U shaped chain plates

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Yoramy
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U shaped chain plates

Post by Yoramy » Thu Apr 12, 2018 6:13 pm

Hi,
There's watter leaking through, I believe, at least two of the chainplates fitted on my Conway ketch. These are the Fw standing rigging lines running to midmast just below the spreaders. The fittings are U shaped with two legs penetrating the deck. However inside the cabin there's only a single visible plate with bolts/ There's obviously some rust on them but no cracking I could discern anywhere on the deck fitting or the plate inside. There's also water damage on the cabinetry exactly where these, and at times visibl water running in the cabinet from the chainplates.
1) Does anyone have experience with uninstalling and einstalling these?
2) Is there a second backing plate and web for each of these U fittings, it's just not visible being behind the saloon cabinet face, or does the U fitting has a single centered bolt going through the deck?
3) does anyone have experience removing (and reinstalling ...) the whole saloon cabinet face in order to gain access to all the 3 fittings (3 on each beam) for inspection or replacement?
there's an aritcle about a flawed U shaped chain plate http://www.bmse.co.uk/articles/decking-u-bolts/ relating to the oceanlord I believe but I could not find my answers there.
Many thanks for your comments!
images attached:
starboard backing plate in cabinet
Image

port plate in head cabinet (top & bottom)
port u-shaped fitting (shot through the hatch)
starboard U-shaped fitting (next to gangway)
water damage in cabinet face where the backing plates are approx.
cabinets close up and long shot
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mikebuggy
Posts: 137
Joined: Tue Jan 20, 2009 5:42 pm

Re: U shaped chain plates

Post by mikebuggy » Sat Apr 14, 2018 10:48 pm

Good evening.
I'm a yacht surveyor, and wrote that article in the BMSE forum, re U-bolt type shroud attachments and chainplates!
I'm afraid you will have to bite the bullet on these as a matter of priority. Getting at them, and getting them out is a right 'P.I.T.A' but you will just have to steadily plod your way through and work out how to do each one. Sometimes Westerly did not use the best grade S/S on their fastenings, as it was more of an expensive rarity back then than it is these days, and it was less fully understood. You have 3 issues going on here:
1. Leaking through the deck, into the surrounding woodwork and possibly into the deck core or core reinforcement. Using a small cheap moisture meter, check the deck area surrounding each chainplate to see the extent of any moisture penetration.
2. Because of the weakening of the sealant over the years and slight compression of the deck, the shroud chainplates 'work' (or flex) at the 'neck' just beneath the deck plate. This, combined with corrosion, causes fatigue failure at this point. There have been several incidents, including dismasting, across all the 'Ocean' range, particularly involving the most stressed shrouds of all, the Aft Lowers.
3. Corrosion. Both age related surface corrosion/oxydation and also crevice corrosion. The latter will typically occur on the shafts inside the deck holes where water pools but there is no oxygen. Ordinary corrosion/oxydation will present on older fastenings, particularly low grade nuts and chainplate structures which are constanly being wetted.

Failure of these fittings and fastenings can be be without warning and often have pretty serious, sometimes life threatening results. I ALWAYS advise owners in my Survey Reports to check all these fittings regularly and that ALL U-bolts should be replaced on all boats at the very least at 'mid-life'. I also advise that a proportion of the fastenings should be replaced at intervals and certainly before any long voyages.
The in-cranking angle of deck chainplates is also very critical. The shroud pull must be directly in line with the 'set' of the U-bolt otherwise early failure will result.
Sorry to sound so severe, but I'm afraid you have some serious but rewarding homework ahead!

Yoramy
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Re: U shaped chain plates

Post by Yoramy » Sun Apr 15, 2018 10:35 am

Hello mike and thank you for the reply.
im still not sure - the U fitting above deck connects to a single bolt chainplate below deck, like the one I see in the cabinet, or are there two bolts for each U fitting?
The two legs of the U fiiting are simply embedded in the hull with no nuts below, and should be pulled by force? then there's a single nut and bolt (or two?) at the center of the U fitting, going thru deck?
removel and later reassembly of the cabinetry face in the main cabin will be necessary to get to all 6 fittings. is this something you have seen done before? any tips?
re-crancking angle - you are refering to the angle between the U and the plate it is welded to? If I manufacture a new U fitting, exactly the same dimensions and angle of the existing one, that should suffice in terms of recrancking angle?
My boat is a 1979 Westerly Conway ketch, is it one of the Ocean range?
the fact that my masts are both relatively short, and each sail area smaller than sloop type sails, means that the stress on the shrouds and chainplates is lower?
many thanks!
Yoram

mikebuggy
Posts: 137
Joined: Tue Jan 20, 2009 5:42 pm

Re: U shaped chain plates

Post by mikebuggy » Wed Apr 18, 2018 9:47 pm

The U-bolts have 2 legs with nuts on the end of each leg. Usually EACH leg is bolted to a metal chainplate or bracket below decks, and these often run down either side of a bulkhead, or other piece of joinery below. So when you see a single nut and chainplate, you will usually find the other leg is often on the reverse side of the same bulkhead.
Sometimes however the U-bolt is bolted to a plate under the deck and a single bar or bracket leads from this plate down to a bulkhead or other solid piece of the boat. For this method there is usually a backing plate on the back of the bulkhead.
For smaller shrouds though there may just be a thick timber or stainless backing plate under the deck, with no chainplates.
A cranking angle is required whenever the U-bolts on deck are placed 'in-line fore and aft' as is with most Westerlys. This had to be done to allow them to be fixed squarely to the bulkheads below. The cranking angle is then the inward angle of lean of the U itself on deck relative to the deck. This is so the shrouds and the 'U' are all in a direct smooth line down to the deck. The actual U itself (well its actually more an A shaped these days) is bent above the deck plate. Do not bend the shafts below the deck plate. The Ocean range were all the later boats right up to the big ones. I used this as an example, but the principle of failing U-bolts is the same whatever the boat.
On some boats though (usually not westerlys) the U-bolts are not 'in line' fore and aft but are installed on deck around the mast with their axes/deck plates aiming in at the mast. This makes the 'hoops' automatically line up with the rigging.
Use A4 (316) stainless stuff if you can rather than the earlier cheaper stuff.
Getting into the cabinetry will be an art. I'm afraid, I have no tips, but cutting access panels is not a problem and you can always make nice timber lids to cover any holes...at least you can always get acccess afterwards! I'm not sure what you mean about the 'saloon cabinet face'...if you mean the main bulkhead....don't cut into that!...in fact don't cut into any bulkheads if you can avoid it. Better to cut through shelves brackets lockers etc either side. Where are you by the way?

Yoramy
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Re: U shaped chain plates

Post by Yoramy » Tue Apr 24, 2018 5:32 pm

Thanks Mike.
I'm not sure how can to replicate the existing cracking angle. If I get the existing U and plates to a metal shop will they be able to create identical parts I can install myself with the proper angle?
Those two legs of the U ate they embedded in resin through the deck or just screwed from below with a nut? Removing them will be destructive to the deck area?
I believe what I have is two legs below deck, one on each side of the bulkhead, and the aft leg/ plate is behind the cabinet. This is the lower fw wire, running from mid mast below the spreaders to the fw U of the three.
The next wire aft is going from mast head through spreader tip to deck U, and the one aft of it is going from mid mast to the last U aft. Both these are not around a bulkhead, but behind the saloon cabinet face. These cabinets I will have to cut holes into, 6 of them, in order to gain access. Sad but seems to be a must.
I can't be certain I totally understood your description of the cranking angle requirements, to be honest
I'm in Faro Portugal.

mikebuggy
Posts: 137
Joined: Tue Jan 20, 2009 5:42 pm

Re: U shaped chain plates

Post by mikebuggy » Fri Apr 27, 2018 2:49 pm

The U-bolts are not glassed into the deck, but t hey are heavily sealed in. Just undo the nuts below (the nuts are locked against each other so you have to hold the upper nut while you loosen the lower one first). You will need a crowbar or strong piece of pipe and some wooden blocks to act as a hinge on deck while you lever the U-bolts out. You can hammer the hoops fore and aft a bit at the same time to encourage the legs to start lifting out.
Yes a local workshop can replicate tyhe cranking angle (inward bend) you need. Make sure they bend the hoops and not bolt the legs.
Ref rigging names: The front chainplates take the forward lower shrouds, the mid chainplates take the cap (also called upper) shrouds, and the aft chainplate takes the aft lowers. On larger yachts with 2 spreader sets the mid chainplate often has to take 2 sets of wires (upper and intermediate).
Hope that helps

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