Chain plate problems? - Page 3 - SailNet Community
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post #21 of 41 Old 10-19-2009
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I'd be open to a set for the 34 as well (1997).
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post #22 of 41 Old 10-19-2009
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Quote:
Originally Posted by Waltthesalt View Post
Rust isn't necessarily a problem. .... This is a cosmetic not structural problem........
Sure, I'm in total agreement, but what's a treatment for the cosmetic problem? ....any ideas out there?
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post #23 of 41 Old 10-20-2009
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I bought a set for my 1985, 34 about 4 years ago from Pacific Seacraft (When they were in CA). I think they were $100 each. If I were to do it again, I would probably have them fabricated with drilled holes, instead of the square punched holes. Now that I think acout it, the cracks seemed to radiate from the corners of the squares. The drilled holes would eliminate that problem.
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post #24 of 41 Old 10-20-2009
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Rust blooms on any stainless cyclically loaded part should be a strong warning for two phases of degradation going on: 1. fatigue cracks and 2. crevice corrosion.

Fatigue endurance of most stainless steels is only approx. 1 million load cycles above 30% of the Ultimate Tensile values. Fatigue is 'additive' and may begin at stresses lower than 30%. Once the cracking begins crevice corrosion inevitably begins in the microcracks of the fatigue.

Id replace the bolts totally with 316 stainless, and then properly torque them down so that the whole mating 'surfaces' carries the load, not 'just the bolts'.

The chainplates should be examined very carefully for fatigue cracking (discoloration, surface rust, 'satinization' of the surface, etc.)... you can also remove them and perform some (Magnaflux) dye penetrant checking - exposed any invisible microcracks - most automotive machine shops can do Magnaflux type testing. Any area that the plates are 'bent' are usually high subject to microcracking, etc. Any plates that have done the equivalent of 'one circumnavigation' should be replaced.
Replacement plates should be flat sanded then mechanically 'mirror-polished' (follow by electropolishing if you have the extra $$$) to enhance fatigue endurance and corrosion resistance. Mill finish is 'not good enough' for chain plates, nor is any sharp edges, gouges, 'sharp' chamfers for the boltholes, deep scratches .... they should be 'perfect'/smooth/polished if you want them to last. I'd also get 316 St. Steel for the plates, preferably Stainless that is accompanied by documentation of strength, etc. (Mill Certifications) ... to avoid the 'asian crap' that is being sold for 'stainless'.

Last edited by RichH; 10-20-2009 at 01:17 PM.
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post #25 of 41 Old 10-20-2009
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Hi, I have a 1987 Crealock 34, #68. I'd also be interested in the bulk ordering of chain plates.
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post #26 of 41 Old 10-20-2009
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Quote:
Originally Posted by tager View Post
Contrary to what you might think, stainless bar is pretty cheap. It is not rocket science to make up a chainplate, either. I think if you took off the existing ones, ordered up the metal, and did most of the work yourself, you could get a machine shop to do the bends for pretty cheap.
NO SIREEEE. One doesnt simply bend stainless into shape and then expect the piece to last under cyclic tension, etc. For chainplates you DO NOT want 'sharp creases' at the bend or you induce whats known as a 'stress riser' - significantly weakens the mechanical load bearing of the metal. If you need 'bends', you want very long radiused bends ... and a shop/fabricator that 'knows' how to bend stainless without 'work-hardening' it.
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post #27 of 41 Old 10-20-2009
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Green Mountain A29 corrosion remover does a great job of removing rust from stainless (or steel). Also helps with corrosion of chrome plated equipment such as winches. This stuff seeps down between bolts and nuts (and chainplates) and helps to remove surface rust from any metal it can reach. I find that brushing or scrubbing is very rarely required. Just squirt it on, wait, and rinse it off. It's not supposed to hurt fiberglass, although I've never left it on the fiberglass for very long--wipe it off with a rag or paper towel.

FSR should take care of the stains on the fiberglass. Use it specifically as directed on the container.
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post #28 of 41 Old 10-21-2009
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Unomio, I googled Green Mountain A29 & found nothing related to a corrosion remover. Any clues about finding this product?
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post #29 of 41 Old 10-21-2009
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I couldn't find a Web presence, either. I purchased a gallon at Beacon Marine in Ventura, CA. They're a small, family-owned store, but they take phone (and VHF!) orders. Not sure what shipping regulations would be for this stuff. It doesn't hurt your hands with prolonged contact any more than Clorox does, though (personal experience).
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post #30 of 41 Old 10-21-2009
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Quote:
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Sure, I'm in total agreement, but what's a treatment for the cosmetic problem? ....any ideas out there?
have you considered Titanium? 6al-4v would be an excellent choice for this application, with your old plates as templates it would not be that expensive to fabricate. (I was quoted about 600 for all chain plates on my kp44 plus hardware). Use the same grade bolts and never worry about chain plates again. Stronger (way, way stronger), lighter and no more corrosion in the hard to inspect areas. I love Ti, its physical properties are what 316 should be! For those of you that think it is too expensive, look again the price has changed a lot in the last 10 yrs.

Nate
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