SPECIAL REPORT 95-17

Northern Sea Route

Reconnaissance Study

A Summary of Icebreaking Technology

Devinder S. Sodhi June 1995
Abstract

Since the advent of steam power, icebreakers have been built to navigate in

ice-covered waters. The hull forms of early icebreakers were merely an

adaptation of open water hull shapes, by sloping bow angles more to

create vertical forces for breaking ice in bending. However, these bow forms

were found to be unsuitable for sea-going vessels because they push broken ice ahead of them. This experience led to construction of all sea-going

vessels with wedge-shaped bows from 1901 to 1979. With the introduction of low-friction coatings and the water-deluge system, it is now possible

to operate ships with blunt bows efficiently in broken ice. New developments in marine propulsion technology have also been incorporated to

obtain better icebreaking efficiency and performance. Both fixed-pitch and

controllable-pitch propellers are in use. Nozzles surrounding the propellers

are also used to increase the thrust and to reduce ice–propeller interaction.

Electrical and mechanical transmission systems have been used in icebreakers to improve the characteristics of the propulsion system. Though

many types of prime movers are used in icebreakers, medium-speed diesel

engines are the most popular because of their overall economy and reliability. Appendix A is a description of the Russian icebreaker Yamal, which

is one of the largest and most powerful icebreakers of the world today.

Appendix B contains an inventory of existing ships that are capable of

navigating in at least 0.3-m-thick ice. Some of the present icebreakers are

capable of navigating almost anywhere in the ice-covered waters of the

Arctic and the Antarctic, and multi-purpose icebreakers have been built to

operate not only in ice during the winter but also in open water doing other

tasks during the summer. With sufficient displacement, power, navigation

equipment, and auxiliary systems, future icebreakers that can operate independently year-round in the Arctic and the Antarctic are well within the

known technology and operational experience.

For conversion of SI units to non-SI units of measurement consult ASTM

Standard E380-93, Standard Practice for Use of the International System

of Units, published by the American Society for Testing and Materials,

1916 Race St., Philadelphia, Pa. 19103.

This report is printed on paper that contains a minimum of 50% recycled

material.
Special Report 95-17

Northern Sea Route

Reconnaissance Study

A Summary of Icebreaking Technology

Devinder S. Sodhi June 1995

Prepared for

U.S. ARMY ENGINEER DISTRICT, ALASKA

Approved for public release; distribution is unlimited.

US Army Corps

of Engineers

Cold Regions Research &

Engineering Laboratory
PREFACE

This report was written by Dr. Devinder S. Sodhi, Research Engineer, Ice Engineering

Research Division, Research and Engineering Directorate, U.S. Army Cold Regions Research and Engineering Laboratory. It represents a part of the investigations supporting a

Reconnaissance Study of the Northern Sea Route. The project was funded by the U.S. Army

Engineer District, Alaska. Dr. Orson Smith was the Project Manager.

The author is indebted to Leonid Tunik and Alfred Tunik for compiling the information

on icebreakers (presented in Appendix B); Captain Lawson Brigham, Commanding Officer of the USCG Polar Sea, for providing information, photographs, suggestions, and

valuable background material; Dr. Jean-Claude Tatinclaux, Chief, Ice Engineering Research

Division, for providing many references and for reviewing this report; Kevin Carey, Research Hydraulic Engineer, Ice Engineering Research Division, for technically reviewing

the manuscript; and Walter B. Tucker, III, Chief of the Snow and Ice Division, for providing

information on, and photographs of, the icebreakers at the North Pole. The author thanks

the members of the Reconnaissance Study team for their guidance and suggestions.

The author also gratefully acknowledges the dedicated work of the following CRREL

personnel in the preparation of this report: Nancy Liston and Elizabeth Smallidge for

procurement of publications and reports, Matthew Pacillo and Edward Perkins for preparation of the figures, and Lourie Herrin for typing assistance.

The contents of this report are not to be used for advertising or promotional purposes.

Citation of brand names does not constitute an official endorsement or approval of the use

of such commercial products.

ii
CONTENTS

Page

Preface ................................................................................................................................ ii

Introduction........................................................................................................................ 1

Early history ................................................................................................................ 1

Recent history ............................................................................................................. 5

Inventory of icebreaking ships ........................................................................................ 6

Sizes and dimensions ........................................................................................................ 7

Beam ........................................................................................................................... 7

Depth ........................................................................................................................... 7

Draft ........................................................................................................................... 7

Maximum deadweight .............................................................................................. 7

Hull forms........................................................................................................................... 8

Bow shape ................................................................................................................... 8

Midbody shape ........................................................................................................... 10

Stern shape .................................................................................................................. 10

Icebreaker performance with different hull forms ............................................... 11

Structural design of polar ships ...................................................................................... 12

Classification of polar ships ..................................................................................... 12

Ice loads and pressures ............................................................................................. 12

Materials ...................................................................................................................... 13

Welding ........................................................................................................................ 14

Plating .......................................................................................................................... 14

Framing ........................................................................................................................ 14

Propulsion system ............................................................................................................. 15

Propellers ..................................................................................................................... 16

Shafting ........................................................................................................................ 17

Mechanical transmission components .................................................................... 17

Electrical transmission systems ............................................................................... 17

Azimuth propulsion drive ........................................................................................ 18

Prime movers .............................................................................................................. 19

Auxiliary systems .............................................................................................................. 21

Low-friction hull coating .......................................................................................... 21

Heeling system ........................................................................................................... 22

Air-bubbler system .................................................................................................... 22

Air-bubbler–water injection system ........................................................................ 23

Water-deluge system ................................................................................................. 23

Power and performance ................................................................................................... 23

Fuel consumption rates ............................................................................................. 23

Performance prediction ............................................................................................. 24

Future icebreakers ............................................................................................................. 28

Summary............................................................................................................................. 30

Literature cited ................................................................................................................... 30

Appendix A: Information about the nuclear icebreaker Yamal .................................. 33

Appendix B: An inventory of existing ships that are capable of navigating in

at least 0.3-m-thick ice cover ............................................................................. 35

iii
ILLUSTRATIONS

Figure Page

1. The Russian icebreaker Yamal, the Canadian icebreaker Louis S. St. Laurent,

and the U.S. icebreaker Polar Sea during the expedition to the

North Pole in August of 1994 ......................................................................... 3

2. Significant events in the development of polar ship technololgy

since 1955 ........................................................................................................... 4

3. Design evolution of Russian polar icebreakers ................................................ 5

4. Taymyr-class shallow-draft nuclear icebreaker ................................................. 6

5. Dimensions of vessels ........................................................................................... 7

6. Maximum deadweight vs. overall length of all vessels listed in

Appendix B ........................................................................................................ 8

7. Main features of bow forms ................................................................................. 9

8. Different shapes of icebreaking bows ................................................................ 9

9. Hull form of the Finnish multipurpose icebreakers Finnica and

Nordica ................................................................................................................ 10

10. Icebreaking capabilities of three sister ships with different bow

shapes in terms of speeds in level ice of different thicknesses

at a power level of 16.2 MW ........................................................................... 11

11. Ship speed vs. equivalent ice thickness during tests in broken ice

with three sister ships having different bow shapes .................................. 11

12. Measured effective pressure vs. contact area .................................................... 13

13. Plane strain fracture toughness vs. temperature for two grades of steel ..... 13

14. Pressure vs. deflection, showing domains of different behaviors from

small to large deflection .................................................................................. 14

15. Shaft power vs. year of construction for icebreaking ships ........................... 15

16. Shaft power vs. propeller diameter for icebreaking ships .............................. 16

17. Differences between diesel-mechanical and azimuth installations .............. 19

18. Prime movers installed on icebreaking ships ................................................... 19

19. Outboard profile and topside deck plan of the Swedish icebreaker

Oden .................................................................................................................... 22

20. Power vs. beam for icebreakers .......................................................................... 23

21. Icebreaking performance: bollard pull/beam vs. ice thickness .................... 23

22. Speeds and power levels of U.S. icebreaker Polar Sea during her

transit from 23 March to 4 April 1983 ........................................................... 25

23. Number of ramming operations during the transit of U.S. icebreaker

Polar Sea from 23 March to 4 April 1983 ........................................................ 26

24. Specific net thrust vs. speed at maximum shaft power, indicating

propulsive performance .................................................................................. 27

25. New “iceraking” concept, as proposed by Johansson et al. ........................... 29

TABLES

Table

1. Selected important icebreaking voyages in recent years ................................ 2

2. Estimates of daily fuel consumption for a Polar-class icebreaker .................. 24

3. Fuel consumption rates of a few Russian ships according to the

information given in the brochures of the Murmansk Shipping

Company ............................................................................................................ 24

4. Performance criteria for a Northwest Passage icebreaker .............................. 28

5. Comparison of design parameters of proposed Northwest Passage

icebreaker with those of the Yamal ................................................................. 28

vi
INTRODUCTION

In the last four to five decades, many developments in icebreaking technology have taken place

through the application of modern marine technology to the design and the operation of polar

ships. Innovative ideas have been implemented to

improve the propulsion systems and to reduce the

resistance encountered during icebreaking. Present

navigation and information systems (e.g., ice maps,

satellite images, etc.) aboard polar ships enable

navigators to identify ice features along the transit route in near real time and to chart a tactical

course. As a result of this, it is possible to travel by

ships to remote polar regions that were thought to

be unreachable only a few years ago. Many nations have contributed to this development by designing and building polar ships and by launching voyages to various regions of the Arctic and

the Antarctic. Some of the landmark voyages during the last four decades are listed in Table 1

(Brigham 1992). Recently, Russian nuclear-powered icebreakers have regularly traveled to the

North Pole. In August of 1994, the U.S. icebreaker

Polar Sea, the Canadian icebreaker Louis S. St.

Laurent and the Russian nuclear icebreaker Yamal

(App. A) met at the North Pole (Fig. 1).

The impetus behind these technological advances has come from:

1. The exploration for natural resources around

the Arctic Basin.

2. The development of the Northern Sea Route

by the former Soviet Union, as an integral

part of development of the entire Russian

Arctic.

3. The need for multi-mission ships for the

transportation of personnel, logistics and

marine research in the Antarctic.

Although exploration for hydrocarbon resources in the southern Beaufort Sea has almost

stopped, plans are being discussed for developments in the offshore areas of the Russian Arctic

to produce hydrocarbon resources and to transport them to world markets. Future shipments of

these resources will have significant effects on the

development of the Northern Sea Route.

From the perspectives of a master mariner, the

performance of icebreakers depends on the construction limitations of the vessels and the skills

in ice navigation of their captains (Toomey 1994).

Although the technological improvements incorporated in the design and construction of an icebreaker help to increase its performance in ice, it

is essential to have a skilled captain and crew operating the ship to exploit these advantages to the

maximum extent. Therefore, the training and the

experience of the crew operating an icebreaker are

important elements in its performance. A knowledgeable, skilled captain, supported by extensive

information, can prevent or quickly overcome

many difficulties along a route.

Early history

Johansson et al. (1994) have given an account of

the early history of icebreaking ships. Breaking ice

with ships was not possible before the advent of

steam power. One of the earliest icebreakers,

named Norwich, was introduced in 1836 on the

Hudson River. She had paddle wheels for propulsion and was very effective in breaking ice, remaining in service for 87 years.

By the end of the nineteenth century, only fixedpitch, screw-type propellers driven with steam

power were installed on new icebreakers. Early

icebreakers were not powerful, and the hull form

was basically adapted from open water hull shapes

by sloping the bow angles more to create a vertical force to break the ice in bending. Many innovative designs were proposed and built to increase

icebreaking efficiency. For instance, the highly sucNorthern Sea Route Reconnaissance Study

A Summary of Icebreaking Technology

DEVINDER S. SODHI
Table 1. Selected important icebreaking voyages in recent years (after Brigham 1992).

Polar ship/flag Time of year Route/location Significance

Lenin Summer 1960 Northern Sea Route World’s first nuclear surface ship comUSSR mences icebreaking escort duties

Manhattan Autumn 1969 Northwest Passage Experimental voyages to test the feasiUSA bility of commercial tankers in the Arctic

Louis S. St.Laurent and Aug 1976 Northwest Passage Successful escort of a drill ship from the

Canmar Explorer II Atlantic to the Canadian Beaufort Sea

Canada

Arktika Aug 1977 Murmansk to the North First surface ship to reach the geographic

USSR Pole and return North Pole (17 Aug)

Sibir’ and Kapitan Myshevskiy May–Jun 1978 Northern Sea Route (north First high-latitude “trans-Arctic” ice escort

USSR of Novosibirskiy Islands)

Polar icebreakers and Navigation season Barents and Kara seas First successful year-round navigation from

icebreaking carriers 1978–79 Murmansk to Dudinka on the Yenisey River

USSR

Polar Star and Polar Sea 1979–86 Bering, Chukchi, and Arctic marine transportation (“trafficUSA Beaufort seas ability”) studies around Alaska

Polar Sea Jan–Mar 1981 Bering Sea to Beaufort Sea First winter transit to Pt. Barrow, Alaska

USA

Polar Star Dec 1982–Mar 1983 Antarctica First high-latitude (above 60°S) circumUSA navigation of Antarctica in modern times

Leonid Brezhnev and Oct–Nov 1983 North coast of Chukotka, Rescue of 50 cargo ships trapped in ice

12 other icebreakers Siberia

USSR

Arctic Aug 1985 Bent Horn, Cameron First cargo of crude oil from the

Canada Island Canadian Arctic

Vladivostok and Somov Jun–Sep 1985? Near Russkaya Station, Rescue of Soviet Antarctic Expedition

USSR Hobbs Coast, Antarctica flagship drifting in heavy ice

Three SA-15 icebreaking Nov–Dec 1985 Northern Sea Route Experimental navigation season excarriers tension with sailings from Vancouver

USSR to Arkangel’sk

Icebird Fall 1985– Australian Antarctic Bipolar resupply operations to

FRG Summer 1986 stations and Japan to Antarctica and Prudhoe Bay

Prudhoe Bay, Alaska

Polarstern Jul–Aug 1986 Weddell Sea, Antarctica Winter oceanographic operations

FRG

Sibir’ May–Jun 1987 Central Arctic Basin Evacuate drift station 27 and establish

USSR drift station 29; second surface ship to

reach the geographic North Pole (25 May)

SA-15 icebreaking Summer 1989 Europe to Japan via the Soviet arctic carriers under charter to

carriers Northern Sea Route Western shippers for commmercial voyUSSR ages across the top of the Soviet Union

Rossiya Aug 1990 Central Arctic Basin Transit to the North Pole (8 Aug) with

USSR Western tourists aboard

Arctic Jun 1991 Northwest Passage to the Earliest seasonal surface ship transit

Canada Polaris Mine, Little in eastern reaches of the Northwest

Cornwallis Island Passages; mine reached 23 Jun

Sovetskiy Soyuz Jul–Sep 1991 Central Arctic Basin and Transit to the North Pole and along the

USSR Northern Sea Route Northern Sea Route with Western tourists

Oden and Polarstern Aug 1991 Central Arctic Basin International Arctic Ocean Expedition;

Sweden and FRG reached the North Pole on 7 Sep

Sovetskiy Soyuz Jul and Aug 1992 Central Arctic Basin Reached the North Pole on 13 Jul and

Russia 23 Aug

Yamal Jul and Aug 1993 Central Arctic Basin Reached the North Pole three times

Russia on 13 Jul, 8 and 30 Aug

Yamal and Kapitan Branitsyn Jul 1994 Central Arctic Basin Reached the North Pole on 21 Jul

Russia

Yamal Aug 1994 Central Arctic Basin Reached the North Pole on 5 and 20 Aug

Russia

Louis S. St. Laurent and Polar Sea Aug 1994 Trans-Arctic Ocean Reached the North Pole on 22 Aug;

Canada and USA Bering Strait to Svalbard encountered Yamal at the North Pole

2
a. Near the North Pole.

b. View from Yamal (Polar Sea is last in line).

Figure 1. The Russian icebreaker Yamal, the Canadian icebreaker Louis S. St. Laurent, and the U.S.

icebreaker Polar Sea during the expedition to the North Pole in August of 1994 (photos courtesy W.B.

Tucker, III).

3
4

Figure 2. Significant events in the development of polar ship technology since 1955 (after Brigham 1987).

Bow
Recent history

Figure 2 shows a summary of significant advances in the polar ship technology during the past

four decades, as outlined by Brigham (1987), made

by Finland and the former Soviet Union, and by

the U.S., Canada, Germany and Japan. Together, Finland and the Soviet Union have made enormous

contributions to the development of polar ships.

The Soviet Union first used nuclear technology

to power the icebreaker Lenin, which was built in

1959 with a propulsive power of 29 MW (39,000

hp). The Finnish shipbuilder, Wärtsilä Shipyard

(now Kværner Masa-Yards), built many icebreakers for the Soviet Union and created extensive design evolution during the years of the development

of conventionally powered icebreakers. Recently,

these two technologies have merged, as shown in

Figure 3, to develop the Taymyr-class (Fig. 4), shallow-draft polar icebreakers built in Helsinki with

Soviet nuclear propulsion systems installed in St.

Petersburg.

Similarly, developments in the U.S. and Canada

have contributed to changes in key areas of icebreaking technology (e.g., hull and bow form, gas

turbines, and controllable-pitch propellers). In

1969, the U.S. modified tanker Manhattan had tenfold the displacement of earlier icebreakers, giving her great ramming capability. In the early

1980’s, modern hull and propulsion technologies

were also applied to Antarctic ships (e.g., Japan’s

Shirase, and Germany’s Polarstern). The bows of

three icebreakers were converted to the newly developed Thyssen-Waas bow: Max Waldeck in 1980,

Mudyug in 1986 and Kapitan Sorokin in 1991. The

results of full-scale trials in open water and in ice

indicate that this change in the bow of Mudyug

has increased her icebreaking capability in level

ice at reduced power requirements (Milano 1987).

However, there were problems with wave slamcessful “spoon-shaped” bow was first proposed

and built by Ferdinand Steinhaus of Hamburg in

1871. In 1892, Weedermann invented and patented

a device to be placed in front of a ship having a

bow not suitable for icebreaking on its own. These

devices are still used on Dutch rivers and canals.

By 1900, it was well understood that, while ships

with blunt bows are efficient in breaking level ice

in sheltered areas, such as rivers, lakes and other

protected areas, their performance in rubble ice is

poor because they have a tendency to push broken ice ahead of themselves. On the other hand,

ships with wedge-shaped bows and sharp stems

did not have any tendency to push rubble ice. This

experience led to all sea-going ships built between

1901 and 1979 having a wedged-shaped bow and

a sharp stem (Johansson et al. 1994). Over the years,

the wedge-shaped bows became known as “conventional” bows, and the other shapes as “unconventional” bows.

The development of the bow form remained

stagnant in the early and middle part of the 20th

century (Johansson et al. 1994). This can be attributed partly to other priorities caused by the two

World Wars and by the slowdown of economic

acivity during the large-scale recession of the 1930s.

Despite this stagnancy in bow design, other innovations were introduced during this time. The Russian icebreaker Yermak, built in 1899 and fitted

with propulsive machinery of 7.46 MW (10,000

hp), had considerable effect on the icebreaking

technology at the turn of this century by becoming a pioneer in many untested offshore areas. In

1933, diesel-electric propulsion was introduced on

the Swedish icebreaker Ymer. In 1947, twin bow

propellers were introduced on the Canadian icebreaking ferry Abgeweit. (However, the use of

bow propellers has now been discontinued because of their interference with ice.)

Figure 3. Design evolution of Russian polar icebreakers (after Brigham 1991).

5
icebreaking ships and multi-purpose ships will be

dictated by the needs of future developments and

trade.

INVENTORY OF

ICEBREAKING SHIPS

Icebreaking ships that will be built in the future

may have their designs based on the present state

of icebreaking technology and may also incorporate innovative developments in many areas of

marine technology. Past experience can help designers avoid mistakes, but accepting the present

status too rigidly can also discourage them from

innovation. Improvements in the design of icebreakers should result from a full understanding

of the current status of icebreaking technology.

Information on most of the icebreaking ships in

the world is given in the appendix of the review

paper by Dick and Laframboise (1989), and an

updated and a modified version of this list is also

included in the appendix of a report by Mulherin

et al. (1994). The latter database contains information on icebreakers and icebreaking cargo ships

from the following countries: Argentina, Canada,

Denmark, Finland, Japan, Sweden, United Kingdom, Russia (or former Soviet Union), U.S. and

Germany.

An inventory of all ships that are capable of

navigation in at least 0.3-m- (1-ft-) thick ice has

been prepared for this study. This information has

been assembled in an electronic database and is

also presented in Appendix B. The database conming in open water operations during high seas,

and with the front of the ship pushing rubble ice

(Ierusalimsky and Tsoy 1994).

In 1979, the Canadian icebreaker Kigoriak was

built with a spoon-shaped bow for operations in

the Beaufort Sea. Extensive full-scale experience

indicated that even this modern version of the

spoon-shaped bow was not immune to the icepushing problem. However, these problems were

solved by using epoxy paint and a water-deluge

system to reduce friction between the broken ice

pieces and the hull. The water-deluge system lifts

several tons of water every second and pours it on

top of the ice in front of the bow. This helps to move

the ice pieces past the ship by submerging them.

In the early 1980s, several ships in Canada were

built with spoon-shaped bows. Some of the recent

icebreakers built in Europe have also been built

with these bows, e.g., the Swedish icebreaker Oden,

built in 1989, the Russian icebreaker Kapitan

Nikolayev, converted in 1990, and the Finnish icebreakers Finnica and Nordica, built in 1993 and 1994.

With the introduction of low-friction coatings

and auxiliary systems, the capabilities of present

icebreakers are greatly enhanced so that they can

make steady progress in all types of ice conditions.

With sufficient displacement, power and auxiliary

systems, future icebreakers that can operate

independently year-round in the Arctic are well

within the known technology and operational experience (Keinonen 1994). As in the past, the construction of future icebreakers and icebreaking

cargo ships will be closely linked to economic conditions and pressures. Choices between dedicated

Figure 4. Taymyr-class shallow-draft nuclear icebreaker (after Brigham 1991).

Single Pressurized Water Reactor

(USSR)

2 Main Steam Turbines

(USSR)

Power Unit Automation

and Control System

(Finland)

2 Main Generators

(West Germany)

3 AC Propeller Motors

(Finland)

Shallow-draft

Design (~8 meters)

(Finland)

Low Friction

Hull Coating

(Finland)

Hull Air Lubrication

System

(Finland)

Ship Systems Operate at

Air Temperatures to –50°C

(USSR & Finland)

Icebreaking Bow 

and Hull Form

(Finland)

Cold-resistant

Hull Steel Plates

(USSR)

6
tains technical and other forms of information on

each series of ships. Technical information consists

of length, beam, depth, draft, deadweight, displacement, propulsion machinery, nominal speed,

bow shape, propulsion power, fuel capacity, fuel

rate, etc. Non-technical information consists of the

name (or former name), names of sister ships, ownership, shipyard and year of construction, home

port, ice classification, etc.

SIZES AND DIMENSIONS

The main dimensions of a polar ship are its

length, beam width and depth. The draft is the

depth of the ship’s keel below the waterline,

whereas the depth is the distance between the keel

and the deck. The depth of water in which a ship

can operate without touching bottom depends on

the draft. Figure 5a shows plots of the dimensions

of icebreakers (cargo ships not included) as compiled by Dick and Laframboise (1989), whereas Figure 5b shows the dimensions of all ships as compiled in the database given in Appendix B. The

scatter in the plot of data in Figure 5b is greater

than that in Figure 5a, because ships listed in Appendix B are not only icebreakers but also other

ships having some icebreaking capability. The

trends of the lines shown in Figure 5a pertain only

to icebreakers, whereas the lines of best fit shown

in Figure 5b pertain to the data on vessels listed in

Appendix B.

Beam

In Figure 5a, the mean length-to-beam ratio of

icebreakers varies from 3.6 to 4.6 for lengths from

40 to 140 m respectively. North American vessels

are narrower than those from Finland, Sweden and

Russia. This may be attributed to the practice of

convoy escort used in the Baltic Sea and Russian

Arctic. The line of best fit in Figure 5b has an intercept of 6.7 m and a slope of 0.102 m/m.

Depth

In Figure 5a, the mean length-to-depth ratio of

icebreakers varies from 8.9 to 8.2 for lengths from

40 to 140 m respectively. This ratio is high for supply vessels and low for conventional icebreakers.

The line of best fit in Figure 5b has an intercept of

0.6 m and a slope of 0.08 m/m.

Draft

In Figure 5a, the mean length-to-draft ratio of

icebreakers varies from 11.4 to 12.2 for lengths from

Figure 5. Dimensions of vessels.

b. All vessels included in the inventory of ships

listed in Appendix B.

40 to 140 m respectively. Draft, like other dimensions, is usually defined by the operating requirements of the ship. The line of best fit in Figure 5b

has an intercept of 2.2 m and a slope of 0.042 m/m.

Maximum deadweight

Figure 6 shows a plot of deadweight at maximum draft vs. the overall length of the vessels

listed in Appendix B. The curve shown in Figure 6

is a best fit quadratic curve having the following

equation

40

30

20

10

0 40 80 120 160 200

Beam, Depth, Draft (m)

Beam

Depth

Draft

Length (m)

a. Icebreakers (cargo ships not included) (after Dick

and Laframboise 1989).

250

40

30

20

10

0

Beam, Depth, Draft (m)

50 100 150 200

Length (m)

Beam

Depth

Draft

0

7
Dmax = –4545 + 18.81 L + 0.61 L2

where Dmax is the maximum deadweight and L is

the overall length of a vessel.

HULL FORMS

The primary consideration for the choice of hull

form of an icebreaking ship is the lowest power

required to make progress in ice. Power in open

water, maneuvering and protection of propellers

from ice are some of the secondary considerations.

The following are factors that need to be considered

while selecting a hull form (Dick and Laframboise

1989):

1. Performance in ice of all types.

2. Performance in open calm water.

3. Performance in heavy weather in open

water.

4. Maneuvering capability.

5. Overall dimensions.

6. Ease and cost of construction.

7. Ease of repair and type of ship (e.g., cargo,

icebreaker, etc.).

Because some of the objectives listed above are

in conflict with each other, the best hull shape is

one that takes into account the overall operations

of a vessel. Most of the sea-going icebreaking ships

have been constructed with conventional bows.

However, there have been a few departures from

this trend in the recent past, and a few ships have

been built with unconventional bows out of particular considerations of costs, icebreaking efficiency or maneuvering. Auxiliary systems have

to be furnished so that a ship with an unconventional bow can operate effectively in rubble ice as

well as in level ice.

Bow shape

The bow shape of an icebreaker is characterized

by five basic design features, shown in Figure 7.

Flare angles contribute to the efficiency of

icebreaking and ice block submergence, whereas

waterline angles contribute to clearing efficiency.

Buttock angle and stem angle are associated with

the flare and waterline angles, and these also contribute to breaking and submergence efficiencies.

The progression in the design of icebreaker

bows over the last two decades has been to increase

flare angles, to reduce waterline angles and to reduce stem and buttock angles (Dick and Laframboise 1989). These changes have resulted from a

systematic series of model tests to produce a more

efficient icebreaking bow. Over the years, the values of stem angles of icebreakers have decreased

from 30 to 20°.

The selection of bow shape is greatly influenced

by the mission profile of a polar ship. Different

bow shapes that have been used are shown in Figure 8 (Dick and Laframboise 1989), and a brief discussion of each follows.

Straight stem with parallel buttocks

This shape has been commonly used for Soviet

and Finnish icebreakers since the 1950s, as demFigure 6. Maximum deadweight vs. overall length of all vessels listed in Appendix B.

40

30

20

10

0 100 200 300

Length (m)

Maximum Deadweight (tons)

D = – 4545 + 18.81L + 0.61L2

max

50 x 10 3

8
Spoon bow with reamers

The spoon-shaped bow has been more efficient

because this shape allows a constant frame flare

angle throughout the bow length. As mentioned

earlier, this shape was used in the past, but its use

was discontinued because of its high resistance in

heavily snow-covered ice, and its tendency to push

broken ice in front of the ship. With the introduction of bubbler systems or water wash systems,

these problems have been overcome.

A modification of this shape was reintroduced

on the Canadian icebreakers Canmar Kigoriak, built

in 1979, and Robert Lemeur, built in 1981. The extended beam at the shoulder (reamers) with the

abrupt change in shape eliminates midbody resistance by cutting a wider channel in ice, but it causes

extra resistance in open water. Recently, this shape

was also used in the European icebreakers Oden,

Kapitan Nikolayev, Finnica and Nordica. The hull

form of the Finnish multipurpose icebreakers

Finnica and Nordica is shown in Figure 9, which

also shows the icebreaking stern and the bi-directional reamers on the sides.

Flat

of Side Buttock

Angle Stem

Angle

H

Lf

Flare

Angle B

Waterline

Angle

Figure 7. Main features of bow forms (after Dick and Laframboise 1989).

Straight Stem

with Parallel Buttocks

ConcaveStem

(White Bow)

Semi-spoon Bow

with Chines

Flat Family

High Frame Flare Angles

(Melville Bow)

Spoon Bow

with Reamers Thyssen-Waas Bow

Figure 8. Different shapes of icebreaking bows (after Dick and Laframboise 1989).

onstrated by the Moskva-class icebreakers in the

1960s, and the Urho-class Baltic icebreakers in the

1970s.

Concave stem (White bow)

Although the concave stem had been used in

earlier icebreakers, R. White developed this particular shape in 1969 for efficient icebreaking and

ice clearing. This bow shape was used in the U.S.

icebreakers Polar Star and Polar Sea, built in the

mid-1970s, in the Canadian icebreaking cargo ship

Arctic, built in the late 1970s, and in the Canadian

R-class icebreakers, built between 1978 and 1984.

Because of the concave stem, this bow shape has

higher frame flare angles close to the stem.

High flare angles (Melville bow)

This shape was developed to reduce the

icebreaking component of ice resistance. Recently,

the Canadian icebreaking cargo ship Arctic was

modified to this type of bow, and its performance

increased from 1 to 4 m/s (2 to 8 knots) in 1-mthick ice.

9
Semi-spoon bow with chines

This shape is similar to the spoon bow shape,

except that the extended beam (reamers) are replaced by shoulder chines. This shape has been

used on vessels working in the Beaufort Sea, and

it has improved icebreaking performance. But it

has had some detrimental effect on the open-water resistance.

Flat family

These shapes are similar to the spoon bow and

semi-spoon bow shapes, except that flat plates

have been used to reduce the construction costs.

This shape was developed as a compromise between icebreaking capabilities and construction

costs. This type of bow has been used on the Canadian vessels Arctic Nanabush, built in 1984, and

Arctic Ivik, built in 1985, both being used for ice

management in the Beaufort Sea.

Thyssen-Waas bow

This type of bow shape is a significant departure from a conventional icebreaking bow. The bow

first breaks the ice by shearing at the maximum

beam of the ship, and then breaks the ice in bending across the front of the bow. This shape is characterized by flat waterlines at the extreme forward

end, extended beam, a low stem angle with an ice

clearing forefoot, and high flare angles below the

waterline. The ice clearing capability is so good

that the channel behind the ship is about 85% free

of ice. As mentioned earlier, the vessels that have

been fitted with this type of bow are the Max

Waldeck (1980), the Mudyug (1986) and the Kapitan

Sorokin (1991).

Of the seven bow shapes listed above, the first

three can be called “conventional” or “traditional,”

because these shapes retain the smooth hull, which

offers the least resistance in open water. The other

four shapes are “unconventional” or “nontraditional,” in that these shapes are a distinct departure from the smooth hull shapes. Each shape has

some benefits and some drawbacks. Therefore, the

selection of a bow shape should be based on a full

understanding of the operational requirements of

a ship.

Midbody shape

The midbody shape of a polar ship is characterized by three parameters: flare angle, parallel sides

and longitudinal taper (Dick and Laframboise

1989). The objective of midbody flare is to decrease

the resistance caused by it while passing through

the channel broken by the bow. Some of the icebreaking cargo ships have a long, parallel midbody.

Some of the icebreakers have forward shoulders

to break a wider channel to eliminate any ice resistance from a parallel midbody. Similarly, a midbody with longitudinal taper eliminates ice resistance aft of the forward shoulders. This shape has

been used on barges pushed by small tugs that

operate in sheltered water. The drawbacks of longitudinal taper in the midbody are higher construction costs and an increased probability of getting stuck in pressured ice. A longitudinally tapered midbody is not used on icebreakers or

icebreaking cargo ships.

Stern shape

All icebreakers must move astern in ice. Some

icebreakers may move back only in the previously

broken channel or in broken ice. But there are those

icebreakers providing a support role that must

break ice while moving astern. Depending upon

the mission profile, these ships may have an ice

breaking–deflecting stern shape, as shown in Figure 9. The main concern while moving astern is

the ingestion of ice blocks into the propellers. Despite many innovative stern designs and shrouded

propellers, there is still considerable interaction between ice and propellers (Dick and Laframboise

1989).

Figure 9. Hull form of the Finnish multipurpose icebreakers Finnica and Nordica (after

Lohi et al. 1994).

10
Figure 11, giving the results of the tests conducted in freshly broken ice in their own channel,

shows that the performance of Kapitan Nikolayev

is better than that of the other two ships. For tests

conducted in broken ice in old channels, Kapitan

Nikolayev performs better than Kapitan Dranitsyn.

In old channels full of broken ice, Kapitan Sorokin

had a tendency to push broken ice ahead of itself

when it was not able to reach a speed of 3–4 knots

(1.5–2 m/s). Three rounded knives in the bow of

Kapitan Sorokin work efficiently to break level ice,

but they also obstruct the flow of broken ice underneath the bow. At times, the buildup of an ice

pile can bring the ship to a standstill, and force it

either to ram through the pile or to seek a new

path. While operating in drifting broken ice at

speeds up to 3–4 knots, Kapitan Sorokin showed

tendencies to push ice. The performance of Kapitan

Nokilayev improved in drifting ice fields.

Both ships with the Thyssen-Waas and conical

bows must reduce speeds in severe seas because

of considerable wave slamming in a head sea, resulting in longer travel times.

Ierusalimsky and Tsoy (1994) have compared

the cost savings as a result of conversion of bow

shapes from conventional to the two types of unconventional shapes. According to them, Kapitan

Nikolayev, with the conical bow, had reduced operational costs and increased profitability, whereas

similar measures for Kapitan Sorokin, with the

Thyssen-Waas bow, were less favorable than those

for the ship with the original bow. It should, howFigure 10. Icebreaking capabilities of three sister ships

with different bow shapes in terms of speeds in level ice of

different thicknesses at a power level of 16.2 MW (after

Ierusalimsky and Tsoy 1994).

Icebreaker performance with

different hull forms

Ierusalimsky and Tsoy (1994) presented the results of full-scale tests conducted on three Russian

sister ships of the Kapitan Sorokin series with different hull forms: Kapitan Sorokin, converted to a

Thyssen-Waas bow in 1991, Kapitan Nikolayev, converted to a conical bow (similar to the spoonshaped bow) in 1990, and Kapitan Dranitsyn, still

with the original, wedge-shaped bow. The data on

the performance of these ships were obtained over

3 years, enabling a determination of any cost saving resulting from the conversion to bows of different shapes.

For breaking a level ice sheet in forward motion, Figure 10 plots ship performance in terms of

the continuous speed of these three ships in equivalent ice thicknesses. The plots in Figure 10 show

that Kapitan Sorokin with the Thyssen-Waas bow

has the best icebreaking capability among the three

in level ice, closely followed by the Kapitan

Nikolayev with the conical bow. The performance

of these two ships is much better than that of

Kapitan Dranitsyn with its original bow. While

breaking a channel in fast ice, Kapitan Sorokin left

up to 40% of the ice in the channel behind it,

whereas the other ships left 80–90% of the channel

filled with ice. A similar test for backward motion

in level ice revealed their performance in reverse

order as that for forward motion.

Figure 11. Ship speed vs. equivalent ice thickness during

tests in broken ice with three sister ships having different

bow shapes. The ships were tested in their own channels (after Ierusalimsky and Tsoy 1994).

8

6

4

2

0

0.8 1.2 1.6 2.0 2.4

Equivalent Ice Thickness (m)

Speed (knots)

2

1 3

1. With Original Bow (1978)

2. With Thyssen-Waas Bow (1991)

3. With Conical Bow (1990)

4

3

2

1

0

Speed (m/s)

20

16

12

8

4

0 0.4 0.8 1.2 1.6 2.0 2.4

Equivalent Ice Thickness (m)

Speed (knots)

1

2

3

1. With Conical Bow (1990)

2.With Thyssen-Waas Bow (1991)

3. With Original Bow (1978)

10

8

6

4

2

0

Speed (m/s)

11
ever, be noted that Kapitan Nikolayev is fitted with

stainless steel compound plate in the ice belt area,

which may be effective in reducing the chances of

getting stuck in ice.

STRUCTURAL DESIGN OF

POLAR SHIPS

Structural design involves the selection of material and sizes of plates and frames for maintaining the structural integrity of a polar ship under

loads from waves and ice during its normal operation (Dick et al. 1987). As a result of research

and experience, much has been learned about the

nature of ice loads and the mechanics of ice failure. Full-scale measurements of ice loads on many

ships have yielded an empirical description of ice

forces and pressures that is used in design. The

magnitude of ice loads, the existence of significant

damage and the emergence of affordable nonlinear finite element analysis packages have together

led to the wide use and acceptance of plastic design (plastic design allows some deformation of

the structure under extreme ice loads).

Classification of

polar ships

All commercial vessels, including most icebreakers, but excluding government-owned vessels, are classified according to the rules developed

by six classification societies: Lloyds Register (LR),

Det norske Veritas (DnV), American Bureau of

Shipping (ABS), Bureau Veritas (BV), Germanischer Lloyd (GL), and Russian Register of Shipping

(RS). Besides the rules of the classification societies, there are three national sets of rules to control

navigation in ice-covered waters: Finnish–Swedish, Russian and Canadian. The classification of a

vessel is used for insurance and to comply with

the international regulations, such as the Safety of

Life at Sea (SOLAS) and prevention of pollution.

Government-owned vessels are also surveyed for

compliance with recognized national and international standards.

The classification societies are responsible for

approving the design and supervising the construction of individual vessels to ensure conformity with the standards set by international conventions and by the classification of that vessel.

The vessels are subjected to annual and special

surveys throughout their lives (Toomey 1994).

The ice classification of a vessel depends on its

capability to resist damage while navigating in ice

under normal handling conditions. Unfortunately,

there are so many classifications by the different

societies that it is difficult to establish equivalency

among them (Santos-Pedro 1994, Toomey 1994). A

limited equivalency among the ice classifications

of the various societies is given in the Appendix A

of a companion report by Mulherin (1994). At present, an effort is underway to standardize ice

classes as international navigation through Arctic

routes, such as the Northern Sea Route and the

Northwest Passage, becomes more attractive for

shipping products between the North Atlantic and

the North Pacific (Santos-Pedro 1994). While comparing the ice-strengthening requirements according to the Russian Register Rules and Canadian

Arctic Shipping Pollution Prevention Regulations

(CASPPR), Karavanov and Glebko (1994) have

presented an extensive comparison of the ice loads,

section modulus and shear area of frames, and

thickness of shell plating. The new CASPPR (1989)

regulations call for smaller scantlings and thinner

shell plates than those required by Russian Rules

because CASPPR allows a certain amount of plastic deformation of the structure under extreme ice

loads.

Ice loads and pressures

Compression of ice at low strain rates results in

creep deformation with or without micro-cracking. The constitutive relations between stress and

strain for creep deformation at low strain rates are

well known. At higher strain rates (>10–3 s–1), the

ice fails in a brittle manner, resulting in instabilities caused by macro-cracking. The failure mechanism for brittle failure has not been fully understood. Failure loads or pressures also depend on

the state of stress, e.g., uniaxial vs. multiaxial. At

present, the dependence of compressive failure of

ice under multiaxial loading at different strain rates

is being studied by researchers all over the world

(e.g., Frederking 1977, Richter-Menge et al. 1986,

Smith and Schulson 1994, etc.).

There have been attempts made to relate the

forces exerted on a ship or a structure by crushing

of ice to the uniaxial compressive strength of ice,

but these attempts to obtain empirical relationships

through the use of many coefficients have not been

fruitful. Although much has been known about the

forces from flexural failure and compressive failure of ice at low strain rates, the understanding of

brittle failure is still incomplete at high rates of

loading and in a multiaxial state of stress. Results

of small-scale indentation experiments on freshwater ice indicate that brittle failure is activated at

12
tures. The fracture toughness of steel depends on

the operating temperature and on the rate of loading. In Figure 13, the plane strain fracture toughness of two types of steel has been plotted with

respect to temperature for three rates of loading.

Steel fractures in a brittle manner, without any

warning of impending failure, when the stresses

are of sufficient magnitude to propagate a crack

from a flaw or small crack in the material. The criterion for crack propagation in linear elastic fracture mechanics is that an existing crack will grow

when the stress intensity factor at the crack tip is

greater than the fracture toughness of the material. For nonlinear material behavior, the causes

for brittle fracture have now been established, and

the relationships among the cause of fracture, the

toughness of the material, the flaw size and shape,

the loading rate of the structure, and the temperature are understood. From this understanding,

materials and welding techniques have been developed to increase the reliability of ship structures.

It is the consensus of many operators that the steel

used in the present generation of polar ships is

mostly adequate (Dick et al. 1987).

There are currently two procedures for specifying the type of steel to be used in different parts of

a ship: “design by rule” and “design by analysis.”

Design-by-rule procedures require the designer to

consider service temperature and to select steel

grades that have adequate notch toughness. Design-by-analysis procedures require the designer

to consider the magnitude and the rate of loading

that may be applied during the life of a component, and to design that component with adequate

reliability according to its importance. The designby-analysis approach places a large responsibility

on the designer, but it may provide a more reliable

and economical design than that by the designby-rule approach.

The midbody region of a ship will experience

vibrations excited by shocks at the bow, but the

vibratory stresses have much longer rise time than

shock-induced stresses, resulting in small chances

of initiating a fracture. However, the static stresses

from vibrations may be high enough to cause fracture in the primary structure of a ship. Ships have

experienced brittle fracture in the midbody region,

and because damage in this area is potentially more

catastrophic than damage to the bow, materials and

welding techniques should prevent both crack initiation and propagation. Because small cracks and

defects in a material are inevitable, the material

selected must have crack arrest properties to stop

crack propagation.

Figure 12. Measured effective pressure vs. contact area

(after Masterson and Frederking 1993).

140

120

100

80

60

40

20

Temperature (°F)

– 200 – 160 – 120 – 80 – 40 0 40 80 120 160

0

Temperature (°C)

– 120 – 80 0 40 80 – 40

Impact

Grade 'EH' Steel

Grade 'A'

Longitudinal

Requirements

Transverse

Requirements

Plane Strain Fracture Toughness ( ) MPa m

Impact

Intermediate

Static

Static

Intermediate

Figure 13. Plane strain fracture toughness vs. temperature for two grades of steel (“A” and “EH”) (after Dick

et al. 1987).

high rates of indentation, resulting in nonsimultaneous contact between the ice and the indentor.

Design values are taken from empirical relations

obtained from full-scale measurements of ice pressure. The data on effective pressures obtained from

full-scale measurements during ice–ship and ice–

structure interactions (Masterson and Frederking

1993) are plotted with respect to contact area in

Figure 12, and these data provide empirical values for effective pressure to be used in design.

Materials

Considerable effort has been devoted by classification societies and regulatory authorities to the

selection of steel grades suitable for use in the structure of ships that are exposed to very low temperap = 8.1A– 0.572

3 m Pond Inlet

M.V. Arctic

Kigoriak

Hans Is. ('83)

Hobson's Choice ('89)

Molikpaq (May '89)

Flat Jack

Mean

0.1 1.0 10 100 300

Area (m ) 2

Pressure (MPa)

0.1

1.0

10

100

1000

2

13
Welding

After selection of steel, welding is the next most

important component in the reliability of the structure of ships (Dick et al. 1987). Welds in ships must

withstand the corrosive effects of seawater, stresses

caused by cargo, icebreaking operations and waveinduced motions. The biggest variable in welding

technology is the skill of the welder, especially

when working in confined spaces. To determine

the reliability of a structure, the designer of a ship

must take into consideration the flaws in the material as well as in the welds. The importance of

quality control in welding can be assessed from

the statistics that 95% of all defects in a structure

originate from defects within the welded zone.

The fracture toughness of a weld depends on

the method of weld deposition, including the rate,

the number of passes, heat input and electrode size.

The variations in weld toughness may be larger

than those of the parent materials. Caution should

be exercised not to degrade the toughness properties of a weld by using large electrodes and fast

rates of deposition in the interests of cost saving.

Research on reducing the accelerated corrosion of

welds is under way in different parts of the world.

Plating

The plating contributes the largest component

to the structural weight of most ships and, together

with the frames and the stringers, it forms the stiffened panels that resist the loads on a ship (Dick et

al. 1987). While the weight of a ship can be reduced

by reducing the plate thickness and by increasing

the framing, this increases the cost of fabrication.

When a rectangular plate supported by frames

on four sides is loaded by uniform pressure that

acts perpendicular to its surface, the deflections

and the stresses in the plate can be calculated by

the small deflection theory of plate bending, as is

usually done for structural analysis. This theory

ignores the membrane stresses that develop because of large deflections and yielding of the material. As a result of ignoring the membrane action, the load carrying capacity estimated from

small deflection theory is small compared to those

obtained from large-deflection theories and experiments.

Figure 14 shows plots of load vs. deflection obtained from experimental results and two plastic

analyses—one that considers elastic flexure followed by formation of three plastic hinges without any membrane action, and the other that considers only ideal plastic membrane action. The

loads in the plots have been made nondimensional

with respect to the collapse load predicted by the

formation of three hinges without membrane action, and the deflection is made nondimensional

with respect to the plate thickness. Figure 14 shows

that the curve depicting the experimental load-carrying capacity of a plate is initially close to that

predicted by elastic flexure theory for small deflections, and then it approaches that predicted by the

plastic membrane action theory for large deflections. This suggests that thick plates form plastic

hinges before the membrane action is activated

(Ratzlaff and Kennedy 1986).

Framing

The frames support the shell plates and resist

the loads on the shell by bending and shear deformation. Inspection of ice-damaged vessels has revealed that failure takes place consistently in the

supporting frames rather than the hull plating

(Dick et al. 1987, DesRochers et al. 1994). Frames

have several components: the shell plate that acts

as a flange, a web, an internal flange (optional),

end brackets (optional), tripping brackets (optional) and cutouts (optional).

 Figure 14. Pressure vs. deflection, showing domains of

different behaviors from small to large deflection (after

Ratzlaff and Kennedy 1986). Along the vertical axis, the

applied pressure P is made nondimensional by Pc, the pressure at which collapse (point C) is assumed to take place by

formation of three hinges without membrane action. Along

the horizontal axis, the maximum deflection W is made nondimensional by the plate thickness t. The curve labeled E

represents elastic flexure with an elastic membrane up to the

complete formation of an edge hinge. The curve labeled F

represents elastic flexure without membrane action, followed

by the formation of the first hinge and then three hinges. The

curve labeled N represents ideal membrane action.

8

6

4

2

0 2 4

W/t

P/Pc

A C

Experimental Results

N

F

E

14
The proposed CASPPR allow a certain amount

of plastic deformation of the structure under extreme ice loads, and they provide factors to account

for the post-yield buckling of stiffened structures.

DesRochers et al. (1994) compared the stability of

flat bars with that of angle sections in a stiffened

structure. When a structure is designed for buckling according to linear analysis, flat bars are

avoided because angle sections have large moments of inertia to resist bending. However,

DesRochers et al. (1994) found that the use of flat

bar sections increased the stability of the composite structure beyond the yield point of the material, whereas the structural stability decreased with

the use of angle sections as yielding progressed

through the frame. The structure of the Canadian

icebreaking cargo ship Arctic has been redesigned

according to CASPPR to carry full ice loads without failure.

The Swedish icebreaker Oden is the first icebreaker designed according to the technology behind the proposed CASPPR, making it possible to

use a large frame spacing of 850 mm instead of the

normal 400 mm (Johansson et al. 1994). This has

resulted in considerable cost savings in construction. After the voyage of Oden to the North Pole,

inspection of the structural damage revealed some

indents in the shell plating between frame stations

30 and 76 on both sides, and some deformation in

the side and bottom frames (flange, web and

bracket), but this damage was not serious. The

damaged frames were reinforced, but the indents

in the steel plates were left as they were (Backman

1994).

PROPULSION SYSTEM

The major components of the propulsion system of an icebreaking vessel, or any ship, are the

propellers, shafts, transmission systems and prime

movers. The number of propellers varies between

one and three. Developments in propulsion systems that have taken place during the last four to

five decades are reflected in those of existing icebreakers and icebreaking cargo ships, and these

become apparent in the plot of shaft power vs. the

year of construction (Fig. 15). Some of the special

features of propulsion systems, such as controllable-pitch propellers and mechanical transmissions, nozzles and various electrical transmissions,

have been highlighted in Figure 15.

The dc–dc electrical transmission has been commonly used since its introduction on the Swedish

icebreaker Ymer in 1933. Although this system is

still being used on many icebreakers, new mechanical and electrical transmissions have been introduced on newer icebreakers and icebreaking

cargo ships. Since 1966, the number of ships with

controllable-pitch propellers and mechanical transmissions is steadily increasing. The Russian LASH

vessel Sevmorput, delivered in 1986, placed all of

its propulsion power on one shaft using a controllable-pitch propeller and mechanical transmission,

thus doubling the power transmitted per shaft

from 16.65 to 29.42 MW (Fig. 15b).

One of the main reasons to use direct mechanical transmission is to cut down the losses in transmission. Since 1978, propeller nozzles have been

fitted to icebreakers to increase thrust and to prevent propeller damage by reducing ice ingestion.

Nozzles have been installed on most of the Beaufort Sea ice management–supply vessels, whereas

Polar Sea and Polar Star have operated in ice without nozzles since 1976. Recently, azimuth-mounted propulsion units have been installed on the

Finnish icebreakers Finnica and Nordica and it is

Figure 15. Shaft power vs. year of construction for

icebreaking ships: (a) electrical transmission system, and

(b) mechanical transmission system (after Dick and

Laframboise 1989).

Electrical Transmission

 DC-DC

 AC-DC

 AC-AC

0

0

1940 1950 1960 1970 1980 1990

5

10

15

20

25

30

35

Year of Construction

Power Per Shaft (MW)

b

5

10

15

20

25

30

35

Power Per Shaft (MW)

a

Mechanical Transmission

 CPP

 CPP in Nozzle

4 3 13 6

3 15

2

2 3

19

2

4

15
likely that this system will be used in

future ships, because it offers good

maneuverability in broken and intact

ice.

The selection of a suitable propulsion system is based on the intended

functions of an icebreaking vessel.

The requirements of a propulsion system are:

1. Reliability of full power on demand to navigate safely in the

Arctic.

2. Flexibility of operating efficiently and economically in

open water as well as in heavy

ice at a range of power levels.

3. Maneuverability to allow rapid change of load, speed and

power.

4. High power-to-weight ratio to

deliver the required power, with machines

as compact and light as possible.

While many combinations of prime movers,

transmission systems and propellers may be proposed for a given ship, very few particular systems would fit a given mission profile (Dick et al.

1987). Ships requiring a large range of power can

be fitted with multiple engines or combined-system installations, which permit the numbers of

engines to be run according to the power requirements of various ice conditions, to achieve the best

combination of fuel efficiency and performance.

In the following sections, a brief discussion is given

of each of the main components of a propulsion

system.

Propellers

Both fixed-pitch and controllable-pitch propellers have been installed on polar ships. Fixed-pitch

propellers have been used for many years, and

these are still being installed on most icebreaking

ships. However, controllable-pitch propellers have

been used on polar ships with increasing frequency

since 1966 (Dick and Laframboise 1989). A plot of

shaft power versus propeller diameter is shown

in Figure 16, where fixed-pitch and controllablepitch propellers have been identified. The azimuth

thruster units installed on the Finnish icebreakers

Finnica and Nordica have fixed-pitch propellers in

a nozzle.

The selection of propeller type depends on the

propulsion system used. Nonreversing transmission systems, such as diesel–geared or gas turbine–

60

40

20

0 2 6 10 8

Shaft Power (MW)

Propeller Diameter (m)

4

USSR

LASH Polar

Star

SA-15

Icebreaking

Dredge

Fixed Pitch

Controllable Pitch

Figure 16. Shaft power vs. propeller diameter for icebreaking ships (after Dick and Laframboise 1989).

geared, may use controllable-pitch propellers to

obtain astern thrust and to ease over-torque

requirements. Reversing systems, such as any of

the electrical systems, may used fixed-pitch propellers because over-torque does not affect an electrical system.

The design requirements of a propeller depend

on the mission profile of a vessel. The aspects influencing the design of a propeller are (Dick et al.

1987):

1. Loads and strength requirements.

2. Selection of material.

3. Effects of nozzles.

There are two types of interactions between ice

and propellers: ice milling and ice impact. Ice milling takes place when an ice block is large or is

trapped between the hull and the propeller. During an instance of milling, ice is either crushed or

sheared by the blades, and the loads can be damagingly high. Ice impact is caused by small-size

ice pieces that are accelerated through a propeller

or thrown out radially and pushed around the edge

of the propeller disk. The loads from ice impact

are relatively moderate, but it happens more frequently.

For propellers in a nozzle, the chances of ice

milling are small, and the magnitude of the loads

generated are also small in comparison to those

for open propellers. The factors that influence the

ice loading on a propeller have been identified, but

the ability to determine the ice milling–impact

loads is not well developed because of the complex interaction between ice and propellers. The

16
design of an ice-strengthened propeller must meet

the dimensions and the strength requirements of

the classification societies.

The material used for the propeller blades of

polar ships must have high stress and impact resistance qualities. Stainless steel and bronze are

commonly used for ice-strengthened propeller

blades. Because stainless steel has a higher erosion

resistance and higher ultimate and yield strengths

than does bronze, stainless steel propellers have a

slender and efficient blade profile. Most of the existing bronze controllable-pitch propellers are operating in nozzles, whereas most stainless steel

controllable-pitch propellers fitted to icebreakers

are open propellers. For example, bronze has been

selected for the propellers of recent Canadian icebreakers, and the open propellers of the U.S. icebreakers Polar Star and Polar Sea are made of stainless steel.

Propeller nozzles are used to increase the thrust

over a range of ship speed, and to protect the propeller from ice. Thus, the nozzles have an indirect

influence on the design of a propeller by reducing

the load levels and thereby reducing the strength

requirements. Ships equipped with nozzles, e.g.,

Kigoriak and Arctic, have operated successfully in

ice with very few problems. Some of the shallowdraft vessels, however, have occasionally experienced clogging of their nozzles in rubbled or

ridged ice. Nozzles have been installed on the azimuth-mounted propellers of Finnica and Nordica,

and these are being considered for future highpowered ships.

Shafting

For large icebreaking ships, the diameters of

propeller shafts are large because of high power

and high torque requirements. The range of diameters of the shafts installed in existing icebreakers

is from 380 mm in Polar Stern to 980 mm in the

Russian SA15 cargo ships. The basis for designing

shaft diameter is that the propeller blade should

fail before the shafting. The method to calculate

the shaft diameter depends on the modulus of the

propeller section and on the ratio of the ultimate

strength of the propeller blade material to the yield

strength of the shaft material. The requirements of

hydrodynamic torque and ice-induced torque are

specified by the classification societies. Shafts are

generally made of forged carbon steel, although

in some cases low alloy steel forgings are also used.

There is considerable saving in weight when highstrength steel is used.

One of the major problems found with large

vessels is the misalignment of the shaft bearings.

The sources of the misalignment problem are (Dick

et al. 1987):

 1. Deflections in the hull.

 2. Eccentric thrust on the propellers, which

causes bending moments in the shaft.

 3. Insufficient axial and radial bearing flexibility.

 4. Changes in the height of bearings, gear case

or the engine because of thermal expansion.

Dick et al. (1987) have discussed other elements

of the shaft line components, such as couplings,

seals and bearings.

Mechanical transmission

components

The operating speed of steam reciprocating engines and slow-speed diesel engines is low enough

that the power can be transmitted directly through

a shaft between the engine and a propeller. This is

the most efficient form of transmitting power to a

propeller, because the only losses incurred are at

the bearings. However, most prime movers, such

as medium-speed diesel and steam and gas turbines, have an output speed that is too high to

obtain the best propeller efficiency. A speed-reducing transmission must be used to deliver power to

the propellers at the optimum speed.

As shown in Figure 15b, many icebreakers and

icebreaking cargo vessels have been fitted with

mechanical transmission of power since 1966. Most

of these vessels are driven by one or more mediumspeed diesel engines and a set of single-reduction

gears, except the Russian LASH, which is driven

by a steam turbine. A clutch or fluid coupling is

used between an engine and a gear system. In a

few icebreakers, flywheels have also been used to

smooth out the transient, ice-induced torque.

The gearboxes that are installed on polar ships

are within the experience of the manufacturers. The

largest gearboxes installed on any icebreaker are

those on the U.S. icebreakers Polar Sea and Polar

Star, which are powered by combined gas turbine

and diesel-electric systems. The Russian SA15

cargo ships have been fitted with large gearboxes

with twin inputs, each delivering 7.5 MW, and connected through fluid couplings to limit overload

torque.

Electrical transmission systems

Four types of electrical transmission systems are

available for polar ships. These systems are listed

according to their chronological order of develop17
ment: dc–dc, ac–ac, ac–dc, and ac–FFC–ac. An ac

system is preferred because of its light weight and

higher efficiency. The problems of commutation

in dc systems are not present in ac systems.

The advantages of an electrical transmission

over a mechanical one are that the characteristic

of the drive can be exactly matched with the mission profile of a ship, and that the total power for

the ship can be divided among a number of engines. There is flexibility in the placement of generators in a ship. An electrical system also isolates

the prime mover from the overload torque caused

by ice loads on the propellers. The disadvantages

of an electrical transmission system are the higher

costs, greater weight and larger space requirements.

With medium-speed diesel engines as prime

movers, the dc–dc system is most commonly used

in icebreakers. The maximum speed of a dc generator must be less than 100 rpm owing to the limited capacity of the commutator brushes to transmit current. The advantages of a dc system are its

simplicity, ease of control, good torque characteristics (especially at low speed) and lower cost than

other electrical systems. In comparison to mechanical transmission systems, the disadvantages of this

system are its higher cost, greater weight and volume, lower transmission efficiency (about 85%)

and a relatively high requirement for manpower.

The ac–dc system combines the advantages of

ac generators with the precise speed control of dc

motors. The generated power, in three-phase

alternating current, is converted with low losses

to direct current by the use of thyristors, which

were developed in the 1960s.

The ac–ac propulsion system is based on synchronous motors. The speed is changed by changing the speed of the prime mover. It is the simplest

and least expensive. This system, while perhaps

being the economical choice for open water ships,

is not suitable for icebreaking ships. The generator and the motor may fall out of synchronization

when the propellers are subjected to large ice loads.

Other disadvantages of this system are the low

torque at start up and the excitation of resonant

vibrations.

The ac–ac system with Full Frequency Control

(FFC), or a cyclo-converter, is the most suitable but

also the most expensive ac–ac system. It has been

used in the Finnish icebreakers Otso, Finnica and

Nordica, in the Russian Taymyr-class icebreakers

and in Canadian light icebreakers. By employing

cyclo-converters, the motors can be precisely and

steplessly controlled by a highly reliable control

setup. Its advantages are the availability of full

torque over the entire range of speed, no loss of

synchronization, operation of the prime mover at

its optimum speed, and the availability of power

for auxiliary systems from the main generators.

Its main disadvantages are the high capital cost,

high volume and weight, and relatively poor overall transmission efficiency of 90–92% (estimated),

although the transmission efficiency of ac–FFC–

ac systems is higher than that for ac–dc and dc–dc

systems.

Azimuth propulsion drive

Azimuth propulsion drives have been installed

on different types of vessels, such as icebreakers,

cargo ships, ferries, cruise ships, etc. One of the

Lunni series tankers, Uikku, was converted in 1993

to accommodate 11.4-MW azimuth propulsion

drives (one of the world’s most powerful units),

replacing the original medium-speed diesel, gearing, shafting and controllable-pitch propellers. Installation of these units on the multipurpose icebreakers Fennica and Nordica has produced excellent icebreaking and maneuvering capabilities.

With their advanced hulls (designed to give excellent seakeeping in open waters [Fig. 9]), these vessels can make continuous progress through 1.8-

m-thick ice. Their icebreaking capabilities are also

very good when they are moving astern. The azimuth thruster units allow these ships to turn on

the spot in ice conditions. Lohi et al. (1994) give

the results of full-scale ice tests with Fennica during her trials in the Baltic.

There are two commercial azimuth propulsion

systems available—Aquamaster and Azipod. In an

Azipod unit, an ac electrical motor is located inside the pod, whereas the motor is located above

the azimuth thruster units in Aquamaster drives.

The motor, controlled by a frequency converter,

directly drives a fixed-pitch propeller, which is either open or placed in a nozzle. These drives azimuthally move 360° and supply full power in all

directions.

Figure 17 shows the difference between conventional diesel–mechanical and azimuth propulsion

systems on an arctic tanker. The azimuth system

has the following advantages:

1. Gives excellent dynamic performance and

maneuvering characteristics.

2. Eliminates the need for long shaft lines, transverse stern thrusters, controllable-pitch propellers

and reduction gears.

3. Allows new ways for designing machinery

and cargo spaces.

18
60

50

40

30

20

10

0

0

1940 1950 1960 1970 1980 1990

5

10

15

20

25

30

35

Year of Construction

Power Per Shaft (MW) Total Power (MW)

Medium Speed Diesel

Slow Speed Diesel

Steam Turbine

Gas Turbine

a

b

Figure 18. Prime movers installed on icebreaking ships:

(a) total power vs. year of construction, and (b) power

per shaft vs. year of construction (after Dick and

Laframboise 1989).

Figure 17. Differences between dieselmechanical and azimuth installations

(after Kværner Masa-Yards and ABB,

no date).

Diesel-mechanical Propulsion System

Azimuth Propulsion System

4. Reduces noise and vibrations.

5. Provides operational flexibility, resulting in

lower fuel consumption, reduced maintenance

costs, fewer exhaust emissions and adequate redundancy with less installed power.

In late 1990, the propulsion system of the Finnish waterway service vessel Seili was converted

from diesel-mechanical propulsion to azimuth

(Azipod) propulsion. The performance of this vessel was tested in 65-cm-thick, level ice in the Gulf

of Bothnia. Laukia (1993) reported that, besides

good maneuverability and icebreaking capability

in level ice and first-year pressure ridges, the vessel broke ice better when moving astern than while

moving ahead. There are unconfirmed reports

that new vessels with two types of hulls at each

end are on the drawing boards of shipyards: a

smooth bow for moving forward in open-water,

and an icebreaking stern for moving astern

through first-year ice in sheltered areas.

Prime movers

The characteristics of an ideal prime mover for

an icebreaking ship are reliability, flexibility, maneuverability, robustness and over-torque capability (Dick and Laframboise 1989). These characteristics have been discussed earlier for the propulsion system. The prime movers used currently in

polar ships do not have all these characteristics,

but in combination with a suitable transmission,

the overall propulsion system can approach the

above-mentioned ideal characteristics.

Figure 18 shows two plots of total installed

power and power per shaft versus the year of construction. In Figure 18 different types of prime

movers have been identified. Each type is briefly

discussed in the following.

Gas turbines

Only two icebreakers, the USCG Polar Star and

Polar Sea, are fitted with gas turbines. Each ship

has three aero-engine derivative gas turbines, each

driving a controllable-pitch propeller through a

gearbox. These turbines are used only for heavy

icebreaking, and a medium-speed diesel-electric

propulsion system is used for cruising and light

icebreaking. The Canadian icebreaker Norman

McLeod Rogers was initially fitted with two indus19
trial turbines, but they were replaced with medium-speed diesel engines because of high fuel

consumption.

Turbines are unidirectional engines, and the

astern operations must be provided by the transmission, usually through an electrical system, a

reversing gear or a controllable-pitch propeller. The

advantages of gas turbines over other prime movers are their high power-to-weight ratio and their

compactness. Their main disadvantages are the

high fuel consumption and maintenance requirements.

Steam turbines

Only the Russian nuclear-fueled icebreakers and

icebreaking cargo ships are fitted with modern

steam turbines. The Canadian icebreaker Louis S.

St. Laurent was fitted with a steam-turbine–electric system, but a diesel-electric system was installed during the ship’s major reconstruction program, completed in 1993. The efficiency of a steam

turbine is about 20%, compared to 50% for modern marine diesel engines (Dick et al. 1987). Similar to gas turbines, steam turbines are unidirectional engines, and astern operations must be

handled by the transmission. Turbines can operate at any power level, but the fuel efficiency is

poor at reduced power levels.

Medium-speed diesel engines

Medium-speed diesel engines have most commonly been used as prime movers for the propulsion of polar ships because of their compactness,

light weight, fuel efficiency and good reliability

(Dick and Laframboise 1989). Their disadvantage

for use as prime movers is their lack of significant

over-torque capacity. However, this shortcoming

is overcome by using an electrical transmission,

which damps out the high torque transients and

stops them from being transmitted to the engine.

A few icebreakers are fitted with these engines

driving controllable-pitch propellers through

gears. Some of the direct drive systems consist of

fluid couplings to prevent engine stall under the

most severe propeller overloads.

In the past 15 years, medium-speed diesel engines have undergone developments that have

allowed them to have better fuel economy, burn

heavier grades of fuel, increase routine maintenance intervals and increase the power per cylinder. Some of the largest engines of this type can

generate about 22 MW at 400 rpm in 18 cylinders

arranged in a vee form (Dick et al. 1987). The engines operate in one direction, and separate provisions, in the form of controllable-pitch propellers or reversing gears, are used for astern operations. Typical specific fuel consumption of the

engines is between 170 and 200 g/kWh, and the

consumption of lubricating oil is between 1.5 and

3 g/kWh. Most medium-speed diesel engines for

icebreakers use turbochargers to improve their fuel

efficiency in open water. Diesel engines are basically constant torque machines in the 50–100%

range of speed. At a given load, torque may exceed the rated capacity by about 10%. The flexibility of diesel engines is acceptable because they can

operate between 25 and 35% of their rated speed,

depending upon the characteristics of a particular

engine. It is expected that medium-speed diesel

engines will continue to be the preferred prime

movers for polar ships of all sizes in the near future (Dick et al. 1987).

Slow-speed diesel engines

The Russian LASH ship Alexey Kosygin is the

only polar ship fitted with two slow-speed diesel

engines, each delivering 13.4 MW to directly drive

fixed-pitch propellers (Dick et al. 1987). This type

of engine was specifically developed for ship propulsion. They operate on the two-stroke cycle, are

reversible, and are directly coupled to propellers,

mostly of the fixed-pitch type. The range of their

rotational speed is between 60 and 225 rpm. The

range of cylinder bore diameter is from 250 to 900

mm. The maximum power per cylinder is about

3.7 MW. This type of engine is large and heavy,

and it can only be fitted to vessels that can provide

a large engine room and carry the extra weight:

bulk cargo ships, oil tankers and container ships.

Ferries, Ro/Ro ships and barge carriers have limited head room and are generally fitted with medium-speed diesel engines. These engines are not

suitable for polar ships because of their poor maneuverability and flexibility.

Developments in the last 15 years include the

use of constant pressure turbocharger technology

and the adoption of extra-long strokes. This has

enabled slower propeller speeds without the use

of gears, resulting in higher propulsion efficiency

in large bulk carriers and oil tankers. The specific

fuel consumption of these engines is below 160 g/

kWh for large economical engines, and about 175

g/kWh for small engines.

Combined prime movers

The reason for combining two different prime

movers in a ship is to improve the overall fuel

economy. This is done by either recovering the

20
waste heat and converting it to mechanical work,

or by operating each prime mover according to

load demands to obtain better fuel economy. The

first option has not been used in icebreakers so far.

The USCG icebreakers Polar Sea and Polar Star

are the only polar vessels fitted with two types of

prime movers. In these ships, there are three gas

turbines (total 45 MW or 60,000 shp) and three diesel-electric propulsion systems (total 13.4 MW or

18,000 shp) for each of the three controllable-pitch

propellers. Each shaft can be turned either by the

diesel-electric or the gas turbine power plant. Either one or two 2.24-MW (3000-shp) diesel-electric drive units, or a single 15-MW (20,000-shp) gas

turbine, can be used to drive each shaft. For example, diesel engines could supply power to the

wing shafts, while a gas turbine could turn the

center shaft. Gas turbines are used for heavy icebreaking, whereas the diesels are used for cruising and light icebreaking. This is a good example

of combining two different systems to meet widely

differing load demands for the sake of fuel

economy.

AUXILIARY SYSTEMS

There have been other developments to improve

the performance of polar ships besides those in

propulsion systems and hull shapes, such as the

use of low-friction coatings on the hull, air-bubblers to lubricate the ice/ship interface, air-bubbler–water-injection systems, and the water-deluge (or wash) system to pump a large volume of

water on the ice ahead of the vessel. These improvements have also contributed to increase the

icebreaking capability of polar ships beyond the

limit for which they were designed. A brief account of each auxiliary system follows.

Low-friction hull coating

Depending on the age of a vessel, the coefficient

of friction between ice and unpainted hull plating

can be in the range of 0.2 to 0.3, which is high in

comparison to the friction coefficient in the range

of 0.05 to 0.17 between ice and a low-friction coating. As discussed later, the factor to account for

the friction of old steel in the expression for ice

resistance of an icebreaker is twice that for Inertacoated steel plates (Keinonen et al. 1991).

Prior to the 1970s, there was no suitable coating

available that could withstand interaction with ice.

Only anti-fouling paint was applied to the hulls to

minimize biological growth on the hull surface,

and this would wear off during first few days of

icebreaking. In the early 1970s, the importance of

hull–ice friction on the ice resistance was demonstrated through full-scale and laboratory tests. A

measure of the force attributable to static friction

acting on a hull can be obtained by gradually increasing the level of power to initiate forward

motion of a ship that was stopped in ice and then

measuring the steady-state velocity at that same

power level. For ships having uncoated hulls, this

power level corresponds to a 3-knot (1.5-m/s)

speed of advance, whereas for a ship with lowfriction coating, the initiating power levels are

equivalent to a speed of 0.5 knots (0.26 m/s) (Voelker

1990). The power required for an icebreaker with a

low-friction coating to become unstuck is much

lower than that for ships without any coating.

Mäkinen et al. (1994) have given an historical

account of the development of low-friction coatings in Finland, where the first effective hull coatings were developed by Wärtsilä Shipyard (now

Kværner Masa-Yards). Liukkonen (1992) developed a theoretical understanding of hull–ice friction and found a functional relationship between

the coefficient of friction and the normal force. This

functional relationship was verified by full-scale

measurements of normal and frictional forces with

the help of instrumented panels installed in the

bow and the sides of icebreakers.

Mäkinen et al. (1994) have listed the requirements of a good low-friction coating. A few of these

are reasonable cost, high bond strength with and

good corrosion protection for the base material,

and resistance to all of the following: wear, high

normal pressure, low temperatures and changes

in temperature. Tests were conducted on many different coatings; Inerta 160 and stainless steel were

selected for full-scale testing and further development. Another coating by the name of Zebron

was also found to be suitable, but its use has decreased with time, perhaps because of lower resistance to wear.

Inerta 160 has been applied to hundreds of ships

currently in service (Mäkinen et al. 1994). It is applied with a two-component spray gun, which has

heating equipment to keep the temperature of the

paint between 40 to 50°C. Two problems associated with the application of Inerta 160 were corrosion of cast iron propellers and corrosion of hull

surfaces. These problems were corrected by using

stainless steel propellers and cathodic corrosion

protection.

An important property of a coating is to withstand the deformation of the base material. In the

21
Figure 19. Outboard profile and topside deck plan of the Swedish

icebreaker Oden.

Heeling system

In earlier times, the crews of cargo

ships that were stuck in ice found that lifting a heavy weight by a crane and swinging it sideways helped to free the ship.

This experience led the designers of icebreakers to install heeling tanks on each

side of a ship and to provide for pumping large amounts of water back and forth

between the tanks. The continuous rolling motion of a ship facilitates its progress in ice with less power.

Now most operators consider the heeling system important for improved

icebreaking and maneuvering. Almost all

Baltic icebreakers have heeling tanks. The

Swedish icebreaker Oden was fitted with

a fast heeling system that allows full heeling in 15 seconds (Backman 1994). This

has enabled Oden to make continuous

progress in heavy ridges. Oden is also fitted with

turning reamers located above the ice surface on

each side just aft of the bow (Fig. 19), and when

the ship is heeled over, one reamer comes in contact with ice to help the ship to turn sharply into

the heel (Johansson et al. 1994). Thus, a heeling

system in combination with the turning reamers

has improved the maneuverability of Oden by decreasing the turning radius. With improved

maneuverability, polar ships are often able to make

progress in thicker ice than they have been designed for, by finding a path of least resistance

through the weaknesses in an ice cover. This is

demonstrated by the successful voyage of Oden in

1991 with the German icebreaker Polarstern to the

North Pole.

Air-bubbler system

An air-bubbler system releases large volumes

of air through nozzles into the water below the ice

in the bow and midbody portions of a ship. When

the air rises to the surface, it brings water with it

between the ice and the hull, thus reducing friction between them.

This system was first introduced on the Finnish

icebreaking ferry Finncarrier in 1969 (Johansson et

al. 1994). It has since been installed on vessels with

conventional bows, such as the Lunni class of

icebreaking tankers, the Canadian icebreaking

cargo ship Arctic, and the Russian SA15’s. The results of full-scale trials indicate that a bubbler

system may help in reducing friction only in the

low-speed range (less than 2 m/s or 4 knots). There

case of Inerta 160, the wear-off starts at the cracks

caused by the deformation of the shell plating at

the edges of the ship’s frames. The wear-off is

intensified in heavily loaded areas, such as the ice

belt in the ship’s forebody, and during operations

in heavy ice and especially in the presence of soil

or sand mixed in ice. To correct this deficiency in

Inerta 160, stainless-steel-coated surfaces, though

expensive, were developed because of their high

wear resistance and low-friction properties. Cathodic protection systems were developed to reduce the corrosion risks before compound steels

with stainless steel claddings were installed in the

ice belt regions on two Otso-class icebreakers for

testing. Later, stainless steel compound plates were

installed on the Russian icebreaker Kapitan

Nikolayev and the Finnish icebreakers Finnica and

Nordica with very favorable results.

The cost of applying Inerta 160 and installing

stainless steel compound plates is, respectively,

about 2 and 40 times the cost of applying conventional paint (Mäkinen et al. 1994). However, the

extra cost of applying Inerta 160 may be offset by

longer periods (4–5 years vs. 1 year) between reapplications of the coating, while compound steel

does not require any repair or reapplication. There

have been no corrosion problems with compound

plate; however, the cathodic protection systems

must be permanently activated, even during the

summer. Investigations are currently underway to

use copper-nickel compound plates as an alternative to stainless steel compound plates (Mäkinen

et al. 1994).

22
is no measurable benefit of an air-bubbler system

on ships with unconventional bows. Captains of

Bay-class Great Lakes icebreakers report that air

bubblers are very useful for docking or leaving the

docks under ice conditions.

To assess the effectiveness of hull lubrication by

an air-bubbler system, the ratio of shaft power

saved at a given speed in level ice to the power required to operate the system is computed. If this

ratio is more than one, there is a net power saving

in operating the system. According to the data compiled by Keinonen et al. (1991), this ratio for the

air-bubbler system of hull lubrication is generally

less than, or in some cases barely greater than, one.

The reason for such low efficiency is that lubrication is not provided around the bow waterline, where it would be most effective.

Air-bubbler–water injection system

This system, installed on the German icebreaker

Polarstern, injects air into the water being pumped

to nozzles at the sides of the ship below the ice.

Air–water jets have also been installed below the

water on the Canadian icebreaker Ikaluk and the

newly converted Russian icebreaker Mudyug. The

ratio of power saved to the power expended is

about one (Keinonen et al. 1991).

Water-deluge system

Recent developments, such as the water-deluge

system and low-friction epoxy paint, have allowed

the use of unconventional bows on sea-going vessels (Johansson et al. 1994). A water-deluge system throws several tons of water every second on

top of the ice ahead of the bow. This not only reduces friction between the ice and the hull but also

submerges the broken ice pieces to help them move

down under the hull. This was first installed on

the Canadian icebreaker Canmar Kigoriak, which

was fitted with a blunt spoon-shaped bow, to solve

the ice pushing problem experienced with unconventional bows in the late nineteenth century. One

time, when the water-deluge system was frozen

solid, the Kigoriak could not make good progress

through a broken ice cover because of the ice-pushing problem. With the water-deluge system operating perfectly a few days later, she was able to make

good progress in this same broken ice field

(Johansson et al. 1994).

According to the data compiled by Keinonen et

al. (1991), the power saved as a result of operating

a water-deluge system is much greater than the

power expended. These data were collected for the

Canmar Kigoriak during icebreaking with a bare

hull and also with an epoxy-coated hull.

On the Canadian icebreaking supply vessel Robert Lemeur, this system has been effective in reducing the resistance by 20–30% over the entire speed

range (Dick and Laframboise 1989). On the Swedish icebreaker Oden, the water-deluge system has

been upgraded to act as a bow thruster by directing the flow to one side of the ship. With a control

system and a modified nozzle design, it is possible

to obtain a side force of 0.1 MN at the forward tip

of the ship.

POWER AND PERFORMANCE

As expected, installed power increases with ship

size as represented by ship beam. The power-versus-beam plot of the data on existing polar ships

(Fig. 20) shows a trend of increasing power as a

function of beam. Except for a few data points,

there appears to be a well-defined relationship

between power and beam.

Using information on the performance of existing polar ships in ice, Dick and Laframboise

(1989) plotted the bollard pull/beam vs. the ice

thickness an icebreaker is capable of breaking at a

speed of about 1 m/s or 2 knots (Fig. 21). For comparison, the data are normalized on performance

for a speed of 2 knots. There appears to be a welldefined minimum performance. For a particular

bollard pull/beam, the range of ice thickness above

a minimum performance value represents an improvement in icebreaking capability of the hull

shape. Figure 21 shows that the most recent ships

have more efficient hull forms.

40

60

20

0 10 20 30

Power (MW)

Beam (m)

SIBIR

Polar

Star

Terry

Fox

Supply Boats 

Figure 20. Power vs. beam for icebreakers (after Dick

and Laframboise 1989).

23
Ice Thickness (m)

0 0.5 1.0 1.5 2.0 2.5

Bollard Pull/Beam (tonnes/m)

25

20

15

10

5

Polar

Star

Arktika

Taymyr

Terry Fox

Shirase

Urho

New Arctic

Robert Lemeur

New

Max Waldeck Mudyug

Kigoriak

Polar

Stern

SA 15

Minimum

Performance

Bollard Pull/Beam (kN/m)

–250

–200

–150

–100

–50

–0

Wrangell Is Pt. Barrow .

St. Lawrence Is.

Nome

Cape Lisburne

Pt. Hope

USA

Nunivak Is.

St. Matthew Is.

St. Paul Is.

St. George Is.

Ice Edge

Dutch Harbor

Aleutian

Islands

170°

180°

160°

55°

50°

60°

65°

70°

Russia

6.2-7.2 m/s

@ 23.9 MW 

3.1-4.6 m/s

@ 9.0 MW 

6.2 m/s

@ 11.2 MW 

4.6 m/s

@ 6.0 MW 

5.1 m/s

@ 14.9 MW 

7.2 m/s

@ 16.4 MW 

3.6 m/s

@ 9.0 MW 

6.2-7.2 m/s

@ 9.0 MW 

7.2-8.2 m/s

@ 9.0 MW 

Figure 22. Speeds and power levels of U.S. icebreaker Polar Sea during her transit from 23

March to 4 April 1983 (after Voelker 1991).

Figure 21. Icebreaking performance: bollard pull/

beam vs. ice thickness. Bollard pull is measured or

calculated; data are adjusted for a speed of 2 knots (after Dick and Laframboise 1989).

24
Table 2. Estimates of daily fuel consumption for a Polar-class icebreaker.

Fuel consumption rate

Ship status (gallons/day) (tons/day)*

Stationary—systems providing only

normal hotel services 4,000 12

Open water transit (three propulsion diesel) 14,000 42

Icebreaking (six propulsion diesel) 25,000 75

Icebreaking (diesel on wing shafts,

gas turbine on center shaft) 35,000 105

Icebreaking (three gas turbines) 60,000 180

* Relation used for conversion: 1000 gallons/day ≈ 3 tons/day.

into the Alaskan Chukchi Sea. Figure 23 identifies

sections of the route where ramming of the ice was

required to make headway. The number of rams

and the average shaft power used are also given

in Figure 23.

According to the brochures of the Murmansk

Shipping Company, the rates of fuel consumption

of three classes of ships (Norilsk, Mikhail Strekalovskiy and Dimitriy Donskoy) are listed in Table 3.

Performance prediction

Keinonen et al. (1991) compared the performance of 18 major icebreakers of different sizes

and types to establish methods of expressing and

estimating their performance in terms of ship design features and parameters. The data were obtained from full-scale trials of icebreakers in different geographical areas as well as in different ice

Table 3. Fuel consumption rates of a few Russian ships according to the information

given in the brochures of the Murmansk Shipping Company.

Daily consumption rate (tons/day)

Storage In port

Type of capacity Cargo No cargo

Ship fuel or oil (tons) Underway operation operation

SA15’s Diesel oil 783 2.0 2.0 1.0

Noril’sk High viscosity

Class fuel 3743 76.0 7.0 3.0

Lubricating oil 185 0.6 0.1 0.1

Mikhail Diesel oil 329 5.0 2.5 2.5

Strekalovskiy High viscosity

Class fuel 1348 43.1 7.3 7.3

Lubricating oil 52 0.3 — —

Dimitriy Diesel oil 329 5.0 2.5 2.5

Donskoy High viscosity

Class fuel 1348 43.1 7.3 7.3

Lubricating oil 52 0.3 — —

Fuel consumption rates

The fuel consumption rates of medium-speed

and slow-speed diesel engines have been mentioned earlier. These rates may have been obtained

for open water conditions. Data on the actual fuel

consumption of icebreakers working in ice are very

scarce.

Voelker (1990) has summarized the mean fuel

consumption rates of 16 Polar-class ship deployments to the Alaskan Arctic (Table 2). The rate of

fuel consumed depends on the ship’s activity and

the power plant being used. The Polar Sea and Polar Star can each generate up to 13.4 MW (18,000

shp) using diesel-electric propulsion systems. Alternatively, they can generate up to 45 MW (60,000

shp) by engaging their gas-turbine power plants.

In Figure 22, Voelker’s route map shows the sustained speeds for various power outputs during a

midwinter expedition through the Bering Sea and

25
Figure 23. Number of ramming operations during the transit of U.S. icebreaker Polar Sea

from 23 March to 4 April 1983 (after Voelker 1991).

Wrangell Is Pt. Barrow .

St. Lawrence Is.

Nome

Cape Lisburne

Pt. Hope

USA

Nunivak Is.

St. Matthew Is.

St. Paul Is.

St. George Is.

Ice Edge

Dutch Harbor

Aleutian

Islands

170°

180°

160°

55°

50°

60°

65°

70°

Russia

10 Rams

@ 23.9 MW 

33 Rams

@ 34.3 MW 

7 Rams

@44.8 MW 

220 Rams @ 34.3 MW 

14 Rams @ 44.8 MW 

14 Rams 

@ 23.9 MW 

147 Rams

@ 34.3 MW 

15 Rams

@ 9.0 MW 

53 Rams

@ 23.9 MW 

information, readers are referred to their paper and

to the reports prepared for that study. A summary

of their performance predictors is given below.

Resistance in level ice

For chined ships, an expression for ice resistance

at a speed of 1 m/s is given as

R1 = 0.08+0.0177 CS CH B0.7 L0.2 T0.1 H1.25

{1 – 0.0083 (t + 30)} {0.63 + 0.00074 σf}

{1 + 0.0018 (90 – ψ)1.4} {1 + 0.004 (φ – 5)1.5}

conditions. Though most of the hulls were coated

with Inerta, a few hulls were bare steel, and one

hull was fitted with a stainless-steel band at the

waterline. Performance measures included in their

study are level-ice hull resistance, propulsive performance, hull lubrication, ridge resistance, turning performance and open water resistance. According to Keinonen et al. (1991), these results were

compiled to understand the influence of key parameters on the performance of icebreakers. The

key parameters chosen for this comparison were

simple and obvious to all observers. For detailed

26
where D = turning diameter (m)

LWL = length of waterline of ship (m)

x = reamer width relative to midbody

length (%).

For rounded vessels with fully effective rudders, and in level ice of thickness equal to 60%

of the icebreaking capability at 1m/s

D/LWL = 0.022 (PMB)1.75 + 3

where PMB is the percentage of waterline length

representing a parallel midbody (%).

For rounded vessels with partially effective rudders, and in level ice of thickness equal to 60% of

the icebreaking capability at 1 m/s

D/LWL = 0.14 (PMB)1.5 + 3.

Open water resistance

For chined vessels, open water resistance is expressed in terms of Froude number

R/Disp = 1.1 Fn

1.64

where R = open water resistance (kN)

Disp = ship displacement (tons)

Fn = Froude number 

v gL /  



v = ship velocity

L = ship length between perpendiculars.

For vessels of rounded shapes, open water resistance is expressed in terms of Froude number

R/Disp = 0.4 Fn

1.68.

Propulsive performance

Propulsive performance is defined as the ratio

of net thrust to the shaft power (or specific net

thrust). Keinonen et al. (1991) compared the propulsive performance of different icebreakers at full

power. The data are shown in Figure 24a for different speeds for ships having ducted propellers,

whereas similar data for ships with open propellers are shown in Figure 24b. A comparison of the

data for the single-screw, ducted, controllable-pitch

system of Kigoriak and Arctic with that of twinscrew, open, controllable-pitch system of Terry Fox

shows that the net propulsive performance of the

ducted systems has an advantage of 27% over the

open system at low speeds. However, this advantage decreases at higher speed until both systems

have the same specific net thrusts.

where R1 = resistance in level ice at 1 m/s (MN)

CS = water salinity coefficient (saline = 1,

brackish = 0.85 and fresh = 0.75)

CH = hull condition factor (Inerta = 1, new

bare steel = 1.33 and old bare steel = 2)

B = ship beam (m)

L = waterline length of ship (m)

T = draft of ship (m)

H = ice thickness, taken to be ice thickness

plus half the snow depth (m)

t = ice surface or air temperature (°C)

σf = flexural strength of ice (kPa)

ψ = average flare angle in bow region (°)

φ = average buttock angle in bow region

(°).

For rounded-shoulder ships, an expression (using the same symbols) for the ice resistance at a

speed of 1 m/s is given as

R1 = 0.015 CS CH B0.7 L0.2 T0.1 H1.5

{1 – 0.0083 (t + 30)} {0.63 + 0.00074 σf}

{1 + 0.0018 (90 – ψ)1.6} {1 + 0.003 (φ – 5)1.5}.

Energy to penetrate an

unconsolidated ridge

Based on the full-scale data, an expression for

the energy to penetrate an unconsolidated ridge is

given as

ER = 0.25 AC AR CS CH {1 – 0.0083 (t + 30)}

{1 + 0.012 (90 – ψ)}

where ER = energy for ridge penetration (MJ)

AC = largest cross-sectional area of vessel

(m2)

AR = ridge depth × ridge profile length

(rubble only) (m2)

CS = water salinity coefficient (saline = 1,

brackish = 0.85 and fresh = 0.75)

CH = hull condition factor (Inerta = 1, new

bare steel = 1.33 and old bare steel = 2)

t = ice surface or air temperature (°C)

ψ = average flare angle in bow region (°).

Turning circle diameter

For vertical-sided chined vessels, and in level

ice of thickness equal to 60% of the icebreaking

capability at 1 m/s

D/LWL = 38 × 0.56x

27
b. Open propellers.

Figure 24. Specific net thrust vs. speed at maximum shaft power, indicating propulsive performance (after Keinonen et al. 1991).

a delivery scheduled for mid-1998.* Its displacement will be 16,303 tons, and its length, beam and

maximum draft will, respectively, be 128 m, 25 m

and 9.75 m. The propulsion systems will consist of

22.4 MW (30,000 hp), medium-speed diesel engines

with ac–ac electrical transmission to drive two

fixed-pitch propellers. Model tests indicate that it

will be able to break 1.6-m-thick, level ice continuously. It will have a dynamic positioning system

to support oceanographic research.

The design and model testing of a new U.S. Arctic Research Vessel has been completed (Kristensen et al. 1994), but it is not known at this time

when this research vessel will be built. This vessel

will support science missions in the Arctic well into

FUTURE ICEBREAKERS

At present, some of the largest icebreakers, such

as the Russian Yamal, are capable of operating in

multi-year ice without any concern for possible

damage, often at speeds in the range of 15–20 knots

(7.7–10.3 m/s) (Brigham 1994). The icebreakers of

this class are strongly built, with a robust propulsion system. Because of nuclear power, their unlimited endurance sets this class of ships apart from

the rest of the icebreakers in the world. Detailed

information about the icebreaker Yamal by R.K.

Headlands of Scott Polar Institute is given in Appendix A, which states that the maximum ice thickness Yamal can penetrate while navigating is estimated to be 5 m, and that Yamal has broken through

individual ridges estimated to be 9 m thick.

The contract to build an icebreaker, named Healy,

for the U.S. Coast Guard has been executed, with

* Personal communication, A.D. Summy, Captain, U.S.

Coast Guard, 1994.

0

0

0.04

0.08

0.12

0.16

0.2

2 4

Speed (m/s)

6 8 10

Net Thrust/Power (N/W)

Kicoriak

M. V. Acrtic

Polarstern

Oden

a. Propellers in nozzles.

Kigoriak

Terry Fox

Polar Class

R-Class

H. Larsen

A. Harvey

Louis S. St. Laurent

Bay Class

OTSO

0

0

0.14

0.12

0.10

0.08

0.06

0.04

0.02

2 4

Speed (m/s)

6 8 10

Net Thrust/Power (N/W)

28
for the Northwest Passage is slightly bigger in size

and displacement than Yamal, but the designed installed power (from diesel engines with a mechanical transmission to two controllable-pitch propellers in nozzles) is less than that of Yamal, which is

equipped with three propellers driven by nuclear

power through an electrical transmission. Auxiliary systems for the Northwest Passage icebreaker

include water wash and heeling tanks, as well as a

stainless steel belt with Inerta coating elsewhere.

Figure 25 is a sketch of an “iceraker,” as proposed by Johansson et al. (1994). The proposed

iceraker has a vertical-sided, 50-m-wide hull that

also has a submerged cantilever in front of and on

each side of the vertical, wedge-shaped bow. At

the edge of this cantilever, air is introduced into

the water at a depth of about 15 m. Seven spurs

are located on top of the cantilever at a transverse

spacing of about 20 m. The spurs create a 120-mwide channel of broken ice by deflecting a floating

the next century. The ship will have an overall

length of 103.6 m, waterline length of 93.9 m, maximum beam of 27.1 m, depth of 12.2 m, draft of 9.1

m and a displacement of 11,684 tons. The vessel

will have a flat bow with a ridge in the middle to

break ice in bending and to clear it on the side,

and a double hull to comply with the CASPPR

guidelines. The propulsion system will include diesel engines of 15 MW (20,000 hp) and two-ducted

4.1-m-diameter controllable-pitch propellers.

As mentioned earlier, it is well within known

and proven technology and experience to design,

build and operate an icebreaker year-round independently in the Arctic. Keinonen (1994) has set

down the performance criteria of a proposed icebreaker for the Northwest Passage, as given in

Table 4. The design parameters of the icebreaker

are given in Table 5, in which the values of those

parameters for Yamal are also given for comparison. It can be seen that the icebreaker proposed

Table 5. Comparison of design parameters of proposed Northwest Passage icebreaker (Keinonen 1994) with

those of the Russian icebreaker Yamal.

Proposed values for a

Northwest Passage Values for the Russian

Parameter Unit icebreaker icebreaker Yamal

Displacement ton 30,000 23,460

Water line length m 140 136

Length of parallel mid body m 70 no data

Beam at water line m 30 28

Draft m 14 11

Hull design concept type four-section bow conventional, straight

wedge shaped, double

Stem/buttock angle degrees 17 17

Flare/frame opening angle degrees 60 —

Shaft power MW 40 56

Propellers number/type 2CP in nozzles 3FP

Drive system engine/transmission diesel/mechanical nuclear/steam turbine/

electrical

Reamers type—width m two way—2 m none

Appendages names stern pods, shilling ice horn

rudders, bottom wedge

Auxiliary systems types water wash, heeling air bubbler

Hull coating types Stainless and Inerta polymer coating

coating with cathodic

protection

Table 4. Performance criteria for a Northwest Passage icebreaker (after Keinonen 1994).

Performance Criteria/measure Requirements

Level ice 2 knots at continuous speed 3 m

Multi-year ice Thickest broken ice on first ram 8 m

Backing Thickest level ice ice broken in a continuous motion 2 m

Turning Thickest ice below which turning circle is smaller than 10×Lwl 2 m

Extraction Wind speed in which able to extract (also needs to be able to 15.4 m/s

extract after any ram) (30 knots)

29
hull of a ship, it has now become possible to build

icebreakers with improved bow shapes to cope

with any type of ice. The developments in marine

propulsion systems were also incorporated into the

icebreaking technology to obtain higher efficiency,

reliability, flexibility and maneuverability. Development of auxiliary systems, such as heeling tanks,

air-bubbler systems, water-deluge systems, lowfriction coatings, etc., allows an icebreaker to perform effectively in ice conditions more severe than

those for which they were designed.

A description of the Russian nuclear-powered

icebreaker Yamal is given in Appendix A. An inventory of ships that are capable of navigating in at

least 0.3-m-thick ice is presented in Appendix B.

LITERATURE CITED

Backman, A. (1994) Five years operational experience with the Swedish icebreaker Oden. In Proceedings, 5th International Conference on Ships and Marine Structures in Cold Regions, March, Calgary,

Alberta, Canada, p. R1–18.

Brigham, L.W. (1987) Emerging polar ship technology—an introduction. Marine Technology Society Journal, 21(3): 3–5.

0 20 40 60 80 100 120 140 160 180 200 (m)

Water Line

Ramming Multi-year Floes (30 m)

Loose Pack (24 m)

Breaking Solid Ice (18 m)

Figure 25. New “iceraking” concept, as

proposed by Johansson et al. (1994).

ice sheet upward sufficiently to fracture it. The air

released from the edge of the cantilever produces

a current to take the broken ice pieces past the 60-

m-wide main body of the iceraker. While moving

through broken ice, the iceraker is submerged to a

deeper level so that the spurs do not contact the

ice. To break a thick (8-m) multiyear ice floe, the

iceraker is submerged even deeper and allowed

to strike the floe to split it in a single impact.

The proposed “iceraker“ represents an innovation that may not become a reality for a long time.

Enormous economic driving forces must be

present to encourage building this type of vessel

that is such a great departure from existing icebreaking ships.

SUMMARY

The current status of icebreaking technology has

been presented, along with a brief history. The

improvements in bow designs to break level ice

efficiently were suggested more than a hundred

years ago. However, those designs could not be

implemented in sea-going ships because of icepushing problems. With the help of new developments to reduce friction between the ice and the

30
Brigham, L.W. (1991) Technical developments and

the future of Soviet Arctic marine transportation.

In The Soviet Maritime Arctic (L. W. Brigham, Ed.).

Annapolis, Maryland: Naval Institute Press.

Brigham, L.W. (1992) Modern icebreaking ships.

In The Shipping Revolution: The Modern Merchant

Ship (R. Gardiner, Ed.). London: Conway Maritime

Press, p. 154–158.

Brigham, L.W. (1994) Observations of the Russian

icebreaker Yamal. Memorandum dated 2 September (unpublished).

Dick, R.A. and J.E. Laframboise (1989) An empirical review of the design and performance of

icebreakers. Marine Technology, 26(2): 145–159.

Dick, R.A., D.N. Baker, E.W. Thompson and H.C.

Cheung (1987) Arctic Ship Technology. Transport

Canada Report TP 8094E. Ottawa, Ontario:

Melville Shipping Ltd.

DesRochers, C.G., E.J. Crocker and I. Bayly (1994)

Post yield buckling of stiffened panel structures.

In Proceedings, 5th International Conference on Ships

and Marine Structures in Cold Regions, March,

Calgary, Alberta, Canada, p. K1–11.

Frederking, R. (1977) Plane-strain compressive

strength of columnar-grained and granular-snow

ice. Journal of Glaciology, 18(81): 505–516.

Ierusalimsky, A.V. and L.G. Tsoy (1994) The efficiency of using non-traditional hull lines for icebreakers. In Proceedings, 5th International Conference

on Ships and Marine Structures in Cold Regions,

March, Calgary, Alberta, Canada, p. S1–10.

Johansson, B.M., J. Ciring, W. Jolles, E. Stalder

and R.D. Rowe (1994) Revolutionary icebreaker

design. In Proceedings, 5th International Conference

on Ships and Marine Structures in Cold Regions,

March, Calgary, Alberta, Canada, p. O1–34.

Karavanov, S.B. and Y.V. Glebko (1994) New Russian Arctic regulations versus CASPPR. In Proceedings, 5th International Conference on Ships and Marine Structures in Cold Regions, March, Calgary,

Alberta, Canada, p. C1–10.

Keinonen, A. (1994) Icebreaker for North West

Passage, a designer’s perspective. In Proceedings,

5th International Conference on Ships and Marine

Structures in Cold Regions, March, Calgary, Alberta,

Canada, p. W1–10.

Keinonen, A., R.P. Browne, C.R. Revill and I.M.

Bayly (1991) Icebreaker performance prediction.

Transactions, The Society of Naval Architects and Marine Engineers, 99: 221–240.

Kristensen, D.H., B.L. Hutchison, A. Keinonen,

and K.-H. Rupp (1994) Ice-breaking and open

water performance prediction of the new UNOLS/

NSF Arctic Research Vessel. In Proceedings, 5th International Conference on Ships and Marine Structures

in Cold Regions, March, Calgary, Alberta, Canada, p.

N1–18.

Kværner Masa-Yards and ABB (no date) Azimuthing electric propulsion drive: Azipod. Helsinki,

Finland.

Laukia, K. (1993) Service proves electric propulsion design. The Motorship, February.

Liukkonen, S. (1992) Theoretical approach to

physically modelling of kinetic friction between

ice and ship. In Proceedings, 11th International Conference on Offshore Mechanics and Arctic Engineering, Calgary, Alberta, Canada, vol. IV. New York: American Society of Mechanical Engineers, p. 213–222.

Lohi, P., H. Soininen and A. Keinonen (1994) MSV

Fennica, a novel icebreaker concept. In Proceedings,

5th International Conference on Ships and Marine

Structures in Cold Regions, March, Calgary, Alberta,

Canada, p. M1–14.

Mäkinen, E., S. Liukkonen, A. Nortala-Hoikanen,

and A. Harjula (1994) Friction and hull coatings

in ice operations. In Proceedings, 5th International

Conference on Ships and Marine Structures in Cold

Regions, March, Calgary, Alberta, Canada, p. E1–22.

Masterson, D.M. and R.M.W. Frederking (1993)

Local contact pressures in ship/ice and structure/

ice interactions. Cold Regions Science and Technology, 21: 169–185.

Milano, V.R. (1987) The Thyssen/Waas icebreaking hull form. Marine Technology Society Journal, 21(3): 75–87.

Mulherin, N. (1994) Northern Sea Route reconnaissance report: History and present status of operations. USA Cold Regions Research and Engineering Laboratory, Report to the U.S. Army Engineer

District, Alaska.

Mulherin, N., D.S. Sodhi and E. Smallidge (1994)

Northern Sea Route and icebreaking technology:

An overview of current conditions. USA Cold Regions Research and Engineering Laboratory, Miscellaneous Paper 3520.

Ratzlaff, K.P. and D.J.L. Kennedy (1986) Behaviour and ultimate strength of continuous steel

plates subjected to uniform transverse loads. Canadian Journal of Civil Engineering, 13: 76–85.

Richter-Menge, J.A., G.F.N. Cox, N. Perron, G.

Durell and H.W. Bosworth (1986) Triaxial testing

of first-year sea ice. USA Cold Regions Research

and Engineering Laboratory, CRREL Report 86-16.

Smith, T.R. and E.M. Schulson (1994) Brittle compressive failure of salt-water columnar ice under

biaxial loading. Journal of Glaciology, 40(135): 265–276.

Santos-Pedro, V.M. (1994) The case for harmonization of (polar) ships rules. In Proceedings, 5th In31
ternational Conference on Ships and Marine Structures

in Cold Regions, March, Calgary, Alberta, Canada, p.

D1–8.

Toomey, P.R.M. (1994) A master’s perspective on

the performance of icebreakers. In Proceedings, 5th

International Conference on Ships and Marine Structures in Cold Regions, March, Calgary, Alberta,

Canada, p. V1–16.

Voelker, R.P. (1990) Arctic marine transportation

program, 1979 to 1986, executive summary. Report

No. MA-RD-840-90004 prepared by NKF Engineering, Inc., Arctic Technology Group, Columbia,

Maryland, for Maritime Administration, Office of

Technology Assessment, Department of Transportation.

32
The ship is one of three Rossiya class icebreakers

leased to the Murmansk Shipping Company

by the Russian Government (her sisters are

Rossiya [launched in 1985] and Sovetskiy Soyuz

[1990]).

The name is derived from a Nenets word meaning

“End of the Earth,” also applied to the Yamal

Peninsula.

Her keel was laid on 25-V-1986 in St. Petersburg

and she was launched on 28-X-1992

Registered number M 43048 and International Call

Sign UPIL.

Length overall 150 m, at waterline 136 m. Breadth

overall 30 m, at waterline 28 m. Draft 11.08 m.

Height, keel to mast head: 55 m on 12 decks (4 below water).

Ice knife, a 2-m-thick steel casting, is situated about

22 m aft of the prow

Displacement 23,455 tonnes; capacity 20,646 gross

registered tons.

The cast steel prow is 50 cm thick at its strongest

point.

The hull is double with water ballast between

them. The outer hull is 48 mm thick armor steel

where ice is met and 25 mm elsewhere.

Eight bulkheads allow the ship to be divided into

nine watertight compartments.

Ice breaking is assisted by an air bubbling system

(delivering 24 m3/s from jets 9 m below the

surface), polymer coatings, specialized hull

design and capability of rapid movement of

ballast water. Ice may be broken while moving ahead or astern.

An M1-2 or KA-32 helicopter is carried for observing ice conditions ahead of the ship.

The ship is equipped to undertake short tow operations when assisting other vessels through

ice.

Searchlights and other high intensity illuminations

are available for work during winter darkness.

Complement 131: 49 officers and 82 other ranks.

Power is supplied by two pressurized water

nuclear reactors using enriched Uranium fuel

rods.

Each reactor weighs 160 tonnes, both are contained

in a closed compartment under reduced pressure.

Fuel consumption is approximately 200 g per day

of heavy isotopes when breaking thick ice. 500

APPENDIX A: INFORMATION ABOUT THE NUCLEAR ICEBREAKER YAMAL

(Reproduced from an unpublished description given by R.K. Headland of

Scott Polar Institute, Cambridge University, UK)

kg of Uranium isotopes are contained in each

reactor when fully fueled. This allows about 4

years between changes of the reactor cores.

Shielding of the reactor is by steel, high density

concrete and water. The chain reaction can be

stopped in 0.6 seconds by full insertion of the

safety rods.

Used cores are extracted and new ones installed

in Murmansk, spent fuel is reprocessed, and

waste is disposed of at a nuclear waste plant.

Ambient radiation is monitored by 86 sensors distributed throughout the vessel. In accommodation areas this is 10 to 12 μRöntgen/hr,

within the reactor compartment, at 50% power,

800 μRöntgen/hr.

The primary cooling fluid is water, which passes

directly to four boilers for each reactors; steam

is produced at 30 kg/cm2 (310°C).

Main propulsion system: each set of boilers drives

two steam turbines that turn three dynamos

(thus six dynamos may operate). 1 kV dc is

delivered to three double-wound motors connected directly to the propellers.

Electricity for other purposes is provided by five

steam turbines turning dynamos that develop

a total of 10 MW.

There are three propellers; starboard and midships

ones turn clockwise, port turns counter-clockwise. Shafts are 20 m long. Screw velocity is

between 120 and 180 rpm.

Propellers are fixed, 5.7 m diameter and weigh 50

tonnes; each has four 7-tonne blades fixed by

nine bolts (16 tonne torque applied); inspection wells allow them to be examined in operation.

Four spare blades are carried; diving and other

equipment is aboard so a blade may be replaced at sea; each operation takes from 1 to 4

days (three such changes have been necessary

on Rossiya icebreakers since 1985).

A propulsive effort of 480 tonnes can be delivered

with 18–43 MW (25,000 shaft horsepower)

from each screw (total 55.3 MW [75,000 shaft

horsepower]).

Power can be controlled at a rate of 1% a second.

Maximum speed is 22 knots (40 km/hr); full speed

in open water is 19.5 knots (35 km/hr); breaking ice 2–3 m thick can be done at 3 knots (5.5

km/hr) continuously.

33
Maximum ice thickness that can be penetrated

while navigating is estimated as 5 m; individual ridges estimated at 9 m thick have been

broken through.

Helm controls one rudder, which turns 35° either

way, operated by four hydraulic cylinders

powered by one of two pumps. It is protected

by an ice-horn for moving astern.

Steering may also be provided by directing air jets

of the bubbling system (comparable to use of

bow-thrusters).

Auxiliary power is available from three diesel generating sets: 1 MW (1×) and 250 kW (2×).

Anchors: two 7-tonne anchors with 300 m of chain

each, and four ice anchors.

Four deck cranes are aboard; the largest pair can

lift 16 tonnes each.

Sea water distillation: two vacuum stills can supply 5 m3 of fresh water an hour each (240 m3/

day).

Differential ballast tanks are suitable fore and aft,

and athwart the ship; the pumps are capable

of moving 1 m3 of water a second.

Ship has 1280 compartments (cabins, storage areas, machine rooms, etc.).

Sufficient provisions and supplies can be carried

to operate for 7 months.

Safety equipment includes: 1 launch, 2 fully enclosed lifeboats, and 18 inflatable life rafts.

34
APPENDIX B: AN INVENTORY OF EXISTING SHIPS THAT ARE CAPABLE OF

NAVIGATING IN AT LEAST 0.3-m-THICK ICE COVER

(Inventory compiled by Leonid Tunik)

35

[The paper version of this report includes the material listed in the Table of Contents above, but is not

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inside cover of this report for ordering information.]

TABLE OF CONTENTS

INTRODUCTION .............................................................................................................................................. 36

REGULATORY AGENCIES ............................................................................................................................... 36

REGULATIONS. .................................................................................................................................................. 37

SHIPS INCLUDED .............................................................................................................................................. 37

SCOPE OF DATA................................................................................................................................................. 38

NOTES TO THE PRINTED EDITION........................................................................................................... 39

NOTES TO THE ELECTRONIC EDITION.................................................................................................. 40

DATABASE FILE STRUCTURE ........................................................................................................................ 40

LIST OF TABLES INCLUDED ....................................................................................................................... 40

MAIN TABLE DESCRIPTIONS ...................................................................................................................... 40

LOOK-UP TABLE DESCRIPTIONS .............................................................................................................. 43

TABLE RELATIONSHIPS ............................................................................................................................... 44

ACRONYMS USED ........................................................................................................................................... 45

REGISTER NAMES ......................................................................................................................................... 45

BOW SHAPE .................................................................................................................................................... 45

COUNTRY ........................................................................................................................................................ 45

SHIP TYPES ..................................................................................................................................................... 46

PROPULSION MACHINERY .......................................................................................................................... 46

BIBLIOGRAPHY ............................................................................................................................................... 47

INDEX OF SHIP SERIES BY ICE RANK .................................................................................................... 51

INDEX OF SHIPS WITH SERIES NAME .................................................................................................... 54

LIST OF SERIES AND SHIPS WITH SPECIFICATIONS ........................................................................ 60

LIST OF SHIP OWNERS WITH SHIP NAMES .......................................................................................... 225
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Auxiliary systems Icebreakers Inventory of icebreaking ships

Hull forms Icebreaking history Propulsion system

UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED UL

Northern Sea Route Reconnaissance Study: A Summary of Icebreaking

Technology

Since the advent of steam power, icebreakers have been built to navigate in ice-covered waters. The hull forms

of early icebreakers were merely an adaptation of open water hull shapes, by sloping bow angles more to create

vertical forces for breaking ice in bending. However, these bow forms were found to be unsuitable for sea-going

vessels because they push broken ice ahead of them. This experience led to construction of all sea-going vessels

with wedge-shaped bows from 1901 to 1979. With the introduction of low-friction coatings and the waterdeluge system, it is now possible to operate ships with blunt bows efficiently in broken ice. New developments

in marine propulsion technology have also been incorporated to obtain better icebreaking efficiency and performance. Both fixed-pitch and controllable-pitch propellers are in use. Nozzles surrounding the propellers are

also used to increase the thrust and to reduce ice–propeller interaction. Electrical and mechanical transmission

systems have been used in icebreakers to improve the characteristics of the propulsion system. Though many

types of prime movers are used in icebreakers, medium-speed diesel engines are the most popular because of

their overall economy and reliability. Appendix A is a description of the Russian icebreaker Yamal, which is one

of the largest and most powerful icebreakers of the world today. Appendix B contains an inventory of existing

ships that are capable of navigating in at least 0.3-m-thick ice. Some of the present icebreakers are capable of
13. ABSTRACT (cont’d).

navigating almost anywhere in the ice-covered waters of the Arctic and the Antarctic, and multi-purpose icebreakers

have been built to operate not only in ice during the winter but also in open water doing other tasks during the

summer. With sufficient displacement, power, navigation equipment, and auxiliary systems, future icebreakers that

can operate independently year-round in the Arctic and the Antarctic are well within the known technology and

operational experience.

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