Chain Plate Broken

[rob.lovelace]

IMG_2201.JPG (29.64 KiB) Viewed 5432 times

After a shake down trip to Tassie last month I've been going over the boat checking for anything that needs tidying up and came across this. Port side forward chainplate is broken top and bottom, and the Starboard shroud plate is also broken. I am going to replace the forward ones with SS rod and gusset the shroud plates.

[Phillip]

Rob,

Shaun and I have never seen a chain plate like that before.

Has anybody else got that bracket on their chain plates?

Phillip and Shaun

Sheltering in Fame Cove, Port Stephens from the coming East Coast Low!

[Miker]

I've of seen anything like it, and whilst I've only seen about 10 -12 Top Hats inside, I don't think they're necessary.

It appears to me that the chain plate u bolts are still in good condition, although you should remove the paint to help the stainless stay stainless. The cracking looks like it may be caused by the deck flexing under the occasional heavier stress load. This flex would be much better because it spreads the upward loading of the u-bolt plate which is moulded into the deck, than having all the stress on this one angled bracket IMO.

Perhaps have a qualified shipwright look at it for a professional opinion, but I doubt having the bracket welded the way it is would add to the strength of what are already very strong mounting points for the standard chainsplate u-bolts.

[bearmcnally]

Rob, I'm no engineer ! But I have done a bit of boat building and fitout over the years . The couple of things I see looking at your photo's are .The metal brackets I don't thing are doing anything at all apart from stopping the true loads being spread over the proper areas . The other one is the lack of glassing that has been done to join the hull flange to the deck (if any) you can see this by the hair line cracking between the hull flange and the deck,this seems to run back to the main bulkhead ?
The area under the deck should be reinforced with structural plywood or similar and then glassed over as this takes and spreads the load over the deck and hull, which is then glassed to your main bulkhead. The Bulkhead should also be bolted through to stop the glass separating from from the plywood. You might find too that the brackets have stopped the designed flex /movement in the deck and having let go that might be a good thing ?

Regards Bear

[rob.lovelace]

the upper shrouds are bolted through the deck and then through the bulkhead via angle brackets and although one is cracked they look like they work. the lowers use a angle bracket that's glassed into the hull and deck and has a brace between that's broken. I've had one engineer look at it and he said he has seen the same thing happen before and the flat bar should be rod so it can work under load without breaking. there is no plywood glassed in under the deck anywhere, except the winches backstays and headstay.

[Miker]

Rob, I reckon Bear is right. There should be a rather thick section of timber sandwiched between the deck fiberglass. It's not that visible on my boat, but I know that it's much thicker where the chainsplate u-bolts go through the deck. In some cases you can't even see the timber, but it would be there for sure.

The bracket set up I you have there is taking the full load of all the stress on that one piece of bar, and has no flex whatsoever. The u-bolts going through the deck as they do, means the load can't be spread anywhere but on that bracket. There really does need to be some flex.

Perhaps pull one of the u-bolts and see how thick the deck is, it should be fairly easy to see how thick it is, and whether there is additional stress points.

[Tales]

White Tie had only the normal bit of stainless steel strap backing up the U bolts so I don't think anything more is really needed myself.
Tales deck is 27mm thick glass (no ply) so it is a substantial bit of material.
The deck is bound to move a little as you tension the rigging so if the additional braces were laminated in with no load on the shrouds they will be taking all the load until they break and things return to normal.
Cheers,
Tom

[rob.lovelace]

just spoke to a shipwright it is a method used but he said it should be stronger although 3mm shouldn't have broken under load. I just got of a Swanson 27 which had exactly the same set up only stronger. That owner said it my have had some electrolysis who knows. anyway it is what it is, I'll repair and reinforce it and keep my eye on it on the trip north. I'm hoping the sea will be kinder than Bass Strait was.

[bearmcnally]

Rob ,this is how Swanson did their chain plate construction in a nut shell . I think the 32's plates were S/S plate approx 600 x 50 x 10 and had 2 plates welded across with holes drilled in them which were then bolted into the plates glassed into the hull .The 38 had a larger size but the same set up. It was critical that these chain plates pulled directly up and not at an out and up effect .

Cheers Bear

[rob.lovelace]

yep that's it, exactly .