JMacLeod,
I don’t think anyone has successfully kept TC255 fishboxes dry, even with new boats with new gaskets. One posted about having a vacuum effect when trying to open the lid (running the macerator pump with the lid closed could do that) and water STILL got in.
My PO drilled holes in the bottom of the channel around the lid perimeter but still had water collect in the fish boxes. How water can ‘climb’ uphill out of that channel rather than run into the bilge through those holes is a mystery. Some suspect a ‘capillary action’ is to blame.
I personally think that the Universe is entitled to have it’s mysteries, and this is just one more of the major ones.
As long as you NEVER put fish in there, the easiest fix for cruisers is to simply disconnect each fishbox drain hose at the macerator input and lay it flat in the bilge so all fishbox rainwater drains into the bilge to be taken care of by the auto bilge pump as needed. This is easy to reverse at any time. We store the stern anchor, line, fenders, engine flush hose, etc on a Dri-Deck layer so anchor doesn’t bang up the fishbox.
My observation over the past 7 years has been that nuisance amounts of rain or washdown water prefers to dribble into the fishboxes rather than finding its’ way out via the two aft scuppers. This invites the worst-case concern about what would happen if the TC255 cockpit is pooped by a large wave (hopefully with the cabin door closed). If it didn’t capsize, how much would exit by the scuppers vs via closed and latched fishboxes? I suspect that the extra weight on the fishbox lids might prevent much further intrusion compared to nuisance water and that most would exit out the scuppers. I hedge my bet with Rule 2700g/h Gold bilge pumps replaced every 5 years.
One owner rigged a float switch into the fishbox (would require drilling a hole in the fishbox itself for the wiring). All such switches allow ½ to 1 inch of water to remain, and the switch itself takes up room and is subject to damage by whatever you throw in there.
I wouldn’t worry about it and instead plan the next Adventure.
But let us know if you find a better solution!
John