Dave

I've never heard an engineer (worth his salt) say or even admit "It will never work". Of course there is diminishing returns.

However, most sailboat sails are such an inefficient foil.

There are an infinite number of foil sections that could be used and an infinite number of construction details that could be incorporated into a wing sail.

You could make the sail have an inflating leading edge (coupled with battens) back as far as you would like, as the "Wills Wing" "Ram Air" hang glder did.

They simply had a scoop that collected the air. As the glider went faster more air went into the foil which of course stiffened it.

You could also have wing warping as the "Wright Flyer" did and as do modern hang gliders. This is easily accomplished with pulleys etc..

As far as wind gusts, all aircraft deal with them. Wind tunnels are only for prediction.

All you need is a designer to look at different concepts and then look at the people around who have grappled with the same problems.

Wind surfers were using (I don't know if they still are) double surface to increase efficiency of the sails.

Actually wind surfer sails all have an instant aeronautical advantage over sail boats. They all have a sleeve which slides over the mast. Just this sleeve is an advantage because you get a linear flow of air from the mast on back. You eliminate the interference drag of the mast / sail connection. When you consider the airfoil has disrupted airflow right from the mast, this has to be a large drag component.

As far as speeding through lulls is concerned, soft sails I would predict would be very inefficient because in a lull they can flop around whereas a stiff airfoil is not prone to flap and consequently doesn't waste energy doing it. That's (one reason) why mylar sails are used. Whenever you hear your sail flap, you are hearing energy dissipate. By placing the mast at the correct spot (In a wing sail) you eliminate a lot of the fighting with the sail that we do when sailing. This fighting while very macho (requires pulleys etc.) is really a waste of energy.

BTW there is a nice pic of a wing sailed cat in Jan. 2004 Popular Science page 40. An ad for Canon digital printing. While it is beautiful to look at I can see where a solid wing mast like that might pose logistics problems in high winds and when storing.

However after saying all of this about that, I completely understand why wing sails were disallowed from racing. At this stage in development, the concepts put forth are not practical from the point of view of the average racer, similarly I suspect foils are regarded in the same light.