Here's the problem. After about an hour in light to moderate winds, I noticed my port chainplate had pulled away from the hull a bit, tearing the hull on either side as well. Scary. Brought it in, and on closer inspection, this is what I have;

The chainplate is riveted to the hull with 4 (5?) rivets. It looks like, and I can only assume this is the way it is built, that there is a backing plate that is riveted to the hull and chainplate. I'd love for someone to confirm if this is correct.

The top rivet has totally pulled out, the second is stretched. The lower ones are fine.

The hull has ripped for about 1.5 inches on either side of the chainplate. This is not good, and I really, really hope this is not overly structural to the attachment.

So, here are my questions. The first, obviously, is how did this happen? I can't think of a scenario where the chainplate could be pulled away form the hull. The only thing I can think of is I yanked out on it while getting out/off the wire. I wouldn't think that could tear the hull, though.

What's the fix? Ideally, I'd have a quick fix to get me through the season, and a "correct" fix once I have the boat back home and in the garage. I'm thinking for the quick fix, is to remove the blown rivets, replace, drill the end of the tears to keep the cracks from propagating, seal it and keep an eye on it untill a can strip and fix correctly.

I'd love to hear from any ne who's seen this, or can offer up help for the fix.

Thanks

Chris

Chris,
You have serious structural problems. But they can be fixed. I have a hard time believing you could have pulled the chain plates off or even tore them. This requires replacing the rivets like you said. I don't know what you mean when you say "drill the end of the tears to keep the cracks from propagating" It sounds like you just want to keep the tears in check but you need to do much more. If you want to sail this boat thoughs chain plates need to be repaired strong and better than new if possible. because you don't want a major mast failure. (mast falling over). If your good with fiber glass it can be fixed. I've redone by Hobie after a storm smashed it into a bulkhead over and over. If you send me a few pics I'll help you out.
Fair & Safe Sailing ..
Jeff

Thanks Jeff

I'm quite sure it can be fixed. I guess I really need to know what the structure is underneath to know how to proceed. I've built everything from bike frames to skis in composites - have no doubt I can fix it. Just don't want to pull the boat off the lake right now if I can fix it for the short term.

Drilling the end of the crack is just a short term fix to prevent the crack from propigating.

To be clear, the chainplates themselves have not failed - just there attachment.

Chris

FWIW, here's the inside of a 5.2 hull.



You can see at the top right, the chainplate is just the single metal strip riveted to the outside of the hull, and then there's a single piece of glass laid over it.

I had a similar problem as you describe on my 5.2. The SS rivets were a bitch to get out on mine. I had two of them that needed to be replaced, and the tears in the hull (really common on 5.2s) extending out from the chainplate hole. I sanded it all down a bit after removing the rivets, filled the holes with epoxy, epoxied one piece of glass over the sanded area, the filled with fairing compound and sanded smooth. Works great.



edited by: yurdle, Aug 07, 2010 - 03:49 AM

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Rob
OKC
Pile of Nacra parts..
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The chainplates are like a cross with about a 6 inch metal piece running across the shroud chainplate just underneath the deck where the hull and deck meet. This prevents it from pulling out. Check with the factory and order 2 and replace them both

if i were you i would take more inside pics of the chainplate area. if there is a cross bar inside, like a hobie?, you'll need to pop the decks off for the repair

from the 1 pic so far it looks like there may NOT be a cross piece.....................if there isn't you may be able to butch some kind of repair without removing the decks

but once the chainplate starts moving it's hard to see how a stronger repair can be made without deck removal...

Rob - Thanks - thats just the picture I need. I'm assuming that rectangular "bulge" is some form of backing plate that's laid into the glass?

Drilled out the blown rivets today easily enough. Not quite as bad as I expected. Looks like the best fix is to go ahead put in a port aft of the chainplate so I can access the inside and either re-rivet, or more likely, just through-bolt it with something close to 1/4-20. Then, this winter, I'll pull the chainplate and glass over the damaged area as you did (can't glass & sand on the beach here...).

Any complications on installing a port? I assume cut the opening (correctly!) then screw & seal in? Any concerns with putting it close to the chainplate? Seems there should be some compressive loads there? My gut feeling is it may be better to go with a larger port and get maybe arms length away.

Hullflyer, Erice - thanks for the replies. I don't think, however, that it's a cross shaped chainplate. Pretty sure they were installed after the hull was laid up. With no stock port, not sure how you'd get it in originally. Also, I think my construction is identical to the picture above. Unless I'm missing something, there is no deck to remove.

Thanks

Chris

Chris,
Not sure what year boat you have, but there might be a bulkhead to contend with. You certainly don't want to install a port over one. If it were me, I would consult with Jack before cutting into the deck. I have done this several times, but not on the 5.7.



edited by: mummp, Aug 07, 2010 - 08:29 PM

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Philip
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Quote

Rob - Thanks - thats just the picture I need. I'm assuming that rectangular "bulge" is some form of backing plate that's laid into the glass?

The bulge is created solely by the back of the blind rivets. They're riveted into the glass and that's it. Certainly not rocket surgery, and certainly not as strong as it could be. However, after redoing mine, and keeping the same style (although I DIDN'T repair that glass backing after removing the rivets) it seems stiffer than ever, which hopefully is strong enough. I've certainly stressed the boat enough since then (although I don't think I've double trapped..) and it's done fine.

The grey portions of the top of the hull are 'removable' decks. I've pulled a couple -- it's also not tricky, but you do want to be careful if you're going to reuse the same ones.

Like Philip said, I'd consult someone that knows better before cutting if you don't otherwise have access to the inside of the hulls.

Philip - how could I go about 'consulting Jack' if I had a suitable question?

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Rob
OKC
Pile of Nacra parts..
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Performance Catamarans 714=835=6416, ask for Jack. I have replaced them in P-19s, Nacra 5.8, Nacra 6.0s and they all were shaped like a cross with the 2 pieces welded together. The 5.2s, which were earlier boats may be different, I am sure that the factory will give you the proper information. Remember they are in California, so there may be a time zone difference.

I've seen 2 early 80s 5.2s from the inside, and they're definitely just a strap with no attached crossbar. Thanks for the contact info.

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Rob
OKC
Pile of Nacra parts..
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Good to know about the deck(s) being removable. I always assumed it was just part of the hull. For sure, I'd prefer not to replace it unless I have to. What's the trick for removal?

Thanks

Chris

go to www.catsailor.com and do a search. I remember a whole thread about deck removal on the site.

Or you can try this right here on this site.
http://www.thebeachcats.c…pictures&g2_itemId=22767

I have a 1984 Nacra and earlier this year the chainplate holding the tramp pulled off and about 10 rivets popped off, and was able to fix it pretty easy. I had to buy a 4 inch inspection port a 3 foot strip of aluminum from Home Depot and 10 stainless steel bolts with locking nuts. I took the tramp off first of course. Used a jag saw and cut an opening for the inspection port. I lined up the aluminum with the chainplate and drilled the 10 holes in it. I then put a lot of sillicon around each hole and slid the aluminum in the ispection port and held it under the chainplate and by feel was able to put the washer and nut under it and tighten it with the chainplate on top of the hull and under that was the strip of alluminum. That is stronger than it was before and you can't tell by looking anything happened except for the new ispection port.