Aft Lower Shroud popping out of deck!

[Tim Good]

We tacked yesterday and the deck chainplate for my aft lowers popped yesterday. The actual threaded bar had sheared below the deck.

Can I presume that a little water had got in and then over time it can corroded through the top of the threaded section?

Note we’ve sailed quite hard over the last few years and particularly coming back from the Azores recently. Had a rig check but clearly it wouldn’t pick up on something like this.

I’m now wondering if I should check all my deck fittings for the rig.

 

[pvb]

I’m now wondering if I should check all my deck fittings for the rig.

You were lucky! Best to check all the others.

 

[Baggywrinkle]

What PVB said ..... .... get the lot checked and thank your lucky stars it wasn't worse. Might have been over-tightened at some point and weakened?

 

[TernVI]

Looks a bit skinny compared to the bottlescrew?

 

[Boathook]

I would check the whole lot.

 

[vyv_cox]

Looks like stress corrosion cracking. See this page Stress-corrosion cracking and especially the Westerly Oceanmaster history. Nearly half of the total number of chaiplate bolts were affected.

 

[geem]

Looks like stress corrosion cracking. See this page Stress-corrosion cracking and especially the Westerly Oceanmaster history. Nearly half of the total number of chaiplate bolts were affected.

The chainplate looks a little lightweight compared to the size of the bottlescrew. Will this have any bearing on the failure?
I am not a fan of that style of chainplate. I had a similar failure on my mizzen mast a while ago. I think there are better ways of designing more sturdy chainplates

 

[alahol2]

Happened to one of mine a few years back. I removed checked and reseated/replaced all my chainplates. I suspected crevice corrosion inside a cored deck.

 

[Tim Good]

Happened to one of mine a few years back. I removed checked and reseated/replaced all my chainplates. I suspected crevice corrosion inside a cored deck.

Was it a total nightmare removing all the carpentry? Most of mine are behind layers of non removable cabinets.

 

[Rappey]

I am not a fan of that style of chainplate

Could you explain why, just interested as i have a similar style ?.

 

[PetiteFleur]

Similar happened to me years ago on a Jaguar 27 - the chain plates were 'U' bolts on the deck and noticed an apparent leak from one of them under the deck. Noticed that one of the nuts was not tightened fully so tried to tighten and the nut promptly sheared! Removed the 'U' bolt and there was obvious crevice corrosion on the remaining leg. Found a Wichard replacement 'U' bolt which was identical in size, removed them one by one and replaced them all. They all had evidence of crevice corrosion. Glad it was found before anything happened!

 

[alahol2]

Was it a total nightmare removing all the carpentry? Most of mine are behind layers of non removable cabinets.

No, all mine were inside cabinets and some under headlining but were relatively easy to access with a little contortion.

 

[geem]

Could you explain why, just interested as i have a similar style ?.

The type of chainplate that is a bent stainless steel rod to make a hoop then welded to a plate is full of stresses. Its stressed from bending then stressed from welding. If they are not perfectly inline with the direction of pull they flex every time the load increases and decreases. I have had failures on these chainplates a number of times but never on a simple bar type chainplate.
Heres a recent failure on a mizzen chainplate. This chainplate is lightly loaded with just 6mm rigging wire but the chainplate is made from 10mm stainless steel rod. The rod extends through the plate in the photo to a backing plate under the deck.

 

[Rappey]

I've now just read vyv Cox link and know the answer to my previous question and also thank you geem. ?
My chainplate is virtually identical to the one in your pic.
They are 37 yrs old and same diameter as rigging. Often wondered about whether they should be changed.
I'm even more concerned in that 6mm rigging broke a 10mm chainplate..

 

[Tim Good]

Just a follow up from my snapped U Bolt. As people have suggested I got them all replaced with decent custom made chainplates and updated the bolt size whilst I was there. In all it was just two aft lowers and 1 babystay.

 

[Bilgediver]

I've now just read vyv Cox link and know the answer to my previous question and also thank you geem. ?
My chainplate is virtually identical to the one in your pic.
They are 37 yrs old and same diameter as rigging. Often wondered about whether they should be changed.
I'm even more concerned in that 6mm rigging broke a 10mm chain plate..
[/QUOTE ]

I agree with Vic and suspect your chain plate had become seriously weakened due to crevice corrosion which may have been the result of water penetrating past the poor deck seal. I noticed a discolouration around the nut on one of my similar fittings whist ashore with mast down. I did a simple test with a short ring spanner and at a surprisingly low torque the fitting failed on one leg. I also replaced the others just in case. This failure is well clear of the weld at the plate.

I would suggest that anyone with this type of fitting at least checks for signs of water penetration and or discolouration around the nut/threads .

 

[alexincornwall]

Had a similarish occurrence myself with an aft lower a couple of weeks back. I noticed it had lifted from the deck. Upon investigation, it was evident that the locking bolt wasn't even making contact with the primary, which had somehow worked its way lose. Simple fix, but could have been worse. Have since gone to the effort of checking every chainplate on the boat.

There was a little surface rust on the fitting where moisture had obvious got in. Would anybody care to advise as to whether I should have replaced the fitting altogether, or would this be considered fine?

 

[Rappey]

Is just a piece of steel plate on the underside of the deck all that supports that fitting ?

 

[Tim Good]

There was a little surface rust on the fitting where moisture had obvious got in. Would anybody care to advise as to whether I should have replaced the fitting altogether, or would this be considered fine?

If it’s more than 7 years old then I would replace. Very difficult to know if crevice corrosion is working. Looks like an easy one to replace anyway.

 

[alahol2]

If you managed to tighten it down hard, chances are it's OK. I'd check that there's no possibility of water in the deck... push a coloured tissue through, leave for a few minutes, make sure it comes out clean and dry. Order up a spare fitting, just in case.