Greathead's life-boat was an open rowing boat, 3o feet long. She had no other source of buoyancy than cork could give her, no other means of ridding herself of water than by baling, no other means of propulsion than by oars. That the largest of the modern motor life-boats are twice as long is the smallest part of the dif ference. Instead of baling tins they have automatic valves which empty out the water as fast as the sea can pour it in. Instead of cork they have as many water-tight compartments as a modern battle-cruiser. Twenty holes might be knocked in each side, and they could still go on with their work. They are practically un sinkable. Instead of oars they have engines so designed that they can go on running when completely submerged, so long as the air-intake is above water. They have cabins; electric searchlights; line-throwing guns, with a range of 8o yards; and oil-sprays for spraying oil on heavy seas. The largest of these life-boats, the Barnett Twin Screw type, has two engines, each of 76 h.p. She has 15 main and ioo minor water-tight compartments, and two cabins with accommodation for between 5o and 6o people. In a calm sea she could take 30o people on deck. Under most condi tions of bad weather she could in safety carry 1so people in addi tion to her crew. She carries enough petrol to be able to travel 500 miles at a cruising speed of 8 knots, and her maximum speed is 92 knots. This may not seem a high speed, but a life-boat is not built for high speed, but so that she can maintain her speed under practically any conditions of weather.
All the Institution's engines for motor life-boats use petrol for fuel in order to obtain the greatest power for a given weight. The earliest types were adaptations of various designs of commercial engines, the most successful being an adaptation of an engine built by Messrs. Tylor and Company for lorries. It was, however, soon found that a water-tight engine was essential in order that it might continue to work even when the life-boat had been holed in the engine-room. As there was no such engine on the market the Institution produced a design of its own for a six cylinder 76 h.p. engine, and the first was built in 1923. This has been followed by an improved type, of which there are two variants, one being a four cylinder engine producing 4o h.p. and the other a six cylinder engine producing 6o h.p., one, or two, of these engines being installed in a life-boat, according to its size and type. A light 35 h.p. engine has also been adapted to the Insti tution's requirements for use in the specially light type of life boat built for launching from the beach.
slipway. For a slipway to be built, however, it is necessary that the shore should be steep enough to give a sufficient depth of water for launching the boat at any state of the tide. Slipways, for the most part, are built of reinforced concrete, the longest, at Porthdinllaen, Carnarvonshire, being 351 feet in length. The usual slope is 1 in 5. The great majority of houses with slipways fel.
motor life-boats are provided with power winches for hauling up the boats. On flat sandy beaches life-boats are still launched off a carriage which is taken out into the sea, until a sufficient depth is reached to float the boat, and a specially light type of motor life boat is built for such stations. Instead of horses, motor caterpillar tractors are now used at an increasing number of stations; these tractors not only drag the life-boat down to the water's edge, but push it out into the sea.
Modern Life-Boat Equipment.—All motor life-boats are pro vided with a line-throwing gun, specially designed for the Insti tution by the Birmingham Small Arms Company. The gun is simi lar to a carbine, with Martini Henry breech action. The line is coiled up in a tin cylinder which fits over the barrel. One end of it is attached to a hollow steel projectile, and this projectile has a rod down the centre, the rod having the diameter of the bore of the gun. The gun is "loaded" by slipping the projectile over the muzzle so that the rod goes inside the barrel, while the rest of the projectile fits outside it, in the space between the barrel and the cylinder holding the line. The projectile is fired with a small cordite cartridge, which has a very small recoil, and as the weight of the gun, complete with projectile and line, is only 141b. it can be easily handled. There is no need for firing sights, and the cor rect angle at which the gun should be held is automatically ob tained by a small plumb-bob suspended from a leaf-sight fixed at an angle of 3o degrees. The line used is -Ain. in diameter, and it can be thrown a distance of sixty to eighty-five yards, according to the conditions of the weather.
The majority of motor life-boats are provided with electric searchlights, specially designed to be water-tight and simple to manipulate. They are of two kinds, a portable searchlight of oo candle-power, and a mounted searchlight of 2,000 candle power, the latter being used only on the largest type of boats. The largest type of life-boat, the Barnett twin-screw, is provided with a net, stretched amidships, into which those on board the wreck can jump as the life-boat lies alongside.