We will now proceed to give some further explanations of the character and specialities of our coast Life-boats and their equipment, and more particularly of the famous, world-renowned, self-righting Life-boat of the National Life-Boat InstitutIon, which has been pronounced by our hardy boatmen and fishermen who go afloat in her as the best and safest boat that was ever launched from our shores.
Although the word Life-boat has not in itself any definite meaning, it is generally understood as signifying a boat specially constructed for saving life in storms and heavy seas, when ordinary open boats could not attempt to do so except at the imminent peril or certain death to those within them.
What, then, are the causes which make ordinary open boats unsafe in rough seas? And in what manner are those causes removed in Life-boats?
The principal causes of a common open boat being unsafe in a heavy broken sea are its liability to fill with water and swamp from a wave breaking into it, or by its upsetting, and loss of stability from all water within it falling to one side with every motion of the boat. It is therefore obvious that the chief requirement of a Life- boat is the counteraction as far as possible of these defects.
The qualities necessary in a Life-boat may be thus summed up :
I. Extra buoyancy.
2. Self-discharge of water.
8. Strength of build.
We will now proceed to observe, as clearly as can be done in the absence of technical language, on each of these characteristics, and devote separate chapters to some of the most important of them.
The chief peculiarity of a Life-boat, which distinguishes it from all ordinary boats, is its being rendered unsubmergible, by attaching to it, chiefly within board, water-tight air-cases, or fixed water-tight compartments under a deck, or empty casks. This property, in one or more of the above forms, is common to all Life-boats, although some possess it in an inadequate degree, or badly distributed. So long as the necessary space for rowing and working the boat, and for the stowage of shipwrecked persons, is not interfered with, the amount of this “extra buoyancy” cannot be too great.
Extra buoyancy may intelligibly be defined as the excess of floating property in any body immersed in a fluid, the expression of which in pounds indicates the number of pounds’ weight of any other body that it is capable of floating in addition to itself. Thus a log of fir timber, the specific gravity of which wood is about half that of water, will float with only half its body immersed, the remaining half representing its extra buoyancy. A piece of dry fir-wood has therefore extra buoyancy about equivalent to its own weight.
This important property in a Life-boat should be sufficient in amount to enable it to be loaded with people, and nearly filled with water, without its then being so deeply immersed as to be unmanageable.
Especially it is essential that the spare space along the sides of a Life-boat, within board, should be entirely occupied by buoyant cases or compartments; as when such is the case, on her shipping a sea, the water, until got rid of, is confined to the midship parts of the boat, where, to a great extent, it serves as ballast, instead of falling over to the lee side and destroying her equilibrium, as is the case in an ordinary open boat. Barrels or casks, which do not conform in shape to the sides of a boat, but leave large interstices to be occupied by water, are not suitable vehicles for providing extra buoyant power. The north country or Greathead class of Life-boats, of which those at Shields may be considered the type, have their extra buoyancy provided by a watertight deck at the load-water line, the space between which and the boat’s floor is formed into water-tight . air-chambers ; water-tight compartments are also built along the sides of the boat, within board, sloped from the gunwale to the deck, thereby effectively excluding any water shipped from settling on one side. The excellent Life-boats designed by Messrs. Lamb & White, of Cowes, which have been extensively supplied to ships and yachts, and to the Coast Guard, have their buoyancy affected by similar air-compartments along the sides, extending from the gunwale to the boat’s floor, but without any enclosed space under the deck.
The large sailing Life-boats on the Norfolk and Suffolk Coasts, which are admirably adapted to the work of going out to wrecks ashore on far outlying sandbanks — such being the special requirement of that part of the coast – have very wide detached air-boxes or tanks, strongly made, to correspond in form with the boats’ sides, and extending from the thwarts to the floor ; but they have no deck. The Institution’s Self-righting Life-boats have a water-tight deck at the load water-line, and detached air-boxes along the sides, from the thwarts to the deck. A great amount of extra buoyancy is also in these boats derived from large end air-cases built across their bow and stern, and occupying from 5 ft. to 6.5 ft. in length from the stem and stern posts to gunwale height. These cases are chiefly intended to provide self-righting power ; but in the event of the boat being stove in, and the space below the deck being filled with water, they alone have sufficient buoyancy to float her. Thus, in a 33 feet Lifeboat the buoyancy obtained by the end air-cases above the line of flotation is 4.5 tons , in the side air-cases the buoyancy is equal to I.5 tons ; and the buoyant space under the deck is equal to 53 tons.
Self Discharge of Water
The second peculiar characteristic of a Life-boat, and which is closely allied to the preceding, although it is not possessed by all Life- boats, is the capability of self-discharging in a few seconds any water which may be shipped by the breaking over of a sea, or by a boat being suddenly thrown on her beam-ends. Indeed, without this property, the full advantage of extra buoyancy is not realised, as without it all water breaking into a boat must remain in her, and become a shifting cargo, settling more or less on one side or at one end, with her every motion.
This self-discharging power is accomplished by means of the water-tight deck at the load water-line, and a sufficient number of large open tubes, having their upper orifices at the surface of the deck, and their lower ones at the boat’s floor, passing through the space between the deck and the floor, but hermetically closed to it ; thus providing an open communication between the interior of the boat and the sea, yet without suffering any leakage into the air-chambers under the deck. In some Life-boats these tubes are kept always open ; in others, plugs movable by hand, and having lanyards or handles to them, are fitted, to be withdrawn on water being shipped. In the self-righting boats the tubes are fitted with self-acting valves, which open downwards only, So that they will allow any water shipped to pass down-wards, whilst none beyond a trifling leakage can pass upwards through them. This valve is a simple plate, fitting the tube at its upper end, and made to turn on an axis on one side of its centre, as does an eccentric wheel. It is so balanced as of itself to remain shut, and on the slightest pressure of water from below, to shut still closer, whilst, on water falling on it from above, the pressure on the larger division of the plate, being necessarily greater than on the smaller, opens it downwards. Valves, unless self-acting and of very simple construction, are objectionable ; but these are found to answer admirably, and some which have been fifteen years in use are still efficient in the Life-boats of the Institution.
It will be at once readily understood that, as the deck is placed at or above the load water-line, any water which is above it will be above the outside level of the sea with which it has through the valves and tubes a free communication ; and that, in obedience to the common law of fluids, which binds them to a uniform level, it must instantly, by its own gravity, pass through the valves until none remains above the surface of the deck ; or, if the boat be very deeply loaded, until the level of the water outside, and of that within the boat, shall be the same. This quality of self-relief of water can, of course, only be possessed in perfection in boats with a raised water- tight deck at or above the load water-line.
Other Life-boats have no relieving holes at all, and, if filled by a sea, their crews have no resource but the primitive, slow, and laborious process of baling with buckets ; to do which the oarsmen must take in their oars, and, for a time, disable their boat.