The propulsive power of a saildrive is P=F*v, which is P=0.5*rho*v_appwind^2*v*Ssail*Cn, with Cn as aerodynamic force coefficient, and ssail=lluff*chord
The windenergy is Pw=0.5*mass_air*vwind^2 or Pw=0.5*rho*vwind^2*Acapture*v, with Acapture is the cross section area of the wind affected air mass. A simple but wrong assumption would be 1/4*pi*lufflength^2)
Boat speed v and apparent wind will depend on wind speed vapp^2=vwind^2+v^2.

eta=P/Pwind, with all assumptions take into account leads to:
eta=4/pi*chord*cN/lufflength*(1+(vboat/vwind)^2)

eta must be <1, (the Betz law in only applicable for standing wind power plants, not for moving. Sail are not like wings, but as well not like wind turbines )
anyway we could deduce vboat/vwind = sqrt(lufflength/chord-1). Hence more chord is less speed, which is something what you have in mind, I guess.

Now I make a realty check: I was sailing with my wife on our 14sqm sail area, 8.5m luff length Javelin 16, around 225kg. My friend was sailing his T solo and Uni (around 17.5sqm and 9.x m luff, 230kg). Light winds, we had all difficulties to get the hulls out of the water. As long as we were sailing Uni, we was pretty much the same speed. However once we open our genaker (low luff of about 6m, but lots of chord), we took off and was ways faster. This happend not only one day.

So what is wrong with the theory above? It is the assumption of the capture area, because it depends not on luff length, but on sail area. If I remember right, there is good explaination in "The origins of lift" from Arvel Gentry, somewhere on the internet.


No, in strong winds the adavndage disappears. It is sometimes better, sometimes equal on these courses, but worse when beating. That's way I think Hobie has different customers in mind. More recrational sailors than racers, which are probably the bulk.

Cheers,

Klaus