How wide is to wide ?

How wide would you like your cat to be (if towing was not an issue)

1/2 the length is the old Rule-of-thumb.   

I am thinking wider might be better if you have a kite as it gives you some lift.

What do you thing ?

When the kite is flying it gives some lift. 

Drive harder does not necessarily mean faster......  More load on the rig / platfrom plus more drag.  More power sailing like Hobie 18 compared to efficiency like an A Class.

This is just my personal opinion which is based on no real research other than boats I have sailed before and how they felt to me.  Therefore I may be wrong, but have the manufactures using these rudders actually tank tested them.  And why don't you see them in other development classes including the C Class which is at the forefront of technology.

I would love to take an F16 without foils downwind (and around the course) in a variety of wind strenghts / sea state against an F16 with foils and compare boat speed.  This I hope would answer some questions.  I personaly question weather T foils are benificial.  I also believe you can settle a boat and drive a boat hard (and faster) through improved sailing techneques and reading what the boat is and will do, earlier.

In summary, I do believe T foils would help reduce pitching a little, but the resulting drag and compramised performance when the T foils are not needed would far out weigh any small benifit they may have.