: I dare say that hull shape has more to do with (initial) stability
: than width. I would agree that in most mass produced consumer
: boats wider is more stable because they all use a very similar
: hull shape. You can draw up to boat with the same waterline
: width but one is rounded bottom and one is flat bottomed and
: flat bottom is going to feel more stable.

: A perfectly round shape 24" wide will be extremely unstable, I
: dare most of us could not keep it upright, but it you could keep
: it upright it would be very fast.

But there is a fundamental reason why you do not have a 24" perfectly round hull shape. It is not an issue of stability. To have a 16.5 foot kayak that had a perfectly round hull requires it to draw 12" of water. To push such a boat that deep requires about 800-900 lbs of weight.

Such a boat would, in fact, be VERY VERY stable using classic stability curves because since the bottom was so far down (12") the center of gravity of the paddler/boat is quite low. I have calculated such curves.

When you have a wide boat (24" waterline) you do not have any choice: you cannot have a rounded hull because that displaces too much water. It HAS to be on the flat side.

Only very thin boats can have completely rounded cross-sections. Now they have multiple reasons why they are unstable. The fact remains that if you know the waterline width of a kayak of average length, you have a very accurate assessment of how its classic stability curve will look.

Try this exercise with either Kayak Foundry or BearboatSP or any program that does stability curves. Design a two kayaks, one which is 1" narrower at the waterline than the other. Do anything you want with the hull shape / cross-section and you will find that you cannot make the wider boat less stable (using classic stability curves) than the other. At 1/2" it is damn hard to do.

There is a caveat inherent in all this discussion. Classic stability curves do not completely correlate with what people will perceive as stable.