Keeping your Hull in Shape
The strength of a cedar strip boat is derived from the combination of fiberglass and epoxy resin on both sides of quarter inch cedar strips. The cedar is the shape, beauty, and carrier, fiberglass is the strength, and epoxy is the glue that binds it all together. Leave out any of these and you may need to deal with problems. The most common issue is when you have your hull glassed on the outside and it is off the forms sitting in slings and you are working at sanding and fairing the inside (canoes and rowboats). This can go on for weeks or months. During this time the epoxy on the outside is coming to a full cure and the glass skin is overcoming the cedar hull. The typical result is that the hull opens up and the builder doesn't discover it until he goes to install rails or a thwart and finds out that a canoe hull that was supposed to be 35" wide is 38-39" wide.
What To Do:
Let's say you have a symmetrical canoe. Measure the distance from sheer to sheer point on the center (zero) form. This is how wide the inside of your hull should be. As soon as you take the hull off the strongback you should put a strap around it and draw it in to the correct width based on the measurement mentioned above. Leave the strap there as much as possible while you are sanding the inside of the canoe and certainly it should be there when you aren't working on the inner hull. Also, it would help if you picked a couple of forms that are equidistant from the center of the canoe, say form 4 or 3 and do the same thing. In addition you could cut a stick to the zero form width, place it at that location, and draw the hull to the stick. This will set up a resistance both ways.
When you have the hull ready for fiberglassing, take the straps off in order to apply the fiberglass, but as soon as it is wet out, install the straps again. You want the inner glass to cure while the hull is in the correct shape.
You should install the inwales, outwales, then the decks in that order. While you are installing the inwales, you should have at least the center strap around the hull. If you don't you may distort the hull because the force of clamping up the ash inwale on one side can radically push that side outward.
Once the inwales are installed, move the straps to the scuppers in the inwales. This will hold the hull in the correct shape while installing the outwales without them being in the way. Eventually, the center yoke or thwart will take the place of the strap. Install the decks between the inwales while the straps are held to the inwales.
The concept is similar for kayaks. Our forms have an internal strongback going through the center. When the outer hull is glassed the forms are removed from their uprights and the hull is set into slings. The forms stay inside the hull while we strip the deck. Take some 3" shrink film and wrap it around the hull at each station. Apply clear packing tape over the shrink film. The packing tape will keep the film from stretching. Now the deck can be stripped right over the shrink film and packing tape.
When you take the forms out of the hull, treat it just like a canoe by laying straps around it to hold it in shape. If you don't do this you will have a problem when you go to glue the deck onto the hull.
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