SALVAGING. Salvage work, or the raising and recovery of sunken ships and cargoes, has always had a fascination ; first, for the reason that very little is known of the subject by the outside public ; and secondly, because the spirit of adventure appeals to us still, although possibly in a modified degree corn pared with that which sent our forefathers out to search for hid den treasures in far-off lands.
Salvage engineering has always been confined to a small num ber of the engineering profession, although it is a highly technical business, where skill, experience and determination are pitted against wind and sea. It necessitates trained men and special appliances and is a work that must be carried on night and day whenever the elements permit.
Marine salvage may be divided up under a few principal headings : ( i) The raising of vessels sunk in deep water by means of pontoons, etc.
(2) Raising by the application of compressed air to expel the water.
(3) Refloating of ships stranded on rocks or sand where the bottom is damaged and temporary repairs have to be made by divers, and where pumping plant of different descriptions is used to free the vessel of water.
(4) Uprighting of capsized vessels, etc.
As an example, one of the most modern type is composite built ( 7of t. long by Soft. wide), fitted with triple expansion engines, and has a speed of 14 knots. She accommodates about 8o officers and men, consisting of engineers, artisans, divers, motor engineers, electrical engineers and others. Her equipment consists of portable pumping plant of 5,000 tons per hour, which can be transferred to the wrecked vessel, portable oil-driven air compressors, portable electric lighting plant and electric sub mersible pumps which work under water.
At thd mastheads the vessel has powerful electric arc lamps of 5,000 c.p., with sufficient length of water-tight cables to allow of them being placed on the wrecked ship and operated by the salvage ship's dynamos ; also searchlights, submarine arc and incandescent lamps for the divers, submarine oxyacetylene burn ing plant for cutting plates under water, also a complete equip ment of submarine pneumatic drilling machines up to Sin. in
diameter, pneumatic hammers, rock-boring drills and submarine photographic apparatus. She is fitted with long-range wireless telegraphy. Being constructed of wood she is able to remain along side a damaged ship in rough weather.
At one time steam pumps were entirely used in salvage opera tions, and were supplied with portable boilers so that they might be placed on board a wreck. They performed very excellent service, generally under most difficult conditions. To place such heavy gear on board a wrecked ship from a salvage craft rolling alongside on a winter night required a large amount of skill and care. When placed in position they had to be connected up to the portable boilers, and steam had to be raised before they were available for pumping. It was also necessary to place a supply of coal on board if the ship's bunkers were not available, and this supply was often washed away. Steam pumps are still re tained on board the salvage ship, as they are able to perform work that the present type of pumping plant cannot do; for instance, sand, coal, grain and even copper and iron ore can be discharged by them from under water.
The internal combustion engine (q.v.) went a great way to revolutionize salvage pumping plant. It was much lighter than the steam pump, required no boiler, and the fuel could be carried to the wreck in barrels or drums in an ordinary ship's life-boat. Further, when not required for work it can be stopped and started again in a few minutes, while steam has always to be kept on the portable boilers of the steam pumps. The advantages of the oil motor-driven centrifugal pump will be obvious; it is just as efficient for pumping water as the steam pump, saves in cost of running, takes up less stowage space and uses paraffin or gasolene as fuel, which can generally be obtained without difficulty. The sizes in general use are i 2in. and 6 inch.