|Toby Churchill's amazing plywood coracle
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It must be due to my quarter Welsh blood that the coracle has always fascinated me - though there are respectable Scottish and Irish coracles too. The coracle seems to be far too simple a boat for the English, whose only contribution to sensible boat building seems to have been the Parrett flatner - and even that had a thwartships rounded bottom and cant frames fore and aft.
Despite the Greenwood Trust's excellent booklet, the dimensions of coracles are rather hard to come by, probably because your Welsh poacher built each one according to what materials were to hand (or could be stolen) rather than to workshop drawings. However I did once copy from somewhere authoritative that a coracle was 50in long, with the forward edge of an 8in plank seat amidships. The seat was 42in long, which gives the beam, and the seat sat on three 12in long uprights, which gives the depth. The seat was originally cleated to the underside of the 2in deep gunwale.
This gives us quite enough information about the coracle to begin knocking one out. You will gather from this that pre-drawn plans did not feature greatly in this lark.
First buy your sheet of 4mm ply. (My vegetarian daughter would not let me murder a bullock, so ply it had to be.) Cut three 11in wide strips across the 4ft width. These butted together will give you a circumference of 12ft and if the beam is flattened to 42in the length will probably be somewhere near the desired 50in. Out of the corners of the remainder cut two 11in by 4in butt straps. Glue the lot together on a flat floor using the finished edges of the ply to line them up. Pin or staple through the butt joints so that you can remove the fastenings later. You could always leave clenched copper fastenings in, but with PU glues there is no need.
When the glue is thoroughly dry, form the plank into a hoop, overlapping the last foot or so, and clamp the hoop, so it gets the idea of being round. If you don't overlap it you will only get a teardrop with a pointed end. Cut another butt strap and take a couple of short battens, and fiddle about until the joint is held flat by the battens and you can glue and pin/staple the third butt joint. See photo. This is probably the hardest part of the process.
When your hoop is ready to play with, you have to get it to the ovoid shape required. Mark the inside of the hoop at 2ft intervals, once in the middle of each butt joint and once between. This will give you opposite points to measure between. I made a batten with blocks 42" apart and sprung the hoop between them. I called one of the butt straps the stern, and the mark between the other two butt straps the bow. I pulled the two top edges of the hoop together with a bungee strap and used an off-cut of MDF to keep them the right distance apart. When I do it again, I will make a more sophisticated jig on a pallet, so the boat comes out more nearly symmetrical.
Now cut 9 off 2" by 4' strips. These are to laminate the gunwale. I fitted the inside ones which fit up to the butt straps first, followed by one more lamination inside and out. Stagger the joints to avoid weak spots. On the outside, you will need a short filler piece to allow for the greater circumference.
Unlike the old coracles, this one has buoyancy tanks. The tops of these fit up under the gunwale, and the sides of the tanks conveniently give the shape to the bottom. The length of the side depends upon the width you want the central well to be: I chose about 22in, which gave a tank side length of some 43in. I stuck half-inch wide strips of ply vertically down the hull side for the tank sides to ledge against to increase the gluing area. Remember to leave the 4mm gap between the top end of the strips and the gunwale, to let the tank top slide in later. In order to give the tank top and sides some support there is an internal web inside each tank, and scraps of ply glued 4mm under the gunwale for the tank top to rest on. Sketches of tank sides and webs attached. The web fits to the tank side between two strips of ply, and to the hull side with a triangle egg-box joined to it. (see sketch). If you are organised enough, fit a Ĺ to ĺin square strip to the inside top of the tank side before fixing. I did it after the bottom was on, so I had to scarf it to get under the gunwale. This stiffens up the tank, and will form the centre of the carrying handles, later on.
Once the tank sides are fitted, you can cut the bottom. (see sketch) This is wider at the stern than the bow, and when it is fitted to the tank sides the aft end of the bottom will be pulled towards the gunwale with a Spanish windlass (bit of twisted string). The thinking behind the shape of the bottom is that we want buoyancy at the bow so we can lean forward to get some power in, but an easy run aft to minimise drag.
When the bottom is fitted you can fill the gap between it and the side. I planked it with radial 2" strips of ply, because I had some cut with the grain which failed as gunwale laminations. Although it looks a long-winded way of doing things, it was quite quick. I marked each stave with pencil, cut it with a jigsaw, wedged it into the gap and glued it with half-hour PU glue, and held the pieces with masking tape. I tapered every fifth one or so to keep them roughly radial.
Clean up, sand, two coats of polyester resin, and glass tape the chine, and bottom to tank side joints inside and out. I covered the staving with 6in wide tape. Decide whether you want handles in the tank corners (advised) and make them. I made an octagonal Chinese lantern held together with rubber bands and cut it into four to make the hand guards. Fit guards to inside of tank sides, drill for saw blade, glue tank tops on, then cut sides and tops in way of the handles. The photos and sketch should give you the idea.
The seat is a plank whose top is level with the tank tops. You could build it in, but I wanted mine removable for a purpose yet to be revealed. The waterline is painted about 1 Ĺin above the bottom edge of the side. The stroke is a sculling stroke side to side which becomes a figure of eight as you get used to it, and you will start using your hips, and the swing of the boat, to counteract the tendency to rotate. One of my photos actually shows a wake behind the boat, so I must be doing something right!
For my next trick, I'm thinking about a smaller one-sheet coracle, possibly to go in the back of the car. If one went for something about 48 by 36in, one could cut across an 8í by 4í as follows:
∑ 27in for three 9in deep side pieces, including 4in butt straps off the end of each
∑ 18in for nine-off 2in deep gunwale laminations
∑ 24in for the main bottom piece
∑ 16in for the bevelled sides of the bottom
Which should leave you enough for the bow under-transom and maybe a little box seat. (Not forgetting the saw cuts, of course.)
Here's my planned construction method. Make hoop, constrain to squarish 3 ft by 4ft, laminate gunwale. Cut and fit 2ft wide by 3 to 4 in deep bow transom, at 45 degrees to vertical. Cut 2ft wide bottom, and fit/curve to lower end of bow transom and stern. This will leave two melon slices to fill in each side. The first one will be difficult, as Iíll have to hold the curve of the bottom in place while I work out/take off the shape of the melon slice; but once Iíve got the shape itís a simple stitch and glue or tape job. This cuts out all that staving, and uses the bottom to make its own shape, instead og using the buoyancy tank sides Ė which we havenít got enough wood for in one sheet anyway.
Reinforce all joints with tape and resin and off you go.
What I donít know is whether 3ft beam would allow enough stability to sit high enough to paddle. If we are allowed bits of real tree in addition to one 8 by 4ft sheet, then Iíll have a 36 x 8in plank fitted under the gunwale, with three struts down to the bottom, as in a real coracleís seat. In fact you could fit the seat early to help shape the bottom.
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