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aboard one side of the ship, he should immediately take precautionary 

 measures. 



Explosives are used as an auxiliary means for getting the ice 

 breaker through difficult obstacles. The heretofore accepted opinion 

 that channels of various lengths could be made by using explosives 

 has been proved to be impractical. Nevertheless, an ample supply 

 of dynamite or demolition mines should always be carried by the ice- 

 breaker to destroy ice belts separating one lead from another which 

 cannot otherwise be forced by the icebreaker. Before a charge is 

 placed, the ice must be examined for a spot which would offer the 

 least resistance. The explosion creates cracks in the main part of 

 the ice belt and weakens the ice sufficiently to facilitate breaking by 

 the icebreaker. 



"WHien forcing heavy fields, the icebreaker sometimes encounters 

 pressure ridges stretching a great distance. Explosives can also be 

 of help in such cases. The ridge must be examined before placing 

 the charge so that the maximum effect is obtained from the explosion. 

 From the experience of the icebreaker Kra^ssin, the best location for 

 placing explosives is abeam of the forward stack of the icebreaker 

 at a distance dependent on the weight of the charge. The charge 

 is placed in a deep hole almost at the lower edge of the ice. At 

 the time of the explosion the icebreaker shoidd be going full astern 

 on both engines. The concussion of the explosion plus the work of 

 the engines free the icebreaker and enable her to run astern. Even 

 if cracks fail to appear, the ice between the hummocks will never- 

 theless be weakened. Mines are usually used to liberate the vessel 

 when beset or to provide swinging room. To follow up the advantage 

 after the explosion, the icebreaker must immediately go forward into 

 the ice. If the ice is motionless, results usually are good. If the 

 ice is under pressure, all the above measures might fail. In such 

 cases it is necessary to wait until the pressure of the ice diminishes 

 and start anew. 



TOWING IN ICE 



\Vhen piloting vessels in close pack of medium thickness, it is some- 

 times necessary to take them in tow on account of ice pressure, engine 

 trouble, or propeller or rudder damage. All icebreakers are pro- 

 vided with necessary towing equipment. The latter consists of a 

 tow winch and towline reeled on the winch drum; the end of the 

 towline is provided with a large strap which is led through a specially 

 constructed block at the stern indentation. The towing drum should 

 be located as far forward as possible in order that the vertical angle 



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