A centre-board boat, somewhat deeper, with more rise of floor, also with less length to beam, than the one of 17ft. length, may perhaps be a handier boat in narrow water, where frequent tacking is inevitable, and at the same time be not more laboursome to row. A diagram for such a boat is given on Plate IV., with body plan represented by Fig. 67, and, in order that the drawing may be utilised for boats of varying sizes, tables have been compiled to different scales, so that a boat of 10ft., 12ft., 15ft., or 20ft., can be built therefrom.
The displacement (or weight of water which the boat displaces when immersed to the load line, or, in other words, the weight of the boat, including everything she carries) of each boat, as given, is not mathema tically correct, and need not be so considered; it is only given as a guide for the builder in ballasting, and it may be necessary or convenient to sail the boat lighter or deeper.* With regard to ballast, it will be found in practice that every passenger on board who sits to windward is of more value than an equal weight of ballast in the bottom of the boat would be. Of course there will be a limit to the number of passengers it is desirable to take in a boat of 12ft., and probably most men will conclude that one besides the helmsman is enough. When sailing in smooth water, shifting the ballast to windward can be largely indulged in if a practised hand besides the helmsman is on board to look after it ; but in a sea the ballast should be well secured.
The sail dimensions given are for cruising, and are not so large as those of the gigs raced at Surbiton; the difference is about equal to one-seventh the linear dimensions—that is to say, the sail of the 14ft. boat, or any of the other boats given, would be one-seventh longer in the foot, one-seventh longer in the head, one-seventh longer on the luff, and one-seventh longer on the leech for a racing outfit.
In all cases where measurements are given they must be adhered to, as the drawings are too small to work from, and " fairing" the moulds will be a matter of judgment.
Siding (thickness) of keel amidships, 5in. ; ditto at stem, 3in. : at damped, 3iin. Moulded depth of keel, 6in.
The 10ft. boat, planked with sin. mahogany, would weigh, inclusive of centre-plate and case, sails, and spars, about 2cwt. Thus it would take 4cwt. of ballast and one person of 8st. (lcwt.) to bring her down to the intended load line; but she might with advantage carry one more passenger or lcwt. more ballast. Every additional cwt. would sink her an inch deeper ; but it is of little use crowding a large quantity of ballast in a shallow boat in the hope of making her stiff. For light rowing the plate, ballast, and sails could be removed.
The 12ft. boat, inclusive of sails, spars, and plate and case, would weigh, with the same thickness of plank, about 24cvit., and should have at least 2cwt. of ballast, or one person and lcwt. of ballast, besides the helms man, for sailing with the large balance lug sail.
The 14ft. boat with 4in. plank, and including centre plate and case, spars, and sails would weigh about newt., and would require from 3cwt. to 4cwt. of ballast, according to the number of passengers on board.
The 15ft. boat would be planked with lin. stuff, and would weigh, inclusive of centre-plate and case, spars and sails, about 3cwt., and would require 3cwt. or 4cwt. of ballast, according to the number of passengers on board.
The 20ft. boat would weigh, inclusive of centre-plate and case, spars and sails, about 7cwt. To get her down to the load line, she would take four passengers of 12st. each, and about half a ton of ballast. As such a large boat is not adapted for rowing (excepting on emergencies), it would be advisable to have 5cwt. of iron cast in the form of a keel, with a slot in it for the centre-plate to work in. An iron keel, 12ft. long, with an average width of 4in. and depth of 34in., would weigh about 5cwt. The iron keel forward would extend as far as the mast and aft to within 3ft. of the stern post. A filling-up piece of wood, well rounded up towards the stern post, will finish the keel off aft, and the same forward tapering to " at the scarph of the keel with the stem. The iron keel should be 44in. deep in its mid length, and 3in. at either end. Transversely it would, of course, taper to match the taper of the under side of the wood keel. The beat cruising rig for such a boat would be the balance lug, foresail, and mizen, of about- the extreme proportions given for the 17ft. boat (Plate V.) ; but the mast should be stepped one foot farther aft, and the boomkin for the foresail should be shortened one foot.
Centre-board, boats such as shown in the diagram, are peculiarly adapted for shifting-ballast, as the centre-plate case makes a kind of fore-and-aft bulkhead which will always prevent the ballast sliding to leeward. Still, sliding is not the only danger accompanying the practice of shifting ballast. If a man is single-handed, he might be unable in an emergency to trim his shot bags or other dead weight in time, or his mate may be unable to do so, and it cannot be too often impressed upon the young boat sailer that he must well look after loose ballast in the bottom of a boat (secure it if possible), and never be tempted into carrying a lot of sail on the strength of the ballast being shifted-to windward.