RESTRICTED 

 CONDUCTING THROUGH ICE 



In following the icebreaker, a convoy must keep dead astern 

 of her. If the icebreaker alters course, all ships must turn in suc- 

 cession to the new course. By looking for independent channels, the 

 ships break up the convoy and may get stuck. Thus, the icebreaker 

 is compelled to return and break out each ship separately, thereby 

 delaying the whole convoy. 



Since passage through floes and ice fields is more difficult, the ice- 

 breaker increases her speed, and by striking the ice, crushes or breaks 

 it ahead of her. The ships astern must then watch their distances 

 carefully and try to enter the channel made by the icebreaker before 

 it closes again. 



If the icebreaker should encounter a solid ice obstacle where a 

 glancing blow is struck by the stem, she will be thrown backwards 

 and sideways in the direction of least resistance. The ships follow- 

 ing close astern will be unable to make a quick enough turn and may 

 receive damage through striking the heavy ice. This is particularly 

 true of single-screw ships. This sudden change of direction or zig- 

 zagging must be expected when proceeding through ice of varying 

 structures and strength. Under such circumstances, the icebreaker 

 should not make too rapid a return to the original course and should 

 avoid aggravating the zigzag. 



Young ice is often covered with snow and, at first, all young ice 

 seems exactly the same. However, an experienced eye can sometimes 

 detect obstacles such as snowdrifts which probably indicate the pres- 

 ence of concealed hummocks. Such ice will be more difficult to over- 

 come, not only for the icebreaker, but for the entire convoy. Though 

 the ice is seemingly even, the route must be chosen so as to avoid 

 this hummocky ice. The absence of hummocks and unevenness, in 

 general, is the only sign of passable ice in winter. 



When it is necessary to pass through ranges of hummocky ice which 

 cannot be outflanked, the hummocks must be crushed in a direction 

 at right angles to their crests. If, however, the hummocks have cracks 

 at an angle to the general line of the crests, the cracks should be fol- 

 lowed. It is much easier to maintain the course in close pack consist- 

 ing of small blocks than in a floe or ice field. 



In summer there are many signs indicating the passability of the 

 ice. Observe whether the ice has been softened by the sun, or if it 

 still retains its winter hardness, and the number of hummocks en 

 route. Experienced icebreaker captains and ice pilots consider that 

 greenish or greenish-blue ice is the hardest to crush. Such ice should 



RESTRICTED 93 



