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In close pack, the second method is employed when the first is not 

 fully effective. In this operation the vessel is used as a lever to force 

 a path between the floes. Upon gaining entrance of the stem of the 

 ship by ramming, the bow is brought up against that floe which is to 

 be forced to leeward or in such direction that space is made available 

 for the vessel's movement. The engines are then placed on full speed, 

 and with full rudder the vessel is pivoted with the bow hard against 

 the floe. The ship then acts as a fulcrum and etfectively overcomes 

 the inertia of the floe in contact which slowly picks up motion in the 

 direction impelled. Sallying is often helpful in working a small vessel 

 through narrow leads. Vessels should always be kept clear of corners 

 and projecting points of ice masses as such points become the foci of 

 pressure. In working the pack by slewing, skillful use must be made 

 of the rudder to prevent the stern from swinging into the ice. 



Polar pack ice, if it exists in close pack of over eight-tenths coverage 

 with small leads only, should be avoided. To traverse it when the 

 coverage is seven-tenths or below, the second method above, which 

 has been employed to break the field ice in Melville Sound, may be 

 used. Thus, the tendency would be to keep small chunks from breaking 

 off the i^ack and upending and decrease the danger to the propellers. 

 The ice would tend to move away in a horizontal direction. 



SPEED OF ADVANCE 



Successful ice navigation is basically a matter of speed through the 

 ice. Pack ice, unless very open, must be entered at the lowest possible 

 speed, which should be increased only after observing the state of the 

 ice and the extent to which it is possible to pass through it. The 

 possible speed through ice is determined primarily by two factors, 

 the amount of surface covered, and the possible force of impact with 

 the ice without damage to the ship. Wlien possible, maintain way 

 on the ship at 2 to 5 knots so as to have some control of the rudder. 

 Coasting into the ice with engines stopped results in the loss of efl'ective 

 rudder control. 



Ships must be prepared to back down emergency full at all times. 

 When a "stop bell" is rung up, the propeller must be stopped, by back- 

 ing steam if necessary. 



When ice does not cover more than six-tenths of the sea surface, 

 the speed of a vessel passing through it without an icebreaker will 

 depend on the distribution of leads and polynyas. If the distribution 

 is suitable for navigation, the speed may even be increased to full 



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