The Polar Icebreakers: In a Class by Themselves

The U. S. Coast Guard acquired a vastly increased icebreaking capability with the construction of the USCGC Polar Star (WAGB-10). She is the first of two Polar-class icebreakers to be built by Lockheed Shipbuilding and Construction Company of Seattle, Washington, and the first icebreaker since the USCGC Glacier (WAGB-4), commissioned in 1955, to join the Coast Guard. The second ship of the Polar class, the Polar Sea (WAGB-11), will be commissioned late this year or early 1977. According to the latest information available, the Polar-class ships will be the world’s most powerful fossil-fueled icebreakers. More importantly, the Polar class possesses several unique features which, in my opinion, will draw considerable attention not only from icebreaker sailors, but also from all other professional seamen and many laymen alike.

To acquire a feel for what the “most powerful fossil-fueled” icebreaker can actually do, we should examine a sample situation. Let us assume that a body of water such as Puget Sound is frozen over from bank to bank (fast ice) with homogenous sea (salt water) ice which is six-feet thick and one-year old (annual ice) with no snow cover. A Wind-class icebreaker could break that ice by backing and ramming under full power at a rate of perhaps 75 feet per ram. By contrast, the Polar-class icebreaker is designed to break such ice at a steady speed of three knots when utilizing full turbine power. In an actual situation, which occurs annually, two Wind-class icebreakers require seven to ten days to break a channel into McMurdo Station, Antarctica, for the resupply ships. I do not consider it to be far-fetched to predict that one Polar-class icebreaker could do the same job in one-half the time.

The Polar Star and her sister ship will be able to achieve the foregoing by virtue of a very powerful main propulsion plant, an improved hull design, and an overall increased mass. The power for main propulsion is obtained from a combined diesel or gas (CODOG) turbine plant. While this type of propulsion plant is not unique, the employment of controllable-pitch (CP) propellers in icebreakers is. As has been noted previously in the Proceedings (See N. C. Venzke, pp. 80, July 1975), the Polar class is the second Coast Guard class of cutters to utilize the CODOG plant and the fourth to utilize gas turbines. The Polar Star's configuration centers on a diesel-electric/geared turbine plant which delivers power through three 34-inch diameter shafts. In the diesel-electric mode, six 3,500 h.p. ALCO V-16 diesel engines are the prime movers for alternators which supply main propulsion electricity through rectifiers to the three DC 6,000 h.p. main motors. Also in this mode, a total of 18,000 shaft horsepower (s.h.p.) is available for use during open water cruising and icebreaking in moderate ice.

Table 1 Comparative Icebreaker Data

Although the diesel-electric plant in the Polar class utilizes relatively conventional technology, it does have at least one advantage over that of the Wind class—flexibility. The Polar class gains added flexibility in that four diesel/ alternator units may be electrically connected to each of the main drive motors. Of course, only two of those units may provide power to a given main motor at any one time. This important feature was not incorporated in the Wind class. As a result, the older icebreakers cannot shift a diesel/generator from one shaft to the other to balance power output in the event of engine casualties. There have been times in some Wind-class icebreakers when two of the three engines on a shaft were inoperative, causing an imbalance which degraded icebreaking efficiency to a degree far more than the loss of horsepower would indicate.

When the Polar-class icebreaker encounters ice which cannot be broken when she is under diesel-electric power, the three gas turbines will be employed. As most readers are aware, the gas turbine is a relatively small, lightweight package which readily provides available power. In this new class of ships, each of the three Pratt and Whitney FT4-A12 turbines is connected to a shaft through a clutch and a reduction gear. Each turbine is capable of producing 20,000 s.h.p. continuously and possesses a short period boost capability of 25,000 s.h.p. Remember, either the diesel-electric or the gas-turbine plant may be employed at a given time on a given shaft, but not both.

For those unfamiliar with gas turbines, the installed turbines are non-reversing (rotate in one direction only). The obvious reversing problem created by this limitation was resolved in the Polar class by use of the CP propeller. The Polar Star uses three, four-bladed, 16-foot diameter Escher Wyss CP propellers, which under turbine operation turn at approximately 175 r.p.m. Some seamen might question: “Are they strong enough?” After all, their basic construction including the hydraulic control system is much more complex than the conventional fixed-pitch propeller. In the Wind Class, and in the Glacier, it is proper to reduce power to establish a low r.p.m. when ice is about to strike the sturdy stainless steel propellers. Failure to do so has resulted in numerous snapped blades and shafts. In the case of the Polar class, the propellers cannot be operated at a low r.p.m. and are designed to shift pitch from ahead full to back full in 20 seconds while milling ice with 20,000 s.h.p. Despite the fact that they are fabricated from stainless steel, having a yield strength of p.s.i., I must admit that the mere thought of milling ice with propellers causes me to shudder!

Technical studies and practical experience, however, indicate that an icebreaker’s propellers are most vulnerable to ice damage when they are stopped for reversing direction, as is the practice in the older icebreakers. In addition, the naval architects and engineers for the Polar class have designed an extra safety margin into the blades. I would add that the Polar-class propellers have no protection other than the fact that they continuously rotate and are located well below the water surface since the ships have 33½ foot drafts.

Finally, there is one point for reflection. The Polar class has a maximum horsepower (s.h.p.) to displacement (tons) ratio of 5:1, in contrast to 1.66:1 for the Wind class. I consider that this ratio provides a rough indicator of the relative performance potentials of the Polar Star and the Polar Sea.

The Polar-class hull design is superb and should be both efficient and sufficiently strong to withstand the rigors of high-powered icebreaking. For those unfamiliar with icebreaking techniques, an icebreaker is configured to maximize icebreaking through the combined forces of the ship’s forward motion as she rides onto the ice and the downward pull of gravity. The Polar-class bow is the result of rigorous engineering analysis and utilizes the basic stem shape designed by Captain Roderick M. White, U. S. Coast Guard. His ideas were also incorporated into the bow design of the SS Manhattan for her Northwest Passage operation.

Good bow lines are not the entire answer, however. The ship must be sturdy as well as efficient. The Polar class has frames which are spaced 16 inches apart with the internal structure based upon a grillage system. The forefoot and stern frame are heavy castings of HY-80 steel. The shell plating and associated internal framing is fabricated from CG-537M steel (carbon/manganese-silicon steel) which has been quenched and tempered. That composition and heat treatment provides extremely good, low-temperature qualities. Insofar as yield strength is concerned, it tests at 50,000 p.s.i., as compared to the 33,000 p.s.i. yield strength of the mild steel used in the Wind class. The ice belt, or shell plating, which comes in contact with the ice is particularly sturdy in the Polar class. Its thickness ranges from one and % inches in the forward and after portions to one and % inches amidships. The rudder is afforded some protection by a rudder shoe which shields the rudder when backing down, provided that the rudder is not positioned in excess of 10° to either side of the centerline. Despite the fact that the Polar class has a hull sufficiently rugged to meet the rigors imposed by her powerful main propulsion, I voice a word of caution. The Wind-class icebreakers also had hull strengths commensurate with their power, nonetheless poor icebreaking techniques or bad luck occasionally resulted in unnecessary and costly damage.

The third reason for the Coast Guard’s high expectations of the Polar class is its large mass. Obviously, at a given ramming speed, a 13,000-ton icebreaker should be considerably more effective than the 6,500-ton Wind-class icebreaker.

While I have noted the salient characteristics of high power, improved bow design, and large mass which should result in an outstanding icebreaker, it is also important to discuss how this new ship is to be controlled. The bridge controls are rather conventional and include an “iron mike” for steering, pilot house engine controls, and remote steering and engine controls in the aloft conning station. On the other hand, the main propulsion controls are far from being “conventional.” The entire main propulsion plant is designed for unmanned operation with the exception of those watch personnel required in the engineering control center (ECC) and for the roving watch. From ECC, all main propulsion equipment can be activated, secured, and monitored. The entire watch, consisting of no more than four men, can keep watch over the main propulsion and auxiliary plant by using the many instrument panels, mimic panels displaying the condition of each shaft, and the propulsion alarm and monitoring system (PALMS). The PALMS is a computer-controlled monitoring system which is the primary reason why a small watch can maintain safe and reliable propulsion operations. It continuously scans and checks 500 machinery parameters such as temperatures, pressures, r.p.m., etc., sounds alarms when the values depart from acceptable ranges, permits visual display of certain data, and prints-out a machinery log at specified times. If PALMS detects an abnormal condition, an alarm will sound and the abnormal item will be visually identified by a flashing light on a mimic panel in ECC. By depressing an alarm acknowledge button on a mimic panel, the alarm will cease sounding and the parameter can be displayed on the digital unit on the appropriate mimic panel. However, the light will continue to flash as long as the alarm condition exists. Selected items such as lube oil pressure systems have a two-stage alarm which, if the parameter exceeds the second stage, will cause the affected equipment to be secured. The system does not eliminate ultimate human control over any given situation. Equipment that would be secured by PALMS would also be secured as a rational watchstanding procedure if the engine spaces were manned. The net saving of such a system is seven watchstanders per watch in comparison to the Wind-class icebreakers which require approximately 11 persons to man their far less sophisticated plants.

Habitability in the Polar class is as modern as the engineering. Single, double, and four-man staterooms are the only accommodations available. Most officers have single staterooms; all chiefs and first class petty officers share double staterooms. Enlisted personnel junior to first class petty officers share four-man staterooms. There is little comparison with the Wind class in which lower rated personnel share 60-man quarters. Even the modern Hamilton-class cutters can not match the Polar class’ accommodations. The new icebreakers have quite adequate lounges, a library, and a gymnasium. The drab traditional color schemes have been replaced by bright colors and modern decor. The efforts to improve the individual sailor’s lot during long polar deployments are commendable and were made possible through the employment of reduced manning techniques, low maintenance materials, and the new crew augmentation concept. As a result, the Polar Star is manned by 138 officers and enlisted men which is a marked reduction from the 170 typically assigned to a Wind-class icebreaker. That reduction is even more impressive when one considers the relative sizes of the two classes of ships. In any event, the reduced personnel allowance plus the larger ship made spacious accommodations possible in the Polar class.

The Polar Star and the Polar Sea will operate under a three crew-two ship concept. (The Polar Star personnel refer to this as the red, white, and blue system.) When the decision was made to build the Polar-class icebreakers, it was decided that they should be deployed for a higher percentage of the year than previously planned. Obviously, this would provide for better use of very expensive ships and avoid the need for a third one. However, some provision had to be made to protect the crews from excessive periods at sea. Under the new concept, the two ships will be deployed for 240 days per year, whereas any crew member will not be away from home port in excess of 180 days. Ideally, each ship will deploy for two four-month cruises per year with two two-month in port periods. Each of the three crews will be divided into two sections headed by the commanding officer and executive officer respectively. Each crew will serve on a given ship for a one year continuous period. Upon arrival in port, one crew section will be relieved and rotated ashore for a six-month period. While ashore, the third crew will assist in ship maintenance when the icebreakers are in port and participate in training. Under this system, a given crew section will serve in one icebreaker during one period and in the other during the second period. Because the commanding officer will not always have the same crew during successive periods of sea duty, this concept is slightly different than the Navy’s blue and gold crew system.

The Polar Star underwent extensive ice trials during October, November, and December 1975 in the Bering Sea area and north. These trials were conducted under instrumented conditions in varying ice conditions for the primary purpose of validating design matters, determining actual icebreaking effectiveness under both modes of propulsion, and calculating fuel consumption and overall operation of the ship in ice. As the results of these tests are analyzed and more are conducted, I believe the true worth of this class will be realized.

In summary, the Polar-class icebreakers are extremely powerful, sturdy, heavy, and comfortable ships. In all areas they far exceed like characteristics in the Wind-class icebreakers. And, although I am not as familiar with the Glacier, I believe that a similar statement could be made in her case. Furthermore, this new class has a most impressive grouping of major innovations and thoughtful designs, only a few of which I have noted here. Consequently, I am most enthusiastic about the class and predict that the Polar Star and the Polar Sea will prove to be outstanding icebreakers.

Finally, it might appear that I have treated the grand, old Wind-class icebreakers harshly. That was not my intention, as I truly learned to respect them in three antarctic and five arctic deployments. Thus, I hope that the Polar-class ships exceed their designer’s expectations in the same manner that the Winds exceeded theirs throughout the past 30 plus years.