the actual “T” foils don't hold any weed (their rake lets any weed “slide” off) but the rudders (or any other rudder system for that matter), will catch weed, in exactly the same way they would normally with or without T foils.
True, however when a standard rudder catches weed, you can kick the rudder up quickly to clear, or fly a hull enough to get the rudder out of the water. With the T foil, you can not kick the rudder up and flying a hull will not see the weed fall off the bottom. The only way to clear it would be to lift the foil partly up, hang over the back and use your hands... = SLOW
The foils primary function is that they reduce "pitch", both nose down and nose up,
They may reduce pitching, however when the boat is not trimmed with the foils perfectly horizontal..... ie too much nose down or nose up..... What about the resulting drag as the foils are fighting the trim of the boat???? It may not be pitching but it would be like running with the hand break on if not trimmed correctly. These foils are non adjustable also. I believe the I14s will trim their foils neutral for down wind raking the rudder further back (nose up) as the breeze increases. Then they rake the rudder forward (nose down) for the upwind legs.
I here a lot of 'Talk' about how good they are, but am yet to see it backed up by hard data after controlled professional testing. Hence why I am the skeptic.
Then, of course, there is the bonus of being able to make radical “bear away” (or up) maneuvers with or without kite and the bows never dipping more than a couple of inches.
This is effectively using the foils to fight against the boats tendency to drive the nose down. The foils fighting against this = drag..... Better to use crew weight more effectively to control the boat trim and better seamanship on the maneuvers ie smoother maneuvers instead of using the foil as a hand break to keep the bow out.
Also, sometimes you need to round up quickly, lifting the bow up…… Such as when you are surfing down a wave in pressure and want to flick the nose up over a wave before plowing into the back off it.
The performance figures ARE slightly subjective as some were taken from race “finish time” differences between the two cats and calculated against the elapsed time of the races, while many more were taken “free” sailing over a variety of distances and comparing the two different times between the cats to their overall times for those distances, and as such I am not “claiming” them as being “written in stone”, but, the greatest difference we had was 12.5% and the least difference was 4%. More importantly, there never was any time that we tested, in any condition, where the cat with T foils was equaled by the non-foiled one, which would seem to indicate definitively that, what ever the exact difference is, there is a distinct advantage using T foiled rudders.
As an aside Stephen when we added the spinnaker to the F14 our yardstick dropped 11%. (And the F14 is one of, if not the only cat with spinnaker where the area of the spinnaker is quite a bit less than the area of the working sail(s))
To use the Tornado as an example which saw a yardstick adjustment after not only a kite was added, but a larger main sail and addition of extra trapeze........ The big T's yardstick dropped initially 4.35% from a VYC off 69 to 66. Later adjusted down to 65 which is a 5.8% drop from the original yardstick.
So if you were seeing differences anywhere near this let alone in the double figures.... You have other factors adding such a large influence on the results, that it renders your results inconclusive.
I doubt very much that the addition of foils will see anywhere near the performance increase that adding a spinnaker to a boat would.
