LAUNCHING OF SHIPS IN RESTRICTED WATERS. 205 



suited to obtain the desired frictional resistance. These two questions were solved 

 by numerous experiments, and actual trials on vessels launched. 



As to the coefficient of friction, the figure given by Hiley in the article pre- 

 viously mentioned is 0.08. All available information in handbooks and experiments 

 on a small scale indicated, however, that the coefficient of friction was much higher 

 than this, presumably about 0.2. To check this figure and to test the apparatus, the 

 hydraulic brake developed for the California was mounted on a temporary stand 

 and run with full pressure, using one friction wire in one of the grooves. The co- 

 efficient of friction deduced from these experiments is about 0.24, and the results 

 obtained indicate that this value remains practically constant for all loads and all 

 speeds of the wire rope. 



As to the type of wire rope to be used, it was obvious that the wire strands 

 on the outside of the rope would have to lie exactly parallel to the axis of the rope 

 in order to prevent "rifling." It was evident, after the first experiments, that the 

 wire would score the grooves in the cast-steel blocks, but so long as the scores re- 

 mained parallel to the blocks, the action of the frictional pull on the wire ropes was 

 entirely satisfactory, causing no unlaying or tightening up of the strands. There 

 was some question as to whether a solid rope was necessary or whether a rope with 

 hemp core would not be more suitable. The latter rope, being more elastic, is less 

 likely to seize in the grooves, and for this reason has been used in all the launch- 

 ing operations with this. brake. There had also to be considered the possibility of 

 one or more strands breaking inside the brake and causing a jam. In this event the 

 wire rope would likely be broken or the chain pendant to the ship carried away. 

 During the several launchings, the outside wires in the strands have been perceptibly 

 flattened by abrasion, but in no case has any strand parted or any wire rope jammed. 

 In this connection it is interesting to note that the same wire ropes were used as fric- 

 tion ropes in the launching of three large ships, and now are in condition for use 

 with at least as many more. From the experience gained at the Mare Island Yard 

 the most satisfactory type of wire rope is 2-inch diameter, black, plow steel, 6 

 strand, -^y wires each, one hemp center, ordinary lay and 137 tons breaking strength. 

 Particular care was required under the specifications for the rope to have the indi- 

 vidual wires in each strand laid parallel to the axis of the rope at the point of fric- 

 tional contact. 



In connection with the launching of the battleship California the number of 

 brakes necessary was determined from the data and experience in the use of the 

 brakes used in launching the Kanawha, Maumee and Cuyama. In these latter 

 cases two brakes were used with satisfactory results. Therefore, by comparison 

 of the relative launching weights and velocities, the number of brakes required for 

 the California was ten. 



It was also considered necessary to have more definite control over the pres- 

 sure to be applied to the friction blocks, and the screw, nut and bull wheel scheme 

 was abandoned for hydraulic cylinders and pistons, as shown in photographs and 

 plans. The experiments conducted showed that two pressure cylinders were suffi- 

 cient in lieu of three. 



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