These chainplates are around 13 years old. I noticed very soon after I installed them that they were rusting very quickly so I've kept a good eye on them over the years.
This picture of the Port Aft Lower chainplate shows the reason that I decided that now was the time to replace them.
The material is slightly magnetic so I don't think they were 316 stainless. I have decided to replace them with bronze C61400 plate. I have up-sized them from 1/4" to 3/8" thick. Overkill I know but I don't ever want to do this again.
Anyway, the interesting thing is that when I removed the stainless steel backing plate I discovered that when I replaced them 13 years ago I, or whoever was inside the boat, inadvertently trapped and crushed a negative wire behind it.
You can see a small hole in the insulation.
Here is a pic of the top of the backing plate.
It's a little difficult to see because of the reflection of the flash, but you can barely see a little pit in the metal that lines right up with the hole in the wire.
Here's the thing; When I pulled the bolts from that chainplate, the port aft lower. There were three bolts that were completely corroded through. In the next forward chainplate, One bolt was completely corroded through. None of the bolts from the other chainplates were corroded anywhere near that much.
I spoke to Ron from Ever After Marine here in Saint Petersburg, an electronics specialist, and he said that he didn't think that the squished ground wire would have anything to do with that. Though he did say that it was an unusual coincidence.
The boat hasn't been sailed that much and for most of the last decade she has been kept on a lift out of the water and I almost always turn the battery selector switch to Off when I'm not sailing.
I have a hard time believing that the squished wire didn't have something to do with the condition of that chainplate and the bolts.