Actually David I think you are thinking about a hydrofoil...which is a boat/ship who's hull comes completely out of water when up to speed...What I was talking about is if you ever watch a fast ship or race boat run from the front you will see it only has about 1 foot of its hull in the water with the whole packge rocking about side to side on that cushion of air.
Really fast cats are very unstable without the assistance of stablizers on the top of the boat like little wings and rudders. Next time the Ofshore Powerboats are racing on ESPN, watch the cats run...
