There is no "detectable" extra drag from the foils, in fact the opposite seems to be more the “consensus”, 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. The helm is balanced at all times with or without both hulls in the water. The foils primary function is that they reduce "pitch", both nose down and nose up, (from 2 knots to 20 plus knots) and keeps the hull platform sailing virtual horizontal to the ambient water surface at all times, and thereby stopping the mast and sail from "darting" forward and back as the hulls pass over surface undulations, this keeps the sail working more consistently (and efficiently). It greatly surprised us when looking at sailing attitude comparisons between the two cats on video, of just how much the mast of a cat without foils oscillates in relatively “flat” water and light winds when compared to a cat with foils that showed next to no pitch. Then, of course, there is the bonus of being able to make radical “bear away” (or up) manoeuvres with or without kite, and the bows never dipping more than a couple of inches.
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 equalled 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))
And ROBI you are absolutely right, it’s a “pain in the butt” not being able to put them in the standard sail box, that’s why we are altering our moulds for our sail boxes so that we can do just that (quote) “just throw them into your sail box”.
