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arrangement in having a watch on each wing of the bridge with author- 

 ity to take action when a propeller is in clanger. If signaling is neces- 

 sary, ice-breaking vessels, because of their relatively short length and 

 broad beam, lend themselves to a simple system of visual signals, sucli 

 as hand motion or flashlight, whereas telephone communication may 

 introduce an element of lag. 



Go astern in ice only with extreme care ; put the rudder amidships, 

 and keep a sharp lookout for ice under the quarter. Again, a twin- 

 screw vessel is at a particular disadvantage when backing in ice, owing 

 to the great likelihood of pieces of ice being sucked in toward the ship 

 and jamming between the propellers and the side. One system for 

 working astern when breaking ice which has been found expeditious 

 is to: 



( 1 ) Allow the screw to wash the ice astern for a few minutes before 

 backing, 



(2) Back full until just before contact with debris, then 



(3) Stop and allow momentum to carry the vessel well into the 

 debris. 



(4) When all ice has surfaced, give a kick ahead and stop. 



(5) Back full again, repeating the process until the ice canal is of 

 sufficient length to ram it full speed on the next lunge. 



The line of a crack or lead in an ice field is usually normal to the 

 direction of the movement of the field. A new crack will thus form 

 according to the direction of the wind and current, and either widen out 

 into a lane or form a new hummock. A field of ice does not necessarily 

 crack in its thinnest part ; frequently cracks are found passing through 

 hummocks, leaving thin, half-melted ice holding it together. How- 

 ever, in many cases this half-melted ice is completely destroyed when 

 the wind changes. 



When a crack in a floe is but partly made, it is sometimes possible 

 for a ship, by ramming her way into it, to complete the crack and widen 

 it into a lane. A vessel may also force her way through an ice field 

 of young ice, or through a bridge connecting two floes, if the bridge is 

 not too thick and heavy. Great care should be taken in such opera- 

 tions, for old and heavy pieces of ice can withstand the impact of the 

 most powerful vessel ; even fairly stout ships can then suffer damage, 

 but vessels that have been specially constructed for use in ice are usu- 

 ally so strong that their engines cannot force them against the ice with 

 sufficient force to injure them by a head-on impact. Ships so con- 

 structed can charge the ice again and again, backing away for each 

 charge. Under such conditions, when it is a matter of seconds from 



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