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route in open water is generally shorter than the more direct one in 

 ice, and the selected track should pass through areas of thin ice or 

 open water, regardless of the length of the voyage, provided the 

 depths along the route are adequate. Consideration must also be 

 given to the assistance which may be forthcoming from the prevailing 

 wind and current. In some areas, even in heavy ice, such help is pro- 

 nounced. Course changes must be gradual, if practicable, since most 

 cases of ships getting stuck occur when sharp turns are made by the 

 icebreaker. The speed of the convoy must be decided upon by the 

 captain of the leading icebreaker. Speed through the pack varies 

 from 4 to 7 knots. The higher speed is desirable due to the better 

 maneuverability of large ships, but the ice conditions will govern. 



In a convoy composed of vessels reinforced for ice navigation, a 

 speed of 6 to 7 knots can be maintained if the route lies through 

 open pack of about 50 percent coverage with leads of clear water and 

 if the captain of the leading icebreaker is certain that the ships fol- 

 lowing him will not meet with heavy ice. It must be remembered 

 that frequently the ice on the surface thaws under the sun's rays and 

 is washed away, whereas the submerged part lasts much longer, thus 

 forming underwater projections of ice protruding for several yards. 

 Ships following the icebreaker must be aware of the danger of passing 

 close to large floes. If a vessel cannot keep off the ice, it should 

 request the icebreaker to widen the channel. 



Wlien navigating in close pack of 70 to 80 percent ice coverage, 

 speed must not exceed 5 knots. In such ice, the convoy follows the 

 channel, which does not remain open long after the passage of the 

 icebreaker. Therefore, the spacing must be decreased to IV2 to 2 

 ship lengths to enable the ship to move in as clear a channel as 

 possible. Higher speeds not only increase the danger of hitting the 

 ice but also the possibility of colliding during sudden stops of the 

 icebreaker or other ships in the convoy. In the channel itself, danger 

 from underwater ice projections decreases somewhat as these are 

 destroyed by the icebreaker, although this hazard reappears on entry 

 into areas of thin ice. If a single-screw vessel must back down sud- 

 denly "full astern" without warning while passing through an ice- 

 covered channel, the stern will kick to port and the bow to starboard. 

 Such action will probably cause damage to the propeller, rudder, and 

 starboard side of the ship. To avoid collision with the ship ahead, 

 it is preferable to ram the ice to one side of the channel, bow fore- 

 most, rather than to risk damage to the rudder and propeller by 

 backing down on heavy ice. 



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