No it doesn't increase the drag hugely. Just look at the NACA Charts
the thing is you are using tunnel data on the one hand and practical expectations of existing sails on t'other. Tunnel data is for a theoretical wing with no ends in a constant steady flow, the air around the sea isnt a lot like that. It could be, but more often than not it isnt.
The one example I have seen described 'Atlantis' has a wing 5.37 x 1,45m, 7.78 sq m. Thats 83sq ft. Now Im not so used to this but tell me how much less than other catamaran examples is that? Is it still 3x? I must say his interpretation of Clmax of 1.8 to be rather 'optimistic', we wouldn't ordinarily expect see figures like that without a flap, or flap and slat.
The other thing was about flaps, moving geometry doesn't come for free. Even a simple split flap adds weight and loads and arent so simple to organise. This is why they are uncommon on ultralights for example where they need to keep structures light. The additional loads generally need another spar in the afterpart of the wing. IE. They become 2 spar wings where there was just one, 3 where there were two.
Because the flow develops a camber even at mild flap depressions, and this moves the balance centroid a long way aft. Now if you are talking about a sailboat with a centre of effort that just moved aft by, I dont know what, about a metre?, what do you think happens.
Another conundrum I would like to see satisfied is what happens when by some phenomena the wing is hit by a gust or wave square on, and this is what I meant about unforeseen loads. Because now the Cdo is closer to 1, and this would be unnatural for an aircraft wing. It isnt unknown for flat stalling aircraft to break the main spar and lose their wings.
I noticed too you seemed unsure of the reynolds number, heres a one line way of working that out:
Reynolds number at sea level is written: Re = 6378 x fps x chord length
This because sea level cu ft air weight given as slug (0.00238) and subsequently viscosity, is used for engine performance. Sorry I only know how to work stuff out in imperial figures...
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Posted by: robriley@rocketmail.com
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