CENTRE BOARD.
The strength requisite to resist the strain of a heavy centre-board in. lumpy water can be given to the case without much addition of weight. The sides of the case should be rabbeted into the keel, and fastened by dowels (a, Fig. 128) two inches apart. A piece of wood about one inch square is then screwed with alternate vertical and horizontal fastenings int the keel and into the side of the centre-board case, as represented i Fig. 128. The slot through the keel is cut about two inches longer tha the inside dimensions of the case, so that the cross ends of the case g down through the keel, and are through fastened to the keel. Each sid of the case is bound with a strip of brass from the deck to the keel at t1 part where the greatest friction takes place, in order to protect the woo This brass is marked T in Fig. 128, and is about lin. wide and thie In order that the canoe may be easily moved about in general cruise and travelling, it is necessary that the ballast and centre-plate shall readily removable ; 601b. is quite heavy enough for a plate for convene handling, and three square feet of wrought iron plate, tin. thick, gii about this weight. (See " Weight of Boiler Plate " in the Appendix.) The plate, after being cut into the shape and fitted to the case, shi be galvanised to prevent rust, and to thus keep it smoother, so as to less frictional resistance in the water. The cost of galvanising should exceed I id. per pound. The plate is slightly increased in weight thickness by galvanising, a fact which must not be lost sight of in fit the case.
The shape of the plate should be designed so as to place the weight as low as possible, and give a large surface for lateral resistance, but at the same time there should be plenty of grip in the trunk when the plate is lowered to the full extent. The ordinary triangular shape is not the best for a heavy plate, the part left in the trunk being so narrow as to throw an undue amount of strain on the sides of the case. The annexed diagram (Fig. 129) A, B, C, D, is a very good shape, its length being 2ft. 9in., and breadth lft. 4in. The dotted outline shows the part of the plate remaining in the case when it is lowered 18in. below the keel band, the limit of drop allowed by the Royal Canoe Club rules.
The projecting arm is of the full thickness, and has a hole through its upper edge, D, which forms a handle by which to lift the plate in or out of position, and a small hole at E takes a pin above the deck, to support the centre-board while the chain is being placed in position for hoisting or lowering. The edges of the plate, from A to C and C to B, are sharpened to reduce resistance in the water, and the angle C is rounded off to prevent its catching in the ground when the canoe is being hauled astern with the centre-board not quite housed in the trunk. If a small area of canvas only is carried, or if no intention exists of sailing in strong winds, it may be better to use a lighter centre-board, of say *in. plate, and then the pro jecting arm, D, is doubled or trebled by pieces riveted on, so as to make it *in. thick, to fill the trunk and prevent undue play. The after-end of the centre-board is raised or lowered by a galvanised short link chain the end link is longer than the others, and is shackled to the plate by twc brass lugs (B) and two bolts, as represented in Fig. 130.