Breaking Ice, in Baltimore Harbor
(See page 1304, August, 1924, Proceedings)
Lieutenant Commander Frank Luckel, U. S. Navy.—Captain Disniukes’ very interesting and instructive article indicates that a battleship can break up ice “four or five feet thick.” The thickness of ice is very difficult to estimate accurately even from an observation of the broken floes. The writer has had some experience in ice navigation in the Bering Sea and in Vladivostok Harbor and vicinity. I believe that four or five feet of newly formed ice is an excellent record, even for a battleship. An unarmored vessel such as the old U. S. S. Saturn could break through only about one foot of new ice. It was impossible to break through thicker ice, not because of insufficient power, but on account of the strain upon the frames and the danger of the ice cutting through the plating. In northern waters it is not unusual for ice to cut through the plating of a steel vessel. Of course, this would not be possible with the Kentucky on account of the heavy ram and thick armor.
A specially built ice breaker breaks through the ice not by its ramming action but rather by riding up over the ice which is broken down by the weight of the vessel. These vessels have a clipper bow protected by a heavy ram. They are headed in at a good speed and the ram rides up over the ice which breaks down underneath. The vessel does not come to an abrupt stop but slows down gradually. It is then backed out and the operation repeated until the channel is clear. The ice breaker has twin screws which are well housed in for protection against the heavy ice cakes. The rudder is especially large.
Captain Dismukes stated that “The paths cut through the ice would be almost immediately closed up, thus increasing the thickness due to the piling up of the displaced ice.” Ice that is broken up by a heavy wind and packed in against the shore line does become much thicker when it freezes solid. In channels that are to be kept open for navigation this tendency is overcome by running an ice breaker through the channel once or twice each day. In the intervals between trips of the ice breaker, the broken ice tends to freeze together to a certain extent, but before it becomes very solid it is again broken up. Any current or wind will delay its freezing.
The statement, “In breaking through thick ice, the ship's bow pays off exactly in the direction of the crack,” is well established. The direction of the crack depends upon two factors: namely, the resistance offered by the ice itself, and the direction in which the disrupting force is applied. The former depends upon the thickness, structure and age of the ice. It is obviously not within the capacity of the ship to influence this factor. The second is to a very great extent within the control of the vessel. If a ship is in fairly open water it may be steered in such a direction as to cause the bow to ram the ice at any desired angle. If the vessel is restricted to a lane of open water (as is usually the case) the rudder may be used to influence the crack. Just before the bow brings up, if the rudder is put over toward the side to which it is desired to have the crack tend, the ship’s side will exert a great force on the ice to the other side. This will result in compressing the ice off that bow and, other things being equal, the crack will tend off the other bow. This same result could be obtained by varying the revolution of the main engines. Captain Dismukes states, “If it was desired to make headway to the left it was often advantageous to put the rudder hard right and and back full speed starboard engine, thus throwing her bow violently to the right, then on the rebound to drive full speed ahead on starboard engine with rudder hard left.” This agrees well as to the method and result but it is believed that the determining factor is the force of compression rather than the rebound. Cracks tend to develop in ice fields probably due to the rise and fall of the tide and the surge of the sea. In narrow waters they are usually parallel to the channel so it is of advantage to follow them.
The statement, “we encountered some very thin ice and for part of this channel there was actually open water” is of considerable interest. Owing to current, tide and, perhaps, wind conditions, vessels are able actually to moor to heavy shore ice thick enough to discharge their cargo over, while the ice on the off-shore side would be thin enough to permit shore boats landing alongside. Men have been drowned by falling through a hole in ice which is elsewhere several feet thick.
The statement that "Only once . . . was it necessary to ... get a line to pull her stern around” applies to a twin screw vessel. A single screw vessel, owing to her tendency to back to port, cannot back out of an ice field without assistance. Even with the assistance of a tug it is dangerous to back through broken ice as the floes have a tendency to be drawn into and damage the propellor.
When lying in the ice field it is usually preferable to moor to the ice rather than to anchor. In fact, it may be impossible to gel the anchor through the ice which would necessitate anchoring with the anchor above the ice. The ice has a certain amount of movement and as the vessel moves with it, an anchor would only hamper her movements. Mooring lines secured to holes in the ice will freeze to the ice throughout their length and hold the ship safely in the position desired. In harbors that are kept open by means of ice breakers the shore ice is usually not broken and as a result it becomes very thick. Vessels that drag their anchors will bring up against this heavy shore ice instead of going aground. The extent of the ice field itself is an insurance against grounding, providing the ice holds together. Should a storm come up it is necessary to anchor, as the ice will be broken up and driven to the lee shore to form a heavy ice pack.