Date: 2010-11-19 09:19 pm (UTC)
The Cheapskate's Approach to Canoe Plans, or, How to Save a Few Bucks and Have Some Fun

We will assume that you have decided what characteristics your boat will have: length, beam, depth, sheer, rocker, tumblehome, and anything else you deem important. Using this information, you will need to create some scale drawings from which you will make a model. The point of having a model is so that you can determine hull station shapes for making your construction form. The model will also reveal bad ideas that you may have had (who, me? what bad ideas?) because it just won't look right in three dimensions.

What scale should you use? The bigger the better, since any errors in your model will be exaggerated by the scale multiplier when you go to the full size. For example, suppose you have a one-eighth scale model of a sixteen-foot boat; the model will be two feet long, which is a nice easy size to handle, and would take relatively little effort to make. Now suppose you make an error of a sixteenth of an inch in the model (true to a sixteenth, it's true, you know). Now scale it up by a factor of eight when you draw a hull station cross section. Your minor error is now half an inch, which, I assure you, is going to be very noticeable. So, I like a quarter-scale model, which I think is a good compromise between ease of working and ultimate accuracy. One-third scale isn't out of the question, but any larger than that and you may as well go ahead and build the boat.

You will need three (or maybe four) scale drawings – a profile, which shows length, depth, rocker, and sheer – a cross section at the point of maximum beam – a plan view looking down on the boat from above, which shows the shape at the height of maximum beam – possibly a second plan view showing the shape at the gunwale, which may be useful if there is tumblehome. I usually make drawings on graph paper, which provides handy horizontal and vertical reference lines, but any paper will do if you draw your own reference lines. You'll want a fore-and-aft centerline with parallel maximum beam lines for the plan view. Imagine a rectangle as long as the boat, as wide as the max beam, and divided down the middle the long way. For the cross section, a rectangle as wide as the max beam, as tall as the max depth, and divided vertically at the centerline. Finally, for the profile, a rectangle as long as the boat, as high as the max depth, and divided vertically at the centerline. Do not forget to make copies of your drawings. I like to have three sets, since a lot of work has gone into creating them, and you will need a second set later.

Although ultimately you will only need half-drawings because you will be making a half model (assuming your design is symmetrical left-to-right (and it probably better be!)), I draw both sides to get a better picture of what the boat may actually look like. And, if your hull will be symmetric fore-and-aft, you really only need to draw a quarter of the boat (and make a quarter- rather than half- model), but.....

So, go ahead and draw! I will leave the techniques to you. I use French curves and an adjustable curve (a bunch of little plastic strips that slide against each other) to get the sharp and gentle curves I need. All this can undoubtedly be done efficiently with CAD software if you have it and the proficiency to use it, and access to a printer that can handle the sizes you need. I don't, so I do it the old-fashioned way.

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