My wet rudder
I experienced a water logged rudder in my 351 after 3 years. Two of the first three years were spent in the water all year. I noticed the thing leaking when I pulled her out. I think my problem was enhanced by a shallow slip that worked the rudder in the mud on lower than usual tides. I drilled the thing in key places and sucked the water out using a strong vacume cleaner prior to freezing temperatures. I repeated this process several times, then checked it dry by blowing compressed air into the higher elevation holes I drilled in the rudder. When she was all dry I pressure filled the holes with epoxy resin, sanded and gel coated the area. I used a small diameter drill bit and went no deeper than the voids filled with water. Close examination of the water intrusion revealed osmotic blisters under the gelcoat. I specifically attacked these areas with my technique. I performed this repair after I spoke to Beneteau customer service. Keep in mind I made my repairs in 1998, so Beneteau might have a better technique by now. I also noted Beneteau changed the design of their rudder in the late 1990's with this problem in mind. Good luck.
