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the minimum between ships when navigating in ice with less than 70 

 percent coverage. At the same time, it should be fully appreciated 

 that if this distance is increased the speed of advance of the whole 

 convoy is reduced. 



The channel made by the icebreaker quickly fills with broken pieces 

 of ice. The pressure exerted by this ice on a ship in a narrow channel 

 naturally increases when the distance between ships is increased, and 

 even powerful ships find their speed gi-eatly reduced. This is another 

 argument for maintaining the minimum prescribed distance apart. A 

 sharp lookout must be kept for signals from the leading icebreaker 

 and these must be executed promptly and correctly. The ships ahead 

 and astern, as well as the condition of the ice, must be carefully 

 watched. 



When navigating in thicker ice, the distances suggested above nuist 

 be decreased. In order to avoid damage from the ice floating in the 

 channel, the engines must work slowly and the ship must carry little 

 headway. If the ice is completely unbroken and under considerable 

 pressure, the distance must be reduced to a few yards. Under these 

 conditions the channel will be quickly covered with ice, leaving only 

 a small lead astern of the icebreaker, narrower than the beam of the 

 vessel. If a ship should follow at a distance of 2 to 3 ship lengths 



Figure 21. — Wake left by U. S. C. G. C. Northw'md offer making her way through the ice. 

 Note consistency of the ice left in the channel and the tendency for the channel to fill up after 



passage of the icebreaker. 



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