Broken Chainplate

[gadangit]

Me again. One of the forward bulkhead chainplates that attach to the lower spreader broke while it was at the riggers. It had been flagged by the eagle eyed surveyor as in need of a closer inspection. I didn't get the whole story, but it broke while it was getting cleaned up to be inspected. I'll post some pics when I get the plate back.

The rigger doesn't like the fact that it is a one piece design that has a flange on the deckside that is very similar to the aft bulkhead "deck hold down" chainplates. He believes that contributed to the metal fatigue and eventual failure. I'm not so certain. There is evidence aplenty of water infiltration at the chainplate and corrosion at bulkhead attachment. And, in theory, it is a 40 year old piece of structural metal.

Can someone confirm that this is an original chainplate design?

If so, should we insist on an exact duplicate? Or is a more traditional straight bar with metal coverplate like the rest going to be sufficient?

Offending chainplate is location above my elbow.





Offending chainplate, now permanently banished from boat.:0



Similar style chainplate from aft bulkhead that holds deck, (I meant my mangled interpration of Mr. Stevens very clear post.) mangled interpretation from Mr. Stevens. There is clearly a lot less stress on this chainplate, get tested?

 

[Guy Stevens]

REplace the forward ones without an intragal plate

Replace the forward ones, they are long overdue. The ultimate failure is due to crevice corrosion, that chain plate has done it's duty well and should be recycled to become something new, along with it's partner from the other side. The new chain plates should not have the plate welded onto the chain plate. The cover plate welded to the chain plate makes them a pain in the arse to bed when they leak and to leak more often. A separate plate means easier access to the bedding, and allows for a much better bedding process which will allow for a longer leak free period. Oh and you might as well have the new chain plates made of Ti, they last forever and in the current market are only about 50% more than 316 SS.

The deck hold downs should be removed and checked for crevice corrosion at the plate weld, and where they go through the deck core. The core should be inspected, and if not already done, should be removed around the hole, and filled with epoxy and filler.

It is also time to really inspect the aluminum built in chain plates. You should carefully remove the cover plates, and with a dremmel tool remove enough of the deck top skin to be able to inspect the chain plates. This area can then be filled with epoxy and filler and the deck plate fastened back in place. If done carefully there is no need for any cosmetic fixing of the area. You do need to see what is going on in the area where the chain plate goes through the deck coring. We are most concerned with poultice corrosion in the Aluminum caused from a saturated deck core remaining in contact with the aluminum for an extended period of time.

If there is poultice corrosion, then there is a relatively simple fix for this, but I will leave that solution for another post should you discover that you cap shroud chain plates need maintenance.

Really nothing here that isn't maintenance on a boat of this age, and nothing that should come as a surprise if you had a good surveyor.

Guy

 

[gadangit]

Thanks!

Nothing surprises us really. Not only did we have a good surveyor, but the boat is 40 years old and in need of repair. There are a lot of good things and plenty of bad.

I'll get to inspecting the aluminum in the next day or two...

Thanks again!
Chris

 

[exoduse35]

Really DO consider titanium replacement parts! Edd