Try to avoid large flat surfaces, These are very weak and fail easily.\

A multi chine hull would be a smart move. Lay down the bottom panel (do not make it too wide, length it NOT limited) and have the sides meet at the ends. Make a nice (side) curve from end to end). Then bend (curve) this bottom plate upwards and give it a nice curve over the full length. Hold this curve in place and then hold another plate to the side under say a 30 degree angle and mark the curve at which this plate touches the bottom plate. Cut this curve out in BOTH sideplates. Then attach this curve to the one of the bottom plate and tap it along the seam on both sides.

You now have the beginning of 3-dimensional hulls. Repeat this trick again, now with vertical sides.

You can either stop now and leave the boat open on top or make a copy and tape that to the bottom halve and end up with a closed hull like for a cat or kayak.

Somewhere in the proces you want to add some bulkheads. These are not really needed for strength but they do keep the sides in place and thus remove the risk of buckling failures. Add about 5 to 10 bulkheads depending on the length of the hull. 10 for a 16 foot hull should be enough.

If you do this right then you'll be surprise how strong and stiff these card board hulls will be.

Something comparable is indeed used to make ply Taipans and ply A-cats out of 3 mm ply. And a plate of 3 mm ply feels just like thick paper.

If you cardboard hull were to be saturated with something like expxy then the hull would survive for years.


Good luck.

Wouter