It would be best to phone. I used to go with my 18 ft boat but that was years ago. No helmets were required, but it could get rather hectic when all the little ww boats were there doing their stunts and they may have had an incident.
The only trouble you will run into is that they might not let you in!
They used to allow a max of 15 boats so you had to get there early. Things have obviously changed. No harm in wearing a helmet. You need one for the currents course and playing in rocks anyway.