DOUBLE boats, in some form or the other, are met with all over the world, and the principle is adopted with the main object of acquiring great stability. But, although double boats may have in this way great stability, it must not be supposed that they are uncapsizable. They could be capsized by carrying a heavy press of canvas, or they might be thrown over by a sea, just as a lifeboat is sometimes.
In 1873, the late Mr. H. Melling, of Liverpool, had what he termed a safety yacht constructed on the double hull principle, as shown on the opposite page (Plate XXXVI.). Mr. Melling thus described his boat : "Happen what may, she cannot sink, for even if scuttled she will remain as a strongly-put-together life-raft. She can accommodate herself to draw only one foot of water, although of the size of 15 tons. She can be beached at pleasure without risk of straining. She can be anchored and put into places out of the way of harm or being run down or afoul of, and ride to her anchor in a roadstead, light and buoyant, with little strain on her cable. All is of pine wood, light and buoyant, having no ballast whatever. She has comfortable cabin accommodation on deck, affording a good ' look-out' fore and aft. Galley and stowage berths are in the forecastle, and by a system of casks stowed away in the pontoons and on deck she could carry stores, provisions, water, &c., for a voyage, which as they are emptied and bunged up will add materially to her safety. She made very good weather of it in turning down the Dee and along the Welsh coast over shallows against a strong wind. In running back off the wind she attained extraordinary speed.
" The use of the boards are as follows : if the fore board is down, or part down, it makes her stay in a sea way ; if the aft one be down it holds her steady in scudding, and prevents broaching to ; if they be all down, she holds a good wind and makes no lee way. They can be let down partially or wholly as required by a chain, and can be hauled up by hand. They are weighted to sink by themselves, and house themselves as soon as she touches the ground. Her pontoons are 30ft. long, and 2ft. 6in. in diameter, representing enormous floating power; and, as it is almost unnecessary to say, water-tight pontoons or air chambers are the most powerful principle of buoyancy known. In the drawing her broadside view is given, with the submerged portion shown by dotted lines. The ' end-on' view more clearly shows the power of the vessel, and the peculiarity of her con struction." In the spring of 1868 Mr. John Mackenzie, of Belfast, constructed
a double boat, but without dropping keels. He thus described her : " There are two boats of equal size, each 21ft. keel, 3ft. beam, and 3ft. deep. Each boat is divided by bulkheads into four compartments, two of these being 6ft. 6in. long, so as to be used for sleeping purposes; a hatch is in one compartment and a movable skylight in another, which is also adapted for ventilation ; these hatches are screwed down on indiarubber, and can be made quite air-tight. A keel is provided on each boat, 15in. deep at the stern or heel, diminishing forward to 6in. Bolted to the keel by strong iron knees are stanchions which rise through the deck, on which the rail is fixed ; to these stanchions the cross-beams connecting the boats are fixed, the timbers or ribs also rising through the deck for a similar purpose, where the cross-beams are placed. The skin is lin. thick, being in one board on either side of the keel ; the sides are in two, each 18in. deep, the seams being covered by a continuous strip of wood. By this method there are only four seams in each boat which require caulking, so that leakage is rendered nearly impossible. The boats are connected by five trussed beams, the one at which the mast is stepped being double trussed. A platform rests on these beams, a space of Bin. being left at either side to allow air compressed by a cross-sea to escape from under neath ; from the mast forward this platform is formed of open-work. Immediately under the platform is a chest, 2ft. broad and 6in. deep, capable of carrying 6cwt. of water to serve as ballast in heavy weather. It is provided with brass valves in bottom, which in light weather or in case of accident can be opened, and the water discharged in a few minutes; when the box is emptied, by closing the valves a third chamber or boat is formed, capable of carrying 7cwt. or 8cwt., in case the other two got waterlogged. It may seem strange to place the ballast in the position described; but this extra weight—which is absolutely required to enable the boat to beat up in a strong sea—makes her also stay with certainty and speed by its central position. A boat of this description, no doubt, will carry her sail without ballast ; but no craft with a very light draught will stay in a heavy sea without an additional weight to that of the hull and spars. A helm is attached to each boat, and these, being coupled together by a connecting rod, are worked by a tiller in the centre, so that both are moved in the same direction.