The Mechanical Handling and Storing of Material

336 THE MECHANICAL HANDLING OF MATERIAL spite of these difficulties, however, more coal was transferred than ever before, and justified the opinion, freely expressed by naval observers who witnessed the test, that the cableway was capable of a delivery of 100 tons per hour. It was also observed that the best record was in the last hour of the test, which showed that the mtichine did not have a fatiguing effect upon the men. An important feature is the automatic tension engine, designed and constructed to meet the demands of the Navy Department. This engine, in connection with the marine cableway, has supplanted the sea anchor. It maintains the supporting cable at the requisite tension and deflection independently of the speed of the ships. After the cableway is set up and the engine adjusted for the required tension it needs no further attention, other than oiling, throughout coaling operations. The automatic tension engine is a single drum horizontal engine, having 10-in. by 10 in. cylinders, and capable of maintaining a strain of approximately 3,000 lb. The drum is '20 in. in diameter by 23 in. face, and connected to its shaft through the medium of springs allowing a limited rotation of the drum on the shaft. Changes of tension in the rope cause this drum to rotate to a limited extent. This motion of the drum operates through the medium of a nut, screw, or lever; a controlling valve regulates the amount and pressure of the steam supplied to the cylinders. These changes in tension in the rope are communicated to the steam supplied to the cylinders in such a way that the rope will be paid out or taken up as demanded. That is to say, an increase in tension causes a reduction of steam pressure, permitting the rope to overhaul the engine and restore the tension to normal, while a reduction of tension causes an increase of steam pressure, thereby causing the engine to take up slack and thus restore the tension. The conveying ropes for moving the load along the main cable are operated by two automatic tension engines of smaller power than those for the main cable. 'These are high speed engines, having the spring drum mounted directly on the crankshaft. One of these engines operates the in-haul rope, the other the out-haul rope, pulling in opposition to each other; the automatic control compensates for the lengthening and shortening of the conveying lines as in the main cable tension engine. In addition to the automatic •control, the controlling valves can be manually operated. The manual operating gear of the two engines is interconnected and controlled by a single lever. When this lever stands vertical (mid-position) both engines have the same inpulling power, so that the load remains stationary on the cable. When this lever is moved in the direction in which the load is to travel the inpulling power of the engine controlling motion in said direction is increased, while the inpulling power of the other engine is decreased. In other words, one engine overhauls the other when the load is in transit. In the test which took place on 12th April the tension of this engine was 17,000 to 18,000 lb., and never showed the slightest disposition to slacken nor unduly tauten the main cable. Oil Fuel Bunkering’ at Sea-—The automatic tension engine is the essential element in the marine cableway; it can also be used for supporting an oil hose between two ships when fuel bunkering at sea. The desirability, in a heavy sea, of this automatic tension engine to maintain a uniform tension in the supporting line from which the hose is suspended at frequent intervals will be readily appreciated.