Alctel: Here is a picture of a chain plate/deck interface on my 1980 built Cherubini Hunter 36. Believe it is the original design. For the first several years I owned my boat, I did have leakage issues. Despite raising up the deck plate, digging out the caulk and then repacking. Still leaked. I saw that the main reason was that with constant movement of the shrouds, the seal between the caulk and the vertical chain plate would begin to separate. On the third attempt, I decided to do it a bit differently as in the picture. First I sanded (with 600 grit wet/dry) the area of chain plates to which the caulking would be applied. Then I wiped with acetone to remove all traces oil/salt/dirt. Then over several applications of caulk, I built up the sloping mound. After it set firm over the next couple of days, but before I took the boat out sailing, I tightly wrapped UV resistant electrical tape around the upper caulk/chain plate joint. My thought was the added pressure of the wrap would assist keeping the caulk bond intact against the chain plate. And even if the bond did separate, water running down the standing rigging would be diverted by the tape. Seems to have worked. Five years now with no leaking into the cabin. Even during last winter's El Nino rains.
I did not use marine caulk for this. Instead roofing metal gutter sealing caulk. I had observed at home that the caulking the roofers used 10 years ago at my house was still firmly bonded to the joints of metal gutters they installed. And it was extremely pliable as well. So seemed like a reasonable product to also use for chain plate sealing duty.
