Chain plates Your views and comments

rogersimms

rogersimms

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Hi All

The pictures below shows the chainplates for the upper and lower shrouds on my mizzen mast. It has been leaking for some time and it appears to have rust and stains from the teak decks. The decks look as though they have lifted but shows no evidence of this when looking at the deck head. Also the decks have been planned down so this could be why they look as though they have lifted

My concern is, is the stainless steel still OK. I have been advised to remove the deckhead plates and create a new plate that would cover both shrouds and make the dimensions a little bigger for better support as they do not look big enough. Or do I need to renew everything.

I am in India at the moment and getting anything made in 316 is a problem. I do not want to remove everything and leave the boat for a month to have it made new in the UK. This is the Monsoon Season and I dont think it wise to leave the mast temporarily supported

I am very interested in your comments and views
 
First question is whether the plates and nuts are stainless steel? They look rather rusty, which suggests they might be a 400 series, or even carbon steel, but maybe not 300 series? Test with a magnet, 300 series won't attract but the others will.

It's impossible to know from your photos whether the chain plates are in good condition between the deck. All you can do is undo one at a time and withdraw it, to see whether significant corrosion or other wasting has occurred. Assuming them to be OK you need to prevent further water ingress. Sealant is the easiest method but perhaps not the best. Difficult to say but perhaps there is a seal of some sort that has perished? If you have to leave the boat I see no reason why you should not apply loads of Sikaflex 291 to each joint, check sealing with a hose pipe.

The design of the underdeck plates may not be ideal but personally I see little reason to change them in a hurry. Why not make cardboard patterns of a new single plate with the holes in the right places and have that made up in UK, together with any new seals that you may be able to determine.
 
Any rusting should be investigated, it could be crevice corrosion that has led to the leak.

It would also help if the backing plate was larger to spread the load over a wider area and reduce movement, thus reducing flex and stress on the seal.

Converting the twin plate to single a suggested above would be a good step in the right direction.

Meantime it should be pulled apart and inspected then a temporary seal applied.

Note: When installing the new back plate, fit it dry first to make sure everything lines up.
Then apply some resin mixed with Micro-Fibres and bolt up till you have about a 1 or 2 mm gap all round, leave this overnight and tighten the next day, this will ensure the load is spraed over the uneven existing surface as well providing a good seal.

Hope this helps.
 
It looks to me as if these u-bolts are set in the deck planks so any tension will try to lift the decking.
I am no expert but surely that cant be right. The rigging forces should be transferred to a verticle member (ie bulkhead or outer skin) thru a fixing that is in shear not tension.
 
Well, although it doesn't look like an exquisitely engineered installation, the chain plates have obviously lasted a fair few years, and there probably isn't a lot of load on mizzen shrouds anyway. However, I'd be very wary of the rust stains, and I think the simplest solution would just be to replace them - ideally re-using the existing holes and backing plates for simplicity. If you don't replace them, I don't see how you'd ever be certain that crevice corrosion wasn't present, and U-bolts aren't expensive items (in the overall scheme of boaty bits!).
 
Thanks

Many Thanks for all your replies. I will be buying new fittings in the UK and replacing all 4 on my return, Please can you let me know if these are standard fittings off the shelf or must these be ordered to spec. If ordered to spec is the U bolt one solid piece then bent to the correct radius and then welded to the plate. Lastly any suggestion on where to buy or have made.

Thanks again.
 
U-bolts are standard fittings, produced in a huge range of sizes. You can get round ones or triangular ones. I'd have thought there's absolutely no need to get them custom-made (and you'd be frightened by the cost of doing this!). Just Google for stainless u-bolt deck and you'll find loads of off-the-shelf items.
 
rogersimms said:
Many Thanks for all your replies. I will be buying new fittings in the UK and replacing all 4 on my return, Please can you let me know if these are standard fittings off the shelf or must these be ordered to spec. If ordered to spec is the U bolt one solid piece then bent to the correct radius and then welded to the plate. Lastly any suggestion on where to buy or have made.

Thanks again.
Click to expand...

Sailspar in Brightlingsea will either supply something off the shelf or fabricate it for a reasonable price.
 
My concern would be as much about water getting into the deck structure as whether the U bolts would fail. Very bad construction to have holes through the teak deck where there are so many seams. Take the bolts out as soon as you can and dry out the holes. If you are lucky, water may not have got into the substrate (probably cored grp) and you can seal with epoxy. If the threads and welds are sound, clean off the surface staining and re-bed the fittings in Sikaflex to both seal the stainless and prevent water from getting in.

Then go over the whole of the deck, as it is likely that other fittings that are fastened through the deck will have similar problems.
 
>custom-made (and you'd be frightened by the cost of doing this!).

Out of interest commercial kitchen manufacturers use 316 stainless. We had two pole mounts made each to carry two poles. A marine fabricator wanted 150 quid the pair plus VAT. Kitchen folks wanted 75 quid cash.
 
Tranona said:
Very bad construction to have holes through the teak deck where there are so many seams.
Click to expand...

There really isn't much alternative with teak decks, is there?



Tranona said:
If the threads and welds are sound....
Click to expand...

I'm not sure any ordinary person could tell this for sure. U-bolts are cheap to buy, so it's surely better just to replace them and sleep soundly at night.
 
KellysEye said:
Out of interest commercial kitchen manufacturers use 316 stainless. We had two pole mounts made each to carry two poles. A marine fabricator wanted 150 quid the pair plus VAT. Kitchen folks wanted 75 quid cash.
Click to expand...

Interesting to know that, could be useful in the future. I said the cost could be "frightening" because I actually got a quote recently (from someone recommended on this forum) for a very simple stainless tray-type cradle for a liferaft, to be used with webbing straps to hold the liferaft down. The quote was around £500.
 
pvb said:
There really isn't much alternative with teak decks, is there?





I'm not sure any ordinary person could tell this for sure. U-bolts are cheap to buy, so it's surely better just to replace them and sleep soundly at night.
Click to expand...

Still does not make it a satisfactory method of construction. Sort of OK if the hole goes through one plank, but these fittings go through an area where planks join at different angles - already weak points from the point of view of water ingress should the sealant fail.

The OP says he cannot get SS fitings made where he is, so inspection and re-use is worth a try. I suspect that there is little load on these fittings and a single fitting to take both shrouds could be designed.
 
pvb said:
U-bolts are standard fittings, produced in a huge range of sizes. You can get round ones or triangular ones. I'd have thought there's absolutely no need to get them custom-made (and you'd be frightened by the cost of doing this!). Just Google for stainless u-bolt deck and you'll find loads of off-the-shelf items.
Click to expand...

Go for triangular ones rather than round if you can get ones to fit the old holes. I heard of stories of Westerly stay failures where they had used round U Bolts - and these had failed due to (I think) the higher stresses put into the round version due to its shape.
 
Westerly's also had problems with triangular ones but that was due to them not being cranked to line up with the shroud properly. Crevice corrosion is also a problem where the bedding compound has failed and allowed water to seep underneath the upper plate and get in to the balsa core of the deck. This remains wet and so...
 
It is better to avoid U bolts entirely.You can have plates made with rectangular tangs welded at 90º (vertically)which will be drilled for the rigging screws.The base plates should have four holes to take the bolts through the deck to backplates.U bolts have a very poor reputation.
 
30boat said:
It is better to avoid U bolts entirely.You can have plates made with rectangular tangs welded at 90º (vertically)which will be drilled for the rigging screws.The base plates should have four holes to take the bolts through the deck to backplates.U bolts have a very poor reputation.
Click to expand...

I might agree with you on a main mast, but we're talking a mizzen. U-bolts will be fine.
 
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