Icebreakers

In spite of the fact that many of the coast guard vessels were not designed as icebreakers, the exigencies of the moment of ten require that whatever ships are available must go out and clear channels or render emergency aid. Although primarily concerned with keeping the main channels open and leaving to private equipment the maintenance of passages to docks, the Coast Guard has frequent occasion to break ice into private docks, particularly in small harbors where commercial tugs are not always available. In many cases the livelihood of communities depends on fishing, and water transportation is used for delivery of food, mail, coal, and the movement of passengers and automobiles. The Coast Guard is called upon to render emergency aid to icebound communities by transportation of doctors and patients requiring hospitalization.

The recent increase in the use of gasoline for automobiles and fuel oil for heating and power production has required a year-round delivery service by tankers and barges, especially during cold weather. As many large storage tanks have been built far upstream, it has become important to break ice for the maintenance of these services.

Also of great importance is the clearing away of ice threatening lighthouses, bridges, piers, breakwaters, and dams, and the prevention of dangerous ice jams. Buoys are particularly subject to ice damage, and it is a problem to keep them in place in frozen rivers, especially after the ice has started to break up.

There are two basic types of ice, requiring different tactics to penetrate, and calling for different qualities of an icebreaker. First, there is clear ice, formed by homogeneous freezing in still water. On the other hand, slush ice is a conglomeration of broken ice and snow that frequently packs harbors to the bottom. On the Great Lakes, slush ice, when driven by on-shores gales, sometimes packs into a mass of field ice extending miles out into the lake. In this packed form, it has some tendency to crack and separate. Sometimes, however, it has a mushy quality which causes it to grip a vessel tightly and to fill in behind her. This type of ice is formed partly by wave action on clear ice which forms in rivers and bays and is carried out by wind and current, and partly by the building up of masses of ice by spray along the beach, which break off and float out into deeper water. When a field has formed, several feet of snow may fall and further build up the thickness of the ice. The ice encountered may thus range between the extremes of clear ice and slush ice.

The necessity of keeping harbors and rivers open to navigation has required the use of nearly all the available types of coast guard vessels for icebreaking with, as might be expected, various degrees of success.

Of the 203 gasoline, 75-foot patrol boats, constructed in 1924-25, less than 50 are now in operation. These vessels have been particularly useful for breaking ice in shallow water, as they draw less than 4 feet. The thickness of the wood planking is only 1 3/8 inches, but many of the boats have had 5/8- or 3/4-inch white oak ice sheathing added in way of the forward water line, and in some cases metal sheathing over the wood. However, damage has been reported not only to the hull but to propeller blades and shafting as well, for the vessels are twin screw.

The 125-foot patrol boats, built in 1926-27, have steel hulls, and although not designed as icebreakers, they have A-inch plating at the water line, which has enabled them to perform successful work in ice. They are, however, underpowered for this work. In addition they do not have lines designed for icebreaking, and their twin screws are vulnerable to ice damage. The Pulaski of this class reported in 1934:

. . . entered Norwalk River, encountered solid ice 5 inches thick . . . made slow progress, about 7/10 of a mile an hour. 3:00 p.m. ice hard and from 7 to 8 inches thick, making about 1/10 mile an hour. 6:00 a.m. stopped operations and anchored. . . . Distance broken today three and two-tenths miles. . .

The recently constructed 165-foot patrol boats, like the Thetis, have more than twice the power of the 125-foot class, but their water-line plating is only 1/4 to 5/16 inches thick. They cannot be driven at full power in heavy ice without hull damage. These boats have twin screws and twin rudders, which is a dangerous combination for icebreaking. In 1934, the experience of the Thetis in Buzzards Bay calls attention to an important feature not related to the structural design of the hull:

The condition of the ice was as follows: slush ice closely packed. It was unnecessary to crack the ice, thereby eliminating any danger in dishing or rupturing the shell plating. However, the following difficulties were encountered. The injections to the main engines were plugged up with ice thereby causing the main engines to overheat. The sanitary lines were then cut in for circulating water to the main engines and very shortly it was found that the injections to the auxiliaries became plugged with ice. . .

One of the most unique vessels in the Coast Guard is the Kickapoo. Originally a deep-draft Shipping Board tug, she was converted to an icebreaker. In order to reduce the draft and at the same time increase the displacement, sponsons were added on each side, adding 7 feet 6 inches to the beam. The result was very satisfactory, and this vessel has given good service in Maine waters, breaking ice 8 inches thick without stopping, when frozen from bank to bank. The Kickapoo has broken 14 inches of solid ice by making from one-half to one ship length per jump, then backing for a new start. She is reported to maneuver well in ice, and turns in a shorter space than in open water. In 1933 this vessel reported by dispatch:

. . . Pilot house and other superstructure well shaken up and squeaking due to impact in heavy ice. Foremast should be removed as it is in constant danger of breakage. When we hit heavy ice the forestays sag visibly. . . . One hole in circulation pump caused by ice now patched. . . . Main engine knocking generally due to running at wide open throttle at full boiler pressure, also loose on foundation. . . . When cannot go ahead turn around and break ice stern first and as yet have not stalled when so doing, however this does steering gear no good and resort to it only when in ice jams. . . .

The heaviest ice plating on any coast guard vessel is on the Northland, built in 1927 to replace the ancient Bear for arctic service. The shell is from 1 inch to 1 ¼ inches thick, and the hull structure is exceptionally rugged. Web frames are closely spaced and the decks have heavy beams to act as compression members to resist ice pressure when the vessel is locked in the ice. The Northland was the first coast guard vessel to have extensive welding throughout her construction, which has stood up well in the rigorous service in which she has been employed. The power plant is Diesel-electric, with a single screw, designed to develop 1,000 horsepower. The forefoot is cut up to aid the vessel in bearing down on the ice, but as a result the steering has suffered, particularly when running astern, when she is difficult to handle. Last year, when the Northland was being considered for use on the third expedition to Antarctica, it was intended to fit a skeg at the bow to increase the lateral plane to improve the steering. At the same time, bilge keels were contemplated to reduce the rolling, following her experience in a hurricane when she rolled 65 degrees each side of the centerline. However, increased coast guard activities resulting from the neutrality legislation caused abandonment of the participation of the Northland in this expedition.

The 250-foot turbo-electric cutters of which the Itasca is typical have 3,350 horsepower and a speed of about 17 knots. These vessels are single screw, which is desirable for icebreaking. Although not designed as icebreakers, these ships have been successful in this work up to the limits of the bow framing and the shell plating, which is 1/2 inch to 5/8 inch thick. The forefoot is not cut away, and the stem enters the water with only a slight rake.

The large geared turbine 327-foot Hamilton class cutters are not intended for icebreaking, although the shell was made § inch thick at the water line. With twin screws and a speed of well over 20 knots, these ships are ordinarily used in deep-sea cruising work and seldom have occasion to break ice in harbors.

The lighthouse tenders, which are now operated as part of the Coast Guard, are vessels of very substantial scantlings because of the nature of their duties. Their lines are not designed for icebreaking, but the shell plating is made sufficiently heavy not only to withstand grounding but also to permit their breaking away from the dock or to free themselves if they become trapped in the ice while in service. The lighthouse tenders frequently encounter ice as they are required to keep buoys in place and make regular trips to lighthouses and light vessels regardless of weather conditions.

In 1932 the Coast Guard cutter Escanaba was built especially for icebreaking on the Great Lakes. She was followed by 5 similar ships for coastal service. The Escanaba is 165 feet long, with single screw geared turbine machinery of 1,500 horsepower, with 7/8-inch plating on the water line. Vessels of this class are excellent in appearance and are efficient units not only for icebreaking but in their open water duties as well. The forefoot is cut away to permit the vessel to ride up on the ice and crush it; however, this method is limited to operations in brittle ice of moderate thickness. The type of ice found on the Great Lakes is often so thick that it will support the weight of any vessel that runs its hull upon it. Therefore, on the Escanaba it was found desirable when breaking ice to fill the forward ballast tank to prevent excessive climbing upon the ice. Experiments made with the ballast tank empty showed that the vessel would invariably run up on the ice and hang there, often requiring an hour to free the vessel.

In February, 1933, ice conditions on the Great Lakes were unusually severe. One day the car ferry Milwaukee, after waiting several days for good weather, attempted to leave port. She was stopped by the ice for two days, but finally backed into the harbor, refueled, backed out, and made her way into clear water after three days of effort. Car ferries are 350-foot vessels, designed to operate in ice, and are usually considered as icebreakers. The car ferry Grand Rapids and the SS. Missouri were still stuck in the ice, however, about 200 yards outside the breakwater, trying without success to enter the harbor.

The cutter Escanaba was at her berth, surrounded by 10 inches of solid ice. It seemed reasonable to expect difficulty in working the Escanaba away from the pier, but a single backing movement cast the bow away from the pier and on going ahead the vessel steadily gained speed through the ice. The Escanaba described the situation in her report:

. . . On encountering heavy slush ice near the entrance, full speed was called for and steady progress was being made through slush ice that must have been at least 8 feet deep, and was believed by many local people to extend all the way to the bottom.

At this point the ice against the hull blocked the main condenser circulating water and power was lost just at the time it was most needed. By working the engine ahead slow and shifting the rudder from time to time, the ice was washed away from the hull and after 15 minutes of this it was possible to back out and charge into the ice with sufficient force to reach the Missouri, opposite to and parallel with her in relative position.

This vessel was then fairly fast in the heaviest ice. An irregular shaped berg seen must have measured 8 by 10 feet. This was raised by the Missouri’s propeller from under the surface. Numerous globular masses measured 5 to 6 feet. The rest was small bergs and broken clear ice, packed into a solid field. . . .

The vessels then lay side by side, and after about 15 minutes of turning over, cracks appeared between the two vessels and finally the two moved together. The Missouri became stuck again, and the Escanaba charged down close to and parallel to the Missouri, moving her bodily sideways into clear water. The Grand Rapids was also assisted out. Towards the end of the work, the Escanaba’s main turbine ahead thrust bearing heated up, and she was forced to back and warp a mile to her berth.

In 1934 four harbor cutters were built, the Calumet, Hudson, Navesink, and Tuckahoe. These were about 110 feet long, with Diesel-electric drive, and were really tugboats. They were designed for speed and maneuverability, for use in boarding duty. Icebreaking was not a consideration, and the vessels had only a nominal plating thickness at the water line. When circumstances led to their being assigned to icebreaking, they were not found entirely suitable. The emphasis on speed and maneuverability made a deep forefoot necessary, which was not ideal for icebreaking.

Therefore, when new harbor cutters were built in 1939, the design was modified with more emphasis on icebreaking. The resulting vessels, Naugatuck, Raritan, Arundel, and Mahoning, are among the finest icebreakers in the coast guard service. They are essentially fine appearing, substantial, and powerful tugs, with Diesel-electric drive of 1,000 horsepower. The hulls are of welded construction throughout. Hull plating along the water line is 3/4 inch thick. An unusual stem profile was adopted which gives the advantages of a small angle between the stem and the water line without the loss of steering ability caused by the usual cut-away forefoot. This is accomplished by fitting a skeg below the water line. The stem enters the water at an angle of 30 degrees. To prevent the vessel from becoming locked in the ice by pressure along the hull, and to permit the vessel to free herself in the ice as she proceeds, the sections are sloped outboard at an angle of 70 degrees at the water line.

As early as the time of their trial trips, the Naugatuck and Raritan had occasionto demonstrate their icebreaking ability. Two tankers, the Panoil and Mexoil, were attempting to open the season of navigation on Lake Huron in ice which was from 6 to 15 inches thick. They had made only 3 miles in 24 hours when the Naugatuck arrived. The coast guard vessel was slowed down only to about half speed in the ice. Particularly impressive was her ability to stop in the ice, and then start ahead, without backing first as is customary. The Raritan on her trial trip went out into similar ice conditions and cleared a path for commercial navigation.

As a result of the experiences of the Coast Guard with vessels of many types operating in every possible ice condition, some general conclusions are indicated regarding the general design of icebreakers.

As is usual in most designing work, the solution is a compromise. Some desirable characteristics for breaking ice do not correspond with those for open water conditions. For example, light weight construction cannot be fully utilized if a vessel is to break ice. Not only are rugged water line plating and bow framing required, but the entire structure must be rigid to stand severe shocks and racking caused by the sudden stoppage of the ship in the ice. There should be some consistency between the power provided and the hull scantlings, which should be sufficiently heavy to permit the use of full power without damage to the structure. The use of welding is advantageous to give a flush surface and to avoid rivet leakage, as well as to save weight without sacrifice of ruggedness.

The type of bow used on the Naugatuck class cutters appears to be indicated, as it affords an entrance angle on the water line of about 30 degrees to permit the hull to break down the ice, while the forward skeg below the water line aids in steering. The draft forward should in some services be a minimum consistent with good steering, as it is sometimes necessary to run the vessel almost up on a beach or into small slips to clear a path for small boats. Icebreakers should not be too long, in order to permit short turning, frequently required in narrow rivers and around slips. The use of a slope of something like 70 degrees for the sections in way of the water line appears desirable as it permits the vessel to free easily from the ice and leaves a clean path astern.

The use of Diesel-electric drive appears to be ideal, as it can stand the great variations in load and frequent reversals so often required in icebreaking. Besides its advantages for icebreaking, the Diesel plant has all the well-known advantages in clear water use, such as economy, reliability, flexibility, and maneuverability.

Where steam plants are used, as well as in Diesel installations, particular attention should be given to the locations of circulating water suctions. Probably two suctions should be provided on each side of the ship to prevent clogging the intake: high suctions for clear water use, and low suctions for use in icebreaking.

A single screw and single rudder arrangement is better protected from the ice than twin screw installations with one or two rudders. The rudder should be far enough below the water line so that it can turn freely under the ice, and should be heavily constructed. Similar precautions are required to protect the propeller blades. Shafting should be heavy enough to withstand the increased torsion caused by a propeller blade striking a submerged ice mass as well as to withstand the vibration that is frequently encountered in icebreaking. A rugged steering gear should be installed capable of enduring the severe punishment of icebreaking.

Bilge keels, although often desirable in open water, are particularly subject to ice damage, and should be placed as low as possible, with minimum projection. Bilge keels tend to prevent the vessel from rolling in the ice, whereas it has been found that if the vessel can be made to roll slightly, better progress can be made through the ice. They should not be located too close to suctions, since they might contribute to clogging the suctions with slush ice.

The stern of an icebreaker should be well protected with a guard or heavy hull structure to minimize damage caused by a towed vessel crashing into the icebreaker when the latter becomes stalled in the ice. Anchors should be located clear of probable ice.

Ballast tanks with arrangements for rapid filling and pumping are useful in regulating the trim to suit the particular ice conditions involved. In many cases, the clear water trim is not the best for use in icebreaking. Fresh water tanks should not have the shell plating as a boundary, due to the possibility of contamination resulting from leakage, although this is minimized by welded construction. Good anchor, cable, and windlass equipment are useful for anchoring in fields of moving ice, and a stern anchor is sometimes desirable.

In general, all details in connection with the construction of icebreakers should be as rugged and reliable as possible, for there are few services in which a vessel receives as much punishment and severe treatment as in icebreaking.