When you scale down from a full size ship to a half scale model (to keep the argument simple!) the length, being linear, is halved. The sail area, being an area, goes down to a quarter. (Half the mast times half the yard.) So the model should be more stable than the full sized ship. But the hull, being three dimensional, goes down by the cube root (Half the length times half the beam times half the depth) to one eighth of the full sized ship. So that's why it will fall over unless you add a deep heavy keel. Have I got this right?
