THE LAYING OF SUBMARINE CABLES. 137 



than could be obtained by removing weights, which would only 

 have to be put on again immediately afterwards. 



While cable is running out a considerable amount of power 

 is absorbed by the brakes producing heat on the surfa'-es 

 of the brake wheels and blocks. This spreads to the other 

 portions of the wheels, the bearings and the cable drum, 

 and it is necessary to keep a constant stream of water 

 playing over the brakes and drum to keep the machinery 

 and cable cool. The power absorbed may vary from 50 h.p. 

 to 100 H.P., according to the type of cable, depth, speed 

 of ship and percentage slack. The strain on the cable 

 is of course less while paying out than if the ship was 

 standing with a length of cable equal to the depth hanging to 

 her, and for constant slack the strain is reduced in only a very 

 slight degree as the speed of paying out is increased, but the 

 power absorbed by the brakes is considerably increased under 

 those conditions owing to the greater speed of the drum and 

 brake wheels?. It is not advisable to run the brake much above 

 100 H.p. for temperature reasons, and on this account the speed 

 is not increased beyond about six or seven knots in say 2,000 

 fathoms. It must also be remembered that the greater the 

 speed of laying the more the angle of descent of the cable 

 approaches the horizontal and when sinking in this way the 

 cable cannot accommodate itself properly to the irregularities 

 of the bottom. It is advisable to pay out at a reduced speed — 

 about four knots — when in the neighbourhood of submarine 

 banks, so that the cable may properly sink into the profile at 

 bottom. 



For example, say a cable weighing 22cwt. per 1,000 fathoms 

 (in water) is being laid at 5 per cent, slack in 2,000 fathoms, 

 the cable leaving the ship at the rate of say six knots. The 

 strain on the cable will be about 42 cwt. and the power on the 

 brake about 85 h.p. If now the speed of the ship is increased 

 so that the cable runs out at 7 knots without altering the 

 percentage slack, the brakes will take up about 115 h.p., while 

 the retarding strain remains practically the same. But if 

 it is advantageous to increase the slack in this depth say 

 to 9 per cent., the cable can be payed out at the higher 

 speed with a strain of about 35 cwt. and only about 85 h.p. 

 on the brakes. 



