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be outflanked. This type of ice is sometimes covered with pools of 

 clear water formed durinnf the thaw of snow on the surface of the 

 ice. There are also oval holes caused by the water trickling clown the 

 ice after the snow has thawed. If there is a considerable number of 

 these holes on a field of greenish-blue ice. the field will be weakened 

 and the ice can be forced. It will not be necessary to break the entire 

 field, but only the portions separating the holes. The condition as 

 well as the color of the ice must be considered, and an occasional test 

 at slow speed by the icebreaker is well worth^^iiile. If sections of 

 dirty looking ice occur in areas of light colored ice, the former should 

 provide the easier route, since the darker object absorbs more sun 

 and melts sooner. Even heavy blocks of dark ice are found to be 

 spongy inside and much less compact than the surrounding ice. On 

 impact by the icebreaker's bow, such ice will crack in spite of its 

 thickness. 



The most passable ice is considered to be brash, even though it is 

 completely devoid of leads. Although this ice usually closes up as a 

 result of action of tides and winds, it consists of separate cakes and 

 therefore does not present a serious obstacle for the passage of the ice- 

 breaker or the conducted ships. When the pressure is great, however, 

 even though an icebreaker can get through, the ships astern are 

 usually hindered as the c'hannel behind the icebreaker closes up im- 

 mediately. It must be remembered that in brash, even during pres- 

 sure, ships are in less danger than if they were being pressed by larger 

 and heavier forms of ice. 



When many hummocks are encountered, the icebreaker must first 

 attempt to outflank them. The outward characteristics of the hum- 

 mocky ice indicate to what extent it is navigable. If the hummocks 

 consist of loose blocks not fused together into one solid piece, they 

 are easily destroyed ; but if they are composed of larger masses of ice 

 many feet thick, they are impassable even to an icebreaker. 



For ice navigation the axiom that "the straight line is the shortest 

 distance between two points"' is not necessarily true. Ships must often 

 be taken along tracks unrelated to their general course ; for example, 

 a section of difficult or impassable ice may be dead ahead, while at the 

 same time ice and synoptic charts, plus the information of the ice 

 reconnaissance, show that better conditions are found either to port or 

 starboard of the course. It is clear that in such a case it is necessary 

 to deviate until the section of easier ice is reached, and then afterwards 

 return to the original course. Sometimes, cracks and narrow leads 

 at right angles to the course of the convoy are encountered. If the 

 ice belts between the leads are very heavy and wide, it is better to 



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