5012C.FR

APPLICATION OF ICE BOOMS

FOR OIL-SPILL CLEANUP

IN ICE INFESTED WATERS

FINAL REPORT

April, 2001

Prepared for:

Department of the Interior,

Minerals Management Service,

Engineering and Research Branch, MS 4021,

Herndon, Virginia 20170-4817

Prepared by:

Razek Abdelnour

George Comfort

FLEET TECHNOLOGY LIMITED

311 Leggett Drive

Kanata, Ontario

K2K 1Z8
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Application of Ice Booms for Oil Spill Cleanup in Ice-Infested Waters ii

EXECUTIVE SUMMARY

This report provides the results of a study to assess the applicability of ice boom technology to

aid or extend oil spill cleanup capabilities in broken ice. The technology has been developed

and used successfully at several locations to control the ice. For oil spill cleanup in broken ice,

booms have the potential in a number of ways, such as:

(a) preventing ice ingress into the spill area, thereby providing an ice-free area where

conventional oil spill equipment can operate; and,

(b) providing a means to assist in separating the oil from the ice.

Ice booms may have the potential to assist in many of the scenarios defined in the Alaska Clean

Seas Technical Manual.

Ice booms, in combination with the available support vessels on the North Slope, are expected to

be applicable to oil cleanup in moderate broken ice conditions of up to about 50%. Booms are

also expected to be applicable for some cases in higher ice concentrations of up to 70%.

However, larger vessels with more power, such as icebreakers, would be required for a wide

operating envelope.

Prototype tests should be carried out in the Alaskan Beaufort Sea as the next step in advancing

this technology for reliable usage in oil spill cleanup situations in broken ice in the Arctic. It is

believed that quite conservative assumptions were made in this project in establishing the loads

on the boom, particularly with respect to the under-ice currents at the boom, and their colinearity

with the winds. This was necessary because very little data are available for this case. Field

measurements would be valuable to improve the estimates made here.

A field deployment should be conducted offshore of Prudhoe Bay using a boom of limited size. A

boom with two 500 ft (150 m) spans should be built and deployed using the available support

vessels in the chevron and catenary configurations.

This work should be accompanied with numerical analyses that build upon the results of the field

tests and the work done here.
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Application of Ice Booms for Oil Spill Cleanup in Ice-Infested Waters iii

ACKNOWLEDGMENTS

The oil spill scenarios used in this study were taken directly from those developed by

Alaska Clean Seas, which are reported in the Alaska Clean Seas Technical Manual.

The project benefited from extensive research and field deployments regarding ice boom

technology, which have been carried out over the past seven years by, or on behalf of, the

following organizations:

• New York Power Authority

• Ontario Power Generation

• Hydro-Quebec

• Canadian Coast Guard

These programs produced an extensive knowledge base to define all aspects of ice boom

performance and they led to the development of numerical models to design an ice boom.

Joseph Mullin of the Minerals Management Service of the United States Department of the

Interior was the Contract Office Technical Representative (COTR) for this project.

DISCLAIMER

The opinions, findings, conclusions, or recommendations expressed in this report are those

of Fleet Technology Limited and do not necessarily reflect the views or position of the U.S.

Department of the Interior, Minerals Management Service.
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Application of Ice Booms for Oil Spill Cleanup in Ice-Infested Waters iv

TABLE OF CONTENTS

1 INTRODUCTION AND PROJECT OBJECTIVES .......................................................1

1.1 INTRODUCTION AND BACKGROUND ..............................................................................1

1.2 PROJECT OBJECTIVES ...................................................................................................2

2 TECHNOLOGY REVIEW...............................................................................................3

2.1 ICE-CAPABLE MECHANICAL OIL SPILL CLEANUP EQUIPMENT .......................................3

2.2 ICE BOOM TECHNOLOGY ..............................................................................................4

2.2.1 Historical Perspective and General Objectives for Booms...................................4

2.2.2 Typical General Arrangement for a Boom ...........................................................5

2.2.3 Recent Boom Technology Developments: the Lake Erie Niagara River Boom......6

2.2.4 Recent Boom Technology Developments: the Canadian Coast Guard Booms.......8

2.2.5 Boom Technology Developments: Other Booms...................................................9

2.2.6 Summary............................................................................................................11

3 ICE BOOM APPLICABILITY FOR OIL SPILL CLEANUP .....................................12

3.1 OVERVIEW.................................................................................................................12

3.2 OIL SPILL RECOVERY SCENARIOS ...............................................................................12

3.2.1 Scenario 1: Oil-Spill from an Offshore Structure ..............................................12

3.2.2 Scenario 2: Batch Spill From an Oil Tanker ......................................................14

3.2.3 Scenario 3: Continuous Spill from a Punctured Offshore Pipeline .....................16

3.2.4 Scenario 4: Continuous Spill from a Reservoir...................................................16

3.2.5 Scenario 5: Oil Drifting in a River.....................................................................17

4 ICE LOADS ON THE BOOM .......................................................................................19

4.1 ICE LOADING SCENARIO .............................................................................................19

4.2 CALCULATING WIND AND CURRENT DRAG FORCES ....................................................23

4.3 CALCULATING PACK ICE FORCES................................................................................25

4.3.1 Effect of Pack Ice Concentration........................................................................26

4.3.2 Effect of Pack Ice Thickness...............................................................................27

4.3.3 Effect of Pack Ice Features or Interaction Types................................................28

4.3.4 Effect of Ice Pressure .........................................................................................29

4.4 LOADS ON THE BOOM.................................................................................................30

4.4.1 Wind and Current Drag Forces: Inputs Used and Cases Considered ................30

4.4.2 Calculating Ice Loads........................................................................................31

4.4.3 Calculated Line Loads Acting on the Boom........................................................31

4.4.4 Anchoring or Ship Thrust Requirements for the Boom........................................34

5 ICE BOOM CONFIGURATIONS AND DESIGN CONSIDERATIONS....................36

5.1 ENVIRONMENTAL CONDITIONS ...................................................................................36

5.1.1 Ice Loadings......................................................................................................36

5.1.2 Wave Loadings ..................................................................................................37

5.2 CASE STUDY ..............................................................................................................37
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Application of Ice Booms for Oil Spill Cleanup in Ice-Infested Waters v

5.3 SHIP-BASED BOOM DEPLOYMENT...............................................................................39

5.3.1 Design Summary................................................................................................40

5.3.2 Detailed Design: Calculation of a Pontoon’s Ice Retention Capacity.................44

5.4 FIXED BOOM INSTALLATION.......................................................................................46

6 REQUIRED SHIP PERFORMANCE............................................................................49

6.1 DYNAMIC POSITIONING: REQUIRED SHIP BOLLARD THRUST........................................49

6.2 SHIP TRANSIT TO THE SPILL SITE AND MANEUVERING AT THE SPILL SITE ....................51

6.3 SUMMARY..................................................................................................................52

7 CONCLUSIONS .............................................................................................................53

8 RECOMMENDATIONS ................................................................................................54

8.1 ISSUES REQUIRING FURTHER INVESTIGATION..............................................................54

8.2 RECOMMENDATIONS ..................................................................................................54

9 REFERENCES................................................................................................................55

APPENDICES:

Appendix A Typical Design Drawings of an Ice Boom

Appendix B Discussion on the Report by The MMS, Alaska office
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Application of Ice Booms for Oil Spill Cleanup in Ice-Infested Waters vi

LIST OF FIGURES

Page

Figure 1.1 Oil Behavior and Fate in Broken Ice 1

Figure 2.1 Lake Erie Niagara River Ice Boom 4

Figure 2.2 Ice Boom Schematic 5

Figure 2.3 Lavaltrie Ice Boom 6

Figure 2.4 Yamachiche Ice Boom 7

Figure 2.5 Prototype Lake Erie Niagara River Ice Boom 8

Figure 2.6 Ice Boom Deployed at the Hull2 and EB Eddy Power Plants 9

Figure 2.7 Ice Boom Deployed at the Pickering Nuclear Generating Station 10

Figure 2.8 The Wakefield Ice Boom 10

Figure 3.1 Scenario 1a: Oil Spill From an Offshore Structure 13

Figure 3.2 Scenario 1b: Oil Spill From an Offshore Structure 13

Figure 3.3 Scenario 2a: A Batch Spill From a Tanker 14

Figure 3.4 Scenario 2b: A Batch Spill From a Tanker 15

Figure 3.5 Oil Slick Velocity Versus the Current Velocity 15

Figure 3.6 Scenario 3: Continuous Spill From a Punctured Offshore Pipeline 16

Figure 3.7 Continuous Spill From a Reservoir 17

Figure 3.8 Oil Drift in a River 18

Figure 4.1 “Dead Wedge” Formed Upstream of a Boom in an Open Sea 19

Figure 4.2 “Dead Wedge” Formed Upstream of a Boom in a Channel 20

Figure 4.3 Ice Accumulation and Loading Process in Pack Ice Concentrations

Up to About 8/10 ths 21

Figure 4.4 Ice Accumulation and Loading Process in High Pack Ice

Concentrations (7-9/10ths) 22

Figure 4.5 Triangular-Shaped Ice Accumulation Upstream of the Boom

Placed in Lac St. Pierre (in the St. Lawrence River) 23

Figure 4.6 The Offshore Structure, the Kulluk used for oil exploration in the Canadian

Beaufort Sea during the 1980’s 24

Figure 4.7 Effect of Pack Ice Concentrations on Pack Ice Loads 25

Figure 4.8 Ice Loads on the Kulluk in Managed Ice Conditions With Good

Ice Clearance and No Pressure 26

Figure 4.9 Ice Loads on the Kulluk in Tight Managed Ice Conditions With

Poor Ice Clearance and No Pressure 27

Figure 4.10 Effect of Pressure on the Loads Exerted on the Kulluk 28

Figure 4.11 Line Loads for a Pack Ice Concentration of 3/10ths With No

Pressure 30

Figure 4.12 Line Loads for a Pack Ice Concentration of 5/10ths With No

Pressure 32

Figure 4.13 Line Loads for a Pack Ice Concentration of 7/10ths With No

Pressure 33
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Application of Ice Booms for Oil Spill Cleanup in Ice-Infested Waters vii

 Page

Figure 4.14 Total Anchoring Requirements for a Pack Ice Concentration of

3/10ths With No Pressure 33

Figure 4.15 Total Anchoring Requirements for a Pack Ice Concentration of

30% With No Pressure 34

Figure 4.16 Total Anchoring Requirements for a Pack Ice Concentration of

50% With No Pressure 35

Figure 4.17 Total Anchoring Requirements for a Pack Ice Concentration of

70% With No Pressure 35

Figure 5.1 The Deployment of an Ice Boom in two Configurations (i.e.,

Chevron and Catenary) Upstream of an Offshore Structure 39

Figure 5.2 Boom Maneuvering and Attachment of an Oil Spill Boom to

An Ice Boom 39

Figure 5.3 Pontoon Attached to the Span Cable to Allow Ice Over-Run when

The Ice Load Exceeds the Boom’s Ice Retention Capacity 43

Figure 5.4 Buoy Used to Connect the Tugboat or the Anchor to the Boom 44

Figure 5.5 Schematic of Forces Acting on the Boom 44

Figure 5.6 The Effect of Pontoon Diameter on The Boom’s Ice Retention

Capacity 45

Figure 5.7 The Ice Action on the Pontoon Before Submergence 47

Figure 5.8 Fixed Boom Installation 47

Figure 5.9 Anchoring in Sandy Silt 48

Figure 5.10 Anchor used for Rock Bottoms 48

Figure 6.1 Example Of Ship Maneuvering For Maintaining The Ice

Boom In Position 49

Figure 6.2 Operating Limits for the Largest Vessels on the North Slope 50

LIST OF TABLES

Page

Table 4.1 Maximum Ice Loads on the Kulluk 28

Table 4.2 Drag Force Calculation Inputs 30

Table 5.1: Ship-Based Deployment for Scenario 1a: Design Criteria Used

And Boom Design Developed 40

Table 5.2 Pontoon Parameters Established for the Case Study Design 42

Table 5.3 Fixed Installation for Scenario 1a 47

Table 6.1 Bollard Thrust of Some Icebreakers and Their Capabilities for

Stationkeeping With The Boom 50

Table 6.2 Stationkeeping Capabilities of the Largest Vessels on the North

Slope for Boom Deployments 51
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Application Of Ice Booms For Oil Spill Cleanup In Ice-Infested Waters 1

1 INTRODUCTION AND PROJECT OBJECTIVES

1.1 Introduction and Background

It is generally recognized that current capabilities for cleaning up oil spills in pack ice are very

limited (e.g., S.L. Ross et al, 1998). The reasons for this include the fact that pack ice conditions

tend to disperse the spilled oil widely into thin films or droplets that may coat the pack ice pieces

or be located between them, on them, or below them (Figure 1.1). These films or droplets are

expected to be too thin to burn, or to clean up efficiently using mechanical equipment.

Depending upon the geographical location and the time of year, oil may be released into an

environment ranging from open water to broken ice conditions (i.e., ice floes with varying sizes

and concentrations) to sheet ice conditions. Consequently, a number of scenarios are possible

(Figure 1.1), such as:

(a) floating oil getting mixed between and on the sides of individual ice floes;

(b) oil submerged under the ice floes;

(c) oil encapsulated under the ice floes;

(d) oil mixed in with slush.

Figure 1.1: Oil Behavior and Fate in Broken Ice (after Bobra and Fingas, 1986)

The oil spill cleanup scenario also depends on the source of the spilled oil, which could include:

(a) a batch spill resulting from an oil tanker accident;

(b) a blowout of an exploration or production well;

(c) damage to an underwater pipeline.
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However, whatever the source of the spill, it is generally recognized that presently available

mechanical oil-spill recovery devices cannot operate efficiently in waters containing significant

ice concentrations. This is due to a number of reasons including:

(a) the ice, and its pressure, disperses the oil widely into thin films or droplets. This

significantly reduces the oil recovery efficiency by preventing conventional skimmers

from operating in thick oil pools.

(b) the ice prevents the skimmer from accessing the oil easily.

(c) the oil spill cleanup equipment may be damaged by the ice.

1.2 Project Objectives

The overall objective of this project was to investigate the potential application of ice control

booms for oil spill cleanup efforts in broken ice. Ice control booms may aid oil spill cleanup

efforts in a number of ways, such as:

(a) prevention of ice ingress into the oiled area - this would have the potential to improve or

extend the capabilities of current mechanical equipment by allowing it to operate in

conditions that are ice-free or significantly reduced in ice severity.

(b) providing containment of the spilled oil – this might be achieved, for example, by

surrounding an oiled area that contained ice pieces with a boom. This would aid cleanup

efforts by preventing widespread dispersion of the spilled oil.

(c) improving current capabilities to separate the oil from the ice – this might be achieved,

for example, by towing an oiled ice area with a boom and support vessels at speeds high

enough that the oil is removed from the ice.

The project had a number of sub-objectives (listed below) that were necessary in order to

evaluate the applicability of ice control booms for oil spill cleanup:

(a) define the most likely scenarios where an ice boom could be used for effectively

recovering oil from ice or for preventing the ice from drifting toward an oil spilled area

(b) investigate the operating windows in which an ice boom can be deployed in a broken ice

field. This included a review of the expected ice forces on an ice boom deployed in

various ice concentrations, the resistance capacity of a boom to retain ice, the bollard pull

of a typical icebreakers and tugboats required to keep the boom in place during the oil

recovery operations.
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Application Of Ice Booms For Oil Spill Cleanup In Ice-Infested Waters 3

2 TECHNOLOGY REVIEW

2.1 Ice-Capable Mechanical Oil Spill Cleanup Equipment

Mechanical equipment for the efficient recovery of oil in significant pack ice concentrations is

presently unavailable, despite the fact that a significant amount of research has been conducted

to date. Some of the previous technology development efforts include:

(a) Purves et al., 1977, proposed a circular net for collecting oil from an Arctic oil well

blowout. At that time, information regarding pack ice pressure and its behaviour was

scarce and thus, its effect on an ice boom was also poorly understood. This lack of

fundamental knowledge severely hampered the design efforts.

(b) Abdelnour et al, 1985, conducted laboratory tests of an oil-skimming bow. These tests

showed that the oil-skimming bow, even with the use of a water jet to herd the oil and

move it toward the skimmer, had poor oil recovery efficiency, especially for high ice

concentrations of close to 10/10. The study also showed that the approach would be

difficult to apply under Arctic conditions.

(c) Loset et al, 1992, investigated the concept of using a flexible boom for collecting ice

upstream of a well blowout. These model test experiments showed that significant

research was still required. Field tests were also carried out. Although no published

information was obtained regarding these tests, the work did not result in a commercially

available product.

(d) the current MORICE project – this project is aimed at developing an ice-capable skimmer

(Jensen, 2000). Small scale, preliminary testing has been carried out in the laboratory

and in the field. However, considerable work remains to develop this into a commercial

usable product.

Despite this work, mechanical equipment for reliable oil spill cleanup in pack ice is not

available. The problems encountered may be broadly classified as follows:

(a) containment – pack ice conditions tend to prevent the occurrence of thick oil pools by

dispersing the spilled oil, which results in low oil cleanup efficiencies. Containment is

required for thick oil pools to develop.

(b) separation – it is well known that the oil will tend to be widely dispersed and mixed into

the pack ice. It is necessary to separate the oil from the ice in order to conduct cleanup

operations.

(c) damage due to interaction with ice pieces

(d) access – in many cases, the pack ice would prevent the mechanical equipment from

accessing the spilled oil.
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2.2 Ice Boom Technology

2.2.1 Historical Perspective and General Objectives for Booms

Ice booms have been used for more than 40 years upstream of water intakes at hydroelectric

power plants and in river channels used for navigation for two general purposes, depending on

the particular site being considered:

(a) to prevent ice ingress into an area – Figure 2.1 shows a boom deployed annually in Lake

Erie, at the mouth of the Niagara River by the New York Power Authority (NYPA) and

Ontario Power Generation (OPG). The ice boom is to prevent ice floes and fragments in

Lake Erie from being driven into the Niagara River, which can cause blockage at their

water intakes and results in operation losses.

Figure 2.1: Lake Erie Niagara River Ice Boom

Note to Figure 2.1: This boom consists of 22 spans; is 2.6 km long; and has been deployed

annually in the northeast end of Lake Erie by the NYPA/OPG since 1963.

(b) to accelerate the formation of a stable ice cover – in this case, the boom’s purpose is often

to minimize the formation of frazil ice, along with the trashrack or water intake clogging

problems that are often associated with frazil ice. In other cases, the boom may be placed

to reduce the total ice volume generated in the river.

Booms developed to meet objective (a) above are of most interest for this study as this is one of

the methods by which ice control booms might aid oil spill cleanup efforts in ice.
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Application Of Ice Booms For Oil Spill Cleanup In Ice-Infested Waters 5

2.2.2 Typical General Arrangement for a Boom

It should be noted that ice booms with many different types of general arrangements have been

used to date. However, it is generally recognized that ice booms need to be designed with the

capability to relieve the ice load should it become too great. This is necessary to avoid damage

and/or excessive costs. This capability is achieved by constructing the booms such that the

flotation elements (i.e., pontoons – Figure 2.2) will submerge individually which allows the ice

to over-run the boom in severe conditions.

A typical ice boom section consists of one span cable (as shown in Figures 2.2 and 2.3) or more

span cables. (22 spans are shown in Figure 2.1). The span cable is attached at each end to an

anchor cable or to an anchor placed in the riverbed. Each span has pontoons attached to the

cable with chains, one at each end of the pontoon. These chains maintain the cable at about 1 m

below the water surface. The pontoons are typically about 10 m long and the gap between each

two pontoons is between 2 and 7 m. Buoys are used to facilitate the removal and the deployment

of the boom.

The ice-retention capacity of the boom is directly related to its buoyancy. When the ice load

exceeds the pontoon resistance capacity, it submerges and the ice drifts over the pontoon. This

limits the load on the boom, and reduces the probability of ice damage. The pontoon’s buoyancy

varies with its size and should be selected based on the desired ice retention capacity of the

boom.

Figure 2.2: Ice Boom Schematic
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Figure 2.3: Lavaltrie Ice Boom

Note: This is a close-up view of one 120 m wide span of the 1 km long Lavaltrie Ice Boom. The

current velocity at this location is 0.8 m/sec

2.2.3 Recent Boom Technology Developments: the Lake Erie Niagara River Boom

Traditionally, wooden timbers have been used for the pontoons of an ice control boom. This led to a

number of problems (listed below) that limited the boom’s ice retention capability and performance:

(a) the wooden timbers had little reserve buoyancy, particularly when they were water-logged,

which allowed ice to over-run the boom easily;

(b) the wooden timbers tended to deteriorate and to be damaged easily.

In 1992, the New York Power Authority (NYPA) and Ontario Power Generation (OPG) initiated

a study to assess and improve the performance of the Lake Erie Niagara River Ice Boom, which

had been comprised of wooden timbers up to then. The wooden timber ice boom had relatively

poor ice retention capacity and allowed a significant volume of ice to over-run the boom. This

caused ice to drift into the Upper Niagara River and forced NYPA/OPG to use large amounts of

water to flush the ice over Niagara Falls. The revenue losses resulting from this lost power

exceeded $750,000 U.S. per year.

Significant research and development was carried out over the 1992-97 period to better

understand the main factors affecting ice boom performance, and to develop an improved boom.

An analytical assessment of the “old” timber boom was first carried out. This study concluded

that the Lake Erie Niagara River ice boom would be much more effective if the pontoons had

more buoyancy to provide more ice retention capacity.
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The study also pointed out that the pontoons were being submerged when the loads on the

anchors and the span cables holding the pontoons were less than 5% of their design load, which

showed that the cables and the anchoring system had a large reserve capacity.

The “old” timber boom was next instrumented during the winter of 1993-94 (Abdelnour et al,

1995). This provided useful data for evaluating the boom’s performance and also for the

calibration of numerical models. These models produced the basis for the design of reliable and

efficient ice booms that led to overall improved performance.

The field data confirmed the earlier performance assessment. The ice submerged and over-ran

the boom when the ice load was well below the capability of the boom anchor and span cables.

A recommendation was made in July 1994 to replace the timber pontoons with larger and more

buoyant steel pontoons. These pontoons were expected to increase the boom’s ice resistance by

up to 5 times, compared to the timber pontoons. The steel pontoons were selected based on

model tests, analyses, and field deployments made by the Canadian Coast Guard (CCG) in the

St. Lawrence River (who undertook development efforts in parallel – described in the next

section).

NYPA/OPG next built a prototype ice boom that contained five spans with steel 30” diameter

pontoons (Figure 2.4).

Figure 2.4: Prototype Lake Erie Niagara River Ice Boom

Note: This figure shows the prototype ice boom that was tested. The pontoons in five of the 22

spans were replaced with steel pontoons for this prototype.

The prototype ice boom was instrumented and observed. The new steel pontoons proved to be

significantly better in resisting the ice than the timber pontoons (Figure 2.4). This prompted the
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Application Of Ice Booms For Oil Spill Cleanup In Ice-Infested Waters 8

NYPA/OPG to proceed with the replacement of all the timber pontoons with steel pontoons during

the fall of 1997 (Cowper et al, 1997).

It has operated successfully since that that time. Based on the cost savings associated with

reduced power generation losses, reduced repair costs for the boom, and reduced icebreaker time,

NYPA/OPG determined that the benefit/cost ratio for the “new” boom was 5.5.

2.2.4 Recent Boom Technology Developments: the Canadian Coast Guard Booms

During the same period that NYPA/OPG were undertaking development work, the Canadian

Coast Guard (CCG) embarked on a plan to improve the reliability of winter transportation

through the St. Lawrence River System. This was precipitated by an ice-related event that

interrupted navigation for a long period of time during the 1993 winter.

Laboratory tests were carried out to compare various ice boom pontoons. This was followed by

the use of analytical models to design a boom capable of retaining the ice in 0.8 m/sec currents.

A cylindrical pipe pontoon, with 0.61 m (24”) diameter, was proposed to resist the driving forces

expected for the Lavaltrie site (Abdelnour et al., 1995).

The CCG then built and deployed “new” steel pontoon ice booms in the St. Lawrence River

near: (a) Lavaltrie; (b) Lanoraie, and; (c) Lac St. Pierre. Each of these booms was built with the

purpose of preventing ice ingress into the main areas of the navigation channel.

The Lavaltrie and Lanoraie booms were re-engineered in 1993. The Lac St. Pierre boom, which

was 2.5 km long, was constructed in 1994 to retain the ice along the North East side of Lac St.

Pierre at Yamachiche (See Figure 2.5). The new Yamachiche ice boom resulted in improved

navigation in the St. Lawrence River channel due to significantly less ice obstruction.

Figure 2.5: Yamachiche Ice Boom

Note: The Yamachiche Ice Boom has 22 spans; is 2.6 km long; and has been deployed in the

northeast end of Lac St. Pierre since 1994.
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2.2.5 Boom Technology Developments: Other Booms

The experience gained since 1997 from the NYPA/OPG studies, and the feedback obtained from

the CCG ice booms, led to the development of a robust ice boom design procedure that has been

used for the conceptual design, detailed design, fabrication and deployment of several new ice

booms, including:

(a) the Hull2-E.B. Eddy Ice Boom – This boom was designed and built in 1997 (Figure 2.6).

The site was selected based on field observations carried out during the previous winter, of

1996/97 (Abdelnour et al, 1998). This boom was primarily built to accelerate the formation

of a stable ice cover, and to minimize frazil ice production. However, it was also successful

in preventing ice ingress into the trashracks of the two power plants (Figure 2.6).

The boom was deployed to protect two hydroelectric power plants; one owned by HydroQuebec and the other by E.B. Eddy Forest Product Limited. The boom was placed about

200 m upstream of the two intakes and spanned 225 m across the entire channel width.

Ice Cover Without a Boom Ice Cover After the Boom Was Deployed

Figure 2.6: Ice Cover at the Hull 2 and EB Eddy Power Plants:

Before and After the Boom Was Installed

Notes: 1. These power plants are located on the Ottawa River.

2. The boom was placed to accelerate the formation of a stable ice cover upstream of the two

power plants to reduce power generation losses. The production losses decreased by 80% in 1997,

which was the first year that the boom was installed. The reduction in power generation losses

was sufficient to pay for the cost of the boom in two years.
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(b) one on the Rideau River in Ottawa, upstream of Strathcona Rapids - The Strathcona

boom was deployed to minimize the production of ice in the Rideau River, thus reducing

the cost for ice clearing in the spring. This boom has one span and is about 100 m wide.

(c) one on the Rivière Rouge, upstream of the Chute Bell Hydroelectric Plant, near

Montebello, Quebec. The Chute Bell Boom was designed to protect the hydroelectric

power plant from ice. This boom also has one span and is about 100 m wide.

(d) Pickering Nuclear

Generating Station - In

February 1999, an ice boom

was installed at the

Pickering Nuclear

Generating Station (Figure

2.7). This boom was built to

prevent ice ingress into the

cooling water channel for

the power plant. It is

exposed to waves up to

about 4m high. The

experience base built up

with booms allowed this

boom to be built, designed,

and installed in 4 weeks.

(e) Wakefield Boom – This boom was deployed on the Gatineau River, 3 km upstream from

Wakefield, Quebec (Figure 2.8) in November 1999. The boom is designed to accelerate the

formation of an ice cover early in winter and to hold the broken ice during the spring breakup. This boom performed extremely well in forming the ice and was left in place during the

break-up.

Figure 2.8: The Wakefield Ice Boom,

(installed in November 1999)

Figure 2.7: Ice Boom Deployed at the Pickering

Nuclear Generating Station Ice Boom, in

February 1999
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Application Of Ice Booms For Oil Spill Cleanup In Ice-Infested Waters 11

2.2.6 Summary

Improved ice control booms have been developed that provide much better ice retention capacity.

Steel pontoon booms have been built at many sites to date. Robust design procedures have been

developed to apply the new booms. This shows that booms are a mature technology.
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Application Of Ice Booms For Oil Spill Cleanup In Ice-Infested Waters 12

3 ICE BOOM APPLICABILITY FOR OIL SPILL CLEANUP

3.1 Overview

All presently available oil-spill recovery devices cannot operate efficiently in waters containing

significant ice concentrations. The ice, and its in-plane pressure, significantly reduces the oil

recovery efficiency by preventing conventional skimmers from operating in thick oil pools.

Furthermore, the ice prevents the skimmer from accessing the oil easily. Also, the ice exposes

the skimmer to potential structural damage.

The overall intent of this report is to investigate the application of ice boom technology for

recovering oil in ice infested waters. An ice boom may be useful in a number of types of cleanup

applications as follows:

1) provide a means to prevent broken ice from drifting into the oil-spill area, thereby:

(i) allowing conventional equipment to operate;

(ii) allowing in-situ burning;

(iii) maximizing the operating window.

2) surrounding the contaminated area, thereby preventing dispersion of the spilled oil;

3) providing a means of separating the oil from the ice, in combination with support vessels,

thereby aiding oil recovery by conventional equipment.

3.2 Oil Spill Recovery Scenarios

The oil-spill scenarios are well described in the Alaska Clean Sea Technical Manual, 1999

(termed Manual subsequently). This Manual was prepared for contingency planning in the event

of an oil spill at the exploration sites offshore Alaska. Based on the Alaska Clean Seas Technical

Manual, 1999, six specific scenarios were defined for which the ice boom could be applied, as

follows.

3.2.1 Scenario 1: Oil-Spill from an Offshore Structure

Oil spills can occur in several ways from an offshore structure. Two main cases were depicted in

the Manual:

(a) The first case is when the oil is being released, either continuously, or as a batch spill, from

an island placed in relatively shallow water and where the prevailing wind direction, and

hence ice drift direction, is relatively constant. The boom could be deployed in a Chevron

shape, and anchored at least one hundred meters upstream of the structure (depending on the

size of the island, the type of spill, and other factors), as shown in Figure 3.1.
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Figure 3.1: Scenario 1a: Oil-Spill from an Offshore Structure

(b) The second case is where the structure is in deeper water and where wind direction changes,

and ice drift direction variations, are relatively frequent. The oil could either be released

continuously, as in the case of a blowout, or as a batch spill. In this case, the boom will have

to be continuously realigned with the wind using supply vessels and the distance of the boom

upstream from the structure will be significantly more than 100 m upstream (Figure 3.2).

Figure 3.2: Scenario 1b: Oil-Spill From An Offshore Structure
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In either of the above two cases, the boom would provide an ice-free area in its lee where drifting

oil can either be recovered using conventional oil spill recovery equipment (Figure 3.1) or

burned after being contained in a fire proof boom (Figure 3.2).

3.2.2 Scenario 2: Batch Spill From an Oil Tanker

Figure 3.3: Scenario 2a: A Batch Spill from a Tanker

A batch spill from a tanker (or a pipeline burst) can cause a large ice area to be oiled. In this

case, a supply vessel could tow the boom and surround the contaminated area.

Depending on the ice conditions, the oil spill spreading and the area where the oil is spilled, the

following options are available:

(a) Oil-Ice Separation at Spill Site - For this scenario, the boom would be towed by two supply

vessels through the ice to surround the contaminated area (Figures 3.3 and 3.4) to help

separate the oil from the ice in higher ice concentrations. Oil-ice separation is expected to

occur to some extent as the boom is not a continuous structure. Rather, it consists of steel

pontoons with gaps between them, with the pontoons being connected to a submerged span

cable (Section 2.2). Thus, the boom will contain ice pieces, but it will be incapable of

containing the oil. Hence, when it is towed through the ice by the ships, it may help to

separate the oil from the ice.

The oil can either be burned after being contained in a fireproof boom as shown in Figure

3.3 or it can be collected using conventional oil spill recovery equipment as shown in

Figure 3.4.
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Figure 3.4: Scenario 2b: A Batch Spill from a Tanker

To achieve oil-ice separation, the relative towing speed should be higher than the current

velocity required forcing the oil droplets to move under and between the ice floes.

Laboratory tests in a flume with a level ice sheet (by Cox et al, 1980 and Free et al, 1981)

showed that oil movement would occur under the sheet when the water velocity exceeds

about 0.13 ft/s (4 cm/s).

The oil slick movement rate increased substantially when the current exceeded about 0.3

knots (0.5 ft/s; 15.6 cm/s). See Figure 3.5. This shows that oil-ice separation using a

boom would likely be most successful if the towing rate exceeded about 0.3 knots (0.5

ft/s)

(b) Removal of the Oiled Ice to a Cleanup Site - The contaminated ice could also be towed to

an inlet where the currents are negligible where the ice is less likely to disperse in the

surrounding pack. In this case, the oil recovery logistics become less difficult and can be

completed over longer periods of time.

Figure 3.5: Oil Slick Velocity Versus The Current Velocity (after Cox et al, 1980)
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3.2.3 Scenario 3: Continuous Spill from a Punctured Offshore Pipeline

An oil spill from an underwater pipeline can cause the oil to disperse under the ice without being

easily seen or without it surfacing on the water.

Oil recovery in drifting pack ice of significant concentration would be impossible in this

situation with currently available equipment. A boom deployed in a Chevron shape (Figure 3.6),

could assist in this situation by diverting the ice away from the spill area. This mode of

deployment will reduce the amount of contaminated ice and provide an ice-free area where

conventional containment and recovery equipment could be deployed.

Figure 3.6: Scenario 3: Continuous Spill from a Punctured Offshore Pipeline

3.2.4 Scenario 4: Continuous Spill from a Reservoir

Ice can cause significant problems for a spill from a reservoir located on an inlet, a river or a

shoreline, when the ice is drifting. An ice boom could assist in this scenario by ‘shielding”

conventional cleanup equipment and/or containment booms from the moving ice (Figure 3.7).
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In this case, the ice boom would divert the ice and ensure little mixing between the ice and the

spilled oil. The boom would also provide an open water area for the oil spill recovery equipment

to operate effectively.

Figure 3.7: Continuous Spill from a Reservoir

3.2.5 Scenario 5: Oil Drifting in a River

The recommended response for this scenario in the Manual is to deploy booms across the river,

and to use conventional oil spill cleanup equipment (Figure 3.8). However, this response

technique would be ineffective if large amounts of ice were drifting downstream in the river. Ice

booms could assist here by retaining the drifting ice while allowing the oil to drift downstream to

be later collected by a conventional ice boom (Figure 3.8).

To evaluate the applicability of this approach, it is necessary to consider the currents and ice drift

rates at the site. The ice drift rate should be lower than about 2.6 ft/sec (80 cm/sec), which is

about the maximum current velocity at which ice can be effectively retained by a boom.

Only laboratory test data are available to estimate the relative currents required to achieve

effective oil-ice separation, as described in Section 3.2.2. These data suggest that currents of

more than about 0.5 ft/. sec would be required to achieve extensive oil slick movements under

the ice (Figure 3.5)
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Figure 3.8: Scenario 5: Oil Drift in a River
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4 ICE LOADS ON THE BOOM

4.1 Ice Loading Scenario

The expected ice loads are a very important issue as they will control the operating envelope for

the boom, in combination with the capabilities of the available logistical support platforms. It is

important to note that because the boom is designed to submerge and allow the ice to pass over it

when ice forces become too large (described previously), the boom is not expected to be

damaged should more severe ice conditions (than the design ones) be encountered. However,

this would temporarily render the boom ineffective for oil spill containment or for protecting oil

spill cleanup equipment behind the boom.

The ice loads on the boom will depend on the ice conditions in which the boom is deployed. The

important issues include:

(a) whether the boom will be used in “open sea” conditions or in a channel (termed “river

ice” conditions). This is an important distinction as the shorelines in a “river ice”

condition provide confinement which affect the loads exerted on the boom. Compare

Figures 4.1 and 4.2. Although the equivalent apex angle is typically much less for “river

ice” situations, which would theoretically result in higher drag loads on the boom, the

shorelines provide load relief to the boom as load is transferred to them. The net result,

for a 10/10 ice pack, the ice loads tend to be considerably less for “river ice” conditions.

However, for 3/10 to 7/10 ice pack, the ice load can be considerably less for a boom in an

open sea.

Figure 4.1: “Dead Wedge” Formed Upstream of a Boom in an Open Sea

(b) The type of ice conditions - loads have been evaluated for a boom in pack ice conditions.

Figures 4.3 and 4.4 illustrate the expected ice loading process for this case. Generally,

the interaction will proceed in two steps.
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First, the boom will fill with ice pieces. Then, ice fragments will be diverted past, or

shear past (depending on the ice concentration and pressure), the ice wedge. Clearly, the

maximum ice loads will be developed by the steady-state conditions produced after the

boom has become filled with pack ice fragments and subsequent ice floes are diverted

past the wedge that is formed (Figures 4.3 and 4.4).

Figure 4.2: “Dead Wedge” Formed Upstream of a Boom in a Channel

The total force on the boom (Ftot) is comprised of two general components as described in

equation 4.1.

Ftot = Fdrag + Fice [4.1]

where: Fdrag = the force due to wind and current drag

 Fice= the pack ice force due to the mechanisms in Figures 4.3 and 4.4

Drag forces and pack ice loads are discussed in Sections 4.2 and 4.3 respectively.
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Figure 4.3 Ice Accumulation and Loading Process in

Pack Ice Concentrations up to about 8/10ths
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Figure 4.4: Ice Accumulation and Loading Process in

High Pack Ice Concentrations (7-9/10ths)
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4.2 Calculating Wind and Current Drag Forces

The total drag forces, Fdrag, can be determined as follows:

Fdrag = Fcurrent + Fwind= (τc+ τw) A [4.2]

Wind drag shear stress, τw: τw = ρω Cdw Vw

2

[4.3]

Current drag shear stress, τc: τc = ρc Cdc Vc

2

[4.4]

where:

Fwind = wind drag force on the ice

Fcurrent= current drag force on the ice

A = the effective area of the ice cover affected by the current and wind (termed the “dead

wedge”, and illustrated in Figures 4.1 to 4.4)

Cd = drag coefficient at air-ice interface (Cdw) or at ice/water interface (Cdc).

ρ = specific gravity of water (ρc) or air (ρw).

V = wind speed (Vw) or current speed (Vc).

The effective area of the “dead wedge” was defined for the “open sea” conditions analyzed in

this study (Figure 5.1) by assuming that a triangular-shaped ice accumulation is formed. This

selection is based on past observations that showed a wedge will form with an apex angle

ranging from about 40° to 80° (e.g., Figure 4.5). The apex angle will be governed by the

frictional properties of the ice fragments in the wedge, and by the lateral confinement. The apex

angle will be reduced as the lateral confinement is increased.

Figure 4.5: Triangular-Shaped Ice Accumulation Upstream of the Boom

Placed in Lac St. Pierre (in the St. Lawrence River)
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Because booms will be most applicable to relatively open pack ice concentrations for the case

being analyzed here (described subsequently), the apex angle used for these analyses was

determined from analyses of the frictional properties of the ice fragments in the “dead wedge”.

An investigation into the behavior and properties of pack ice fragments that accumulated in front

of the Offshore Structure, the Kulluk was made (Barker et al, 2000). Gulf Canada Resources

used the structure for oil exploration in the Canadian Beaufort Sea during the 1980’s (see Figure

4.6).

Figure 4.6: The Offshore Structure, the Kulluk used for oil exploration in the Canadian

Beaufort Sea during the 1980’s.

The Kulluk was a moored, 70 m diameter (at the waterline) conical-shaped drilling structure

used in the Canadian Beaufort Sea. It was held on station with a mooring system comprised of

up to 12, 3.5” diameter mooring lines. See (Wright, 1999) for description. (Barker et al, 2000)

found that a value of 27° for φ (the internal friction angle of the pack ice material) produced the

best correlation between the measured and predicted ice loads. Assuming that Coulomb’s

friction law is applicable, the apex angle (θ) of the “dead wedge” can be calculated as follows:

θ = 2 * (45 - φ /2) [4.5]

Equation 4.5 yields a value of 63° for the apex angle for an internal friction angle of 27°. This

value was used for evaluating the area of the “dead wedge” for all subsequent drag force

calculations.

Values of 0.0033 and 0.020 were used for the air/ice surface drag coefficient (i.e., Cdw) and the

water/ice surface drag coefficient (i.e., Cdc) respectively, as these are typical values for a

relatively rough broken ice cover. It is recognized that these values are not constants, and they

vary with both time and ice conditions. However, because several conservative assumptions

were made in determining the drag forces (described subsequently), efforts to account for the

expected variations in drag coefficient (within the range of commonly-used values) were not

considered to be useful.
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4.3 Calculating Pack Ice Forces

The loads produced by pack ice in an “open sea” condition (Figure 4.1) depend on many factors

including:

(a) the pack ice concentration;

(b) the thickness of the pack ice fragments;

(c) the type of features in the pack ice (e.g., ridges), and whether or not ice management

operations are carried out;

(d) whether or not the ice is under pressure.

Extensive reference was made in this project to full-scale data collected with the Kulluk for a

number of reasons, which are listed below.

(a) Loading Scenario - the loading scenario was similar to that expected for the ice control

boom. Compare Figure 4.7 with Figures 4.1, 4.3, and 4.4.

(b) Ice Conditions - the Kulluk data were obtained in pack ice conditions in the Canadian

Beaufort Sea. The Kulluk typically operated in the June to December period.

(c) Width of loading – the Kulluk was a wide structure that allows the measured forces to be

applied (on a line load basis) to other wide structures with confidence. Although it is

well known that ice loads decrease with the loaded area, and with the width of loading or

aspect ratio, the Kulluk is wide enough that a direct application of the measured line

loads to other loading widths will involve very little error.

Figure 4.7: Ice Loading Schematic for the Kulluk (after Wright, 1999)

(Note: the photo referred to the figure caption from Wright, 1999 was not included because it is

of poor quality)
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Ice management by icebreakers is one significant difference between the Kulluk operations and

those for the boom. Most often, the ice approaching the Kulluk was broken up into small floes

by two CAC 2 (Canadian Arctic Class) icebreakers which reduced the loads significantly

(Wright, 1999). However, as will be shown subsequently, the boom is expected to be capable of

operating only in relatively low ice concentrations (up to about 50 to 70%). In this case, ice

management operations become less significant.

4.3.1 Effect of Pack Ice Concentration

Previous studies (e.g., Wright, 1999; Comfort et al, 1999) have shown that this is a very

important factor. A wide range of model test data in broken ice have shown that the ice loads are

relatively low at ice concentrations below about 8/10ths and that they rise substantially at greater

concentrations (Figure 4.8). The best-fit equation to the model test data is as follows:

Load Ratio = 1.13 * 10–5 * C4.94 [4.6]

Where:

Load Ratio = mean load at a given concentration/mean load at 10/10 concentration

C = ice concentration, in tenths

This trend has been generally confirmed by full scale data for the Kulluk (Wright, 1999), which

was a moored conical-shaped drilling structure used in the Canadian Beaufort Sea.

Figure 4.8: Effect of Pack Ice Concentration on Pack Ice Loads

(See Comfort et al, 1999 for supporting information)
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4.3.2 Effect of Pack Ice Thickness

Full scale data for the Kulluk (Figures 4.9 and 4.10 – Wright, 1999) and model test data for a

wide range of floating structures (Comfort et al, 1999) both show that the loads increase with the

ice thickness. This trend reflects a number of processes including:

(a) the forces developed by rigid body decelerations of floes in low or high pack ice

concentrations (Figures 4.3 and 4.4) increase with the mass of the floes;

(b) ice failure forces along the wedge boundary increase with the ice thickness;

(c) frictional forces along the wedge boundary increase with the ice thickness.

Figure 4.9: Ice Loads on the Kulluk in Managed Ice Conditions with Good Ice Clearance

and No Pressure

(after Wright, 1999)
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Figure 4.10: Ice Loads on the Kulluk in Tight Managed Ice Conditions with Poor Ice

Clearance and No Pressure

(after Wright, 1999)

4.3.3 Effect of Pack Ice Features or Interaction Types

It is well known that pack ice is highly non-uniform. The significance of the different ice feature

and interaction types that may occur is illustrated in Table 4.1.

Table 4.1: Maximum Ice Loads on the Kulluk

(Wright, 1999)

Case - Ice condition and thickness Maximum Load Maximum Line Load

(tonnes) ( lbs) (kN/m) (lbs/ft)

Level unbroken ice to 1.2 m 250 551000 35 2400

Small unmanaged ridges: approx. maximum

thickness = 8 m

400 882000 56 3800

Managed ice with good clearance: maximum floe

fragment thickness = 10 m

400 882000 56 3800

Floe fragment impacts 600 1323000 84 5700

Tight managed ice with poor clearance: maximum

floe fragment thickness = 10 m

350 772000 49 3400

Tight managed ice with poor clearance and

pressure: maximum floe fragment thickness = 4m

550 1213000 77 5300
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The following observations can be made:

(a) effect of ice management (which refers to the operations done by Gulf Canada, who

operated the Kulluk, to break up the incoming ice using icebreakers) – this greatly

affected the loads. The loads in unmanaged ice were up to about 5 times higher than the

comparable case for managed ice (Wright, 1999).

(b) effect of ice feature and interaction type – the highest loads were produced by floe

fragment impacts.

(c) effect of ice clearance – the loads were increased when the ice was not able to clear

readily past the Kulluk.

(d) effect of pressure – the loads were increased when there was pressure in the ice. This is

described further in the next section.

4.3.4 Effect of Ice Pressure

It is well known that the ice may become pressurized. For the Alaskan Beaufort Sea, wind stress

is the mechanism most likely to induce pressure in the ice.

However, for completeness, it is worthwhile to note that current-induced pressure has been

observed in a number of other locations (e.g., the Gulf of St. Lawrence).

Ice pressure has two important effects for this project as follows:

(a) the loads are significantly increased when the ice is under pressure. Compare Figures

4.10 and 4.11.

(b) the channel or area behind the boom would be closed and become ice-covered. This

would render the boom ineffective for aiding oil spill cleanup operations.
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Figure 4.11: Effect of Pressure on the Loads Exerted on the Kulluk

(after Wright, 1999)

4.4 Loads on the Boom

4.4.1 Wind and Current Drag Forces: Inputs Used and Cases Considered

Wind and current drag forces were calculated by assuming that these two forces are collinear

which errs conservatively.

Table 4.2 lists the input values used. Upper range values were used for the wind and current

speed to add further conservatism.

Table 4.2: Drag Force Calculation Inputs

Wind Drag Forces Current Drag Forces

Ice wedge apex angle 63° 63°

Wind or current speed 100 km/hr 0.30 m/s

Air or water density 1.293 kg/m31000 kg/m3

Air or water drag coefficient 0.0033 0.020
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Line loads due to drag forces were calculated for boom widths ranging from 230 ft (70 m) to

2500 ft (750 m). As expected, the line loads applied by drag forces increase with the boom

width, as a larger boom width results in a larger ice wedge area.

Ice forces were calculated for the case where there was no pressure in the ice as the boom will

not be effective in pressured ice (described previously). The calculation involved two general

steps:

(a) Define the expected ice load at 9+ to 10/10 the pack ice cover. The upper bound relation

developed by Wright, 1999 for the Kulluk for “tight managed ice with poor ice

clearance” (Figure 4.10) was used to establish this. This selection was made as Wright,

1999 reported that the pack ice concentration ranged from 9 to 9+/10 for this case, and

the relation expressed an upper bound to the data (Figure 4.10).

(b) Define the load reduction expected for pack ice concentrations lower than 9+/10.

Equation 4.6 was used to define this.

4.4.2 Calculating Ice Loads

The ice load for this case was calculated as follows:

Fice (Conc) = Load ratio (defined in equation 4.6) *

Upper bound to field data (defined in Figure 4.11) [4.7]

The ice load was evaluated for ice concentrations of 30%, 50%, and 70%.

As noted in Section 4.3, higher ice loads are to be expected for higher ice concentrations, or

when there is pressure in the ice. However, ice loads are not presented for these cases here as

simple comparisons have shown that these ice conditions impose loads that are beyond the

practical range for a boom.

4.4.3 Calculated Line Loads Acting on the Boom

Ice forces were calculated as described in Section 4.4.2. Drag forces were added to determine

the total force and line load across the projected width of the boom. The calculated line loads are

shown in Figures 4.12, 4.13, and 4.14 for pack ice concentrations of 30%, 50%, and 70%,

respectively.

As expected, the line loads increase with the pack ice concentration.

The effect of the ice thickness depends on the pack ice concentration. At low concentrations

(i.e., 30% and 50%), the line load is insensitive to the pack ice thickness (Figures 4.11 and 4.12,

respectively). This reflects the fact that ice forces are a small proportion of the total force in

these cases. At 70% ice concentration, the loads increase with the pack ice thickness (Figure

4.14) indicating that ice forces are becoming more significant.
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For the ice thickness and boom widths considered, the line loads range from 12 to 115 lb/ft, 38 to

215 lb/ft, and 160 to 680 lb/ft for pack ice concentrations of 30%, 50%, and 70%, respectively

(Figures 4.12 to 4.14).

Figure 4.12: Line Loads for a Pack Ice Concentration of 30% with No

Pressure
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Figure 4.13: Line Loads for a Pack Ice Concentration of 50% with No Pressure

Figure 4.14: Line Loads for a Pack Ice Concentration of 70% with No Pressure
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4.4.4 Anchoring or Ship Thrust Requirements for the Boom

The total anchoring requirements are shown in Figures 4.15 4.16, and 4.17 for pack ice

concentrations of 30%, 50%, and 70%, respectively. It should be noted that the individual

anchor requirements will depend on the number of boom spans across the boom width. This is

considered further subsequently.

As expected, the anchoring requirements increase greatly with the pack ice concentration, and

the projected width of the boom.

For the ice thickness and boom widths considered, the total anchoring requirements range from 1

to 142 tons, 4 to 265 tons, and 18 to 836 tons for pack ice concentrations of 30%, 50%, and 70

%, respectively (Figures 4.15 to 4.17).

Figure 4.15: Total Anchoring Requirements for a Pack Ice

Concentration of 30% With No Pressure
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Figure 4.16: Total Anchoring Requirements for a Pack Ice

Concentration of 50% With No Pressure

Figure 4.17: Total Anchoring Requirements for a Pack Ice

Concentration of 70% With No Pressure
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5 ICE BOOM CONFIGURATIONS AND DESIGN CONSIDERATIONS

This section discusses ice boom configurations and design considerations for a boom that could

be used for most scenarios presented in Section 3. The considerations include the following:

(a) the ice and drag loads on the boom – These govern all aspects of the boom design. These

loads are discussed in section 4.

(b) anchoring requirements and approach – in general two approaches are possible: (i) seabed

anchors, and; (ii) dynamic anchoring with vessels or icebreakers.

Seabed anchors are best suited for cases where large areas need to be protected, as this

would require a large boom, and hence produce large total anchoring requirements. It

also offers a fast response capability should the anchors be pre-installed. The major

drawback of this approach is that the boom costs will be higher, as the boom would have

to be designed to provide protection against ice movements from any direction.

The second approach has the advantage that it is more flexible, and that it would be

applicable to a wide range of spill scenarios. Furthermore, the boom costs will be lower,

and provided that locally-available vessels could be used, the overall costs would likely

be lower as well.

The most appropriate approach depends on many factors including: (i) the scenario in

which the boom is deployed; (ii) the loads on the boom, and; (iii) the boom width

required for it to provide a useful contribution to the oil spill cleanup effort.

(c) the ice retention capacity required – this is governed by the ice conditions and the desired

operating window for the boom. At the detailed design level, the ice retention capacity is

controlled by the buoyancy and number of boom pontoons. The buoyancy of a single

pontoon is largely controlled by its diameter.

5.1 Environmental Conditions

The situations in which an ice boom can be used depend on the ice conditions, the environmental

conditions and the available equipment used for the deployment. Two types of loadings are

important:

(a) ice loadings

(b) wave loadings

5.1.1 Ice Loadings

Ice loads are described in Section 4.

It is important to note that an ice boom is designed to submerge when more severe ice conditions

(than the design ones) occur. This avoids damage and the excessive costs that would be incurred

if the boom were to be designed to withstand all ice conditions.
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Hence, boom design at the detailed level primarily consists of a trade-off between the desired ice

retention capacity and the cost or size of the boom. Anchoring requirements also influence the

design process greatly.

5.1.2 Wave Loadings

Waves are an important design consideration as they can cause damage to the pontoons. Many

of the damages that have occurred to date have resulted from waves causing the ends of the

pontoons to impact with each other.

Obviously, the preferred approach is to prevent these loads from occurring. Rubber bumpers

have also been used to minimize this problem. At the detailed design level, this is done by

maximizing the “gap” (i.e., the distance between individual pontoons) so that end impacts are

unlikely. The “gap” size selection is a trade-off between two objectives:

(a) to minimize the possibility of end impacts; and,

(b) to minimize the amount of ice that escapes between the pontoons. Typically, the “gap” is

set at about 30-50% of the pontoon length.

5.2 Case Study

Scenario 1a in the Manual (Figure 3.1, in Section 3) was used as a case study. Two general

boom arrangements are possible:

(a) Fixed Installation – in this case, the boom would be deployed around most of the full

perimeter of the island (leaving only a few gaps for access in and out of the site), and

held in place using seabed anchors. The seabed anchors would be pre-installed, and in

the event of a spill, the boom would be deployed from either the island or shore using

support vessels and/or barges. The advantages of this approach are that:

(i) support vessels are not required on a full-time basis once the boom has been

deployed which frees them up for other duties;

(ii) this would provide a rapid response capability;

(iii) the boom provides protection against all ice drift directions;

(iv) ice pieces are prevented from “going around” the boom and entering the oiled

area from the sides.

The disadvantages include:

(ii) cost - a longer boom is required, which will result in higher boom costs;

(iii) ice ingress into the central protected area – any ice that over-runs the boom will

collect inside the central protected area unless measures are taken to allow the ice

to escape. This can be alleviated using approaches such as releasing one end of

the boom on the “downstream” side so that this part of the boom “streams” into

the ice. This approach has been used elsewhere (e.g., on the Rideau River) to

allow ice passage at breakup without jamming.
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Application Of Ice Booms For Oil Spill Cleanup In Ice-Infested Waters 38

(b) Ship-based Deployment – in this case, support vessels would be used to keep the boom

on station. The boom would consist of one to two spans and can be deployed in different

modes (Figure 5.1):

(i) 3-Ship Chevron Configuration: three supply vessels are used. One ship (or an

icebreaking vessel if operations are to be carried out in more severe ice

conditions, Section 6) would be used to tow the ice boom to the site. Two more

vessels would be used when the boom is stationed at the oil spill site.

(ii) 2-Ship Catenary Configuration: two supply boats would be used. The boom

would be towed from one end to the site while a second tugboat pulls the other

end of the boom to form a catenary shape.

The advantages of this approach include:

(i) a shorter boom is required (versus a fixed installation) which will reduce costs

and deployment logistics;

(ii) the boom can be maneuvered to take account of shifts in ice movement direction

(Figure 5.2);

(iii) it is a flexible approach. For example, the boom could be used at many locations

or in many scenarios. In this case, it could be stored at a central location and

towed to the spill site. The span could also be adjusted “on-the-fly” (within

limits) by maneuvering the vessels.

The disadvantages include:

(i) support vessels are tied up on a full-time basis, both for keeping the boom on

station, and for maneuvering the boom to keep it perpendicular to the ice drift

direction (which will change throughout the spill);

(ii) vigilance is required on the part of the operators to maneuver the boom

throughout the spill in response to shifts in ice movement direction. This may be

quite difficult to accomplish at all times (e.g., in fog, at night, or in other low

visibility conditions);

(iii) ice pieces may “go around” the boom and enter the spill area from the sides.
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Application Of Ice Booms For Oil Spill Cleanup In Ice-Infested Waters 39

Figure 5.1: The Deployment of an Ice Boom in two Configurations (i.e., Chevron and

Catenary), Upstream of an Oil-Spill from an Offshore Structure

Figure 5.2: Boom Maneuvering and Attachment of an Oil Spill Boom to an Ice Boom.

In practice, some combination of the two deployment modes would probably be done, depending

on the local conditions, to take advantage of the attributes of each approach. For simplicity and

because the details of the scenario are difficult to specify, the two approaches were considered

separately in this case study. The “ship-based boom deployment” is considered in Section 5.3

while the “fixed installation” approach is investigated in Section 5.4.

5.3 Ship-Based Boom Deployment

The boom may be deployed either in a Chevron or Catenary configuration (Figure 5.1).

The main advantages of the Chevron configuration are that:
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Application Of Ice Booms For Oil Spill Cleanup In Ice-Infested Waters 40

(a) it would provide greater stationkeeping abilities by allowing three ships to hold the boom

in place;

(b) it would provide improved capabilities to maneuver the boom.

Vessel requirements are presented in Section 6, along with those of available ships.

5.3.1 Design Summary

Table 5.1 summarizes the design criteria used and the boom design that was produced.

The table provides the appropriate size and the number of required pontoons and their spacing

for a given ice load. Further information regarding key components and issues is provided

below. Appendix A provides a set of typical ice boom drawings as a sample. These drawings

were used for an ice boom deployed in Lake Ontario, where the ice retention criteria was

governed by the relatively thin ice in the area.

Table 5.1: Ship-Based Deployment for Scenario 1a: Design Criteria Used

and Boom Design Developed

(a) area to be protected and required boom width – it was assumed that a 1000 ft (300 m)

wide open water area would be necessary to provide a large enough area that oil spill

recovery equipment could be deployed and operated. This would be about two times the

expected width (or diameter) of a typical offshore production island. Two boom sections

with 500 ft span (150 m) each will provide the required area.

(b) design loads on the boom – designs were developed for an applied line loads of 100 lb/ft

(1.5 kN/m) and 200 lb/ft (3 kN/m) which cover the range of interest for pack ice

concentrations of 30 % to 50 % (section 4).

(c) type of deployment - designs were developed for booms in either a chevron or catenary

configuration (Figure 5.1).

Inputs # ft m dia in dia mm lb kg

Pontoon Length 29.848 9.1

No. of Pontoons: 22 657 200

Cable length 1230 375.0

Span width 984 300.0

Gap between pontoons 24.9 7.6

Weight of Span Cable Carried By One Pontoon: 1.5 38.1 223 101

Weight Of Chain Links Carried By One Pontoon: 200 9 1

Other weights (cable clamp, shackles,etc.) for One Pontoon: 200 9 1

Pipe Pipe wall End plate Length Steel Vol Steel Vol Overall Total Bulk Overall Net Buoy. Span Net

dia. radius thick. thickness Pipe Ends Steel Pontoon Weight Density Specific Force Buoyancy

(in) (in) (in) (in) (ft) (in

3

) (in

3

) Wt.(lb) Vol. (ft

3

) (lb) lb./ft

3

Gravity (lb) (lb)

18''pipe 9 0.25 0.75 29.8 4993 562 1574 52.72 2197 41.66 0.67 1093 24050

24''pipe 1 2 0.38 0.75 29.8 9969 1156 3152 93.72 3775 40.27 0.65 2074 45622

Pipe Pipe wall End plate Length Steel Vol Steel Vol Overall Total Bulk Overall Net Buoy. Span Net

dia. radius thick. thickness Pipe Ends Steel Pontoon Weight Density Specific Force Buoyancy

(mm) (mm) (mm) (mm) (m) ( m

3

) ( m

3

) Wt.(kg) Vol. (m

3

)] (kg) (kg/m

3

) Gravity (kg) (kg)

457 229 6.4 1 9 9.1 0.082 0.00921 715 1.49 998 669 0.67 494 10932

610 305 9.5 1 9 9.1 0.163 0.01894 1433 2.65 1716 646 0.65 938 20737

Submergence Theoretical Friction Theoretical Pipe Pipe Span Net Actual Force Total Anchor Anchor

Resistance Resistance Resistance Resistance dia. dia. Buoyancy Resistance on cable Force Force Force

2D Model(1) Corrected μ = 1.50 ωιτη Φριχτιον (in) (mm) (kN) (kN/m) k N Tonnes Tonnes Tonnes

(kN/m) (kN/m) (kN/m) (kN/m) Catenary Chevron

0.03 0.02 0.5 0.5 1 8 457 107 1.9 563 5 7 29 19

0.6 0.4 1.0 1.0 2 4 610 203 3.6 1,068 109 54 36

(1) the calculated submergence resistance for the pontoon size noted in 2 dimensions.

Metric Units

English Units
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Application Of Ice Booms For Oil Spill Cleanup In Ice-Infested Waters 41

(d) span cable – the required span cable diameter is affected by several factors including:

(i) the span to total length ratio - the total span cable length should be at least 125%

longer than the desired span to avoid excessive loads.

As well, for the case where vessels are used to keep the boom on station, a shorter

span cable will generate significant lateral load that will pull the boats toward the

inside of the catenary. This will reduce the effective span to about 80% of the

nominal value.

(ii) the span – the span cable loads and tensions increase with the span.

(iii) the anchoring or stationkeeping system used – the available anchoring capacity

will impose a limit on the span that can be achieved.

For the case where vessels are used to keep the boom on station, the following

spans are required to provide a total swath with of 1000 ft (see also Table 5.1):

- Catenary configuration: 1 spans @ 1000 ft – cable length per span = 1230

ft; span cable diameter = 1.25 and 1.50 inches for line loads of 127 lb/ft

(1.9 kN/m) and 240 lb/ft (3.6 kN/m), respectively.

- Chevron configuration: 2 spans @ 500 ft – cable length per span = 615 ft;

span cable diameter = 1.25 and 1.50 inches for line loads of 127 lb/ft (1.9

kN/m) and 240 lb/ft (3.6 kN/m), respectively.

(e) Pontoons – pontoon design is controlled by the required ice retention capacity and it

involves the following important issues:

(i) the ice retention capacity of a single pontoon – this is primarily controlled by the

pontoon’s buoyancy and length. Typically, 30 ft (9.1 m) long pontoons have been

used at the booms built to date. The ice retention capacity of a pontoon is

discussed further in section 5.3.2.

(ii) the number of pontoons in a span, or per unit length - in a typical boom, 10 to 13

pontoons would used in a 500 ft (150 m) long span cable

(iii) the required gap between the pontoons to retain ice without incurring waveinduced damage (caused by the pontoon ends being slammed into each other by

waves). Typically, the gap has been set at about 30-50% of the pontoon length.
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The gap between two 30 ft long pontoons can be as large as 20 ft (6.1 m) without

affecting the ice retention capacity of the boom, depending on the type of ice.

When the boom is used in a situation where an ice cover will form, a gap of 20 ft

was found to be sufficient to promote the development of an ice cover within

hours when the ice consisted of thin ice and very small floes. In larger floes, a

larger gap (of say 20 ft) would be acceptable as well.

In a wave environment, a smaller gap between each two pontoons will be

necessary to hold the ice. To minimize the damage to the pontoons, rubber

bumpers have been used at each end to prevent damage and possibly the loss of

pontoon buoyancy.

For this case study, the following pontoon parameters were established (see also

Table 5.1):

Table 5.2: Pontoon Parameters Established for the Case Study Design

Line Load

(lb/ft)

Pontoon Length (ft) Pontoon Diameter

(in)

No. of Pontoons per

500 ft Span

100 30 18 11

200 30 24 11

(f) Attachment of the Pontoons to the Span Cable - Each pontoon would be attached to the

span cable as shown in Figure 5.3. This method allows the ice to run over when the ice

resistance capacity of the pontoon is exceeded. The pontoons are designed to submerge,

and then resurface when the load drops. This guarantees that the impact of a large ice

floe will not cause structural damages to any of the boom components. The chain should

be about 50% longer than the thickness of the ice expected in the area to ensure the ice

can clear the boom when the loads exceed the retention capacity of the pontoon without

causing any damage to the anchor or causing the tugboat to become out of control. In

thick multi-year ridges, this criterion would require that the length of the chain be about

1.5 times the ridge depth, which would be an excessive requirement. Prototype testing

should be done to confirm this length.

(g) Cable Clamps Used to Ensure the Pontoon Will Not Slide Along the Cable – a 3⁄4” fishing

chain with appropriate shackles should be used to connect the cable clamp to the

pontoon.

(h) Junction Plates - junction plates are used to provide an attachment point between the span

cable and the anchor cable, or tow line (for ship-based deployments). See Figure 2.2, in

Section 2 for schematic.
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(i) The Tow Cable (for ship-based deployments) – this should be 150 to 300 ft (50 to 100 m)

long to provide sufficient slack for the ice to clear from both sides of the boom without

adding to the tension at the boat.

(j) Buoys - buoys are used to provide floatation to the junction plate and to allow the anchor

or towing cables to be attached without the need for divers (Figure 5.4). These junction

plates are held by buoys as close as possible to the water surface. The buoy can also be

used to attach a conventional open water boom, should the boom be used in other

scenarios (e.g., Scenarios 2a and 2b - Figures 3.3 and 3.4, respectively).

The ice boom buoys (located about 100 to 200 m apart) could also be used as anchoring

points for an oil-spill containment boom (or fireproof booms) to be deployed downstream

of the ice boom (as described in scenarios 2 and possibly 5). See Figure 5.2. For this

case, the buoys should be equipped with a quick connect/disconnect mechanism, which is

available from most oil-spill containment boom suppliers and manufacturers. The quick

disconnect would make the boom easy to deploy, and to disconnect in case of emergency

with less risk of an oil slick seeping outside the spill area.

Figure 5.3: Pontoon Attached to the Span Cable to Allow Ice Over-Run when the Ice Load

Exceeds the Boom’s Ice Retention Capacity
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Figure 5.4: Buoy Used to Connect the Tugboat or the Anchor to the Boom

5.3.2 Detailed Design: Calculation of a Pontoon’s Ice Retention Capacity

Figure 5.5 describes the forces acting on a pontoon. The pontoon’s ice retention capacity is

governed by the force necessary to submerge it, thereby allowing ice to run over the boom.

Figure 5.6 shows the measured ice retention capacity of various pontoons as well as the line load

predicted by a numerical model developed by Abdelnour et al, 1995.

Figure 5.5: Schematic of Forces Acting on the Boom
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0

2

4

6

8

10

12

14

16

0.51 0.56 0.61 0.66 0.71 0.76 0.81

Pontoon Diameter (m)

Line Load (kN/m)

0

20

40

60

80

100

20 22 24 26 28 30 32

Pontoon Diameter (in)

Line Load (lb/ft)

Numerical Model, Average

Numerical Model, Maximum

Lavaltrie, Steel &Timber, Maximum

Lanoraie, Timber, Maximum

Lanoraie, Timber, Mean

LENRIB, Timber, Maximum

LENRIB, Timber, Mean

LENRIB Steel, all Events 1997

Lavaltrie, Steel &Timber, Average

Event 2 

(submersion)

Event 1

Local Ice 

Run Events

Figure 5.6: The Effect of Pontoon Diameter on a Pontoon’s

Ice Retention Capacity

Equilibrium is established when all the external forces and moments (Figure 5.7) reach a balance:

Total Force (F): F = Fs + Ff [5.1]

Force equilibrium: T • cos (θ) = (B - G - W) [5.2]

T • sin (θ) = F [5.3]

Submergence Force: Fs = (B • Db - G • Dg + W • L/2 • sin (θ) )/Da [5.4]

Friction Force: Ff = μ * B [5.5]

where:

T = tension force of the chain

B = buoyancy force of the pontoon

G = gravity force of the pontoon

W = weight of the chains attached at both ends

L = span cable length

θ = angle formed by the chain and the vertical

Da

 = vertical distance from the water surface to the attachment point

ADb= horizontal distance between the point A (Figure 5.7) and the pontoon's center of

buoyancy

Dg

 = horizontal distance between the point A (Figure 5.7) and the pontoon's center of gravity

μ =friction factor between the ice and the pontoon surface
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Figure 5.7: The Ice Action on the Pontoon before Submergence

The results of field measurements made in Lake Erie and in Lac St. Pierre in 1994 were used to

calibrate the numerical model. Measurements made at the Lake Erie Niagara River Ice Boom in

1997, with 30” (0.76 m) diameter pontoon were used to confirm the model.

5.4 Fixed Boom Installation

Table 5.3 summarizes the design criteria used and the boom design that was produced. Most of

the design issues presented in Section 5.3 for the “ship-based deployment” boom are applicable

to this case as well.

Further information is presented below regarding key components and issues that differ from

those for the ship-based deployment.

1. area to be protected and required boom size – a larger boom would be required (than for a

ship-based deployment) because this approach does not have the capability to adjust to

shifts in ice movement direction. For this case study, it was assumed that the production

island was 400 ft (125 m) in size, and that the boom would need to be 150 ft (50 m) from

the edge of the island on all sides to provide sufficient clear space for oil spill equipment

to operate.

2. configuration: 2 spans each side @ 410 ft (125 m) each span – cable length per span =

515 ft; span cable diameter = 2 inches for line loads of 588 lb/ft (8.8 kN/m).

3. the number of pontoons in a span is 11 and the spacing 16 ft (4.9 m) as shown in Table

5.3.
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4. anchoring – seabed anchors would be used in this case. Two types of anchors have been

used in previous boom deployments depending on the bottom conditions:

(i) marine anchors. These are more appropriate for temporary deployment. They can be

removed easily and re-deployed somewhere else.

(ii) plow anchors. They are buried few feet under the sea bottom and are expected to sink

in and provide the designed pull force – see Figure 5.9

(iii) anchors drilled into rock – see Figure 5.10

Table 5.3: Fixed Installation for Scenario 1a:

Design Criteria Used and Boom Design Developed

Figure 5.8: Fixed Boom Installation

Inputs # ft m dia in dia mm lb kg

Pontoon Length 29.848 9.1

No. of Pontoons: 22 657 200

Cable length 1025 312.5

Span width 820 250.0

Gap between pontoons 16.0 4.9

Weight of Span Cable Carried By One Pontoon: 2 50.8 396 180

Weight Of Chain Links Carried By One Pontoon: 200 9 1

Other weights (cable clamp, shackles,etc.) for One Pontoon: 200 9 1

Pipe Pipe wall End plate Length Steel Vol Steel Vol Overall Total Bulk Overall Net Buoy. Span Net

dia. radius thick. thickness Pipe Ends Steel Pontoon Weight Density Specific Force Buoyancy

(in) (in) (in) (in) (ft) (in

3

) (in

3

) Wt.(lb) Vol. (ft

3

) (lb) lb./ft

3

Gravity (lb) (lb)

30''pipe 1 5 0.38 0.75 29.8 12501 1816 4056 146.44 4852 33.13 0.53 4286 94292

Pipe Pipe wall End plate Length Steel Vol Steel Vol Overall Total Bulk Overall Net Buoy. Span Net

dia. radius thick. thickness Pipe Ends Steel Pontoon Weight Density Specific Force Buoyancy

(mm) (mm) (mm) (mm) (m) ( m 3

) ( m 3) Wt.(kg) Vol. (m3)] (kg) (kg/m 3) Gravity (kg) (kg)

762 381 9.5 1 9 9.1 0.205 0.02975 1844 4.15 2205 532 0.53 1941 42860

Submergence Theoretical Friction Theoretical Pipe Pipe Span Net Actual Force Total Anchor Anchor

Resistance Resistance Resistance Resistance dia. dia. Buoyancy Resistance on cable Force Force Force

2D Model(1) Corrected μ = 1.50 ωιτη Φριχτιον (in) (mm) (kN) (kN/m) k N Tonnes Tonnes Tonnes

(kN/m) (kN/m) (kN/m) (kN/m) Catenary Chevron

1.3 1.0 2.5 2.5 3 0 762 420 8.8 2,207 225 113 75

(1) the calculated submergence resistance for the pontoon size noted in 2 dimensions.

Metric Units

English Units
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Application Of Ice Booms For Oil Spill Cleanup In Ice-Infested Waters 48

Figure 5.9: Anchoring In Sandy Silt

Figure 5.10: Anchor Used for Rock Bottoms

The availability of the ice boom buoys at about 100 to 200 m distance apart will provide anchoring

points for an oil-spill containment boom (or fireproof booms) to be deployed downstream of the ice

boom (as described in scenarios 2 and possibly 5). These buoys can be easily equipped with a quick

connect/disconnect mechanism, available from most oil-spill containment boom suppliers and

manufacturers. The quick disconnect makes the boom easy to deploy in case of emergency with less

risk of an oil slick seeping outside the terminal area.
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Application Of Ice Booms For Oil Spill Cleanup In Ice-Infested Waters 49

6 REQUIRED SHIP PERFORMANCE

The required ship performance depends on the type of operation. This is investigated in a

preliminary manner for the following types of operations:

(a) ships used in a dynamic mode to hold the boom on location;

(b) ships used to tow the boom to the site; and,

(c) ships used to maneuver the boom at the spill site.

6.1 Dynamic Positioning: Required Ship

Bollard Thrust

In this case, the boom would be held on

station by two to three supply vessels or

icebreakers operating under their own power,

as illustrated in Figure 6.1. This arrangement

has the advantage that the boom’s orientation

can easily be changed should the ice drift

direction shift (e.g., in response to a shift in

wind direction).

The success of this operation will depend greatly on the powering characteristics of the ship, and the

experience of the ship captain in maneuvering in similar situations. The ship bow and its hull

geometry are less important for this application (where the ice concentration is less than 7/10ths)

because the ship resistance in broken ice is relatively small when compared with the total load on

the ice boom. The ship could also remain closer to the ice “dead wedge” accumulated upstream of

the ice boom where the ice movement is negligible.

Because the vessels would be operated at low to nil speed in this case, they would be in close to a

bollard condition. Table 6.1 lists the bollard thrust for several available vessels on the North Slope,

and other ice breaking ships used by the US and Canadian Coast Guards.

The pull required on the ends of the ice boom depends on the load on the boom that is controlled by

the drag and ice forces on it (Section 4). The operating limits are shown in Figure 6.2 for the largest

vessels on the North Slope, which are clearly of most interest for this project because they offer the

fastest response capability in a spill situation.

Figure 6.1: Example of Ship Maneuvering for

Maintaining the Ice Boom in Position
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Table 6.1: Bollard Thrust of Various Vessels and Their Stationkeeping

Capabilities With the Boom

Figure 6.2: Operating Limits for the Largest Vessels on the North Slope

Icebreaker Name

Bollard 

Thrust 

(lb)

Boom 

width (ft)

Allowable Line 

Load for two 

ships (lb/ft)

Boom 

width (ft)

Allowable Line 

Load for two 

ships (lb/ft)

Boom 

width 

(ft)

Allowable Line 

Load for two 

ships (lb/ft)

US Icebreakers

Polar Class 1005400 300 6703 600 3351 1200 1676

Mackinaw 206800 300 1379 600 689 1200 345

Juniper 125400 300 836 600 418 1200 209

Bay class 48400 300 323 600 161 1200 81

Canadian Icebreakers

Louis St. Laurent 444400 300 2963 600 1481 1200 741

Terry Fox 418000 300 2787 600 1393 1200 697

Henry Larsen 264000 300 1760 600 880 1200 440

R-Class 253000 300 1687 600 843 1200 422

Type 1100 143000 300 953 600 477 1200 238

Type 1050 171600 300 1144 600 572 1200 286

J.E Bernier 88000 300 587 600 293 1200 147

Sr. H. Gilbert 88000 300 587 600 293 1200 147

Griffon 88000 300 587 600 293 1200 147

Available Tugs in 

the area

Bollard 

Thrust 

(lb)

Boom 

width (ft)

Allowable Line 

Load for two 

ships (lb/ft)

Boom 

width (ft)

Allowable Line 

Load for two 

ships (lb/ft)

Boom 

width 

(ft)

Allowable Line 

Load for two 

ships (lb/ft)

Pt. Barrow 47000 300 313 600 157 1200 78

Pt. Thompson 47000 300 313 600 157 1200 78

Arctic Bear 51000 300 340 600 170 1200 85

Sag River 22000 300 147 600 73 1200 37

Toolike River 22000 300 147 600 73 1200 37

Kavik River 22000 300 147 600 73 1200 37

Arctic Tern 20000 300 133 600 67 1200 33
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Application Of Ice Booms For Oil Spill Cleanup In Ice-Infested Waters 51

The stationkeeping capabilities of the three largest vessels on the North Slope for boom deployments

are further investigated in Table 6.2.

Table 6.2: Stationkeeping Capabilities of the Largest Vessels on the

North Slope for Boom Deployments

Pack Ice Concentration and

Maximum Line Load for

Range of Inputs Considered

(Section 4)

Type of Deployment

3 Ships Used – the Pt.

Barrow, the Pt. Thompson,

and the Arctic River

Type of Deployment

2 Ships Used – the Pt.

Barrow and the Pt.

Thompson

30 % ; 115 lb/ft (1.7 kN/m) Maximum Boom Width

Allowed: 1260 ft

Maximum Boom Width

Allowed: 820 ft

50 % ; 215 lb/ ft (3.1 kN/m) Maximum Boom Width

Allowed: 670 ft

Maximum Boom Width

Allowed: 440 ft

70 % ; 680 lb/ft (9.9 kN/m) Maximum Boom Width

Allowed: 210 ft

Maximum Boom Width

Allowed: 140 ft

It is clear that the available vessels on the North Slope would provide adequate stationkeeping

capabilities for a useful range of boom widths in ice concentrations of 30% and 50%.

The allowable boom width in 70% ice concentration is much lower because the ice loads are

increased significantly. This shows that the available vessels on the North Slope would have limited

capabilities for keeping the boom on station in this ice concentration. Larger vessels, such as

icebreakers would be required in this case.

6.2 Ship Transit to the Spill Site and Maneuvering at the Spill Site

The power required to tow the ice boom in ice-covered waters depends on the ice conditions and the

ice boom length. Because the boom will be most applicable for ice concentrations of 50% or less

(with the available vessels on the North Slope – Section 6.1), the ice resistance is expected to be

relatively low relative to the main requirement (i.e., maintaining station at the spill site).

Furthermore, it is expected that the boom would be streamed from the ship(s) that would further

reduce towing requirements.

It is recognized that a situation may arise where the boom may need to be towed through more

severe ice conditions to reach the spill site. This has not been investigated here because a wide

range of cases is possible, and this was beyond the scope of the project. This would need to be

evaluated on a case-by-case basis.

In most cases, manoeuvring at the spill site is expected to be feasible with the available vessels on

the North Slope as again, the stationkeeping requirements will generally exceed those for

manoeuvring. However, again, a wide range of cases are possible, and extreme situations, such as a

local pack ice intrusion which temporarily brings a large amount of ice into the spill site, would

impose more severe requirements. This would need to be evaluated on a case-by-case basis.
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Application Of Ice Booms For Oil Spill Cleanup In Ice-Infested Waters 52

6.3 Summary

The available vessels have been investigated in a preliminary manner. For pack ice

concentrations less than about 50%, the largest vessels presently located on the North Slope

would be capable of keeping the boom on station for a wide range of useful cases (e.g., 2 or 3-

ship deployments, boom widths, ice thicknesses, wind and current speeds).

At higher pack ice concentrations, the stationkeeping capabilities of the vessels would be

reduced. Deployments with the available vessels on the North Slope would likely require that

the boom width be reduced. Vessels with higher power, such as icebreakers, would be required

to provide a wide operating envelope.

Transit to and from the site will not likely impose the design requirement as these loads (in ice

concentrations of less than 50%) are expected to be less than those during stationkeeping. The

same comment applies regarding manoeuvring at the spill site.

Although more severe cases could arise, they are expected to occur relatively infrequently.

These would need to be evaluated on a case-by-case basis, and have not been considered here

because this is beyond the scope of the project.
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7 CONCLUSIONS

Improved ice boom technology has been developed and used successfully at several locations.

Ice booms have the potential to aid or extend oil spill cleanup capabilities in broken ice in a

number of ways, such as:

(a) preventing ice ingress into the spill area, thereby providing an ice-free area where

conventional oil spill equipment can operate; and,

(b) providing a means to assist in separating the oil from the ice.

Ice booms have the potential to assist in many of the scenarios defined in the Alaska Clean Seas

Technical Manual.

Ice booms, in combination with the available support vessels on the North Slope, are expected to

be applicable to oil cleanup in moderate broken ice conditions of up to about 50%. Booms are

also expected to be applicable for some cases in higher ice concentrations of up to 70%.

However, larger vessels with more power such as icebreakers would be required for a wide

operating envelope.

Prototype tests should be carried out in the Alaskan Beaufort Sea as the next step in advancing

this technology for reliable usage in oil spill cleanup situations in broken ice in the Arctic.
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8 RECOMMENDATIONS

8.1 Issues Requiring Further Investigation

While the results of this investigation are promising, a number of issues require further

investigation before definitive assessments can be made. The most important issues are

considered to be:

(a) ice interactions with the boom – more information is needed to confirm the boom’s

performance in severe ice conditions such as ice ridges, and large floes which may drift

into it.

The amount of ice infill that occurs behind the boom during pack ice movements is

another issue that warrants further investigation. Ice pieces deflected along the length of

the ice wedge are expected to eventually infill behind the boom. This problem will be

exacerbated by any pressure in the ice, although it is expected to occur even without

pressure. As a result, the ice cover is expected to be restored eventually to the upstream

concentration at some distance behind the boom.

(b) the ability to operate the boom using support vessels – testing is required to define

capabilities such as the ability to maneuver the boom, to keep it on station, and to tow it

to the site. Operational strategies need to be developed for possibilities such as the drift

of a solitary large floe that may force the vessels to disconnect or to “collapse” the boom

so that the floe(s) can pass.

(c) operational envelope – only a preliminary assessment was possible in this project, partly

because a wide range of cases are possible and many assumptions would be required to

evaluate them. This should be followed up with more detailed analyses, in combination with

field testing which is necessary to move the technology forward for this application.

It is believed that quite conservative assumptions were made in this project in establishing

the loads on the boom, particularly with respect to the under-ice currents at the boom, and

their colinearity with the winds. This was necessary because very little data re available for

this case. Field measurements would be valuable to improve the estimates made here.

The effect of local high concentrations of ice should be investigated. “Strips and patches” of

ice are known to occur and they have the potential to over-run the boom even though the

boom might be capable of controlling the prevailing ice, on average.

8.2 Recommendations

A field deployment should be conducted offshore of Prudhoe Bay using a boom of limited size. A

boom with two 500 ft (150 m) spans should be built and deployed using the available support

vessels in the chevron and catenary configurations.

This work should be accompanied with numerical analyses that build upon the results of the field

tests and the work done here.
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9 REFERENCES

[1] Abdelnour, R., Gong, Y., Comfort G. (1995), "The Development of a New Ice Retention

Boom for Deployment in the St. Lawrence River", CSCE 1995 Annual Conference, June 1-

3, Ottawa.

[2] Abdelnour, R., Johnstone, T., and Howard, D., 1985, Laboratory Testing of an Oil Skimming

Bow in Broken Ice Field, AMOP Seminar, Edmonton, Alberta.

[3] Abdelnour, R., Nicholson, C., and Gong, Y., 1998, "The Design, Fabrication and

Deployment of an Ice Boom to Protect Two Hydroelectric Power Plant Water Intakes from

Ice Blockages During Winter", IAHR Ice Symposium, Potsdam, NY, USA.

[4] Alaska Clean Seas - Technical Manual, 1999, produced by Alaska Clean Seas, (sponsored by

Alyeska Pipeline and Arco Alaska, Inc).

[5] Barker, A., Timco, G., Sayed, M., and Wright, B., 2000, Numerical Simulation of the Kulluk

in Pack Ice Conditions, proc. IAHR conference, Gdansk, Poland.

[6] Bobra, M., and Fingas, M., 1986, The Behaviour and Fate of Arctic Oil Spills, Water

Science Technology, vol. 18, no. 2.

[7] Comfort, G., Singh, S., and Spencer, D., 1999, Evaluation of Model Test Data for Moored

Structures, PERD/CHC Report 26-195.

[8] Cowper, B., Abdelnour, R., Yuxiang G., and Crissman, R., 1997, “Ice Load Measurements

on the Lake Erie-Niagara River Ice boom: 1996/97”, 9th Workshop on River Ice,

Fredericton, NB, Canada.

[9] Cox, J.C., Schultz, L.A. Johnson, R.P., and Shelsby, R.A., 1980, “The Transport and

Behavior of Oil Spilled In and Under Sea Ice”, Arctec, Inc. Report 460C, submitted to

the US Coast Guard, September.

[10] Free, A.P., Cox, J.C., and Schultz, L.A., 1981, “Laboratory Studies of Oil Spill Behavior

in Broken Ice Field”, Arctec, Inc. Report 570C, submitted to the US Coast Guard,

October.

[11] Jensen, J., 2000, The MORICE Skimmer Project, International Oil and Ice Workshop

2000, Anchorage &Prudhoe Bay, Alaska, April.

[12] Loset, S., and Timco, G.W., 1992, “Laboratory Testing of a Flexible Boom for Ice

Management”, The American Society of Mechanical Engineers, 11th International

OMAE Conference.

[13] Purves, W.F., Abdelnour, R., Nawwar A.M. and Hilderbrand P., (1977), “Novel

Countermeasures for an Arctic Offshore Well Blow-out”, Environmental Protection

Service, Economic and Technical Review Report, August 1977.
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[14] S.L. Ross & Associates, D.F. Dickins & Associates, and Vaudrey & Associates, 1998,

Evaluation of Cleanup Capabilities for Large Blowout Spills in the Alaskan Beaufort Sea

During Large Periods of Broken Ice, contractor report submitted to the United States

Department of the Interior.

[15] Wright, B., 1999, Evaluation of Full Scale Data for Moored Vessel Station-Keeping in

Pack Ice, PERD/CHC Report 26-200.
APPENDIX A

TYPICAL DESIGN DRAWINGS

FOR AN ICE BOOM
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APPENDIX B

DISCUSSION ON THE REPORT BY

THE MMS, ALASKA OFFICE
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Application Of Ice Booms For Oil Spill Cleanup In Ice-Infested Waters B-2

February 13, 2001

Memorandum

To: Razek Abdelnour

From: Joseph Mullin

Subject: MMS Alaska review comments on the draft report entitled: Application of Ice

Booms for Oil Spill Cleanup in Ice Infested Waters.”

We did not concentrate our review on the engineering aspects. We concentrated on the

application aspects as they might pertain to the Alaskan Beaufort Sea. We have addressed the

proposed applications in respect to spring and fall conditions and rated each tactic on the basis of

our understanding of these conditions and the effectiveness of skimming technology currently

available on the North slope. A rating of 1 to 10 was assigned with 10 being the most effective.

This is given in tabular form with comments following.

Understanding that in situ burning, while permissible by the On Scene Coordinator (OSC),

cannot be used to satisfy the State of Alaska planning standard. We included in situ burning as

an application strictly from an operations perspective.

We have included a brief anecdotal description of spring and fall ice conditions upon which our

assumptions for relative effectiveness are based. Without going into specific ice terminology,

they are generally as follows.

Fall Ice

This is newly forming, building ice at below freezing temperatures. It may be composed of

various sized plate’s of varying thickness' to several inches in depth, together with slush that is

the product of grinding and wave action and newly forming ice crystals. This ice mixture has a

tendency to coalesce should any ice force, natural or manmade be applied. None of the

skimming systems presently on the North Slope are effective under these conditions.

Spring Ice

This is older ice in above freezing, melting conditions. It may consist of various sized plates of

varying thickness' some of which may be several meters in depth. There will be little to no slush

ice associated with spring ice so oil may be found between and as a coating rather than

accumulated within and part of the ice matrix.
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Application Of Ice Booms For Oil Spill Cleanup In Ice-Infested Waters B-3

SPRING FALL

ICE ICE

Prevention of Ice Ingress

Fig. 3.1 - 1a - Deflection from Offshore Structure –

Anchored

8 2

Fig. 3.2 - 1b - Deflection from Offshore Structure –

Unanchored

0 2

Fig. 3.2 - 1b – In Situ Burning 5 1

Fig. 3.6 – Offshore Pipeline 8 5

Fig. 3.7 - Spill to

Reservoir(Lake)

0 0

Oil/Ice Separation

Figure 3.3 - 2a – In Situ

Burning

6 1

Figure 3.3 - 2b - Batch Spill 4 0

Fig. 3.8 - Ice Drift in River 0 3

Containment of Spilled Oil

5.2 - Fixed

Installation

0 0

Fig. 3.1 - 1a - Deflection from Offshore Structure - Anchored

Spring: Assuming ice boom could be anchored, that the size of the flows would not overcome

the boom, and wind direction is relatively constant, it may be possible to skim on the lee side of

the island. It may also be possible to manage larger flows with the Bay boats before they

encounter the boom. It is assumed that ice will reestablish itself at some distance behind the

boom and island but likely at more manageable concentrations so as to allow some collection of

oil in that area. The boom and means to deploy it would have to be placed at the island over

winter to make this approach feasible. (Northstar is outside of the barrier Is. whereas areas inside

are likely to still have shore and bottom fast ice when broken ice conditions might be expected to

occur at Northstar).

Fall: The boom itself may be relatively effective in reducing the concentration and size of ice

pieces down wind of it. However, with a gap between the boom sections of between 2 and 7

meters smaller flows and slush will infiltrate the protected area to some degree making skimming

operations marginal at best.

Fig. 3.2 - 1b - Deflection from Offshore Structure - Unanchored.

Spring: Vessels of a horsepower necessary to deploy would be unable to deploy to Northstar

because of the ice fast conditions at West dock.
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Fall: The only benefit to boom management by utilizing vessels would be the ability to reconfigure as an adaptation to wind change. Otherwise comments for Fig. 3.1 - 1a - Deflection

from Offshore Structure - Anchored. Fall would apply.

Fig. 3.2 - 1b – In Situ Burning.

Spring: Several variables to considered here. If the spill were current (fresh enough to ignite)

the problem would be to collect sufficient quantities of oil at a distance from the island where

safe burning could be allowed. As spring ice is larger and heavier, and the ice boom is designed

to depress under heavy loads, there may be ice in significant quantities or size to restrict

collection in the fireboom that is not constructed for sufficient load strength to accommodate

this. It remains a possibility on a case by case basis however depending on size and

concentration of ice floes.

Fall: As in Fig. 3.1 - 1a - Deflection from Offshore Structure - Anchored. Fall, with a gap

between the boom sections of between 2 and 7 meters smaller flows and slush will infiltrate the

protected area and become mixed with the oil to form a more or less coalescent combination. S.

L. Ross reports that oil mixed with this type of ice under freezing conditions is a poor candidate

for burning.

Figure 3.3 - 2a – In Situ Burning.

Spring: Success with this tactic would depend on several factors as discussed in Fig. 3.2 - 1b –

In Situ Burning. Spring. The one additional factor would be the ability to evacuate the oil from

the ice in large enough quantities at a rapid enough rate to accumulate the necessary thickness for

ignition. In addition, the fire boom would be best deployed with vessels in a dynamic

configuration rather than anchored as shown. Under this scenario the oil would spread rapidly to

equilibrium once it escaped the ice boom and the boom would be proceeding away from the

catchment configuration at a rate of .3 knot in order to release the oil. Hence the distance would

become continually greater allowing for maximum spread which is exactly what we're

attempting to avoid. Since this evacuation effect cannot be tested with real oil in Alaska waters

as would be necessary to gather the proper data; this test might better be done at the OMSETT or

similar facility.

Fall: See Fig. 3.2 - 1b – In Situ Burning. Fall

Figure 3.3 - 2b - Batch Spill

Spring: This was rated at a 4 because we felt it would be limited to smaller sized spills. In a

catenary configuration a limited finite amount of ice and therefore oil could be collected. In the

deflection configuration it is assumed that as the ice progresses to the outer end of the boom

while the oil would travel through the openings. The ice might also occur in somewhat lesser

concentrations in the deflection configuration because it is in motion.
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In this configuration, no matter what the starting concentration of ice it will accumulate to 100%

relatively rapidly. Additional ice and oil would then shear off the ice wedge. This would not be

efficient in a large spill. Also, if used the catchment boom would need to be in a dynamic

configuration rather than anchored similar to the Fig. 3.2 - 1b – In Situ Burning. Spring

discussion.

Fall: Given the preceding discussion of fall ice conditions we would be making a snow cone.

Fig. 3.6 - Offshore Pipeline.

Spring: This has some possibilities since the boom could be placed in closer proximity to the

source therefore the skimming could also take place closer to the boom allowing for more of an

open water type operation. This assumes that both the boom and the vessels to deploy it would

be available. These would most likely be available only if they were stationed at Northstar

through the winter and could physically be deployed from there. It's also the only practical tactic

we've seen for this scenario that has a reasonable chance of success. The problem a success

would pose however would be tankage and transportation of the collected oil.

Fall: As in the spring scenario it's the best option we've seen but there are always the same

skimming limitations. One possible tactic might be to collect the oil -in-ice mixture, tear drop it

to allow it to freeze in place and ice mine it when pack ice thickness allows. Even if the force in

the ice pack squeezes the oil out as the pack forms it should stay in a relatively confined area.

Fig. 3.7 - Spill to Reservoir (Lake).

There are no lakes on the slope large enough that spill response can not be accomplished by

existing conventional means.

Fig. 3.8 - Ice Drift in River

Spring: Water depths in North Slope rivers are likely to shallow for ice boom to be effective. In

the spring ice is likely to deflect underneath the boom.

Fall: The only application we can envision would be an aid in building an ice dam which would

seem to exacerbate the problem because there would still be a good rate of flow under or around

the dam.

5.2 - Fixed Installation

We see no benefit to this tactic. It is impractical for offshore installations in the Beaufort.
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RECOMMENDATIONS

We would agree that some deployment of ice boom in the Alaskan Beaufort Sea would be

beneficial to determine it's best use.

It has possibilities when used in the deflection configuration and may have some applications.

Rigorous testing is required, under the ice conditions encountered in the Beaufort Sea, to

determine the extent and duration of open water this boom might produce.

It is recommended that additional testing in moving water (.3 knots) with oil and ice be

performed to determine the rate at which oil is evacuated from the ice through the boom. This

data would be useful in determining feasibility in any configuration where the intent is to capture

oil when the boom is utilized in this tactical fashion.

This would best be done at OMSETT or a similar facility. If there is no means to refrigerate the

test facility fall ice could not be approximated, only spring. This would be most appropriate in

any case given the previous discussion.