[dredmorbius]

A small amount of beam makes a tremendous difference in hull stability.

Anyone who's had experience with rowing shells will be quite aware of this. Beginner's / open-water vs. flat-water shells differ in width by only a few centimetres, but the difference in handling is profound. Both are unstable to the absolute novice, but even a fairly experienced rower from a wider shell will find the handling of a narrower one much more precarious.

(Both are also inherently unstable with CoG well above midpoint, but the dynamic stabilisation provided by the rower or crew is much more critical for the narrower, and faster, shells.)