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With the bow propeller going full ahead, pulling the water out from 

 under the ice ahead, it was seen that the ice would break for a distance 

 of 30 to 40 feet forward of the bow. It appears necessary to keep 

 the bow wheel turning in water in order to get the best results. 

 This practice is not always possible in polar pack ice where it fre- 

 quently becomes necessary to use the ship to break the ice ahead of 

 her in order to make headway. It is generally desirable, even in 

 loose ice, to keep power on the bow screw for protective purposes 

 even though the ship does not gain anything from its use. It has 

 been the practice of the Eastwmd not to hit ice with the bow propeller 

 unless the wheel is actually rotating, in order that the impact of 

 the blow will be taken on the leading edge of the propeller rather 

 than on its face. 



PERFORMANCE 



Reports from the Northtoind^ Edisto^ and Burton Island from opera- 

 tion NANOOK in Greenland waters in 1946, Operation HIGHJUMP 

 in the Antarctic in 1946-47, Task Force 68 in Greenland waters and 

 the Canadian Arctic in 1947, Task Force 39 in the Antarctic in 1947- 

 48, and Arctic winter operations in 1948-49, indicate that the expec- 

 tations of the designers with respect to these ships have been ful- 

 filled. The hulls can withstand impacts against heavy ice at full 

 power. 



Heavily ballasted and using full power on two after-screws, these 

 icebreakers can maintain headway through consolidated pack up to 

 6 feet or more in thickness. At thicknesses of about 8 feet they can 

 penetrate such ice by charging, but there is a tendency for the broken 

 pieces to remain astern in the ship's track. Backing down for a 

 fresh forward run at the ice then becomes somewhat hazardous. The 

 most vulnerable part of the ship is the screws. A simple system of 

 signals is therefore recommended for use between flight deck or dock- 

 ing bridge and navigating bridge in order to avoid swinging the 

 stern into ice with power on the swinging flank. The watch in both 

 motor rooms must be alert for striking of ice by the propellers and, 

 unless general orders to the contrary are received from the bridge, 

 should stop the affected motor. There are times, however, when 

 chances must be taken and the officer on the after-station relied upon 

 to the exclusion of the motor room watch. 



Pack consisting of detached blocks, even if they are large and the 

 water spaces between them small, can be broken at thicknesses of 10 

 to 12 feet. With 35 percent and up of open water, floes as much as 25 

 feet thick can be broken through. Pieces of considerable surface area 



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