Spy photos

Can't imagine what that's about. Slats generally run span-wise rather than chord-wise like in that kite. Never seen a wing that had a chordwise slot just around the area of peak pressure coefficient (just where you wouldn't want it).

Maybe the parasail does give some lift, but the word 'hype' comes to mind. Anyone seen a tandem keel lately (at least the slot is in the right direction on those).

Strawberry, you could almost be an engineer with a diagram like that. You are of course right, but if it really worked you'd have expected the AC teams to have lapped it up !

If you think about aspect ratio and tip losses it seems a very odd thing to do.

From an aerodynamic point of view the sketch by Strawberry is very simpistic but to laymen gets the general theory across.
Chewy, you are however right that it relies on the wind to be a long way aft, and also that air does not flow from the edges to the centre.
The analogy to aircraft and the point made earlier about not having chordwise slots on aircraft explains exactly why this doesnt really work with spinnakers, however the high pressure flow on the inner surface will flow through the slot and clearly does otherwise the "lip" would not inflate. The energy losses in this system would lead to reduced performance of the spinnaker however the small vertical component created by the lip may reduce the tendancy to drop the spinni in the water while dropping it if the halyard is just blown, instead you might actually have to drag the spinni down which I guess if you are shorthanded on a large cruising yacht, not overly concerned with performance isnt a bad thing. For those seeking performance enhancements ie more power its clear that this is not the way forward.

Now we're talking....

link