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The second quality that of insubmergibility is due to air-chambers fixed round the sides of the boat, under the seats, and at the bow and stern. These air-cases are sufficiently buoyant to float the boat even if she were filled to overflowing with water and crowded to her utmost capacity with human beings.
Besides the above advantages, Mr Beeching's boat was fitted with the usual air-cases round the sides, and with a thick stripe of cork outside the gunwale; also with lines hanging over the sides in festoons, so that any one in the water, using them as stirrups, might get into the boat with ease.
And as to metal air-cases, it was found on opening the sides of a life-boat at Woolwich Dockyard, that her copper tubes, supposed to be air-tight, were corroded into holes; for copper will corrode when in contact with sea-water, especially when alternately wet or dry, as is the case in life-boats.
Such are the principal qualities of the splendid lifeboat now used on our coasts, and of which it may be said that it has reached a state of almost absolute perfection. The accompanying sections of the lifeboat exhibit the position of the air-cases and discharging tubes.
At Robin Hood's Bay, Yorkshire, in 1843, the life-boat capsized, three men remaining under her bottom, while others got upon it. The accident was seen from the shore, and five men put off in a coble, fitted with air-cases like a life-boat; but she almost immediately turned end over end, and two men were drowned. The life-boat herself drifted ashore, and the three men under her bottom were saved.
She has moderately small internal capacity under the level of the thwarts for holding water, and ample means for freeing herself readily of any water that might be shipped; she is ballasted by means of water admitted into a tank or well at the bottom after she is afloat; and by means of that ballast and raised air-cases at the extremities, she would right herself in the event of being upset.
Air-cases are very liable to leak, or may be stove in by the sea, or be crushed by coming in contact with the wreck or rocks, but cork can never be injured.
Mr Beeching's boat united all three qualities. Its self-righting principle was effected by means of two raised air-cases, one at the stem, the other at the stern, and a heavy metal keel.
He took out a patent for it on the 2nd November, 1785, and wrote a pamphlet on lifeboats, entitled "The Invention, Principles, and Construction of Insubmergible Boats." His boat was rendered buoyant by means of a projecting gunwale of cork, and hollow air-cases within it; one of these being at the head, the other at the stern. It was ballasted by means of a false iron keel.
The means by which the self-righting is accomplished are two large air-cases, one in the bow, the other in the stern, and a heavy iron keel. These air-cases are rounded on the top and raised so high that a boat, bottom up, resting on them, would be raised almost quite out of the water.
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