Do you think I should replace this?

[Nicholson58]

Originally Posted by transmitterdan

I would definitely replace that one and all the other chain plates too. You are lucky in this case that you can see the crack. Often a crack like this can't be seen with the eye. These cracks caused by corrosion in stainless steel chain plates are not uncommon and have caused more than a few dismastings.

AGREE !!!!

The cracks in our chain plates were so fine they could only be detected by using a DA sander with 800 grit to polish the SS. The crack could be seen then with a jeweler's loop.

Mine are 24" X 1/2" X 3-1/2 - total 4. I replaced with grade 5 titanium. It helped to have a machine shop. If you use Ti, shop around for the material and don't say its for a boat. Prices varied 4:1

If you use SS - specify 316L. DO not even consider 304, 305.

[Nicholson58]

Originally Posted by bletso

Bronze sounds good but which alloy? There are so many with so different properties.

Actually, I work in NDT, i.e. EC, UT, Mag particle, and dye.

Bronze for marine use, curiously, is called marine bronze. Also, admiral metal. You can do a search for this and learn a lot.

Here is a quick discussion you might find useful.
McMaster-Carr

Bronze - Admiral Metals

Naval Brass - Brooklyn, New York - Global Metals

[Trolliet]

No, the question is, 'When and how quickly?', to which the answer is, 'Several months ago'.

[Stumble]

Originally Posted by Nicholson58

Bronze for marine use, curiously, is called marine bronze. Also, admiral metal. You can do a search for this and learn a lot.

Here is a quick discussion you might find useful.
McMaster-Carr

Bronze - Admiral Metals

Naval Brass - Brooklyn, New York - Global Metals

There are probably 1000 different 'marine bronze' alloys. Some of which are suitable for chainplates others would fail in a year. Happen to know the EN alloy number?

Frankly I would go with G2 titanium instead of bronze. These days it's likely to be cheaper, and it will be orders of magnitude more corrosion resistant no matter the alloy bronze you choose. And if you want to upsize the strength switch to G5 titanium, for the same size it will be about 5 times stronger.

[Stu Jackson]

Originally Posted by bsurvey

replace ALL of them, 316 stainless and bed them in 3M 5200. you were lucky

That would define The Final Solution.

You want to seal it, not entomb it.

[Exile]

Originally Posted by Stu Jackson

That would define The Final Solution.

You want to seal it, not entomb it.

Doesn't seem like the application requires an adhesive (polyurethane) at all, but rather a caulking compound, either one of the many polysulfide products out there or butyl tape (my preference whenever feasible). "Entombing" your new chain plates with 5200 seems unnecessary, replete with downsides and no upsides. The advice to replace all of them at this point, regardless of whether add'l cracks are visible or not, seems prudent.