methods must be initiated 

promptly: Remove outer clothing; apply cool water to the body surface; fan 

the body to create air movement; seek emergency medical attention. 

CAUTION! Heat illness is caused by exposure to high 

temperatures and humidity for prolonged periods, and by not 

drinking enough water. Crewmembers suffering from secondary 

illnesses that involve dehydration tend to be more susceptible to 

heat illness. 
 54 

Heat exhaustion results from a decrease in total body water and/or 

circulating blood-volume. It occurs when the amount of water lost by 

sweating exceeds the amount of water intake. The clinical manifestations of 

heat exhaustion include endurance degradation; extreme weakness; 

nausea; headache; fainting; and cool, clammy skin. Management of heat 

exhaustion consists of removing the crewmember from high heat and 

humidity, getting bed rest, and drinking plenty of fluids. 

Heat cramps are painful muscular cramps commonly affecting the lower 

extremities. Heat cramps result when the loss of salt during long periods of 

work or exercise exceeds the amount of salt replaced. Salt is necessary for 

sweating. Note: Salt tables should not be taken. 

Heat rash, otherwise known as ‘prickly heat’, occurs in hot, humid 

conditions, as a result of unevaporated sweat keeping clothes and skin wet. 

Heat rash may affect small areas (patches) of skin or the entire torso. The 

larger the affected skin area, the greater the compromise to sweat 

production and therefore to the body’s ability to regulate body heat through 

evaporation. Following an instance of heat rash, sweat production may not 

return to normal for several (4 to 6) weeks. 

Heat syncope is a benign condition manifested by dizziness and/or 

fainting. Heat syncope results from blood pooling in the lower extremities 

(in dilated vessels in the skin) and thereby reducing blood flow to the brain. 

Management of heat syncope consists of removal from heat, and rest. 

Heat fatigue is a response to acute or chronic heat exposure. Symptoms 

of heat fatigue include decreases in motor skills, cognitive performance, 

and alertness, as well as reductions in performance capacity and 

concentration. Chronic heat fatigue improves naturally through 

acclimatization. 

CAUTION! If a crewmember exhibits heat-illness symptoms, use a

cold-water bath or cold, wet towels to cool her or his core body 

temperature. Seek medical attention immediately. 
 55 

Endurance Tips

To prevent heat illness:

• Never work when the ambient temperature is 104o F or above. 

• Drink water on a regular schedule, even when not thirsty. 

• Drink extra water when sweating heavily. Begin each work period by 

drinking approximately one pint of water. Water is best consumed in 

quantities of no more than one-half pint at a time. 

• Drink extra water if urination becomes less frequent than normal, or if 

urine’s color becomes darker. 

• Replace electrolytes with fruit juices, V-8 juice, or bananas, or with 

commercial sports drinks that are at least 6-percent glucose and 

contain at least 10-25 mEq/L of sodium. Note: In most cases, it is not 

necessary to replace electrolytes specifically, because enough salt is 

obtained from regular meals and snacks. 

• Wear loose-fitting clothes light in color. 

• Seek well-ventilated places. 

• Avoid the use of alcohol or other drugs that can impair temperature 

regulation, such as melatonin, aspirin, and acetaminophen (Tylenol). 

• Adapt to heat exposure by working for 60 to 90 minutes each day 

within the work environment. 

FACT: Heat acclimatization (the process of adapting to heat 

exposure) can be achieved by a minimum of sixty to ninety 

minutes of exercise, or strenuous work, in the heat each day for 

one to two weeks. Adaptation begins to occur within a few days. 
 56 

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 57 

Motion Sickness 

This section describes motion sickness and provides tips on controlling the 

factors that contribute to it. 

The symptoms of motion sickness include cold sweats, endurance 

degradation, dizziness, headaches, yawning, nausea, and vomiting. 

Causes

Motion sickness is caused by an internal conflict in the brain. When we are 

standing on the ground, our brain senses the body’s position relative to the 

ground. This sensory pattern is coded in our memory as a template. When 

we are standing on a moving platform, our brain becomes confused, 

because the information stimulating the sensory system does not match the 

existing memory template. This mismatch creates a series of changes in 

physiology as the brain struggles to create a new memory template. 

A new template eventually forms by way of continued exposure to the 

particular motion state or states causing the confusion. In the case of ‘sea 

sickness’, getting this new template constitutes getting one’s ‘sea legs’. 

Some people get their ‘sea legs’ more quickly than others, while a few 

never get their ‘sea legs’ sufficiently to feel well enough to work. 

WARNING! Motion sickness induces fatigue and deteriorates 

performance. Crewmembers experiencing symptoms should 

sleep as much as possible, and should walk around as much as 

possible in order to help the brain speed up the adaptation 

process. Safety is at risk when crewmembers encounter motion 

sickness, because fatigue and drowsiness are induced until the 

brain adapts to the moving environment. 
 58 

Endurance Tips

Medications are used to control the symptoms of motion sickness or to 

prevent its onset. A list of these medications, together with their side 

effects, is provided in Table 1. 

It is recommended that crewmembers receiving medications to relieve the 

effects of motion sickness be warned that their performance will likely be 

degraded as a side effect of the medication. The captain, department head, 

or mate needs to keep in mind that crewmembers receiving medications 

should not be involved in tasks that might endanger their safety or that of 

other crewmembers. 

If at all possible, crewmembers receiving motion sickness medication, or 

who are experiencing severe symptoms, should avoid shipboard work 

environments. It is strongly recommended that a medical officer closely 

supervise crewmembers using medications for motion sickness. Selfadministration is strongly discouraged. 

Table 1. Medications Used for Motion Sickness 

MEDICATION SIDE EFFECT USE 

Scopolamine2 

Patch 

Drowsiness 

Degrades vision 

Speeds adaptation 

within 72 hours 

Dramamine Drowsiness Reduces symptoms 

Antivert Drowsiness Reduces symptoms 

Phenergan Drowsiness Reduces symptoms 

Amphetamines High blood pressure; 

disrupts heart rate; 

addictive 

Reduces 

drowsiness 

Ephedrine High blood pressure; 

disrupts heart rate; 

addictive 

Reduces 

drowsiness 

 

2

 Scopolamine is the only medication that may help speed up the process of adaptation. 
 59 

Stress 

Chronic psychological stress – the type of stress induced by interpersonal 

relationships, task design, and management style – creates a constant 

drain on crewmember energy levels. 

Causes

Interpersonal relationships: 

• Lack of support from coworkers and supervisors 

Task design: 

• Heavy workload 

• Infrequent rest breaks 

• Long work hours 

• Shiftwork 

• Hectic routine tasks 

• Little sense of control 

Management style: 

• Authoritative management style 

• Lack of participation by workers in decision making 

• Poor communication between management and employees 

• Ambiguity or conflicting requirements 

• Lack of family-friendly policies 

These factors tend to induce physiological responses, such as elevated 

pulse rate and blood pressure, that use up energy even during rest periods. 

Stress 

Task 

Management

Interpersonal 
 60 

Consequences

Normally the hormone epinephrine (adrenaline) is released during lifethreatening situations to provide extra energy for a fight-or-flight response. 

However, this hormone can also be released in response to stress, 

including chronic stress. The presence of adrenaline in the body’s various 

tissues temporarily increases the amount of energy available to the 

individual. Once this energy is released, however, it cannot be restored 

until the stress level is reduced. Hence, it becomes critically important that 

crewmembers not be under a chronically high level of stress. 

In a stressful work environment, crewmembers may have difficulty enduring 

physical and mental challenges. In addition, they may experience frequent 

periods of reduced mental concentration and awareness, states of mind 

particularly undesirable in safety-sensitive work situations. 

The chronic use of over-the-counter pharmacological stimulants (e.g., 

caffeine and pseudoephedrine) to boost concentration and awareness can 

result in decreased attention, irritability, and adverse health effects. 

Therefore, implementation of stress management is a must-do for effective 

endurance management. 

Stress management is particularly relevant for vessels where 

crewmembers work for long periods with little or no opportunity to break 

away from work-related duties. Under these conditions, work-related 

factors such as interpersonal relationships, task design, and management 

style can easily induce chronic stress if not adequately managed. 

Endurance Tips

Stress reduction and morale boosters can render a large pay-off for a 

relatively small investment. For example, one maritime company found that 

FACT: The body’s response to any kind of stress, life threatening 

or not, involves expending energy, and disrupting energyproducing activities during rest periods. Even during sleep, 

stress robs crewmembers of needed energy by disrupting the 

quality and duration of sleep. 
 61 

installing satellite television and making cell-phone time available (e.g., 30 

minutes weekly) to all crewmembers were consistent morale boosters. 

Making shipboard phone use available, or providing shipboard Internet and 

e-mail access, can easily boost morale as crewmembers realize the 

company’s interest in their mental and emotional well being. It can also 

help crewmembers communicate more with their families, and can help 

reduce the amount of time spent waiting in line for a public phone at port. 

Management, captains, and crewmembers can contribute to the control of 

stress-related risk factors by implementing a consistent stress management 

program. The following recommendations provide a well-rounded list of 

ways to reduce stress: 

• Train employees new to their job situation, particularly those recently 

promoted, to implement: 

- Time-management strategies 

- A regular exercise program 

Make a variety of exercise equipment available to 

crewmembers (e.g., treadmill, free weights, stationary bicycle, 

rowing machine) 

Allow crewmembers to have their own exercise equipment 

- Relaxation exercises (needed to reduce anxiety, increase 

concentration, and optimize the quality of rest periods)

• Promote crew participation in problem solving using a team approach 

The process of participation reduces the feeling of alienation, 

promotes feelings of self-worth, and allows individual crewmembers 

to become a valued part of a team effort. 

• Identify and reduce stressful factors, particularly those involving 

interpersonal relationships 

• Maintain good communication with crewmembers, realizing that 

alienation, withdrawal, and lack of participation are signs of stress 

• Provide access to stress-reducing activities: 
 62 

- Implement a nap policy during long work days 

- Provide satellite television 

- Provide consistent mental and physical health counseling 

• Modify the daily menu so that meals are balanced, offering plenty of 

fresh vegetables and fruits, vegetable and fruit juices, whole-grain 

bread, and low-fat meats such as turkey, fish, and chicken (no turkey 

before watch, however, as it can cause sleepiness) 

It is best to consume proteins, carbohydrates, and unsaturated fat, 

and to let the body break down food into glucose, amino acids, and 

fatty acids (see energy explanation in beginning of Section III). 

• Provide a variety of nonalcoholic drinks, and avoid the use of highly 

sweetened soft drinks 

Promote fresh water and fresh fruit or vegetable juices as thirstquenchers of choice. 
 63 

Caffeine 

Caffeine is a stimulant drug. For caffeine to serve as an alertness boost, it 

must be consumed at low levels, and only when needed. 

Consequences

High doses of caffeine can result in increased anxiety, lack of 

concentration, and digestive disorders. Some people develop a greater 

sensitivity to caffeine and experience these symptoms even at low doses. 

Frequent consumption of caffeine can result in addiction. 

Common sources of caffeine include: coffee, tea, chocolate, soft drinks, 

and medications (over-the-counter and prescription).

Endurance Tips

Crewmembers addicted to caffeine should discontinue use and undergo 

withdrawal. Withdrawal can last two weeks and can include headaches, 

attention deficit, endurance degradation, and lack of motivation. Sleep 

patterns should begin to improve within this period, but energetic alertness 

after awakening may not be restored until the withdrawal process is 

complete. 

If withdrawal is not desirable, reducing exposure to caffeine to one 

beverage (cup of coffee, bottle of soda, chocolate drink) per day can be a 

good compromise. 

If caffeine is needed to maintain alertness during daytime hours, a 

physician should be consulted to evaluate the possibility of a sleep 

disorder. 

Crewmembers taking over-the-counter or prescription medications that 

contain caffeine (or another stimulant) should closely follow the dosage 

instructions. 

Caffeine should be used as a stimulant to boost alertness only when 

necessary, and should be avoided altogether within four hours of bedtime. 
 64 

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 65 

SECTION V 

Implementing a CEM 

Program 
 66 

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 67 

V. Implementing a CEM Program 

This section (V) describes how to implement a CEM program in maritime 

operations. 

Implementing a CEM program involves three phases: 

Phase I: Program Development 

Phase II: Program Deployment 

Phase III: Program Assessment

Phase I: Program Development 

Developing a CEM program involves the following: 

• Setting up a Working Group 

• Analyzing the current situation 

• Drawing up a CEM plan 

Setting Up a Working Group

Setting up and training a Crew Endurance Working Group (CEWG) is 

fundamental to successfully implementing a crew-endurance management 

program aboard a maritime vessel. 

The CEWG is responsible for all aspects of implementing a CEM program 

aboard a maritime vessel, including: 

• Identifying the endurance risk factors relevant to the vessel 

• Creating a collaborative network to facilitate implementing a CEM 

program aboard the vessel 

• Devising and deploying a CEM plan specific to the vessel 
 68 

To be effective, a CEWG must include or represent all those individuals 

who stand to be affected by implementation of a CEM program, especially 

regular crewmembers. A CEWG typically consists of the following 

individuals: 

• One or two company officers 

• The company operations or safety manager 

• The captain and the relief captain of the vessel 

• The pilot 

• The first mate 

• The chief engineer 

• Two or more crewmembers, including the head cook 

Because the head cook is likely to be considered unbiased, in being 

outside the chain of command, he or she is often a good choice for the 

CEWG, as is the chief engineer, who would likely be responsible for 

implementing any environmental changes decided on. 

 The members of the CEWG must receive training in identifying and 

managing crew-endurance risk factors; creating collaborative networks to 

facilitate CEM implementations; and devising and deploying CEM plans. 

Typically, the goal of a CEWG is to develop a CEM program for a particular 

situation – in most cases, a specific vessel; however, CEM plans can also 

be set up to apply to an entire company. 

FACT: Controlling factors affecting crew endurance requires the 

development of a supporting organizational infrastructure. 

Without management support, individual crewmembers cannot 

effectively implement endurance management practices. 
 69 

Analyzing the Current Situation

Before drawing up a specific plan, the Working Group must analyze the 

current situation. Table 2 Summarizes the four steps involved: 

Table 2. Analyzing the Current Situation

Step 1 Receive training in CEM principles and practices 

Step 2 Identify system areas of risk 

Step 3 Identify specific risk factors 

Step 4 Propose modifications 

1st Step: Receive Training in CEM Principles and Practices 

The CEWG meets initially to receive training in CEM practices and 

procedures, including how to create collaborative networks; how to identify 

and manage crew-endurance risk factors; and how to devise and deploy 

CEM plans. CEWG members also receive training in how to deal with 

cultural roadblocks: “This is the way we’ve always done it; why change?” 

The CEWG also chooses a leader at this stage. In this regard, it is critically 

important that the CEWG choose a leader who is respected by all 

stakeholders, has authority to make decisions, and who is capable of 

guiding the group away from individual agendas. 

2nd Step: Identify System Areas of Risk 

The process of controlling endurance risk factors requires an analysis of 

the entire operational system of the vessel. This analysis consists of 

CAUTION! Successful working groups avoid personal or 

organizational agendas, and seek improvement of policies and 

crew management practices that will help crewmembers maintain

endurance. 
 70 

identifying the various areas of risk, such as workload, shipboard 

environment, weather, and company policy, as well as the relationship 

between these areas of risk (See Figure 10). 

Figure 10. Operational analysis 

Figure Legend:

Co. Workload The accepted number of jobs at the company level. 

Weather Inclement weather can delay or stop operations. 

 

Individual 

Choices 

Workload 

Work Schedule Diet 

Co. Workload 

Route 

Workforce

Weather

Company Policies 

Regulatory

ENDURANCE 

Shipboard 

Environment Training 
 71 

Workload Heavy workloads require more energy per hour 

from crewmembers. 

Company 

Policies 

Company policies can affect efforts by 

crewmembers to maintain endurance. 

Shipboard 

Environment 

Factors such as noisy, fumy, and light-porous 

quarters can disrupt sleep. 

Training The amount and the focus of crew training can 

affect stamina and alertness factors. 

Work Schedule Irregular or heavy work schedules can leave 

inadequate time for sufficient sleep. 

Diet How much, what, and when crewmembers eat 

impacts on energy, mood, stamina, and sleep. 

Individual 

Choices 

Individual choices (for example, watching TV during 

a sleep period) can affect stamina and alertness. 

Route Vessel routing can determine the type of work and 

the work schedule. 

Workforce The number of personnel allotted to each vessel 

can affect the watch regimen used. 

Regulatory CG regulations determine the maximum number of 

work hours per worker per 24-hour day. 

 

The step 2 analysis (identifying system areas of risk) should be conducted 

over a period of at least 15 days (preferably 30 days) in order to properly 

document duty hours, workloads, and crew-rest routines associated with 

periods of low and high workload. Depending on the geographical location, 

workload may be directly affected by seasonal changes; thus, some 

evaluations must be conducted during both winter and summer seasons. 

Information collected from the step 2 analysis helps CEWG members 

identify the specific risk factors that are currently affecting crew endurance. 

Identifying all these risk factors is fundamental to developing a CEM plan 

for a specific real-world operation. As the relevant risk factors are identified, 
 72 

the CEWG can then develop a specific plan to control the impact of these 

factors on performance and safety. For instance, some of the controls 

applicable to one particular operational situation were as follows: 

• Encourage department chiefs to manage OT work ensuring that all 

crewmembers will have the opportunity to work OT without disrupting 

their rest periods 

• Implement the alternate watch schedule during the underway period 

• Revert to the standard watch schedule during frequent or lengthy inport periods 

• Train crewmembers to take advantage of rest opportunities under 

both the alternate and the standard watch schedules 

• Identify conditions that prevent crewmembers from obtaining 7 to 8 

hours of sleep per day, and develop plans to reduce the total number 

of days of exposure to these conditions 

A key part of the step 2 analysis is documenting the impact of watch, work, 

and training schedules on crew rest and stress levels. Wrist activity 

monitors, used since the early 1980s to document sleep in field conditions, 

are highly recommended for this purpose. These devices, the size of a 

large wristwatch, can provide accurate information on the quality and 

duration of a crewmember’s sleep. 

The data collected with wrist activity monitors can be used to determine 

whether crewmember rest periods occur consistently, and whether they 

occur under environmental conditions that promote the restoration of 

alertness and physical energy from day to day. In addition, these data 

reveal how well personnel take advantage of rest periods. (For further 

details, refer to Phase III: Program Assessment.) 

Note: The U.S. Coast Guard Research and Development Center can 

provide access to wrist activity monitors. 

3rd Step: Identify Specific Risk Factors 

The third step consists of analyzing the operational risk areas shown in 

Figure 10 to identify the specific risk factors (activities, environmental 
 73 

conditions, policies, operational situations) that appear to be affecting crew 

endurance. For example (from the commercial towing industry): 

Work Schedule The current 6-6-6-6 watch schedule 

was not allowing crewmembers 

sufficient opportunity to obtain the 

daily sleep required to maintain 

endurance. 

Diet Crewmembers were eating large 

meals immediately before going to 

bed after watch. Crewmembers were 

consuming large quantities of caffeine 

throughout the day, even close to 

bedtime. 

Individual Choices Crewmembers were consuming 

coffee throughout watches; staying up 

to watch TV, play games, or make 

lengthy phone calls; asking to be 

awakened an hour or more before a 

watch change. 

Crewmembers were being kept 

awake by noises associated with 

crews handling rigging near the 

vessel; slamming doors or banging 

manhole covers; using televisions, 

radios, hand-held VHF radios, etc. at 

high-volume levels. 

Shipboard Environment Crewmembers were being awakened 

by sudden movements of the vessel. 

Crewmembers were being kept 

awake by light entering crew quarters 

through windows and door louvers, 

and by engine noise entering through 

a single engine-room door. 
 74 

Lights in the crew quarters were not 

sufficiently bright for crewmembers to 

adapt to day or night work hours, or to 

become alert quickly upon waking. 

Smoke from the diesel engines was 

sometimes penetrating into 

staterooms, causing discomfort. 

Company Policies Crewmembers were accumulating 

sleep debt because of the ‘no 

napping’ policy. 

Crewmembers were being delayed 

from sleep time by not being able to 

take meals or showers until after 

watch change. 

4th Step: Propose Modifications 

The fourth step consists of suggesting modifications to the system shown in 

Figure 10 that address the risk factors identified in Step 3. 

Typically these modifications involve changing the shipboard watch 

schedule, introducing light-management techniques (to control the Red 

Zone), changing crewmember dietary practices, controlling the use of 

caffeine and over-the-counter drugs, and making changes to crewmember 

living areas. 

Refer to Section II for additional examples. 

Drawing Up a CEM Plan 

Upon completing an analysis of the current situation, the CEWG then 

draws up a formal plan of implementation. This process consists of: 

• Agreeing on and prioritizing modifications 

• Setting up a CEM Final Common Path 

The process involved in arriving at a plan for implementation requires 
 75 

dedication, cooperation, and self-discipline. If individual agendas are 

allowed to take precedence, a meaningful CEM plan cannot be achieved. 

In cases where individual agendas obstruct progress, it is recommended 

that the working group focus on identifying changes (no matter how small) 

that all stakeholders can support. In such cases, actions that elicit 

irresolvable disagreements must be considered ‘long-term projects’. 

Agreeing on and Prioritizing Modifications 

The CEWG must agree on and prioritize the system modifications 

suggested in Step 4 of the analysis process. 

The process of prioritizing system modifications involves placing them into 

one of three possible categories: 

• Those that can be implemented easily 

• Those that can be implemented with more effort 

• Those that cannot be implemented 

It is recommended that the working group place an initial emphasis on 

small or inexpensive modifications that yield relatively large benefits. Larger 

or more expensive changes can then be phased in over time. 

It is paramount that CEWG members make their modification 

recommendations on the basis of information gathered in Steps 1-3, rather 

than on the basis of personal preference or a resistance to change. 

Setting Up a Crew-Management Final Common Path 

In order for a CEM program to succeed, a crew-management Final 

Common Path must be established and maintained. A crew-management 

Final Common Path consists of the following key elements: 

• Setting up a team of onboard coaches to train crewmembers on the 

science and practices of CEM, and to serve as program models and 

monitors 

The team of coaches typically consists of the captain, the pilot, and 

the mate. 
 76 

• Training the coaches in the science and practices of CEM 

Training for coaches is provided by company management, typically 

using resources available from the U.S. Coast Guard Human Element 

and Ship Design Division (202-267-2997). 

• Training the crewmembers in the science and practices of CEM, 

modeling the required practices, and monitoring crew adherence to 

these practices 

Setting Up a Team of Coaches

Effective Crew Endurance Management requires constant encouragement 

and reinforcement. Providing encouragement and reinforcement is 

accomplished by a shipboard team of coaches specifically charged with: 

• Coordinating crewmember training, and documenting crew rest 

during implementation of new work schedules 

• Supporting the overall implementation of CEM practices by modeling 

CEM practice for crew emulation, actively encouraging crewmembers 

to follow CEM practices, and enforcing adherence to the policies and 

procedures of the CEM plan 

• Providing information to vessel officers on how to design and 

implement work schedules that both meet the operational objectives 

of the vessel and do not result in inadequate adjustment to changing 

schedules 

CAUTION! Experience has demonstrated that it is not sufficient to 

simply change a watch schedule from a, for example, 6-6-6-6 

regimen to an alternative regimen such as 7-7-5-5. CEM 

implementation will fail If a Final Common Path has not been set 

up to teach crewmembers how to take advantage of the new 

schedule, how to use light-management techniques, and how to 

ensure that appropriate environmental changes have been made 

(for example, to control noise and light in sleeping quarters). 
 77 

• Providing information to crewmembers on how to maximize 

the benefits of rest opportunities (refer to both Section II and 

Appendix A) 

• Implementing crew-rest protocols that document: (1) the timing and 

number of rest opportunities made available for crewmembers, and 

(2) crewmember efficiency in taking advantage of rest opportunities 

Training the Coaches & the Crew

Successful implementation of a CEM plan on a maritime vessel requires 

that all the relevant players be trained in crew-endurance practices and 

procedures. For the team of coaches, this training is the responsibility of 

the company, typically using resources available from the U.S. Coast 

Guard Human Element and Ship Design Division (202-267-2997). For the 

crew, this training is the responsibility of the shipboard team of coaches. 

The training provided should include sleep and body-clock management, 

stress management, time management, and information concerning such 

risk factors as diet, caffeine use, over-the-counter and prescription 

medications, heat illness, and exercise. 

Phase II: Program Deployment 

Implementing a CEM program requires that all levels of an organization 

share the responsibility for success. This responsibility includes the 

following essentials: 

• Enlisting the support of the full crew 

- Crewmembers are presented with the Working Group’s CEM plan 

as well as the rationale supporting each of its features. In addition, 

MANAGEMENT NUGGET: Successful implementation of a CEM 

plan to improve endurance requires an aggressive education 

program designed to instruct company managers, vessel 

captains, all levels of vessel management, and crew personnel 

on the science and practices of crew endurance management. 
 78 

they are provided with key information and training on crewendurance benefits, factors, and procedures. It is emphasized that 

changes are not being recommended merely for the sake of 

making changes, and that legacy systems are not necessarily the 

best possible systems simply because they have been in place for 

long periods of time. 

- Crewmembers are reminded that all change, including 

implementing a CEM plan, requires making personal adjustments, 

with each adjustment supporting and improving on other 

adjustments. 

- Some benefits are immediately available, such as noise 

improvements and time-management practices. Others, such as 

easier integration back into a home living schedule, and easier 

adjustment back to a vessel schedule, may not be recognizable 

until either after a crewmember has left the vessel or when the 

crewmember returns to the vessel. 

- Crewmembers are invited to make suggestions toward improving 

the Working Group’s plan, and are asked to support the final plan 

toward the mutual benefit of all concerned. 

• Implementing the recommended modifications 

- The CEWG – working with company management, the vessel 

captain, and the shipboard coaches – ensures that all of the 

system modifications recommended in the final CEM plan are 

implemented. 

- These modifications might involve changes in watch schedule, 

changes to crewmember quarters and living areas, new shipboard 

policies, and/or requests to the crew for changes in personal 

choices (relative to diet, fitness, use of caffeine and other over-thecounter drugs, etc.). 

• Coaching the crew toward consistency 

During and after initial implementation, the shipboard team of 

coaches is responsible for: 
 79 

- Coordinating crewmember training, and documenting crew rest 

during implementation of new work schedules 

- Supporting the overall implementation of CEM practices by serving 

as models of CEM practice for crew emulation, actively 

encouraging crewmembers to follow CEM practices, and 

monitoring and enforcing adherence to the policies and 

procedures of the CEM plan 

- Providing information to vessel personnel on how to design and 

implement work schedules that both meet the operational 

objectives of the vessel and provide adequate adjustment 

regimens 

- Providing information to crewmembers on how to maximize 

the benefits of rest opportunities (refer to both Section II and 

Appendix A) 

- Implementing protocols that document the timing and number of 

rest opportunities made available for crewmembers, and that 

quantify the efficiency of crewmembers in taking advantage of rest 

opportunities 

Phase III: Program Assessment

Phase III assessment evaluates how well a newly deployed CEM program 

is working under real-world conditions, and is usually conducted over the 

first 60 days of deployment, during normal operational tempo. Assessments 

conducted during slow- or high-tempo periods may not accurately 

determine true effectiveness. 

As in the Phase I assessment, it is necessary to document the impact of 

watch, work, and training schedules on crew rest and stress levels. The 

same wrist activity monitors used in the Phase I (step 2) analysis are highly 

recommended for use in the Phase III analysis. 

The data collected with wrist activity monitors can be used to determine 

whether crewmember rest periods are occurring consistently, and whether 

they are occurring under environmental conditions that promote restoration 

of alertness and physical energy from day to day. In addition, these data 

reveal how well personnel are taking advantage of rest periods provided by 
 80 

the implemented CEM plan. Methods to test the effectiveness of crew 

endurance plans are provided in several reports published by the R&DC. 

Phase III data provide the CEWG with objective information on crew-rest 

and stress levels during the two-month implementation period. These 

observations can help determine whether additional modifications need to 

be made to the operational system. 

As a matter of good CEM practice, the CEWG should maintain an active 

education program for new as well as veteran crewmembers, and should 

ensure that CEM evaluations are conducted at least semi-annually. 

Summary

The implementation of CEM practices can help company and vessel crews 

enhance their current efforts toward maintaining high levels of crew 

endurance and safety. CEM practices provide a process for optimizing 

alertness and controlling normal operational stressors. 

A key part of implementing a formal CEM plan is forming a Crew 

Endurance Working Group. CEWG members serve as champions of the 

endurance plan aboard vessels while contributing to the maintenance of 

crew endurance industry-wide. 

Further information on equipment, development, and implementation of 

crew endurance plans can be obtained by contacting Crew Endurance 

Team members at U.S. Coast Guard Human Element and Ship Design 

Division (202-267-2997), or the U.S. Coast Guard Research and 

Development Center in Groton, CT (860-441-2600). 
 A-1 

Appendix A 

Sleep Management and 

Circadian Rhythms 
 A-2 

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 A-3 

A-1: Sleep Management 

Sleep cycle

Sleep consists of certain brain activities that progress predictably through 

five distinct stages (see Figure 11): 

Stage 1 is the transition from awake to asleep. This stage is characterized 

by a slowing of brain activity. When aroused from this stage, many people 

believe they were never asleep. After about five to ten minutes of stage 1 

sleep, a person progresses to a deeper sleep, stage 2. 

Stage 2 is characterized by brain activity slower than that typical of stage 1, 

and is considered by many to be the true beginning of sleep. Within 10 to 

15 minutes, brain activity slows even further and progresses into the 

deepest sleep, stages 3 and 4. 

Stages 3 and 4 are termed slow-wave sleep (SWS). It can be very difficult 

to arouse a person from SWS, and once awake, the person may feel 

sluggish for several minutes. After 20 to 30 minutes of slow-wave sleep, 

brain activity reverts briefly back to stage 2 sleep, and is then followed by 

rapid eye movement (REM) sleep (stage 5). 

REM, stage 5 or dream sleep, is characterized by quick eye movements, 

little to no muscle tone, and by very active brain patterns. The first REM 

period of the night is relatively short, lasting five to ten minutes. After REM 

sleep, the sleep cycle repeats itself, returning to stages 2, 3, 4, and 5. 

Each cycle through the four stages lasts approximately 90 minutes, with 

approximately five to six cycles occurring per night. Most SWS occurs 

during the first half of the sleep period, while most REM sleep occurs 

during the second half of the period. Overall, stage 2 sleep occupies the 

majority of the sleep period, followed by REM sleep, and then SWS. 
 A-4 

Stage 1

Stage 2

Stage 3

Stage 4

Awake

REM

0 1 2 3 4 5 6 7

Elapsed Hours of Sleep

Figure 11. Sleep cycle 

This cycle of sleep can be disrupted by such factors as schedule changes, 

frequent awakenings, and medications. Any disruption bringing on full 

wakefulness will cause the brain to start the sleep cycle from the beginning, 

with the result that the full cycle may not then be completed, because of 

time constraints. When chronic disruption occurs, endurance degradation 

ensues. 

Everyday Sleep Management 

The ability to achieve good-quality sleep depends largely on good sleep 

habits. Leaders and personnel should be aware of the following factors that 

can affect the ability to sleep, or the quality of the sleep achieved. 

Planning for sleep

• The amount of sleep each person needs varies; one cannot 

determine individual sleep needs from what other people require.

To determine your own sleep needs, follow this procedure: After at 

least 30 days on the same sleep/wake schedule, go to bed at your 

regular time without taking any sleep aids, and allow yourself to wake 
 A-5 

up naturally (no alarm clock) for three consecutive days. The amount 

of sleep time on the third day is your normal sleep requirement. 

• Sleep aids (medications) should be avoided, except in extreme 

situations. 

• If a sleep aid was previously used, the first and possibly the second 

night of sleep without medication may be disrupted. Falling asleep 

may be delayed, and the person may awaken several times during 

the night. However, this will subside within one to two nights.

• Try to sleep at the same time every day, including weekends. If 

possible, go to bed at the same time and get up at the same time 

each day.

• Alcohol should never be used as a sleep aid. Although sleep onset 

may come more quickly after ingestion of alcohol, actual sleep will be 

more disrupted and less restful after the first one to two hours.

• Avoid eating or drinking substances that contain caffeine (especially 

coffee, tea, or chocolate) four to five hours before bedtime.

• Do physical training no closer than one hour before bedtime; exercise 

has a temporary alerting effect.

Good sleep habits

• When trying to sleep outside the usual sleep period (e.g., during the 

day), prepare as if for a normal sleep period – wear usual sleep 

clothes, darken the room as much as possible, keep noise to a 

minimum, and, if possible, use a white-noise generator, such as a 

fan.

• Use bed only as a place to sleep; do not read, work, or do other 

similar activities in bed. Associating bed with sleep will eventually 

allow sleep to come more easily.

• After 24 to 48 hours of sleep deprivation, do not sleep overly long 

during the recovery period (more than ten hours). Sleeping too long 

may interfere with the normal sleep/wake schedule, and may cause 

significant sleep inertia and lethargy during the day. The normal sleep 
 A-6 

period for an individual is usually sufficient to recover from 24 hours 

of sleep deprivation.

• Take over-the-counter and prescription medications strictly as 

directed.

Problems with sleep

If you cannot fall asleep after about 30 minutes in bed, do not remain in bed 

awake; get up to avoid associations of waking and anxiety with being in 

bed. Stay up several minutes and then try again. Continue to get up if you 

cannot go to sleep within 30 minutes, no matter how many times this may 

occur during the sleep period. Eventually, endurance degradation will take 

over.

A person who has difficulty sleeping during his or her normal sleep period 

should not nap during the day, as doing this may delay sleep onset. 
 A-7 

A-2: Napping 

When the pace of operations and the staffing level permit, naps can be 

used to sustain performance during normal work periods. In such cases, 

leaders should allow time for napping, and should provide a quiet, 

comfortable place for personnel to take short naps as the situation permits. 

Leaders should also educate personnel about the benefits of napping, and 

should inform them that rest is not a substitute for sleep. 

Napping during work periods can reduce performance impairment, but it 

cannot totally alleviate the effects of sleep deprivation. Individual 

differences in sleep needs must be considered in determining nap length. 

Several factors are important to consider when scheduling naps: 

Pre-existing sleep loss

• The best time to nap is before significant sleep loss has occurred. 

Such preventive naps help ward off subsequent performance 

impairments during heavy work schedules. Personnel who nap for 

one to four hours prior to a nighttime work period will show better 

early-morning performance and alertness than personnel who do not 

nap. Preventive napping may be better than napping during a sleepdeprivation period.

• Naps do not totally eliminate the normal circadian dip experienced at 

around 0500, but degradation in both cognitive performance and 

alertness is reduced.

Nap length

• A single two-hour nap during a 24-hour continuous work-period can 

cause performance to be close to pre-sleep-loss levels.

• If longer naps are not possible, several naps of as little as ten 

minutes each, taken over a 24-hour period, can help personnel 

endure continuous operations.
A-8

Timing of the nap

• It is easier to nap when the core body temperature is at its lowest (at 

around 0300 and 1300); it is more difficult to nap when the core body 

temperature is at its highest (at around 1500).

• For several hours following waking from a nap during a circadian dip 

(see Figure 1), sleepiness is higher, and performance is lower, than 

for a nap taken during a circadian peak.

• Early morning naps (0200 to 0600) are beneficial in restoring 

alertness and performance; however, time should be allowed for 

personnel to fully recover from the nap.

Length of time between end of nap and work period

• Performance is generally lowest during the first five minutes after a 

person awakens from a nap (sleep inertia), but usually recovers after 

15 to 30 minutes.

• Extensive sleep inertia is especially likely when a person is awakened 

from slow-wave sleep, which occurs most often within the first two 

hours of sleep.

• Awakening from sleep that follows a long period of sleep deprivation 

leads to high levels of sleep inertia; the longer the sleep-deprivation 

period, the higher the sleep inertia.

Naps during circadian dips should be avoided when crewmembers need to 

return to work immediately upon awakening, because sleep inertia under 

these conditions can be relatively high. 
A-9 

A-3: Circadian Rhythms 

Physiology

The human body (biological) clock controls specific patterns of 

hormones, alertness, and core body temperature. The word circadian

is used to describe biological and behavioral rhythms regulated by 

the human body clock. 

The human body clock normally provides mental and physical energy 

during the day, but not during the night. This energy pattern is stable 

and predictable only if the body clock receives daylight exposure at 

consistent times from day to day. 

Scientific research has demonstrated that mental alertness mirrors 

core body temperature and is inversely related to melatonin levels. 

Melatonin is a hormone produced during the night that regulates 

sleep and the timing of the body clock. 

Consequences of Desynchronosis

Desynchronosis refers to a disruption of synchronized physiological 

functions caused by changes in sleep and work routines, or by travel 

across time zones. The following list summarizes a few specific workrelated consequences caused by jet lag (travel across time zones), or 

by shift lag (shiftwork): 

• Truck drivers have been shown to have twice as many 

accidents between 2400 and 0200 than during the day.

• Locomotive operators have an increased probability of missing 

warning signals when working the night shift.

• Night-shift workers perform worse than day workers on tasks of 

vigilance and reaction times.
A-10 

• Compared to day fliers, aviators flying in flight simulators at 

night have reduced hand-eye coordination, poorer vigilance and 

calculation proficiency, and impaired flight performance.

Desynchronosis Controls 

The following recommendations will help prevent circadian 

desynchronosis. 

Once shift lag or jet lag actually develops, returning to normal can 

require a person to adhere to a consistent sleep schedule for several 

weeks. In other words, desynchronosis symptoms are not likely to 

disappear in just a few days of normal sleep. 

General recommendations

Individual crewmembers and staff personnel planning work and 

briefing schedules should use the following general 

recommendations. 

• After arriving in a new time zone or making a shiftwork 

transition, maintain consistent schedules for sleep, wake-ups, 

exposure to daylight, and naps.

• Avoid changing sleep/wake schedules during days off.

• Always sleep in completely darkened rooms. If sleep must 

occur during daylight hours, wear a black, cloth sleep-mask.

• Strive to sleep at least six continuous hours per day.

• Become aware of how many hours of sleep you need in order 

to feel refreshed and alert upon awakening. Short sleepers may 

need as few as five hours; long sleepers as many as eight 

hours.

• If after sleeping you feel sleepy during the afternoon hours, you 

need more sleep.

• Prevent noise from disrupting sleep periods. If external noises 

cannot be controlled, mask them with the sound of a fan, a 
A-11 

power generator, a commercially available sound-masking 

device, or some other such device, or wear foam earplugs.

• Avoid meals high in fat content for least three days after 

transitioning to a new location or work schedule. 

Gastrointestinal disorders can surface while you are readjusting 

to a new time zone or work schedule.

Napping and circadian desynchronosis

Naps are recommended for certain situations, some of which are 

highlighted below: 

• You should nap whenever you shift from day work to night 

work, cannot sleep more than four to five hours during your 

sleep period, and must work the following night.

• Naps longer than one to two hours are not recommended if 

your next sleep period will take place during the following night. 

In this case, naps taken during the day may interfere with the 

onset and duration of the following night’s sleep.

• When rapid shift rotations are used, personnel should be 

encouraged to use naps during their time off in order to 

compensate for sleep loss incurred during the transition to 

nighttime duty hours.

• When shifting from daytime to nighttime duty hours, 

opportunities for naps may occur:

- During the afternoon (e.g., between 1500 to 1700 hours) 

- In the evening (e.g., between 1600 to 1900 hours) prior to 

reporting for a nighttime duty period (e.g., from 2100 to 0500 

hours)

Research on the effects of the restorative value of naps indicates 

that:

• A 2-hour nap taken in mid-afternoon (e.g., from 1500 to 1700 

hours) results in a greater restoration of alertness than a twohour nap taken in the evening (e.g., from 1900 to 2100 hours).
A-12 

• Naps taken during the mid-afternoon (e.g., at 1500 hours) 

contain more total dreaming time (REM sleep) than naps taken 

at 0300 hours.

• When transitioning from daytime duty hours to nighttime duty 

hours later the same day, a nap at 1500 hours can compensate 

for sleep loss incurred during the assigned sleep period.

• Naps taken in the afternoon can be more restorative than naps 

taken in the evening prior to reporting for nighttime duty. Naps 

taken during a work period after midnight, however, can be less 

restorative than earlier naps, and can induce performance 

degradation for up to one hour. This consideration limits the 

value of a nap after midnight.

Pre-adaptation prior to travel across time zones

While potentially useful, pre-adaptation to a new time zone requires 

considerable coordination and cooperation. Under a pre-adaptation 

plan, personnel typically begin shifting their sleep cycle from their 

current time toward the new sleep cycle several days before 

transition:

• The number of days devoted to pre-adaptation, and the number 

of hours shifted daily, depend on many factors, including the 

number of time zones to be crossed and the amount of 

advance notice received.

• The magnitude of the phase shift should not exceed six hours 

per day, and should range from two to four hours per day.

• Pre-adapting personnel must be given off-hour access to 

finance and personnel services, properly timed meals, and so 

forth; otherwise, they will not be able to adhere to the out-ofphase schedule of their pre-adaptation plan.

• Family members should understand pre-adaptation techniques 

sufficiently to be sympathetic with a fellow family member’s 

need to be out-of-phase with the rest of the family. 
A-13 

Timed light exposure

By carefully scheduling exposure to natural or artificial daylight, it is 

possible to speed adaptation to a new work schedule or time zone. 

Specific suggestions are included in the scenarios provided later in 

this appendix. However, the following general guidelines apply: 

• Light levels of over 1000 lux (dawn brightness) are necessary 

to affect the body’s timing mechanism. Exposures lasting at 

least one hour are effective in resynchronizing the sleep cycle 

and other physiological rhythms.

• For individuals who are accustomed to sleeping during the 

night, working during the day and retiring during the night (e.g., 

at 2200), daylight or sufficiently bright light exposure between 

0300 and sunrise will consistently advance sleep onset 

approximately one to three hours earlier per day. 

The time period between 0300 and sunrise is referred to as the 

advance body time zone, because light exposure in this 

period results in earlier wake-up times and bedtimes. Predicting 

the exact amount of the advance requires information on 

physiological rhythms (e.g., core body temperature or melatonin 

production) that will be impractical to obtain in most field 

situations.

• In eastward travel, seeking daylight exposure during the 

advance body time zone (clock times calculated from the time 

zone that the traveler lived in prior to the trip) for the first three 

days will speed the resynchronization process. Daylight should 

be avoided between sunrise and 1100 local time (these clock 

times are calculated using the destination’s time zone) for the 

first three consecutive days in the destination location. 

The advance zone will shift to earlier times from day to day; it is 

difficult to accurately predict the time range after two days of 

advances without data on physiological rhythms. Therefore, 

after the third day, daylight exposure should be coordinated to 

occur as soon after awakening as it occurred in the origination 

time zone. 
A-14 

• In westward travel, seeking daylight or bright light exposure 

between sunset and 0300 (delay body time zone) will help 

delay sleep onset. The duration of the delay depends on the 

duration of light exposure. In most cases, exposure durations of 

one to three hours will result in significant delays of one hour or 

more, depending on individual differences.

• Artificial bright lights can be used to influence changes in sleep 

prior to or during shift changes or travel, provided that the 

appropriate equipment is available. Bright light banks are 

available from commercial suppliers and appear to be effective. 

Providing a brightly-lit work area for night-shift workers can be 

beneficial.

• Wearing dark sunglasses can minimize unwanted exposure to 

daylight (see eastward travel, above). Very dark sunglasses 

may be ordered from commercial sources. If these are not 

available, conventional sunglasses can reduce light exposure. 
 A-15 

A-4: Shiftwork, Sleep, and Biological 

Clock Management

Shiftwork Maladaptation 

Optimizing crew rest, along with preventing physiological maladaptation to 

shiftwork, can contribute significantly to a person’s ability to endure longterm exposure to harsh working conditions, without compromising work 

performance and safety. Shiftwork maladaptation results from an inability to 

adapt human physiology to rapidly rotating cycles of sleep and work. 

Adapting to nighttime or daytime work requires adjusting physiological and 

cognitive activities that are regulated by the biological clock. The biological 

clock is a physiological mechanism composed of neural networks and 

hormonal outputs that regulate sleep and wakefulness cycles as well as the 

daily availability of energy and cognitive resources. 

Maladaptation to shiftwork schedules, and the lack of energy-restorative 

sleep, result in a multitude of persistent symptoms such as: 

• Low energy 

• Lack of motivation 

• Introversion 

• Reduced and unclear communication with coworkers 

• Apathy 

• Reduced attention to detail 

• Depression 

• Performance degradation during duty hours 

• Degraded endurance 
A-16 

• Reduced safety 

Other health effects such as increased incidence of cardiovascular disease, 

gastrointestinal disorders, and sleep disorders have been documented in 

populations exposed to shiftwork maladaptation (Congressional report, 

1991). 

Inconsistent sleep and daylight exposure reduce safety 

Personnel accustomed to waking up and seeing daylight in the morning 

(e.g., at 0700) are adapted to work during daylight duty hours and to sleep 

during nighttime hours. Their biological clock is day-oriented; adjusted, that 

is, to provide energy and cognitive resources during normal workday and 

evening hours. 

Two peaks of alertness and energy availability will take place throughout 

the day: one in the morning and one in the early evening (see Figure 1). 

Day-oriented personnel will normally experience reductions in energy and 

alertness immediately upon awakening, again in the mid-afternoon, and 

again in late evening. This pattern of energy availability will be maintained 

consistently if personnel obtain good-quality sleep (uninterrupted sleep in 

quiet and dark environments) daily for seven to eight hours. 

However, should the sleep period become reduced to fewer than six hours 

per day, or be frequently interrupted by bright lights, noise, or movement, a 

daily sleep debt will begin to accumulate. The consequences of this sleep 

debt will be first experienced in the degradation of: 

• Alertness 

• Decision-making ability 

• Performance of mental function requiring logical ability 

Persistent sleep debt throughout a week will result in increased daytime 

sleepiness and in degradation of cognitive and psychomotor performance. 

And, as performance fares so fares safety. 

In addition to sleep duration, the stability of the body’s biological clock 

directly affects both alertness and performance. Frequent disruption in the 

daily adjustment of the biological clock adds to a deterioration of alertness 

and performance. For instance, working on the bridge under a watch 
A-17 

schedule that requires waking up at 0700 on Mondays, Wednesdays, and 

Fridays, but requires a 0330 wake-up on Tuesdays, Thursdays, and 

Saturdays, will send conflicting signals to the biological clock, particularly 

during the summer. On the days that wake-up times are required at 0330, 

the clock will receive daylight exposure earlier than usual (at approximately 

0500,) resulting in an advance of wake up times and bedtimes. 

Conversely, on the days the biological clock does not receive the early 

morning daylight dose, bedtimes and wake-up times will be allowed to slip 

to a later time. This advance of body time can be approximately one-half to 

one hour per day. These changes in the body’s timing mechanism affect 

the alignment of daily peaks and troughs of other physiological rhythms 

such as core body temperature (usually high during daylight hours and low 

during nighttime), and production and release of hormones and 

neurotransmitters. 

In general, the biological clock requires approximately three days to readjust to a new regimen, such as a two-hour advance in daylight exposure 

due to earlier wake-up times. This readjustment will take place if the new 

sleep/wake schedule is consistent from day to day. However, if the inputs 

are inconsistent, the clock’s timing can become disorganized in such a way 

that the physiological rhythms under its control will no longer be expressed 

in a predictable pattern. The individual impact results in: 

• Sleepiness 

• Insomnia 

• Deterioration of performance in mental and motor tasks 

Inconsistent inputs to the biological clock are common when personnel 

work nighttime shifts and do not control daylight exposure at the end of the 

shift. For instance, a watch schedule prescribing a six-hour watch during 

the night (e.g., beginning at 2400), then six hours of time off (from 0600-

1200), followed by a six-hour watch beginning at approximately 1200, can 

result in jet lag-like symptoms. In this particular work schedule, if personnel 

(e.g., engineering) work under normal lighting or in dim light environments 

(e.g., the bridge at night), exposure to daylight after sunrise will set the 

biological clock to a daytime orientation. In a daytime orientation, the 

biological clock predisposes the brain and energy cycles for sleep, and not 
A-18 

work, during nighttime. Fatigue-induced deterioration of performance will 

occur during nighttime hours.

Shiftwork maladaptation prevention 

Optimally, sleep must take place during a time of day scheduled by the 

internal biological clock. This clock system (details in next section) 

regulates the timing of sleep onset and wake-up times. Due to evolutionary 

pressures and physiological characteristics, the human body is 

predisposed to work during daylight hours and to sleep during nighttime 

hours. The body’s clock system maintains a sleep schedule in 

synchronization with local sunrise and sunset, and daylight duration. 

Energy cycles regulate the experience of high and low levels of alertness 

throughout the day. Alertness peaks in the mid-morning hours, dips in the 

afternoon hours, peaks again in the early evening hours, and begins to 

decrease in the early night, reaching daily lows in the middle of the night. 

The exact times of these peaks and valleys depend on specific inputs to 

the biological clock system; namely, wake-up times, bedtimes, meal times, 

and, more importantly, the time of daylight exposure (or exposure to 

artificial light). 

Personnel exposed to regular work schedules that facilitate consistency 

from day to day will enjoy the benefits of a well-synchronized biological 

clock. These benefits include regular energy-restoration cycles, and 

predictable peaks and troughs of alertness. In contrast, work schedules 

that impose frequent transitions from daytime to nighttime duty hours tend 

to disrupt energy-restoration processes and thereby to degrade endurance. 

Adjusting the biological clock requires implementing a specific schedule of 

daylight (or artificial-light) exposure, and maintaining a consistent sleep 

schedule. One way to minimize endurance degradation during nighttime 

work is to reverse the biological clock’s synchronization from daytime to 

nighttime orientation. For the clock’s timing to reset energy resources to 

peak during nighttime, work must take place under bright lights 

(approximately 1000 lux or more), mimicking the effects of daylight. Sleep 

must take place in a dark and noise-free environment. Lacking control of 

daylight (or bright-light) exposure times contributes significantly to 

endurance degradation. 
A-19 

If the use of bright, artificial light is not compatible with the work 

environment (e.g., on the bridge of a cutter or the cockpit of a helicopter at 

night), a specific light and sleep management schedule can be designed to 

shift the biological clock toward a night orientation. Because experimenting 

with light-exposure schedules can result in unintentionally inducing chronic 

endurance degradation and jet lag-like symptoms, it is recommended that 

professionals working in the fields of circadian rhythms and sleep 

management develop these light and sleep management schedules. 

The synergistic effects of disrupted sleep (fewer than seven to eight hours) 

coupled with biological-clock disorganization can lead to endurance 

degradation, jet lag-like symptoms, and an exacerbation of psychological 

maladjustment symptoms, such as irritability, depression, and even 

psychosis. Other physiological symptoms associated with this condition 

include cardiovascular disease and gastrointestinal disorders. 
A-20 

[This page left intentionally blank.] 
 B-1 

Appendix B 

Supporting Documents 
 B-2 

[This page left intentionally blank.] 
 B-3 

B-1: References 

Bell, D.S., and Donev, S. (1993). Curing Fatigue. Berkley Books, 

New York, NY. 

Brown, G.(1999). The Energy of Life. The Free Press, New York, 

NY. 

Caldwell, J. (1996). “Sleep Deprivation”, in Crowley, Newton, 

Davidson, Lindsey, and Marcum (Eds.), Leader’s Guide to Crew 

Endurance. Fort Rucker, AL: U.S. Army Aeromedical Research 

Laboratory and U.S. Army Safety Center. 

Caldwell, L. (1996). “Stress and Fatigue”, in Crowley, Newton, 

Davidson, Lindsey, and Marcum (Eds.), Leader’s Guide to Crew 

Endurance. Fort Rucker, AL: U.S. Army Aeromedical Research 

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