This is a crosspost from the YBW forums.After much rebedding of things and several rolls of butyl tape, I'm down to two leaks on my boat that I've been struggling to find. The one in question is in the forward cabin. I've borrowed a snake cam from a friend as access inside is very restricted due to a non-removable GRP liner. That and application of the hose on a sunny day narrowed it down to either the forward hatch, a U-bolt for jacklines or a hole in the deck.
I've rebedded the hatch and filled & drilled the U-bolt holes and it still leaked, so that only left the worst option. With the help of the hose I narrowed it down to a small area of the deck, which had some suspicious looking caulking. The caulking looked different from the rest - it wasn't deck caulking like the rest of the boat, more like black adhesive sealant that had failed in the sun after over a decade and was brittle, rubbing off black streaks and peeling up. I pulled on one part and a strip of sealant came up, and after scraping out some dirt I found the source of the leak - a perfectly round, evidently drilled ~4mm hole right underneath the seams in the decking strips (see photo below).
I then crawled around the foredeck with my nose down and found several more areas of different sealant, all in symmetric areas, two on each side - some of it peeling up as well. I can only conclude that this was part of the process of applying pressure to the teak decking when installing it, which as far as I know comes in pre-made panels (ply-backed) and is then glued (never screwed) into place. I previously assumed it was vacuum-bagged on, but perhaps in 2001 Bavaria instead held it down via these small holes from below, before installing the inner liner and bulkheads. Then filled the remaining seams and holes with nothing more than some black adhesive sealant. Is that a sound theory or does anyone have a better explanation for these holes? They're too symmetric and exactly at the seams to be the result of a deranged previous owner, not to mention too small to affix anything to them.
It's not a big problem, as the deck is cored with closed-cell foam and there are no signs of any core damage or delamination, so I'll let it dry out a bit, drill it for a clean edge and then fill the hole with thickened epoxy before applying actual deck caulking (ordered some TDS SIS-440) to refill the seam (cleaning and sanding the seam will be a bit of a PITA though). I fear I will end up having to do this to all the suspicious areas, of which there are about 12 in various places down the side decks. At least it'll stop leaking then!