John,

I don't know what boat you are sailing, but almost certainly what you wrote makes perfect sense for all boats sharing the following features with yours':

A) The rudder blades are exactly aligned with the boards AND
B) The rudder blades are significantly shallower then the boards.

For all boats sharing this design features, the pivot in the rudder is not so important and the dagger rudder is an excelent choice.

However, some beach cats don't have boards and in this situation the pivoting feature is VERY important.

Other cats have board blades nearly as deep as the rudder blades (ARC 21, for example). If the weight is in the back or there are waves, the boards will be shallower and the rudder can hit the bottom first. In this case, the pivot is also necessary.

Cats may also be designed with the boards positioned differently from the centerline (athwartships) then the rudders and/or inclined in relation to them. In any of this cases, the boards may just miss an obstacle that will hit the rudder - and the pivot is necessary again.

Each cat design will require different rudder characteristics, so there is no "best" rudder design. Each rudder design is best for specific global design purposes and each has its own pros and cons. The best design is the one that better matches the boat's design goals.

The Tornado/A Class/Taipan style is very light, so it is very good for racing without runing aground frequently. In light conditions, a dagger rudder (of equal weight) is even better, because you can reduce the wetted surface with less dramatic rudder aspect-ratio reduction.

For frequent beaching, a pivot rudder is necessary. I dislike the Hobie rudder because it is fragile and difficult to adjust, but it is easy to find replacement parts. The Supercat/ARC rudder is more resistant to abuse and more sophisticated - its only con is that it has more components (springs, bolts, lines, etc) to fail or jam - but they do not fail or jam frequently.

The pivoting dagger rudder mixes features (pros and cons) of pivoting rudders and dagger rudders. It is an interesting compromise for a dual purpose boat, suitable for speed and for frequent beaching. It is obviously not the best design for all cats, but it certainly works. And since it has never been used in cats (as far as I know), its features must be carefully examined before deciding for or against it.

Cheers,
Luiz