Check Your Chain Plates

[Maine Sail]

Maine,
Any chainplate that fails, and fails catastrophically such as in your pic, shouldnt be 'replaced in kind' or replaced with a duplicate; it should be either radicaly redesigned and/or radically 'beefed-up'. Chainplates that fail clearly show evidence that the plate was designed totaly ignoring the endurance limit of the base metal. The fatigue endurance limit for 300 series stainless is typically in the range of 30,000 psi (ultimate tensile 90,000 psi) .... plus the 'factor of safety', necessary for EVERY cyclically loaded structure needs to be increased.
If chainplates were properly designed, in the first place, one would RARELY see 'brittle failure' .... well maybe a few times in a hundred years.

I understand where you are coming from but even on the Ericson forums this is seen as a very, very rare event. There are thousands of this exact chain plate on boats of similar vintage, 1987, not experiencing failures. Maybe they will eventually..? If it were my boat I might look to beef them up but many of these Ericson's are raced very hard and have just not experienced this type of failure so maybe this is one of those "few times"??

 

[Tim R.]

Maine,
Any chainplate that fails, and fails catastrophically such as in your pic, shouldnt be 'replaced in kind' or replaced with a duplicate; it should be either radicaly redesigned and/or radically 'beefed-up'. Chainplates that fail clearly show evidence that the plate was designed totaly ignoring the endurance limit of the base metal. The fatigue endurance limit for 300 series stainless is typically in the range of 30,000 psi (ultimate tensile 90,000 psi) .... plus the 'factor of safety', necessary for EVERY cyclically loaded structure needs to be increased.
If chainplates were properly designed, in the first place, one would RARELY see 'brittle failure' .... well maybe a few times in a hundred years.

Interesting but this part has lasted 22 years on this particular boat. These are not the chainplates. It is a cast U bolt that is the attachment point through the deck to the chainplates. I have the same type of attachment to my chainplates which are 24 years old. My boat has been raced for much of it's life. I believe this failure was not a design flaw but rather a manufacturing defect compounded by corrosion. I searched the Ericson Yachts website and found no other mention of this failure although there is some discussion of water leaks around them.

As for Hunters being better built boats...well, I will just let the experts debate that one. Franklin, chainplate bolts 1 1/2" in diameter? That would make the bolts stronger than the bulkhead it is attached to. Many larger boats have smaller keel bolts than that.

I really have to learn to type faster!

 

[Ross]

I expect that those U-bolt chain plates were forged. They appear to me from this distance to be about 5/8 inch. that would give them a cross sectional area of 0.30sq inches. That times RichH's 30000 psi limit would give 9000 psi maximum allowable loading. Unless someone were lifting the boat by that shroud and shaking it like a dog shakes a rat it was more than adequate for the job. A close examination would probably show a flaw at the shoulder that started the crack. Even if it is half inch the numbers then come up at 6000 psi maximum allowable loading

 

[bffatcat]

chain plate failure a last resort

If you cannot get a machine shop to fabricate a substantial duplicate, You might consider Heavy stainless bar stock. Thru bolted to the outside of the hull and back with a heavy
plate inside. It migth not look as pretty. But It will work and it wont fail