Looking at my chainplates this fall, I saw a crack in the one for the port top shroud. The crack ran from the top bolt hole to (and through) the side of the plate. It was open, brown, and easily seen.
Later, closely examining the other five chainplates, I found smaller closed cracks in all but one. The small cracks were in groups and were visible in the sun when the chainplates were clean and shiny. Several of the chainplates had cracks that were covered by the carriage bolt heads. The one good chainplate was in an area where the boat had been damaged before I owned it, and because of some small differences between that chainplate and the others, I don’t think it was original.
Four of the cracked chainplates only had cracks in their visible surfaces. One had cracks in its face that was against the hull. That was the only chainplate which had failed caulking. It had a small bend away from the hull, perhaps from some past accident, that had separated the caulking from the chainplate.
All of the cracks were associated with the bolt holes. They did not appear to be particularly associated with the corners of the square bolt holes. Most were along the straight sides of the holes.
None of the chainplates had any crevice corrosion.
I bought and installed six new 316L shroud chainplates which I bought from Pacific Seacraft who reported that the original chainplates were 304 stainless steel. I used new 316 carriage bolts and nuts which I bought from McMaster Carr. All were ½”x 1½” except for one that was 2” long. I polished their heads before I installed them. I did reuse the lock washers that were under the nuts. Several of the bolts did not have lock washers, and I did not add them. I caulked the chainplates and bolts with BoatLife Thiokol Caulk.
1988 PSC 34