" The case extends from stem to stern-post, its planks being counter sunk into each, and all riveted together, the heads of which are shown in the drawing. The keel proper is on top of the case, into which the keel is countersunk, and all riveted together. A section of it is shown at a in the transverse section, Fig. 2, Plate II. It is securely kneed to stem and stern post. The case is divided into two compartments by a triangular piece of wood, shown in the centre of sheer plan, shaded. Rivets go through this and both sides of the case, to prevent its closing or opening by warping or straining. The floors are of iron, flat, and bent upon its edge, to fit over the top of keel down side of case, and bolted to timbers acting as clamps to prevent any spring in the case. One is shown is Fig. 2, marked b. In the drawing the keel and floors come above the flooring, as the boat's floor is flat, and area of drop keel large ; but this of course is not necessary in a slightly deeper build.
" The drop keel is in two pieces ; they are hinged together in the centre at f ; the foremost one pivots in the fore part of the case outside the rabbet, as shown in Fig. 1, Plate II., at c. The after keel has a slot cut in it, in which the bolt d works as the keel is raised or lowered. They are raised either by a screw working through a stuffing box on top of the keel proper, or by a rope and tackle, as in the ordinary way, the rope working through a pipe or trunk built up above water, as e ; a wormed wheel would be the most complete, working on the spindle after coming through the stuffing box, but it must be free to rise up in case of striking the ground. On the keel being raised, the upper corners above the hinge will commence to separate, and pass on each side of the triangular piece of wood before spoken of, until they arrive at the top of case, as shown by the dotted lines in Fig. 1, Plate II., which position they will occupy inside the case, the foremost one pivoting on c, and the after one receding aft through the length of the slot spoken of.
" An improvement to the slot and bolt might be to hang the aft end by a rope with tackle, and to have the power of dropping it a little at its after end, to counteract weather helm if necessary. I imagine that this system of building would be much stronger than the ordinary plan of splitting the keel for one-third of the length ; and I see no reason why it should not be applied to large yachts, enabling them to reduce their draught of water by a couple of feet at all events ; and if the keels were made of iron it would keep the weights low." Mr. Arthur James Lane, of Surbiton, invented a similar contrivance (Fig. 3, Plate II.). Mr. Lane proposes that his board should be made of boiler-plate. The fore end of the fore half of the board is pivoted as shown ; at A B the plate is doubled, so as to form a case to receive the fore end of the after-plate. This after-plate works on what might be termed an eccentric pivot, as shown at E. The two plates are pivoted together at D, the after-plate being shut in the fore one as already described. The plates are lifted by a rope or chain (attached to the after-plate), and a barrel as at K. The plates when housed have their centre pivot at H, and the after end of the stern-plate goes into the position shown at F.
So far as we can judge, there is not much to choose between the two plans ; but, on the face of it, that of Lieut. Tipping's looks the best for work, as more of the board is housed at the ends. However, the other plan has, by virtue of the " hump " (which could be increased) a better hold amidships.
It should be noted that Lieut. Tipping's plan, as shown, is applied to a moderately deep yacht, so that the plates are housed under the platform. Mr. Lane's plan, as shown, is applied to a 17ft. shallow centre board gig, for rowing or sailing.
It is usual to give a boat of about 17ft. in length six or seven square feet area of centre-board ; but in Mr. Lane's plan as much as nine square feet are shown. The area of the immersed longitudinal vertical section of the boat is ten square feet, and the centre of gravity (centre of lateral resistance) is in the same vertical line in each, that is 9ft. abaft the fore side of the stem at the load water-line. The weight of the plates, if of iron -kin. thick, would be 2401b. ; if fin. thick, 3001b.; if fin. thick, 3601b. ; this includes that portion of the plates housed when they are down. However, so much board is really not necessary, and quite sufficient hold of the water could be obtained by a smaller board.
In using either of these contrivances, the sails would have to be very carefully balanced by the centre of lateral resistance, and as the pressure would be greater on the fore part of the board than on the aft part (see pages 15 and 23), it will, in practice, probably be found necessary to have the centre of effort considerably forward of the centre of lateral resistance, to bring about a balance. This really means that the fore board will be doing the greater portion of the work in holding the boat, and this ques tion arises : had not the foreboard be better shifted further aft, and the other half of the board done away with altogether, and thus reduce the surface for friction to a minimum ? Numerous contrivances have been suggested to admit of the inside housing of the board being dispensed with altogether, and a very practical plan was proposed a short time ago. It consisted of a single plate of iron pivoted at the far end, and made to rest, when hauled up, on one side of the keel. An extension of this plan formed by adding to the plates and forming them into a kind of fan will be found illustrated by Fig. 60. It will be seen that the leaves of the fan are pivoted to the side of the keel at x. The keel is cut away, and a plate, a, bolted over the chamber, so as to form a kind of box or case to take all the leaves when the fan is shut. See the small sketch. The leaves k, k, k, are connected at their after ends by studs and slots. The fan is closed by a bar, working in a pipe p, as shown. The bar is attached to the lower leaf by a stud, which works in a fore and aft slot, 8. The lifting bar should be jointed, so that when the fan is closed, the handle part, h, will fold down by the side of the pipe. The slots should be cut wide enough to ensure the studs working easily in them. The heads of the studs should be thin, and the edges nicely bevelled off. The number of leaves could be of course increased, but two would in most cases be probably found sufficient and less liable to get locked or jammed.