Aluminum chain plates

[JBsurfin]

Originally Posted by amarinesurveyor

Sorry for my delayed reply. Stainless steel is less prone to elongation of the hole for the rigging attachment, and with aluminum you are then attaching stainless steel to it and will have dissimilar metals together, which will have galvanic corrosion issues. Best to use the same material all the way from top to bottom.

I have a similar setup as this owner with my 83 Dickerson Ketch. Not sure how to post a picture of my removed 1983 aluminum chain plates showing corrosion on only 2, and minimal at best and no elongation of the holes.

They were over 30 yrs old when I replaced them. Some of the orig ones are still in use after pulling and checking the condition.

[Jim Cate]

Originally Posted by amarinesurveyor

Sorry for my delayed reply. Stainless steel is less prone to elongation of the hole for the rigging attachment, and with aluminum you are then attaching stainless steel to it and will have dissimilar metals together, which will have galvanic corrosion issues. Best to use the same material all the way from top to bottom.

In the world of theory what you say is true. However, his original aluminum plates lasted nearly 50 years without failing or even suffering the corrosion and hole degradation that you posit. They also don't exhibit stress cracking or crevice corrosion, common modes of failure in 300 series s/s chain plates (and in younger ones at that).

I prefer using 2205 or other duplex alloys of stainless myself in this application but see no practical problem with use of a marine Al alloy. After all, alloy hulled yachts seem to use alloy chainplates universally, and without endemic problems.

BTW, I note that his plates are made from 1/2 inch thick bar stock. This is thicker than the typical s/s ones on yachts of his size, and the extra cross sectional area makes up for the lower yield strength and may account for the lack of hole elongation.

Jim