MB, I agree that most newer cats seem to have daggerboards which slide vertically, probably because of their hydrodynamic advantages: less drag due to a slot in the hull; the leading edge remains nearly vertical with the board partly retracted (better lift to drag ratio in that position); and the board's center of lift (or "lateral resistance" if you prefer) doesn't move aft as the board is retracted. Apologies if you knew all this stuff and I'm just repeating it, BTW.

However, pivoting centerboards have advantages in shallow water: they're not as prone to get stuck when scraping the bottom and they're really easy to free of weeds (one can even sail with the boards raked back about 45 degrees so the weeds mostly just slide off). And that's why I was asking about the fore-aft rule: it might be nice to design something legal but helpful to the mud sailing crowd.

It would be nice to know the motivation and spirit behind the centerboard rules. What sort of abuses does the rule exist to prevent?