Some help with possible stress cracks in gel coat please.

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TimD
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Some help with possible stress cracks in gel coat please.

Post by TimD » Wed Aug 26, 2015 11:55 pm

My 'new' Minisprints are home and I'm in early stages of putting together a 'schedule of works'.

One of the boats has lived a hard racing life and is in need of some (minor) remedial work before I'll have to paint her.

The other is in reasonable condition (it could probably be sailed tomorrow). However both boats have something in common and that's a fair bit of gel coat crazing on the deck forward of the mast pot.

I'm not sure if this is caused by either tension from the rig (kicker/sheet etc) upwind or compression downhill but I'd like to stiffen up both boats here.

I'm thinking of grinding/sanding out a V shaped channel to form an arrow head facing forward with the point over the cracked areas and then rolling kevlar tape and epoxy in before making good.

The idea is that any tension or compression loads will be spread further around the decks and out to the gunwales.

I've asked on the Minisail forum: Rupert has suggested perhaps using carbon but I've never worked with the stuff. He suggests JimC is the man on here:)

Any suggestions/comments welcome.

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Ed
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Re: Some help with possible stress cracks in gel coat please

Post by Ed » Thu Aug 27, 2015 9:34 am

Carbon is easy enough to work with.....but not sure if it is the right thing to use in this context.

I am not quite sure what your plan is and may need a little more explanation before I could really help.

I understand you want to stiffen up the foredeck.

First thoughts are:

Is deck off or are you taking it off? Most methods I can think of would all presume that the deck is off. Not really sure how much you will be able to do without removing the deck to be honest.

You need to put something thicker and more able to take the strain under the deck and it needs to be bonded in and connected physically with the hull and some form of kingplank/samson post. I would personally put a foam/carbon (or wood/aluminium) strut as you describe and laminate it to bottom / underneath deck. Deck won't be thick enough to improve by laying in a strip of carbon I don't think.

Of course, you could just laminate a sheath of carbon over your decks. It might make a 'little' difference to stiffness, but it would look pretty cool. Better to strip the whole deck off and build new one from foam carbon. Oh feck it, why stop there, why not build a new foam/carbon hull to go with it.....and come to think abouit it, put a new rig on it too.... MX-Ray sail would be good.....I thought of doing this.... Still have the MX-Ray sail. Yours for £25.00

cheers

eib
Ed Bremner
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trebor
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Re: Some help with possible stress cracks in gel coat please

Post by trebor » Thu Aug 27, 2015 10:04 am

If you go over to minisail.org.uk, look up minisprint rebuild under technical, click on my photobucket album, scroll through photos, you will find the fix I did on my Sprint, I fixed ally sheet top and bottom.
Robert
Minisprint 4230
Tinker Traveller 160
Mirror 61147 Anastasia
http://www.aquabatdinghy.co.uk

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TimD
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Re: Some help with possible stress cracks in gel coat please

Post by TimD » Thu Aug 27, 2015 2:03 pm

Thanks guys.

Ed, I see your points; I'm probably asking far too much of a 40 yr old glass boat. If I were to redeck I'd use wood as foam sandwich would put the boat out of class. I suppose I was looking for a quick and dirty fix but thinking on it further I'm better off dremeling out the cracks, filling (with epoxy or should I stick to gelcoat filler?) and accepting and enjoying the boat for what it is.

Rob, I've already had a good look at what you've done (great job!). Didn't you put the Ali plate on the deck as it was full of holes from old fittings. I'll definitely be doing the hull below the mast pot in a similar way to yourself - thanks for that.

Incidently, what did you paint your boat with and how's it standing up?

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trebor
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Re: Some help with possible stress cracks in gel coat please

Post by trebor » Thu Aug 27, 2015 5:48 pm

I fitted plate for a number of reasons, primarily to clean up deck, but a close second was the need to reinforce mast pot, the plate does this in a number of ways it resists flexing towards front of boat and when sheeted in strong winds it resists compression. the plate does not have to be whole of deck, a simple diamond shape would do same job, under plate, deck was extensively drilled to allow plate to get a good grip, plus counter sunk pop rivets, whole thing stuck with Sikaflex, then faired in to rest of deck.

The hull plate was fitted same way, but then overlaid with matting, when ready to "matt" I drilled extra holes through ally and into hull cavity, when gel was starting to go rubbery I turned boat the right way up and gel that had gone inside through holes then sagged over and formed a sort of rivet, then finished off with gel coat filler.

The whole boat was then painted with 2 pack primer, rolled on to get a good thickness, the boat was then glossed with 2 pack gloss.
I did not attempt to get a decent finish with gloss coats, I rolled it and then lightly flatted off once dry, this gives a finish similar to a Topper.
Robert
Minisprint 4230
Tinker Traveller 160
Mirror 61147 Anastasia
http://www.aquabatdinghy.co.uk

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TimD
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Re: Some help with possible stress cracks in gel coat please

Post by TimD » Thu Aug 27, 2015 6:56 pm

Thanks Rob.

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Re: Some help with possible stress cracks in gel coat please

Post by JimC » Thu Aug 27, 2015 9:42 pm

Well, the big question is whether they actually represent something structural, or are simply gel coat crazing because the boats are 40 years old. If there's no significant structural problems, hell. leave it. Easy to get into a new wine in old wineskins syndrome. For anything of consequence I'd use glass not carbon as a better match with existing. I've not used any carbon (well almost none, a tiny little bit round the rudder pintle) on Unskol for instance.

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TimD
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Re: Some help with possible stress cracks in gel coat please

Post by TimD » Thu Aug 27, 2015 9:52 pm

Thanks Jim. A proper look over today in decent sunshine shows the cracks to be just hairline jobs: they mostly occur around stress points but that's a 'feature' of GRP. I'll dremel and fill.
Thanks again all

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