Old composite OK problems.
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Hi all,
Has anyone experienced longitudinal cracking and de-lamination of old GRP hulls?
Along the stringers, either side of the centreboard case and cockpit floor extending from the fore cockpit bulkhead.
Stress cracking, perhaps? Dry lay up? Or is it just that old GRP hulls wring and twist and don’t spring back into shape like plywood ones, ie typical for it’s age K-1826 Early 1980s?
I’ve cut down the crack lines with an angle grinder and scalloped them out wide, then soaked in epoxy resin and used e-glass fine mat, wet it and tucked it as far under the de-laminated areas as I can. Laminating up with more epoxy and e-glass mat and fairing off.
Seems to be stiff and solid again, but not tested as yet as there’s a few other jobs to finish before I float it.
Do you think it will hold, or will it just start cracking again?This is after I bought a glass hull thinking it would be less work than the old plywood Wyche & Coppock K-808…so far that’s not been the case.
Comments invited.
Hi,
It’s not easy to be certain about why your hull has failed like this, but I think it’s most likely that the shell moulding was just too thin, and maybe the material used wasn’t really up to a 40+ year lifespan. The cracking along the stringers and the cb box is probably because the transition from thick to thin (stiff to flexi) is too abrupt – that’s a pretty standard engineering problem:
The other things that may have contributed are the use of too much chopped strand mat in the lay-up, maybe too much resin to not enough glass (makes the lay-up brittle, but it’s a bit tough to believe: most glass boats of the era were struggling a bit to stay under weight), maybe just some technical problem like not very good control of the mix, poor cure conditions, who knows? It’d be quite interesting to know who the builder was – feel free to add your boat to the database (https://www.okdinghy.co.uk/php/boats/ – mostly it seems like the guys who were building plenty of boats back then like Seamark Nunn and Don O’Donnell had it sorted, but maybe you’re going to show that’s not correct?
Dave CooperUnfortunately class records of that era don’t state who the builder of 1826 was (unlike nowadays of course!). The boat was first registered in Feb 1976.
Andy
Thanks for the responses Andy and Dave.
I have no idea who the builder was either, no name plate or indication of any kind. It was without a bulkhead in the bows and has grp bulkheads for the cockpit, originally under-deck controls. Been re-decked at some point but quite a while ago, judging by the number of filled screw holes.
I’ll let you know how it hangs together, testing next week, hopefully.
Cheers
MarkI would definitely put in a front bulkhead to make it safer, working through the mast hole I’m afraid, but it can be done!
Andy
@andy turner wrote:
I would definitely put in a front bulkhead to make it safer, working through the mast hole I’m afraid, but it can be done!
Andy
Andy don’t worry he is a Gynaecologist! :roll:
If the boat has glass bulkheads it is probably an O’Donnel. I can’t think of any other builder who used glass bulkheads, but it must have been one of his first composite boats
Forward bulkhead installed.
Talk about papering the hall through the letterbox. Not pretty, but watertight and effective.
It’s got two big chunks of polystyrene firmly fixed under the deck, so not much chance of sinking, I hope.
Deck is thin though, maybe 4mm ply. No more sitting by the centreboard on “ghosting” days.
Mark.
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