what I did was make 1/2 of a template.
I just make a real rough shape out a cardboard triangle. Then cut it in half by splitting it in half from the top point down to the lower edge. Just makes it easier to handle.
Then I used a drawing compass (the kind you used as a kid to draw circles that has a sharp point on one side and held a pencil on the other)
I made maybe a 1" gap between the 2 points (or whatever distance you need to span the gap between the hull and cardboard), then lay the cardboard against the curve, Take the end of compass without the pencil and set it against the hull edge I want to copy, then carefully pull it along the contour and transfer the curve to the cardboard.
Cut that edge and check it, should be right on.
Now I have that curve I can transfer it easily to the plywood, flip it over for the other edge. Measure the width of the triangle on the boat and draw the 2 curves between them
Might sound complicated but its real easy once you realize what I am describing. Works real well for transferring smaller shapes, like curves along the gunnels etc.
thanks