This is the enlarging of the drawing to the full size of the boat, and is necessary in all boat and ship building. For large vessels, the drawing is made on the floor of the "mould loft," either in one continuous length, or in the case of very long vessels, in two portions overlapping each other. For small work a wide board will answer, 16 ft. long and 2 ft. wide, or less, according to the size of the boat.
On this common roll drawing paper is laid and tacked, and it is divided off, as was described for the detail drawing, except that the half breadth plan will now overlap the sheer plan to save room. Referring now to the detail drawing, a "table of offsets" is made. A sheet of paper is ruled in vertical columns, one for each square station, and also in horizontal lines as follows. In this table is set down the heights above base line of the stem, rabbet and sheer, and the half breadth at the deck, on each waterline, and on the diagonals:
|TABLE OF OFFSETS, CANOE "JERSEY BLUE"|
|Height from Baseline to Gunwale||16||14-1/2||13||11-3/4||11||10-1/2||10||10||10||10-1/8||10-1/2||11-1/4||12||13||14|
From this table the lines are laid down full size on the paper, each distance being measured off on its proper frame or water line, and a long, thin batten of pine run through the spots thus found. As we are now working from a smaller scale to a larger, all errors are increased in the same ratio, and though the small drawing may have been accurate there will be some errors in the large one, and to correct these the same process of "fairing" is necessary, as was before described; running in the water lines, frame lines, and diagonals with the battens until all the curved lines are fair and regular, and the breadths and heights of every point are the same in all three plans. When the drawing is faired the remaining details, such as masts, bulkheads, floor, etc., are drawn in their proper places.
The lines of the drawing now show the outside surface of the plank, but the moulds over which the boat is built must, of course, correspond with the inner surface of planking. In large work the model is often made to the outside of the frames only, then the breadths, when taken off, show the actual size of the frame. If the working drawings are made to include the plank, the thickness of the latter is deducted at some stage of the drafting prior to laying down. In our canoe, for convenience, the drawings will all include the plank, so in making the moulds its thickness, 1/4 in., must be deducted.
To copy the frame lines, a piece of thin board or cardboard A B C D, PlateXIX., is slipped under the paper of the large drawing, adjusted under the line to be copied, and held in place by a couple of tacks. Setting the points of the compasses 1/4 in. apart, a row of spots is pricked through the paper into the board, 1/4 in. inside the frame line, shown by the small circles in Fig. 2. At the same time points on the center line, E F, load water line and the diagonals D1 and D2 are also marked. The board is then removed, a batten run through the spots, and the wood trimmed away to the line. If the drawing is made on a board or floor the lines may be taken off, as in Fig. 4.
A batten about 3/4x1/8 in. is bent along the line on the floor and held down by flat-headed nails. A piece of board is laid on top of the batten and a mark scratched on its under side with the piece of bent wire shown at A. In this case, after cutting to the mark another line must be gauged 1/4 in. inside the edge, and a second cut made to it, after which it is laid on the drawing and the center line, water line and diagonals laid off on it.
To make the complete mould, a piece of 1 in. pine is planed up on one edge, H I, Fig. 5, a center line E F, is drawn at right angles to it, and also the load water line, then the pattern is laid on this board, adjusted to the center and water lines, and one-half marked off; then the pattern is turned over, adjusted on the other side of E F, and that side also marked off, the diagonals being marked at the same time.
As the boat tapers from midships to the ends, it will be evident that the after side of the forward moulds will be slightly larger than the fore sides, and the reverse will be the case with the after moulds, No. X having both sides the same in most canoes. To allow for this bevel, moulds 2, 4; and perhaps 6 must be sawed out 1/4 in. larger than the marks show. The bevels at the deck height and on each diagonal are now taken from the drawing with a common carpenter's bevel, applied in turn to each of the above points, and the edges of the mould are trimmed accordingly.
To complete the mould, a notch K must be cut at the bottom to admit that portion of the keel or keelson inside of the rabbet, as will be explained later. Besides the moulds described there will be required a stem mould (Fig. 6) giving the outline of the stem, a rabbet mould made to the rabbet line (if the stern is curved similar moulds will be required for it) and a beam mould, showing the curve and depth of the deck beams. These should be made of 1/4 in. pine. They are taken off by either of the above methods.
The tendency of light boats is to spread in width in building, to avoid which in a canoe, where a small excess of beam may bar the boat from her class in racing, the model and all the drawings are sometimes made about one inch narrower amidships than the desired beam of the canoe, and the sides are allowed to spread when the deck beams are put in, if they have not done so previously, as often happens unless great care is taken.