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In working very heavy pack ice, all engines must be available for use 

 as needed. The momentum of the ship, combined with proper ballast- 

 ing and use of engine, is the greatest factor in breaking heavy ice. The 

 full power revolutions for stalled conditions should be determined and 

 the ship should make her approach to the ice at the i)redetermiiied 

 number of turns. As the ship is slowed by the ice, more throttle should 

 be applied to keep the shafts at the stalled condition full-load revolu- 

 tions. This procedure gives the maximum power with the least 

 possible strain on the power plant. There are times when the ship's 

 progress is stopped completely and she must be backed down to take a 

 new start and ram the ice. During this backing, caution must be used 

 to see that the ship does not ram heavy ice that has drifted in astern 

 endangering the screws and rudder. Use only enough power to gain 

 stern way. The Northwind recommended limiting speed astern to 

 70 revolutions per minute to avoid clogging injection faster than the 

 de-icing system can take care of it. 



An icebreaker's progress can be slowed appreciably by relatively low 

 snow-covered hummocks with a snow cover of 24 inches or deeper in 

 drifts. If the temperature is not too low, the snow forms a cushion 

 absorbing a large part of the breaking force so that only a small per- 

 centage is effective in actually breaking ice. Frequently, the fuel 

 consumption for one-half mile in this type of ice can be equal to that in 

 340 miles of open water. 



It is also imperative that the rudder always be in the amidships 

 position while backing down. If it is necessary to force back heavy ice 

 that has drifted in astern, the ship should be eased up to the ice as 

 slowly as possible until contact is made, then power applied and backing 

 continued. This method will allow more of the ice to move along the 

 side of the hull at the water line rather than force it directly under the 

 hull into the screws. One to three ship lengths is usually enough 

 starting room for the next lunge at the ice. 



In instances where backing down for new starts is necessary, the 

 ship sometimes become wedged into the pack so tightly that she is 

 unable to back out even with full power. This is a situation where 

 the heeling system can help keep the ship on its way. On at least 

 three such occasions the Edisto was broken free on the first roll so that 

 she was able to move out. On Operation XANOOK II during the 

 summer of 1949, the Edisto reported, "Ship stuck in heavy solid pack 

 ice. Backing and attempted slewing failed to break her loose. Tried 

 small charge of TNT in ice near bow— no results. Commenced heel- 

 ing. Backed clear of the ice. Tried to get stuck again but with the 



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