That is a toughy.

Can you sand down a LARGE block of blue styrofoam. I did a 81" A10 warthog & a 4 engined China Clipper that way.......I think you can do it, as the hull is a continous curve everywhere.
Trace the top veiw and side view.
You can enlarge any views at Staples or a Office supplies place.
Use a band saw at some carpentry place. Begging works. I used 33 grit to rough it. Then 80 grit for final finish. It ....IS.... quicker than a framed wood boat. Make a mistake? White glue & a scrap piece. ONLY use lightweight spackling compound. Only water based paints. test paints on some scrap.

It will NEVER SINK or ROT.

Rich