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older composite boats

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sawman View Drop Down
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    Posted: 15 Nov 20 at 2:12pm
I have been casting around for a cheap single hander thats not a laser for a bit - I have noted a few older composite boats up for sale over the last few months -  OK, Solo mainly. These composites will be from the 70's and 80's so pre FRP and Epoxy I would guess. How does the GRP component fair at this age? Sometimes the deck have been replaced , so they look nice enough but what horrors can be lurking in the white stuff? are they all going to be dog heavy and floppy? 
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Sam.Spoons View Drop Down
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Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 15 Nov 20 at 2:44pm
I'd be wary of anything pre-FRP, at least anything originally designed to be built in plywood like the OK and Solo. GRP and big flat panels were not a happy combination until foam cores gave them inherent stiffness. 
Spice 346 "Flat Broke"
Blaze 671 "supersonic soap dish"
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sawman View Drop Down
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Post Options Post Options   Quote sawman Quote  Post ReplyReply Direct Link To This Post Posted: 15 Nov 20 at 3:00pm
guess thats my gut feeling, really. 
I had a new composite miracle a couple of years ago which was stiff as a stiff thing. But have memories of GRP ents that where dreadful even when new in the 70s/80s. 
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Sam.Spoons View Drop Down
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Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 15 Nov 20 at 3:59pm
I see old composite boats as the worst of both worlds TBH but any polyester/GRP boats gain weight and lose rigidity with age and use. Foam sandwich solves most of the stiffness problems but my mk2 Blaze has put on a few pounds over the years.
Spice 346 "Flat Broke"
Blaze 671 "supersonic soap dish"
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423zero View Drop Down
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Post Options Post Options   Quote 423zero Quote  Post ReplyReply Direct Link To This Post Posted: 15 Nov 20 at 4:03pm
When I did my 'Sprint' I weighed Hull from the beginning, after some months indoors it was over a kilo lighter, so, GRP must have absorbed some water, you then have to think about what frost has done over the years. During refurb, I put four 100mm hatches, for access, plus three 75mm access holes across stern, for bolting Cross brace (Wood inserts had rotted, so, nothing to screw into) when I turned the Hull over a couple of pints of water came from holes across the stern, this water was trapped there. When I was certain hull was thoroughly dry, I coated inside of Hull with 'Thompson' water seal, this would hopefully prevent water take up. Hull after several years appeared to be OK, plenty of stiffness, no cracks appeared or any other signs of damage.

Edited by 423zero - 15 Nov 20 at 4:07pm
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JimC View Drop Down
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Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 16 Nov 20 at 12:35pm
Originally posted by sawman

are they all going to be dog heavy and floppy? 

That's the way to bet. Old school monolithic polyester glass, especially anything involving chopped strand mat was pretty much the all time worst boat building material, certainly inferior to plywood. A "coremat" core was marginally better than solid glass. Any dinghy that has low single figures mm thick skin will be one or the other.
Foam sandwich, and other lightweight core materials, usually 8 - 10mm thick is normally better than plywood, at least if its woven glass skin not CSM. To confuse things some boats will have a thin layer of CSM under gel coat which has cosmetic advantages. Kevlar in the skins usually results in superb durability.
Carbon fibre / epoxy resin / foam core is much better than plywood unless done really badly. I would be extremely wary of anything not foam cored.
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