My experience comes from the small numbers on the measuring tape. I sail an 8 foot pram. I aimed my criticisms at John's plan because his boat is also quite short. In boat hulls there is no way to overcome a very short waterline. That means they are slow while running and very slow while tacking. Saddling yourself with a short waterline and a sail that may or may not be up to par is OK if you are not trying to get someplace. For a while I was in that mode. Happy what I had built worked and not interested in getting anywhere. But, eventually I did try to get places and often had to turn back because it was taking too long. I did everything I could to set the boat up properly so I have no doubts that the only way to more speed is to fly a properly made sail with more square feet.
What John is attempting is to use a low technology method to make a complicated high technology sail. High aspect, bat-winged and battened. And to mount it on a boat that wasn't designed for sail. If it works it will be apparent. If it doesn't work he won't know if it's the boat the, sailing set-up or the sail. By introducing a lot of variables, finding and overcoming the faults will be more than a chore. I think he would further his project by buying a good used sail of an appropriate size and using it till he is certain he has everything else sorted out.

: let's not put too fine a point on it, shall we.
: if you look through the Polysail website you will see pics and testimonials
: that clearly show that they can, and do, work and they work well. a single
: piece of material can be easily cut in such a fashion that it has no
: choice but to create a foil shape once it is tied to the mast and yards
: (or boom).
: sure, i wouldn't expect polysails to stand up all that well on an America's
: Cup racing yatch, but i would not hesitate to use them on ANY day-sailer.
: even trailer-sailers like the Weekender, Voyager, and cabin-built Sharpies
: would be well served by a suit of polysails.
: i used to own a Grampian G-28 that carried $4000 worth of Dacron to make it
: go. my next build will be a Norwegian Faering that will fly a balanced lug
: sail made of polytarp that will cost me about fifty bucks and an
: afternoons labour.
: durability? there are testimonials on the polysail site that show that, if
: properly looked after, some sails are still in service after five years.
: not bad for 50 bucks and an afternoon in the back yard!
: Daren....
: ps; i have no affilliation with Polysails. i just think that it's a great
: idea for small sailboats.