Hmmm. At about 9.00 ff, he discusses how a vessel is stable if the centre of gravity is above the centre of buoyancy, but unstable if the other way around. This must be the explanation for all those yachts with their keels in the air ...
@Recidivist I haven't watched the video however I would guess that what he's saying is if the Centre of Gravity is directly above the Centre of Bouyancy then the boat will happily sit there, but if the CofG moves to the side of CofB then it rapidly looses that stability (maybe I should watch the video).