M_Boats: Question about battens

Hello, on my M-17 (unnamed yet, 1982), I think the second batten from the top is too long, and the third one from the top is missing entirely. As a consequence, in light wind the sail has a funny shape, getting a sharp bend at the battens' line. I'm sure that's not helping me move any faster (and my skills aren't helping it, either :-)). Does anyone know what length the battens need to be, or how to figure this out experimentally? Thanks, Andrei.