What I would do as kenny said, get a block of balsawood and cut itto shape,then cover it with thin plastic card or litho plate.
1. I would cut the plan shape first but elongate it slightly to allow for the curve of the hull.
2. Cut the angle to the left, this is only a straight cut.
3. Cut the angle to the right, the one that is underneith slightly.
4. Offer up the section to the hull and mark off the angel of the hull side, you should have a perfect shape if all cuts are correct, just take your time. ARH

Simple but effective.