Get a large sheet or two of very heavy cardboard or very thin, cheap plywood
Cut out the hull
shape as close as possible in the plywood
and then hold the plywood against the hull
where you want the saddle to fit.
Get a scribing tool or make one with a wood block with a marker attached to one end. Slide your tool around the hull with the marker drawing a line onto the plywood. This will transfer an exact hull curve to the plywood.
Cut the plywood on the line and refit
against the hull to check the fit. Adjust as needed and then use the plywood as the pattern to make your saddles.