Question: Summarize "coaling ships at sea of conveyors".
In the coaling of ships at sea the cableway has rendered great service. The conditions under which this operation has to be carried out present many difficulties, especially in rough water. One of the chief obstacles is the maintenance of the necessary tension on the cable used in conveying the coal from the collier to the ship. The first test in coaling ships at sea, made by the British admiralty, took place in 1890 in the Atlantic at a point 500 m. south of the Azores in water 2000 fathoms deep. Ten ships of war were coaled, each vessel taking enough coal to enable it to steam back to Torbay, 1800 m. away. In this case the collier was lashed alongside the battleship it was feeding, thick fenders being interposed to prevent damage, but nevertheless as the colliers got light they pitched considerably, and one or two sustained dents in their sides. The ships did not roll, being kept bows-on to the swell, which became heavy before the coaling was completed. The coal was taken in by derricks at the main deck ports. It is clear that had the sea been really rough coaling in this fashion would have been impossible.
The most practicable method of coaling at sea yet devised is the marine cableway of Spencer Miller, which has been tried with some success in the American navy. It is intended for use between vessels 350 to 500 ft. apart. The ship being coaled takes the collier in tow, steaming at the rate of 4 to 8 knots; it has been found that a speed of five knots in moderately rough water will keep the cableway taut and maintain a sufficient distance between the crafts. The collier is fitted with an engine having double cylinders and double friction drums, which is placed just abaft the foremast. A steel rope ¾ in. in diameter is led from one drum over a pulley at the mast head and thence to a pulley at the head of shear-poles on the vessel being coaled, and brought back to the other drum. The engine moves in the same direction all the time and keeps on winding in both the strands of the conveying rope. Should the two vessels increase the distance between them during the operation of conveying the coal bags, of which two, weighing 420 lb each, may be fastened to the carrier, the extra rope called for is obtained by slipping the upper strand from the drum; this increases the speed of the upper cable. On the other hand should the distance between the vessels be reduced, this operation is reversed, the speed of the upper strand being reduced. To keep the carriage steady on its return empty, a rope, known as the sea-anchor line, is stretched above the two strands of the conveyor line, and under a pulley on the carriage. This cable is attached to the vessel, resting on a saddle on the shear head, whence it leads through the carriage over pulleys at the head of the foremast and mainmast of the collier, running on astern several hundred feet into the sea. A drag or sea-anchor, usually made of canvas and cone-shaped, is attached to the end of this rope. This anchor is used to support the empty carriage on its return to the collier. The diameter of the cone's base is graduated to the speed of the vessels. Thus in a smooth-water test, with a ship steaming at 6 knots, one 7 ft. in diameter was used, while the same anchor answered its purpose very well with a ship doing 5 knots in rough water.
The results given by this system of coaling at sea are relatively satisfactory. Tests made in the United States navy showed that 20 to 25 tons of coal per hour could be delivered by a collier to a war-vessel during a moderate gale. As the ship was under steam all the time and consumed 3 to 4 tons of coal per hour, the balance of the coal bunkered amounted to between 16 and 20 tons per hour, or say 384 tons in 24 hours. It has been suggested that under service conditions the speed of the towing vessel might be increased to 8 or 10 knots an hour; this would of course increase the coal consumption unless the collier proceeded under her own steam. But in such a case the space between the two crafts might be diminished, which would have the effect of causing the cable to sag and of stopping the work, since the conveyor cable to act properly must be kept taut. In Great Britain the Temperley Transporter Company have taken up this method of coaling at sea, working in collaboration with Spencer Miller, and have introduced several improvements in detail. Their system has been tried by the British admiralty.
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