Actually the reduction in velocity of the air going through the tunnel is more like the slot between the jib and the main on a sailboat, the air coming out the back is high velocity which in turn causes the air going over the top of the boat to increase in speed creating lift, I believe it is referred to as the Kutta effect.

Pat, if Bill's description of the tunnel acting as a venturi is correct, and I believe that it is, the velocity of the air in the tunnel is faster, not slower, and with that higher velocity comes lower static pressure. The boat should suck down onto the water, or more likely, suck water up into the tunnel. The Kutta Effect refers to wings (and sails) which have a sharp trailing edge, resulting in the air over the top of the wing moving faster than the air on the underside of it, thus creating a pressure differential and lift. The sharp trailing edge is essential. I don't see many boats built with a sharp stern, so I'm not sure how they can act as a wing. Sorry to beat this dead horse, but I've seen the 'air cushion' claim made too many times by the marketing types and I'd like to see them 'put up' with some proof of that claim. Bob Deering Juneau, Alaska On 3/7/09 6:46 PM, "Pat Reischmann" <preischmann@msn.com> wrote: > Actually the reduction in velocity of the air going through the tunnel is more > like the slot between the jib and the main on a sailboat, the air coming out > the back is high velocity which in turn causes the air going over the top of > the boat to increase in speed creating lift, I believe it is referred to as > the Kutta effect. > _______________________________________________ > Power-Catamaran Mailing List