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coat of ice becomes an obstacle to further freezing of the water and 

 serves as an insulator between water and air. The temperature of the 

 air is below freezing, while the temperature of the water under the 

 ice is above freezing. This equilibrium may be upset by reducing 

 the thickness of the ice cover, i. e.. by removing a layer of ice. The 

 thinner ice layer will allow the water adjacent to its lower surface 

 to freeze, bringing the layer back approximately to its original 

 thickness. 



Work on setting up the ice dock started in autumn, before the sea 

 became covered with ice. The vessel was placed with its axis along 

 the direction of predominating winter winds so that it would not 

 become surrounded by large snowdrifts. The surface of ice surround- 

 ing the ship must be as thermoconductive as possible and must be 

 cleared of everything that may delay freezing, such as snow, rubbish, 

 wood chips, etc. When the ship had frozen into the ice, the dock was 

 mapped out on the surface of the ice. The workmen then began 

 digging under the ship, grooving out recesses at a great depth. 



The ice dock has a number of sections separated by ice buttress- 

 partitions, from between which the ice is removed. This arrangement 

 allows the weight of the ship to be equally transmitted through the 

 ice onto the water. Should the water break through a thin layer of ice, 

 which may happen if too thick a layer is inadvertently removed, only 

 one section would be flooded, which is but a small part of the entire 

 dock. A dock may be set up for the entire ship or only part of it. 



As the size of the ice pit is larger than the vessel, the pressure on 

 the walls of the ice dock will not be fully balanced and will be consid- 

 erably more than the weiglit of tlie ship. The ice will bend out some- 



Figure 28. — After the ice has been removed from (A), a new layer of ice (B) forms below 

 the ice layer, constituting the bottom of the future ice dock. 



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