I have needed to replace the 1/4" 316 SS chainplates on my boat. They appear to have stress cracks as opposed to crevice corrosion. These plates are 25 years old. They are coming off a 28’ 15,000lb Bristol Channel Cutter.
My first shot at doing this was buying flat bar from online metals. They carry aluminum bronze. After drilling and shaping the plates they needed bent to shape. I took them to a local machine shop that does mostly marine work. They broke 3 before giving up. So at that point I either bought more and had the stock Anneled or looked elsewhere. This would have been very expensive.
I contacted Port Townsend founders, as they were known to cast plates and hardware for the Bristol Channel Cutter. I had in my possession the factory construction manual with detail drawings of the chain plates. I asked if the plates were made to factory specs… “Yes, they were”.
After 2 months the beautifully made chain plates arrived. They were the proper shape. The holes were in all the right places ect. Just like the drawings except…
The plates were 1/2 inch thick at the top area where the rigging would attach. Now this would not be much of a problem if I was using 1/2 turnbuckles. But I have a 4 year old Dynex Dux rig. The hardware (aluminum deadeyes) are sized for 1/4" chain plates.
So now I am stuck again.
I seem to have a few options:
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Buy 8 new bronze turnbuckles and fittings for the Dyneema. Cost ~300 each=2400
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Buy new aluminum deadeyes of a larger size that would fit over the 1/2 inch bronze. I would use some .02" nylon washers for insulation between the bronze and aluminum. Cost~100 each=800
Or, have the plates at the attachment point for the rigging machined down to 1/4". Cost, probably a whole lot cheaper than my other options.
Now my understanding is that manganese bronze is very comparable in strength to SS 316, if not stronger. But the bronze doesn’t work harden and fatigue like SS. Or have the problem with crevice corrosion.
So would I be in just about the same or better position with the bronze cut down to 1/4 as I would have been if I was using 1/4" SS?
Thanks in advance for any imput or advise. This really has me bummed for a number of reasons.
Gary