244 SUBMARINE CABLE LAYING AND REPAIRING. 



The brake wheel is on the same shaft as the drum, and is 

 about 7ft. in diameter. Outside it (as shown at B W) is the brake 

 strap, consisting of a band or hoop of flat iron with hard-wood 

 blocks screwed on at intervals. The blocks bear on the face of 

 the wheel, and the friction on the same can be regulated by 

 tightening gear, which closes up the band. In the figure the 

 hand-wheel for regulating the brake is shown at D, the motion 

 to this wheel being transmitted to the brake-band by two 

 bevel pinions on the right. The lower half of the brake-wheel 

 revolves in a tank of soap and water, to lubricate the wheel and 

 prevent the wood blocks taking fire. 



As the cable comes in, it is necessary to keep it in a straight 

 line and perfectly taut, or it will not run evenly over the drum. 

 For this purpose it is led over the hauling -off sheave H S before 

 passing into the tank. Running in the groove of this sheave is 

 a smaller wheel, mounted in a bracket keyed to a shaft, as shown, 

 and which is weighted by the counterweight fixed at the end of 

 the bracket. This wheel, called the jockey-wheel, is chamfered 

 off on both sides of the face, so as to fit easily in the groove of 

 the sheave when the cable is passing over it, and its duty is to 

 exert a pulling action on the cable in the direction in which it 

 is moving, and so keep it from slipping back or sagging. In 

 order to effect this properly, the sheave H S is driven a little 

 faster than the drum, so as to draw the cable off the drum and 

 keep it taut. That is, the circumferential speed is a little 

 greater than that of the drum. For example, if the drum was 

 18ft. in circumference, and ran at 10 revolutions per minute, 

 the cable would leave the drum at a speed of 180ft. per minute, 

 and the sheave would have to take charge of it and pull it in 

 at a little faster speed to keep it taut, say at 185ft, per minute. 

 Hence, if the sheave had a circumference in the groove of 5ft., 

 it would have to be geared to run at 37 revolutions per minute, 

 or nearly four times the speed of the drum. Of course, the 

 sheave slips past the cable a little, due to the slight excess of 

 speed, but by this means, together with the weight of the 

 jockey-wheel riding on it, the cable is kept perfectly taut. The 

 hauling-off sheave is always run by gearing off the drum shaft, 

 not the engine shaft, as thereby the ratio of speed between the 

 drum and sheave is maintained the same, irrespective of the 

 intermediate gear between the engine and drum. This will be 



