Chainplates

As with any boat with stainless steel chainplates extending through a cored deck, we worried a bit about crevice corrosion where the ss stayed wet in the deck.  We pulled the chainplates for an inspection and found tiny traces of crevice corrosion.  A machinist confirmed that crevice corrosion is sometimes like rot where it can be more extensive inside the metal.

After discussions with various naval architects, we decided to replace the chainplates with bronze.  We used Alloy 954 which conveniently is available from McMaster Carr in exactly the same width as the chainplates.   Bronze is somewhat stronger than 316 stainless, and is immune forever to wasting or crevice corrosion.  1/4 inch bronze plate is delivered slightly over 5/16 in thickness.  We just widened the deck slots to fit the new chainplates.

We reused the bronze bolts after cleaning them up running them through a die when immersed in kerosene, and made new G10 backing plates.  We saturated the main bulkhead in epoxy when the plates were off and covered the bulkhead with a layer of 10 oz X-mat on both sides.

We asked our Naval Architect friends why SS is commonly used for chainplates when bronze is stronger, lasts forever, and the extra cost isn’t significant given the labor.  The answer was that sailors like things to be shiny.  We like never having to think about crevice corrosion again.

 

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