Small Boat Design

Discussions around designing small boats including kayaks and canoes.

Re: Initial Stability and Hull Shape

Thanks. For these purposes, please assume calm water only. This would be the hull of either a kayak where you
could momentarily stand up, or a paddleboard hull where you would always stand up. Though I don't want to veer too far from my specific questions, my larger purpose is to find the the best balance of width and shape providing high initial stability while keeping resistance (both from wetted surface and wavemaking) to a minimum. An interesting note is that with a lighter paddler in a hull this wide, the draft is likely to be only about 2".

So I'm more interested the result dictated by the geometry and physics contributing to stability. Nick's article cited above explains very clearly that at any angle of heel, the hull must submerge the same volume, and that the righting moment of any submerged shape is the distance between the center of gravity (based on the paddler) and the center of buoyancy (based on the submerged hull shape.) Your range of "positive" stability is that where, as the hull is tilted due to a shift in the center of gravity to the side, the center of buoyancy of the resulting immersed hull shape has moved further to the side than the center of gravity.

But then when Nick presents graphs for different hull shapes it gets a little confusing because they don't have the same beam, and when he equalizes the beams, then the waterline widths are different. So I'm asking what the result would be where you have the simplest case -- beam and wlw are the same, i.e., the sides above water are assumed vertical, not flared.