Wansworth
Well-Known Member
Going to look at an old 1966 grp yacht called an Amel Supermistral 24 any info that can help me assess the hull condition. I imagine is pre core material just thick glassfibre
Old grp yachts
- Thread starter Wansworth
- Start date
Stemar
Well-Known Member
https://sailboatdata.com/sailboat/super-mistral-sport-amel
https://sailboatdata.com/sailboat/super-mistral-sport-amel
I don't know that boat, but most early GRP boats were built like tanks. AIUI, the designers didn't know how strong grp was, so they used scantlings suitable for wood. The bottom of the hull in my Snapdragon was the best part of an inch thick! It wasn't until the early 70s that resin prices went through the roof because the oil producers put the squeeze on the West that they started to scrimp a bit. I'd expect some blisters but, unless they're huge, they're just an excuse for you to suck teeth and make a lower offer.
https://sailboatdata.com/sailboat/super-mistral-sport-amel
I don't know that boat, but most early GRP boats were built like tanks. AIUI, the designers didn't know how strong grp was, so they used scantlings suitable for wood. The bottom of the hull in my Snapdragon was the best part of an inch thick! It wasn't until the early 70s that resin prices went through the roof because the oil producers put the squeeze on the West that they started to scrimp a bit. I'd expect some blisters but, unless they're huge, they're just an excuse for you to suck teeth and make a lower offer.
coopec
N/A
Super Mistral Sport (Amel) - Sailboat specifications - Boat-Specs.com
I haven't looked at the s Stemar's specifications above but but apparently the hull (without ballast) is 1500lb (670kg) !!
I haven't looked at the s Stemar's specifications above but but apparently the hull (without ballast) is 1500lb (670kg) !!
Fantasie 19
Well-Known Member
That's a nice looking boat, and an outboard in a well also..! Any views on how well they sail??
Avocet
Well-Known Member
Avocet will be 50 years old next year. Like most early GRP boats, she was laid up ridiculously thick. You may well expect some osmosis, but you'll probably be able to afford to lose a fair bit of laminate before you compromise the strength of the hull. If you can afford the time out of the water somewhere dry, most osmosis problems are quite treatable with modern materials.
srm
Well-Known Member
I remember seeing adverts with photos of early GRP hulls being dropped into the water from a crane with weights fastened on the deck to simulate seagoing displacement. It was part of Lloyds requirements for type approval.
More recently owners of a couple of modern GRP yachts were being very complimentary about my boat, and envious of the thickness of the hull layup. Even more so when I pointed out that we had insulation on the inside and were not suffering from the heat as they were.
More recently owners of a couple of modern GRP yachts were being very complimentary about my boat, and envious of the thickness of the hull layup. Even more so when I pointed out that we had insulation on the inside and were not suffering from the heat as they were.
Rappey
Well-Known Member
Grp over 30 years old becomes brittle. New grp by comparison is a lot more flexible and could possibly be therefore stronger..
Its boatbreakers in portsmouth that brought this to light saying that it was a nightmare using their 360 to crush down newer hulls as they bounced back but old ones were so easy as they just shattered..
Its boatbreakers in portsmouth that brought this to light saying that it was a nightmare using their 360 to crush down newer hulls as they bounced back but old ones were so easy as they just shattered..
V1701
Well-Known Member
Interesting, haven't heard that before, not desirable I suppose and I wonder after how long peak brittleness is achieved. I don't think it would put me off buying an older FG boat, if for no other reason than they're the only ones I can afford to buy...
When I first went to see my 1969 Bowman 26 I couldn't believe how good the hull was, not a single hint of anything amiss anywhere, had been treated with gelshield at some time though...
To OP, get your ball pein hammer out and make like a surveyor, if it doesn't shatter before your very eyes you should be good to go...
Rappey
Well-Known Member
Im not sugesting older grp hulls are likely to fail and im sure they can take the biggest bashing the sea throws at them, but an older solid grp hull does not appear to be as strong as a much newer solid grp hull regardless of thickness.
Avocet
Well-Known Member
That's a difficult one to be objective about. Thinner fibreglass is pretty springy, but I suspect that in 30 years, modern boats laid up thinner, will be pretty much just as hard to crush as they are now. Similarly, I'd guess that a brand new hull laid up to the same thickness and using the same techniques as a 1960s boat, would be quite easy to crush?
srm
Well-Known Member
Interesting.
In the early 70's our canoe club had GRP kayaks. We used to carry 'passengers' astride the aft deck. After a while the aft deck would deflect down, but spring back if pushed from inside. By the end of the summer all aft decks were floppy, held together by the glass mat and shattered granules of resin.
Perhaps the old boats that shatter were hand laid up and resin rich while modern boats, especialy if vacuum impregnated are rich in woven glass and other fibres with a minimum of resin.
Avocet
Well-Known Member
"Deflect"?! What is this "deflect" of which you speak?! 
I think we need to compare like with like here. A kayak won't be laid up anything like as thick as a 60s or 70s yacht, so if the problem is down to repeated flexure of the laminate causing the polyester to crack, that might be a layup thickness thing, rather than an age thing?
I think we need to compare like with like here. A kayak won't be laid up anything like as thick as a 60s or 70s yacht, so if the problem is down to repeated flexure of the laminate causing the polyester to crack, that might be a layup thickness thing, rather than an age thing?
srm
Well-Known Member
I am not suggesting it is an age thing or directly applicable to old yachts. Simply an example of some hand lay up of that period being brittle. The deflection thing was a convex surface becoming concave when used as a saddle but initially springing back.
In engineering, deflection is the degree to which a structural element is displaced under a load (due to its deformation).
Apologies for obviously having upset you and your yellow faced friend so much.
In engineering, deflection is the degree to which a structural element is displaced under a load (due to its deformation).
Apologies for obviously having upset you and your yellow faced friend so much.
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[70521]
Well-Known Member
Having watched the hull flex and the wavelets through a modern hull I'll stick with my 40 year old one thanks
Praxinoscope
Well-Known Member
I would be interested to see some evidence that older GRP boat is not as strong as a new GRP.
Rappey
Well-Known Member
Trawl through boat breakers web site and you will find the evidence ,written by a surveyor and video whilst using their excavator to crush boats into a skip.. thats where i came across it, plus they featured on scrap kings quite a few times.
You can see how easy the older grp shatters but the newer grp is a lot more flexible.
I did try to find it but gave up after endless pages of blogs.
srm
Well-Known Member
The nearest I came to destructive testing of a GRP yacht was in the mid 70's. The boat was a Trintella 29 built early 60s in UK. She broke adrift in hurricane force winds (85 knots or so mean) and was blown sideways on to a pebble and rock beach. Come low water we "borrowed" a JCB and pulled her above the HW mark using wood battens to protect the bilge.
Hull damage was surprisingly low: lots of scraping of the gel coat and one area, about the size of a dinner plate on the turn of the bilge, where the gel coat and laminate was badly crazed. I assume she had landed on a rock there. This area had to be cut out and re-laminated. The hull was not punctured so no water ingress.
Hull damage was surprisingly low: lots of scraping of the gel coat and one area, about the size of a dinner plate on the turn of the bilge, where the gel coat and laminate was badly crazed. I assume she had landed on a rock there. This area had to be cut out and re-laminated. The hull was not punctured so no water ingress.
Avocet
Well-Known Member
Sorry, I think the joke rather missed its mark! No, not upset at all, just as an owner of an older GRP boat that is laid-up like a brick outhouse, "deflection" (in the engineering sense of the word), is an alien concept to me!
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Baggywrinkle
Well-Known Member
When a structure is acted upon by an external force the energy imparted needs to be dissipated. If you are lucky, you can create a rigid, unyielding structure that can dissipate the energy without damage or structural failure, if you are unlucky the damage will simply accumulate at stress points in the structure where it is weakest. This will not necessarily be visible or in the immediate vicinity of the impact.
Modern design methods allow modelling of the forces and stresses in a structure, and yielding is preferable to breakage - the reason why modern buildings can survive earthquakes and aircraft wings can flex without breaking.
This modelling results in patterns and layup plans for hulls which dissipate forces, avoid stress points, but still produce a lighter structure than previous technology delivered. Build it thick only works if you end up with no weak links, and anyone who remembers the yachting press from the 70s and 80s will know about post-production modifications to beef-up chain plates, rig attachment points, bulkheads etc.
Modern boats aren't necessarily 'weak' or 'less substantial' just because they flex more than older designs. Who knows, flexing may actually be an advantage.
Modern design methods allow modelling of the forces and stresses in a structure, and yielding is preferable to breakage - the reason why modern buildings can survive earthquakes and aircraft wings can flex without breaking.
This modelling results in patterns and layup plans for hulls which dissipate forces, avoid stress points, but still produce a lighter structure than previous technology delivered. Build it thick only works if you end up with no weak links, and anyone who remembers the yachting press from the 70s and 80s will know about post-production modifications to beef-up chain plates, rig attachment points, bulkheads etc.
Modern boats aren't necessarily 'weak' or 'less substantial' just because they flex more than older designs. Who knows, flexing may actually be an advantage.
srm
Well-Known Member
Possibly, but there was a very worried German owner of a big Bavaria yacht here a few years ago. His hull was visibly flexing while on passage and he was improvising cross braces etc to try and stop it.
While in Shetland in the 70's I was interested in the traditional open wood boats, based on Norwegian designs. In fact in previous centuries they were bought as 'flat packs' from Norway as the islands lack suitable timber. The Shetland boats were double ended clinker and very lightly framed as flexing in a seaway was regarded as improving performance.
A few pics here, you may be able to make out the frames in open boats:
Shetland boats: At the heart of our heritage | Shetland.org
The Shetland Boat: History; Folklore & Construction.