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going ahead to going astern, it is recommended not to stop the engines, 

 but to reverse directly from ahead to astern. Care should be taken, 

 however, to prevent undue torsional stresses being set up in the shaft- 

 ing which, owing to the low temperature, will have lost part of its 

 safety factor. 



A vessel may attempt to force a way through ice, but only in the 

 absence of pressure from the ice due to the influence of winds or cur- 

 rents. Always avoid pressure ridges of any type. Such ridges are 

 formed on a line roughly perpendicular to the direction of movement 

 of the ice. Cracks may be formed in ice fields along the line of 

 pressure, likewise perpendicular to the movement of the ice. Such a 

 crack is usually covered with thin ridged ice from 1 to 3 feet thick. 

 On the least change of wind the heavy masses may come together 

 again, entirely crushing and grinding the thin ice between. A vessel 

 should, therefore, in no circumstances proceed along through a pres- 

 sure ridge. Other cracks often occur, cutting right through pressure 

 ridges, which may be as much as 30 feet thick; these cracks are simi- 

 larly covered with thin ice. Such a crack should not be entered, unless 

 it is obvious that it will take the vessel quickly out of the whole area 

 affected by pressure. The signs of the proximity of ice and open 

 water given on page 107 must be looked for and used. For example, 

 in a vessel in pack ice, signs of distant areas of open water might be 

 discernible by reflection from the clouds ; course should therefore be 

 set in that direction, if possible. 



Fine weather in the pack usually portends lowered temperatures, 

 close pack, and little open water. Damp misty weather in the pack 

 generally signifies the presence of a considerable amount of' open 

 water with the ice and better conditions for maneuvering, in spite of 

 the poor visibility. The existence of swell or the presence of skua 

 gulls and petrels are signs of more open pack near, with open water 

 not far distant. Blowing whales usually travel in the direction of 

 open water. 



Weather and sea conditions in the pack are variable. Brilliant sun- 

 shine, cloudless skies, and light air may alternate with periods of gales, 

 heavy swell, and grinding floes, when vision is obscured by driving 

 wind and blinding snow squalls. Periods of calm may follow, bring- 

 ing fog and fine mist which form a sheath of frozen rime over the 

 running gear of the ship. Heavy clouds and overcast skies may pro- 

 duce a milky atmosphere in which shadows are nonexistent and dis- 

 tances become very deceptive. 



Ice in the sea, other than fast ice, is in continual movement under 

 the influence of wind or current, causing the various pieces or masses 



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