Tim, there is a long thread on this subject, "Problems with grass, the seaweed kind."

To answer your question, the crew clears the weeds on both the boards and the rudders. The skipper (presuming he or she is also the helmsperson) has to concentrate on steering. It would be hard enough for the skipper to do this while sitting on the boat without losing control of the steering temporarily, but can you imagine how hard it would be for the skipper if he or she is on the trapeze and has to come in on the boat to do it and then go back out on the trapeze? It's much easier for the crew, and the skipper can stay on the trapeze and control the boat with the main to prevent the boat from capsizing while the crew is clearing the foils on the leeward side of the boat. Also, when sailing either upwind or downwind, the jib is cleated, so the crew is free to move about the boat and take care of those chores.

As far as the skipper raising and lowering rudders during a tack to clear boards, that usually is not necessary. If you just do a slow tack, usually the weeds will fall off during the tack. Not so during a jibe, however.

I started the above-mentioned thread about problems with grass to find out how the skipper on a unirig (no crew) is able to handle the problem of clearing weeds. Unless there is a mechanical system for raising and lowering the boards from the same side of the boat, sometimes the only way to do it is to stop sailing, clear the boards, and start sailing again.

The late-summer weed problems in midwest and northern lakes are a big reason why Hobie 16's (or other boardless boats) are often the boat of choice in those places.

By the way, I like Rob Lammerts' suggestion -- convince local authorities that weeds in the lake are bad for tourism -- they foul propellers and they are a safety hazard for swimmers who may become entangled in them and drown. I think I have heard of that device he mentioned for cutting the weeds.