TECH TIPS PAGE TWO

Designing Your Canoe by John Lindman

You know how it is when you see a canoe you like and want to make something just like it. With wood-canvas or stripper canoes that is not a problem, just get a form or plans and there you have it. The same is not exactly true with birchbark canoes. Now in The Bark Canoes and Skin Boats of North America by E.T. Adney he gives measurements but you might ask, what do you have to do to arrive at those measurements. Well here is some data.

There are a few key factors that determine the design of your canoe.
1. Dimension of your building form - the frame you put down on your bark when you build.
2. The height of your height sticks
- your gunwales rest on these and this determines the shape of the sheer (the way the gunwales slope when looking at the canoe from the side)
3. Stem design (the stem piece is what gives the prow its shape)
4. Thwart length - gives the shape of the canoe if you were looking down on it.
5. How close to the end the last gore is cut - it affects rocker.

The width of your building frame is determined by the width of your bark. It must be 4 inches less than your bark so you can sew the side panels or pieces of bark. I was originally told your bark must be at least 36 inches wide. This is not true. Algonquin builders used building frames that were about the same as the finished gunwales. Ojibway builders used narrow frames. Algonquins had big trees. Ojibway out west did not. I have used a 23 inch frame on a canoe that had a finished beam of 40 inches - big canoe. Turned out great. You simply need to know how to adjust for it.

If you use a frame that is about the same as your gunwales then when you put in your ribs it will belly-out about 3 inches. You bend the ribs and place them in the canoe but the canoe walls are at a 90 degree angle to the bottom. When you pull up on the gunwales to adjust to the curve in your ribs, you end up pulling up about 3 inches. What happens if you use a narrow frame. The sides flare out. Unless you want flared sides, when you put in your ribs you will push those sides down. So you have to think with this when you determine the height of your gunwales.

This brings us to the next thing - height sticks. If you want a canoe that is 12 inches deep at center and you have a form that is about the same as the completed beam then you need a height stick measurement 3 inches less. Now think about it. You place these sticks on your form. Your form is about 1 inch thick. The bottom of the gunwale rests on the stick. The gunwale is about 1 inch thick. On top of the gunwale is the cap resting on top of the lashings adds another half inch. So what we have is about 2.5 to 3 inches. So our stick height would be 5 to 6 inches less than our finished height. Make sense. Do you want straight sheer or curve. Height sticks the same height next to the center thwart, and intermediate thwart and then about 1 inch higher at the end thwart give you a pretty straight sheered canoe. Adney gives you some height measurements in his book.

If you turn up your gunwales at the end you will need to split out the gunwales to allow for the bend. Therefore the sharp bend usually starts just after the last thwart.

If you look in the book The Bark Canoes and Skin Boats of North America you can see various stem designs. Those are pretty straight forward.

The inside shape of the canoe - as if looking down from above - is done by the inside gunwale, how the ends are tied, and the dimensions of the thwarts. You can tie just the tips together, or you can tie the ends together down a few inches. It affects the shape. It also affects the entry line of your canoe. After those are tied, insert your center thwart. You can adjust the shape by what you then do with the intermediate and end thwarts.

When you lay out your bark and then put the building frame over it, you have to make cuts in the bark to allow it to bend around the curves of the frame. A narrow frame leaves less of a curve to get around. A wide frame like one the same as your finished gunwales will need more cuts or gores to allow a nice even bend. If you have a narrow frame you do not need to make your gores as close to the front of your canoe as you do with a wide frame. Remember gores are for the curve. If you do not put gores far enough to the tip of the canoe the nose curves up sharply. If you put them too far up then they are unnecessary cuts in your bark.

Lastly how you bend your ribs determines the hull shape. Some do sharp bends and have a flat hull with sharp straight sides. Some like a bit of tumblehome so the bend continues up the side. This rib shape will affect the depth and sheer of your canoe slightly.

All of these factors can be experimented with by making model forms out of cardboard and manilla file folders. Play around with it and notice the cause and effect of the various factors. Check out The Bark Canoes and Skin Boats of North America. Study.

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