REFUELING WARSHIPS AT SEA. 173 



of the marine cableway, was employed simply because the automatic tension engine 

 had not been invented. The sea anchor, as a device for maintaining the tension in 

 the main trackway cable of a cableway, was condemned by every U. S. Trial Board 

 at every test employing it. It was adhered to by the author because its first cost was 

 low and its weight and bulk very slight. It required too much skill and practice to 

 launch it before coaling at sea and to recover it after the operation was over. It 

 could only be used with colliers in tow of warships. 



When the U. S. Navy Department refused to give the sea anchor any further 

 consideration, the automatic tension engine was invented, designed and constructed 

 to take its place. 



The first main cable tension engine built, Fig. 12, Plate 66, was installed on the 

 British collier Muriel. It contained a huge slipping drum. During the coaling 

 operations the engine ran continuously, the drum floating backward and forward 

 under the influence of the slipping friction. The heat developed and the wear of 

 the slipping elements was terrific. The operation was successful but the machine 

 impracticable for general adoption. The British Admiralty refused to adopt it. 

 The author had nothing at the time to offer as a substitute. This machine, however, 

 had the virtue of being a self-contained unit. 



THE AUTOMATIC TENSION ENGINE A NEW MARINE IMPLEMENT. 



The automatic tension engine is a self-contained unit. It has two steam cylin- 

 ders driving a common crank-shaft. A pinion on the crank-shaft drives a gear 

 firmly keyed to the drum-shaft. The drum mounted on the drum-shaft is connected 

 to it by huge coil springs, allowing a limited rotation of the drum on the shaft. 

 Changes in tension in the rope cause the drum to rotate slightly on its shaft. This 

 motion of the drum on its shaft is transmitted to controlling valves and raises and 

 lowers the steam pressure as required. 



This spring drum construction, therefore, is a feeler or detecter of tension 

 changes. The steam for operating the engine is introduced into the cylinders 

 through a novel form of controlling valve. This valve regulates the amount and 

 pressure of the steam supplied to the cylinders. Suitable lever connections between 

 the drum and this valve couple these two elements together in such a way that the 

 steam supplied to the cylinders bears a definite relation to the tension in the rope. 



Fig. II, Plate 65, shows a cross-section of the spring drum of a small automatic 

 tension engine, indicating the threaded hub and running nut together with the con- 

 trol lever and its connection to the pressure controller valve. 



A slight increase in the tension of the cable produces a reduction of the steam 

 pressure, permitting the rope to overhaul the engine and restore the tension to nor- 

 mal. A reduction of tension produces an increase of steam pressure, again caus- 

 ing the engine to act as a take-up to restore the tension to normal. The tension 

 developed by this engine in pulling in is slightly less than the resistance set up in 

 the cable to overhauling, but for all practical purposes the tension is uniform and 

 constant. 



