Mitsubishi Heavy Industries Technical Review Vol. 50 No. 2 (June 2013)
44

Implementation of Ship Energy-Saving Operations with
Mitsubishi Air Lubrication System

SHUJI MIZOKAMI*1

MANABU KAWAKADO*2

MITSUHIRO KAWANO*1 TAKEO HASEGAWA*3

ICHIRO HIRAKAWA*4

Mitsubishi Heavy Industries, Ltd. (MHI) carried out examination of the Mitsubishi Air
Lubrication System (MALS), which was developed as an energy-saving system for ships, with theaim of expanding its target ship types. Blowers exclusive to MALS which are capable of providing
high pressure and large amount of air flow required for installation of the system on bulk carriers,
container ships, ferries and large passenger ships are developed, and outlets and piping systems
related to air supply are standardized. This makes it possible to allow MALS to be installed byshipyards other than MHI. The system has also been considered with a view to retrofitting vessels
in service. As a result of these efforts, MHI can now supply MALS as a stand-alone system or acomprehensive system including accompanying engineering.

|1. Introduction
Revised MARPOL 73/78 Annex VI was adopted in 2011 with the aim of reducing
greenhouse gas (GHG) emissions from the international shipping industry, and the regulations
define schemes for reducing CO2 emissions from ships.
In this scheme, Energy Efficiency Design Index (EEDI), which represents the weight (grams)of CO2 emitted when transporting one deadweight tonnage of cargo one nautical mile, is defined as
an engineering method for indicating the energy efficiency.
The revised MARPOL Annex VI requires that all new ships comply with the regulation tohave an attained EEDI value (an actual calculated and verified EEDI value) below the EEDI value
required in the convention if the shipbuilding contract is placed on or after 1 January 2013.
In the EEDI framework, MALS can be treated as one of innovative energy efficiency
technologies. Responding to the continuing high price of fuel, which results in fuel expenses
accounting for a high proportion of operating costs, there is growing demand of energy-saving
systems.
MHI combines various energy-saving technologies such as ships with low propulsive
resistance, high-efficiency propeller systems, heat recovery from main engine exhaust gas, etc., tooffer environmental friendly ships that respond to customer needs. Among such technologies, theMitsubishi Air Lubrication System (MALS), which feeds air to the ship bottom and covers the hullwith air bubbles to reduce the propulsive resistance of the vessel, was developed as a newenergy-saving device. MALS was installed as the world's first permanent equipment on a module
carrier and succeeded at practical application in 2010.(1) A module carrier has a wide deck area formounting large structures, its draft is shallow and the flat part on the bottom is large. The bottom ofsuch types of ships is easily covered with air bubbles, and therefore it was expected that air
lubrication would result in a significant energy-saving effect.
There are wide variations of ships in terms of size, type, operating speed, and other factors,*1

Chief Staff Manager, Ship & Ocean Engineering Division, Shipbuilding & Ocean Development*2

Manager, Ship & Ocean Engineering Division, Shipbuilding & Ocean Development*3

Yokohama Ship Repair & Marine Engineering Department, Shipbuilding & Ocean Development*4

Chief Staff Manager, Marine Machinery Department, Power Systems

Mitsubishi Heavy Industries Technical Review Vol. 50 No. 2 (June 2013)45

depending on their application. Now the good prospects for the practical application of MALS havebeen determined, and one task for the wide adoption of MALS as an energy-saving device isexpanding its target ship types.
This paper describes, with some examples, MHI's efforts to consider the installation of
MALS on cargo ships such as tankers, bulk carriers, and container ships, which account for the
majority of vessels, and ferries, as well as large passenger ships, to which MHI is making a strong
efforts as a core business.

|2. Efforts to expand target ship types of MALS
2.1
(1)Development of blower for air lubrication system
Required range
In regard to bulk carriers, container ships and large passenger vessels, estimation is
performed under given conditions in order to clarify the required pressure and air flow
capacities of the blower. Although there are naturally various operating conditions such as ship
size and required speed, even for a single type of ship, this estimation considers large ships onwhich MALS works effectively. Table 1 compares the estimation results with that of a module
carrier. Most of the required blower pressure is static pressure that depends on the draft. The
required pressure for the shallow-draft module carrier is no more than 65 kPa, even in theconsideration of margins such as pressure loss. On the other hand, the ship compared in thisestimation has deep draft and then higher pressure exceeding 100 kPa is required. In addition,
the required pressure for VLCCs under a full load condition is, even for only the static pressure,
200 kPa or more, although it is not shown in the table.
Table 1 MALS design conditions and blower specifications
Item

Unit

Length, L
Speed, Vs
Flow rate, Qs
Pressure, P
Blower motor rated power, Pm

mkt
m3/minkPa
kW

Modulecarrier153
13.0
80～12065130～200

Bulk carrier
230
14.0
150～250155
500～840

Container
ship
350
24.0
200～550170
680～1900

Passenger ship240
17.0
100～200100
230～460

The air flow required for air lubrication increases or decreases in proportion to the air
thickness covering the ship bottom (considered as uniform) and ship speed. Along with anincrease of the air thickness, the amount of reduced friction resistance increases, but electric
power consumption for the blower also increases. Therefore it is necessary to determine the air
flow in consideration of the trade-off between the amount of reduced friction resistance and theelectric power consumption of the blower in order to obtain the most efficient energy-saving
effect. As shown in Table 1, large container ships require larger amount of air flow because of
their deep draft and high speed. Supposing that multiple blowers are used in such cases, therequired air flow per blower for ships studied can be considered to be approximately 200 to 300
m3/min.
Blowers required for ships studied are not covered by commercially available general
purpose products in many cases. Because it is necessary to order custom made items or furnish
multiple blowers, development of blowers suitable for MALS is required.
(2) Mitsubishi turbo blower
Blowers are classified into axial flow blowers, centrifugal (radial or turbo) blowers, androtary blowers. The module carrier uses one of the rotary blowers, a Roots blower. As
described above, commercially available Roots blowers are relatively small in capacity withlow pressure and cannot cover all range if they are considered to be used for MALS. Therefore
MHI has developed turbo blowers in order to satisfy the characteristics and specifications
required for blowers used for MALS, taking advantage of design technologies of MHI's
turbochargers for ships and automobiles. Figure 1 shows a structural drawing of the developed
Mitsubishi Turbo-blower for Air lubrication (MTA), and Figure 2 indicates the MTA operating
range. Based on the required ranges that were considered, the size of impeller has beenstandardized and two MTA models with higher and lower capacity have been developed.

Mitsubishi Heavy Industries Technical Review Vol. 50 No. 2 (June 2013)
46

Figure 2 includes the required ranges of the ships studied for comparison purposes. Most ranges
required for air lubrication can be dealt with by using properly MTA and commerciallyavailable blowers depending on the required range. In this document, as a matter ofconvenience, "blowers" include devices that are called "compressors" in a classification basedon compression ratios.

Figure 1

Structural drawing of MTA
Figure 2

2.2

Operation range of MTA

Study for applying MALS

In regard to expanding the target ship types of MALS, points to consider for design thatallows MALS to be installed by shipyards other than MHI are organized. Also recommended
standard specifications and design standard are defined in order to quickly respond customer needs.
(1) Air outlets
The locations of outlets are defined so that the surface of the hull is covered by air as
widely as possible. Typically, low-speed blunt ships such as bulk carriers have a flat bottom,
and high-speed ships such as ferries have a slender hull with a narrow flat bottom. Ships areroughly classified into blunt ships and slender ships. Therefore the locations of outlets are
considered for each. Figure 3 illustrates the water lines and bottom flat areas viewed from thebottom. The upper illustration is a blunt ship, and the lower illustration is a slender ship. For theblunt ship, which has a wide flat area, one outlet is placed near the bow. For the slender ship,
the flat area of which is narrow on the bow and aft, three outlets are placed separately.

Figure 3(2)

Location of air outlets

Chamber
Air supplied from the blower is sent to the chambers located at the outlets, and thenblown from the outlets on the bottom. The air immediately forms bubbles due to the shearing
force of the friction against the seawater, and flows away along the hull. Figure 4 illustrates alongitudinal cross section of a chamber. In this example, the inner bottom plating is used as the
top plate of the chamber. The chamber is equipped with a manhole on the side, and can beaccessed for internal maintenance. The lateral dimension of a chamber is defined inconsideration of ship geometry for each ship individually.
(3) Location and shape of openings
Openings on the bottom are oval-shaped as shown in Figure 5. The dimension andMitsubishi Heavy Industries Technical Review Vol. 50 No. 2 (June 2013)47

number of openings are defined in consideration of the MALS design conditions. The gaps
between openings and the distance from the longitudinal stiffeners or the wall to the openings
are defined in consideration of factors such as stress concentration. The plate thickness at the
openings may be increased if necessary.

Figure 4(4)

Example of chamber configuration

Figure 5 Arrangement and shape of
opening (bottom plan)

Piping diagram
Table 2 lists the components of MALS, including blowers, control valves, inverters,
control panels, operation panels, etc. Air supplied by the blower is sent to the chamber at thebottom through the air piping. Figure 6 illustrates an outline arrangement of MALS.
Table 2 MALS components
Equipment/device
Details
Blower (including air cooler and electric motor) Electric motor driven, Turbo blower
Flow control valve
Sea valve
Cooler inlet valve
MGPW Note 1) injection valve
Blower inverter panel
440 V, Frequency converter
MALS control panel
MALS operation panel (LCD)
15 inch, Touch panel type
Flow meter
Note 1: Marine Growth Preventing Water; MGPW

Figure 6(5)Outline arrangement of MALS

Controls related to MALS
Controls including the MTA start/stop control system and the MALS control system havebeen developed and standardized. Specific explanations of this are omitted here.

|3. Study examples assuming application on full-scale ship
As a preparation for offering MALS to customers in the future, design consideration is
performed specifically assuming a full-scale ship. Because of the difference in cargo and service,different types of ships have substantially different internal layouts. In particular, even for a samekind of ship, it is not too much to say that no two ferries are the same except for sister ships

Mitsubishi Heavy Industries Technical Review Vol. 50 No. 2 (June 2013)48

because the required specifications differ for every customer.
Apart from installation on new ships, when retrofitting of MALS on an existing ship,
sometimes modification of existing facilities may be considered in order to make space for ablower room etc. for MALS. Some examples of MALS study results for various kinds of ships aredescribed below. Based on this study, MALS is going to be installed on a pure car and truck carrier(PCTC), a bulk carrier, and a large passenger ship.
Figure 7 illustrates an example of the layout study of a new ferry. As a result of concern forthe prevention of the effects of blower noise on passengers and crews without impairing cargospace, the MALS blower room is established in the void space under the car deck, and theequipment required for air supply such as the blower, inverter, air cooler, etc., are all placed
together.
Figure 8 illustrates an example of an installation study of MALS on a mega container ship at
its concept design stage. On container ships, placement of the MALS blower room in the bosun
store in the bow is assumed.

Figure 8 Example of installation study of
MALS on mega container ship
Figure 7 Example of installation of MALS
on a ferry

For retrofitting MALS on an existing ship, in addition to equipment installing work, work
planning and engineering to facilitate and enhance efficiency of the work are also important. The
locations of air outlets are determined to some extent based on performance. However, it isnecessary to consider the installation layout of the blower, ancillary equipment such as the control
panel and accompanying pipes, wires and ducts in the limited internal space with lower
construction costs and a work term as short as possible. Shortening the term of dry-dock work is
advantageous also for the customer. Therefore shortening the work period not only by minimizing
the work amount but also by unitizing is required.
Table 3 shows an example of dry-dock work schedule prepared during the study ofretrofitting MALS on an existing bulk carrier. This project adopts a construction method where theadditional equipment such as the chamber is unitized and then replaced as blocks. Because work
space for conveying removed and new blocks in the bottom of the dock is limited, the block
replacement work is divided into two parts. In this project, plans require the docking, modification
work and undocking to take 16 days.
Table 3

Example dry-dock schedule of retrofitting MALS
D 0

1 Dock-in and work preparation(marking etc)
2 Removal of modification part3 Installation of new blocks etc.

1

2

3

4

5

6

7

#1
#2

4 Inspection and testing
5 Painting
6 Ballasting and dock-out#1: Installation of center block#2: Installation of starboard and port blocks

8

9 10 11 12 13 14 15 16

Mitsubishi Heavy Industries Technical Review Vol. 50 No. 2 (June 2013)
49

Figure 9 shows an example of the study of retrofitting MALS on an existing large passenger
ship. Passenger ships have many pieces of equipment and electric components which are densely
arranged. As a result, conveying equipment such as a blower to the installation location, andsecuring space for the addition of chambers for air outlets are difficult. In such cases, possible
measures include changing the layout of the existing tanks. Placing equipment in the limited space
efficiently and maintaining the amount of work at a low level lead to the shortening of the work
period. For design concepts of retrofitting, MHI plans to gain approval in principle (AIP) from
Lloyd's Register of Shipping of the UK.

Figure 9 Example of retrofitting study of MALS on large
passenger ship

|4. Conclusion
MHI considered expanding the target ship types of the Mitsubishi Air Lubrication System(MALS), one of energy-saving methods, in order to promote its prevalence. Because theinstallation of MALS on general merchant ships such as tankers and bulk carriers was the key toattaining prevalence, layouts of MALS equipment on typical types of ships was considered. For the
installation of MALS on large ships, MHI developed blowers exclusive to MALS, because few
commercially available blowers with capacity suitable for MALS existed. The specificconsideration of MALS installation assuming retrofitting work on existing ships in addition to
installation on newly built ships was performed. Through these considerations, MHI has definedrecommended standard specifications and design standard, and also has completed preparation ofengineering work for not only installing MALS on ships built by MHI, but also selling MALS toother ship builders.
In the future, MHI will work on the following tasks with the aim of expanding use of MALS.
- Improvement of energy-saving effect mainly on slender ships through the optimization of air
outlets.
- Offering more proper MALS packages through improvements in the estimation accuracy in theamount of propulsive resistance reduced due to air lubrication.
- Enhancement of customer benefit by enlargement of return on investment through the cost
reduction of the system.

References
1. Mizokami, S. et.al, Experimental Study of Air Lubrication Method and Verification of Effects on Actual
Hull by Means of Sea Trial, Mitsubishi Heavy Industries Technical Review Vol.47 No.3(2010) pp.41-47