w.b.samson@tay.ac.uk
Let me know if you have any ideas in this direction.
I've accidentally blundered into what I think is an easy way to determine plank shapes in glued lapstrake plywood construction. I haven't seen this written up anywhere, so feel free to put it in the next newsletter. It assumes you are using a building mold the way Tom Hill does, in his book "Ultralight Boatbuilding", with a series of ribbands to define where the planks go.
Unlike the Chebacco, Tom's plans and molds are small. He uses 4mm ply, narrow enough to be clamped into place with C-clamps. He clamps some plywood in place and traces the shape from the back by tipping the mold. For me to do that in the Chebacco means getting under the mold between each pair of stations, tracing the shape onto cheap quarter inch ply, and spiling it onto solid gold occume plywood. The pieces are heavy and awkward and the process requires considerable agility. So, a better way.
1. Put the last plank, the one lying on the shop floor, in place on the boat. Mark off where the next plank will land and plane the bevel.
2. Buy, or scounge enough scraps of Mylar that you can tape together a long strip, roughly the shape of the plank, but wider. The joints between the pieces can overlap as much as you want and can be attached with masking or other tape, BUT THE JOINTS MUST BE FLAT. (- no wrinkles or bulges.)
3. Roll up your strip of Mylar, take it to the boat, unroll it and tape it over the space where the new plank will go. It only requires a few hunks of tape. The Mylar MUST LIE FLAT between the bevel of the previous plank and the next ribband. Since Mylar is dimensionally stable it doesn't take compound curves, it will lie just as flat as the next plywood plank.
4. Standing in a civilised manner on the outside of the boat, make little marks every 4 - 6 inches along the bevel line of the prior plank, and the next ribband. If you want to do both sides of the boat use two different pencil colors.
5. Roll up the Mylar, take it into the shop and unroll it over the next piece of plywood. Using an ice-pick, prick right through the Mylar into the plank stock. Remove the Mylar, clamp a batten around the prick points, draw a line, cut with a saber saw, Voilą a plank!
When it's time to do another plank erase the x marks and reuse the same piece of Mylar. After a while it'll have a potfull of stray prick holes in it, but that won't affect its usefulness one whit. If the plank shape changes as you move down (up?) the boat, you can untape your Mylar segments and put them back together again in a little different alignment. In between uses, roll the Mylar up and stick the end in an old coffee can - try that with 20+ feet of spiling board!
I find I can scarf up quite narrow strips of 12mm ply to get my plank blanks, by aligning them under the Mylar and jiggling them 'til they fit. Other than the garboards, which are wider on this boat, I find I can get two whole planks, a port and a starboard, out of a single 4 X 8 sheet. So it's economical of material as well as time.
. . . the ones I've seen go over the boom, with snap-up cutouts for the halliards and topping lift. This way it serves also as a sail cover. This cover was secured along the edge of the deck with eye straps. These straps along the coaming would work at least as well. They'd cut down on the cover flapping - though they might chafe the finish on the coaming edge. The cover is over the cockpit only, (though a tail extends fwd and aft to cover the sail). It's held onto the eye straps with a piece of cord thru eyelets in the cover - a little tedious to put on/take off, but strong and foolproof.
My address is:
Bill Samson,
88 Grove Road,
West Ferry,
Dundee,
DD5 1LB,
Scotland.
Phone +44 (0)1382 776744 (Home)
+44 (0)1382 308611 (Work)
Fax +44 (0)1382 308877
eMail w.b.samson@tay.ac.uk