If you want the design to truly be accurate in shape to the original, any deduction made for the thickness of the hull has to be graduated slightly, depending on the angle that the hull material crosses the forms at. Assume, for example, that we determined that the difference between the thickness of the new w/c hull and the original stripper hull required a 1" reduction in the size of the station forms to make a boat the same size. That's fine at any spot on the form where the hull material crosses our station forms at pretty much a 90 degree angle (as it will on much of the bottom and almost everywhere on the middle station). Figure A in the drawing shows such a hull/station form junction.
However, if we have a strongback with parallel, crosswise stations set up on it (as we would have had for a stripper) and you start approaching the tapered, pointed ends of the boat, the hull material is meeting the stations at an angle (just as the strips did).
If we simply deducted our 1" allowance from those stations, it wouldn't be enough and our finished boat would actually gain girth slightly in those areas. This can either produce a boat that's a bit fuller in places than the intended design, or it can possibly make one that is not a fair shape and has unwanted bulges or hollows here and there. As you can see in drawing B, a 1" deduction in places where the hull crosses the stations at an angle may noy be quite enough if you really want accuracy.
To prevent this problem, the deductions to the station forms need to be made taking the angle at which that particular portion of the hull meets the station in mind. Designers and builders us a home-made gizmo called a bevel board to help make accurate deductions. They are also often dealing with hulls having frames (ribs) and planking that may total 4"-6" thick - a situation where the errors are much larger than they would be on a canoe hull.
I doubt you'll need a bevel board for a canoe, but as you plan your deductions, keep the angles in mind. If you have spots where the angles are in play, you may want to deduct a bit more in those areas to get a fair and accurate hull. Some station forms, like those a few feet from the end, may need no additional deduction on the bottom where the planking meets the form at about 90 degrees, but may need an additional small bit removed on their sides where the planking meets the form at a pretty steep angle. Is all this critical on a canoe hull? Probably not. But it never hurts to have a good understanding of what's actually going on and to be able to compensate for it if and when it's needed.
