Because it's over rated. The effective acceleration of air into the slot over the curve is subjected to the drag of slow moving air on the windward side of the other sail. The cats that have made it work in wind tunnels have a massive beam to overcome this turbulance.
great idea...would be super for downwind, wing and wing, how about a design with one sail, on one hull, forward of the other sail on the other hull.
--you might be on to something...time for the wind tunnel. How about the sail (tube) that spins and uses syntrifical (sp??) force for forward
movement. any engineers??
They stand in the middle at the back to steer cats - right in the middle of where you are planning to build a wind tunnel - the minute they start travelling , the wind is going to start howling through your tunnel and blow the poor sod helming straight off the back. Anyone lashed on to counteract this would just die of exposure in short time