Fig. 447.
The construction of the case or trunk for the centre-board can be understood from Figs. 446 and 447. By either method of construction the trunk consists of two upright posts, or "headledges," cut with shoulders at the lower end, and sides of board screwed to these posts. A slot is sawed through the bottom of the boat of sufficient width and length to give the centre-board free passage—that is, of the dimensions of the opening at the bottom of the trunk. To cut this slot several holes can be bored close together until an opening is made sufficiently large to start the saw. By the arrangement shown in Fig. 446, a plank is taken and a slot is cut in it enough longer than that in the bottom of the boat to include the lower ends of the headledges, which should fit snugly. The sides of the trunk are screwed to this plank from underneath, and the plank is in turn screwed to the bottom of the boat. The headledges can be additionally fastened from the edge of the plank, horizontally. Unless the bottom of the boat is straight, the plank must be accurately fitted to the curve on the under side,—not an easy task (see Scribing and Paring). All the joints should be laid in thick white-lead paint, and at the bottom flannel can be laid in the seam, with lead, or caulking can be resorted to.
By the method shown in Fig. 447, the headledges and sides are fitted to a board on the bottom, or to the keelson, and, after being put in place, strips of plank are fitted lengthways on each side at the bottom and bolted or screwed to the bottom and to the sides of the trunk. The lower edges of these strips must be fitted to the curve of the bottom and the whole made tight, as just shown. Much care must be taken with this work to make tight joints. The inside of the trunk should be painted before putting together, and holes be bored carefully for all the screws (see Boring and Screws).
The centre-board itself can be of wood or of galvanized plate iron and is pivoted at the forward lower corner, and can be raised and lowered by a rod attached to the after corner.
Remember to paint the inside of the boat carefully with at least two coats before putting on the deck, and also that copper nails and brass fittings are better than those of galvanized iron (particularly for salt water) if you can afford them.
The coaming or wash board can be of ½" oak, ash, or elm. The deck can first be laid, lapping slightly over the space to be left open. The line for the coaming can then be marked on the deck, and the projecting wood sawed or trimmed to the line, when the coaming can be bent into place and fastened.
The gunwale-strip, like the stern-post, the rudder, and the tiller, should be of hard wood, as oak. Hackmatack is good for the stem.
Fig. 448.