Figure 39. Hummocks. 



thicknesses, and with cold air temperatures are almost impassible (or even completely impassible) 

 to even the most powerful icebreakers. Cases are known when icebreakers breaking through 

 smorozi, made less progress on the second blow than on the first. On the other hand, with the be- 

 ginning of melting or during strong warm spells, the smorozi disintegrates easily into their com- 

 ponent parts and are the first to disappear. 



Ice frequency, computed in points on a ten-point scale, is of the highest practical importance 

 in navigation. "Ice of five points" means that in a given area of the sea, 50 per cent of its area is 

 covered by ice and 50 per cent is free. The following is a rougher classification of the ice accord- 

 ing to its frequency: 



"Rare ice" (1 to 3 points) — navigation in such ice is possible for all ships and almost without 

 loss of speed. 



Ill 



