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angle to starboard of the course, and so on, alternating the direction 

 of the blows. Breaking the ice in this way leaves the greater part of 

 the icebreaker free, since only the stem hits the ice. The hull from 

 amidships to the stern is in clear water, thus preventing it from being 

 wedged in. If a double channel is too narrow, a triple one is made. 

 The same method, though a bit more complicated, is used. 



One blow is made to port, but at a greater angle than for a double 

 channel. The second blow to starboard is also at a greater angle. 

 The third blow is directed against the tongue of ice which protrudes 

 in the middle. In this way the triple channel is broken. The time 

 taken to break a channel in young ice about 4 feet thick is considerable, 

 and it has required 40 working hours, on occasion, to break a 7-mile 

 channel in such ice. 



While navigating in heavy ice, there is danger of damaging not only 

 the escorted vessels but the icebreakers as well, though they are well 

 equipped for fighting ice. In the forward part of the ship the most 

 vulnerable place is the curved plating of the bow. This may be 

 damaged by striking the ice if the blow is not taken on the stem. 

 The draft of the vessel is also of great importance, since the plating 

 at the water line is usually strongest. Vessels should therefore be 

 so loaded and trimmed that only this strongest plating will be in 

 contact with the ice. In the after part it is the propeller that is 

 exposed to danger. In fact, while in ice it is the most vulnerable 

 part of the ship. It is often assumed that blades are damaged only 

 when a vessel is going astern. This, however, is not always true. 

 The blades can be damaged or lost while going ahead as well. Some- 

 times large blocks of ice pass under the ship's hull and turn on edge. 

 Such ice is very dangerous and may damage the propeller. If the 

 captain or watch officer observes a heavy block of ice on edge, close 





Figure 23. — Modified herringbone method of breaking a wide lane. 



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