
My paddle book has some measurements for a selection of paddle blades. The official method is to measure the elevations onto a piece of ply, then use a French curve to make a nice curvy shape. This gives the shape of half the paddle on the plywood. Cut the ply to get a half template, and then mark around the template onto the paddle blank twice to get the complete shape.
The trouble is, I found this wasn't very accurate, and my first paddle was slightly out because it was impossible to line up the template exactly symmetrical to the first side when marking out the second side.
(The image to the left has some pixellation which is why it doesn't look quite symmetrical, but printed full size, it is.)
Making a full template was slightly out too, because it was impossible to link up the marked-out points with the french curve accurately enough on the different sides of the template.
The solution was Turbo CAD.
This CAD package allowed me to mark out the template lines, and then link the ends of the template lines using a bezier or spline curve. Using the snap facility of the package, the curve is snapped to the ends of the template lines. The spline or Bezier algorithm gives the right shape. Because its a CAD package, it comes out perfectly symmetrical.
Print it out at 1:1 onto about 3 sheets of A4 and voila, a full size symetrical paddle template.
Hopefully this will translate to a symmetrical plywood template and a perfectly symmetrical paddle.