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Does Fibreglass Weaken Over Time?

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Created by Shanty > 9 months ago, 26 Jun 2019
Shanty
QLD, 487 posts
26 Jun 2019 11:26AM
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i know I have said this in someone else's thread but I have all of a sudden become very interested in it. Does fibreglass weaken over time? Would, say an S&S 34 like Morning Bird have a stronger hull than say Perie Banou purely because Morning Birds 12 years younger? Let me know what you think.

rumblefish
TAS, 824 posts
26 Jun 2019 12:49PM
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To my knowledge it depends on how it's built.
Interesting thoughts on different boats....
The Laser - Top guys buy a new hull and try and leave it in a warm shed over summer to let the boat harden. But then (I believe because they are cheaply built) a Laser gets soft and it not usually competitive at the top levels after 3-4 seasons of hard racing.

The Etchells- Well built and although I don't know about hardening, I know old boats are very competitive, like 20+ years old.

senile67
10 posts
26 Jun 2019 12:48PM
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shanty, fibreglass can weaken over a very long period of time, through stress, fractures and neglect.
but imho a well looked after yacht ( like say morningbird ) will still be sailing around australia when you are singing sea shanties to st. peter.
i can imagine in 50 yrs a greenie having heart palpinations over all the toxic non-renewable fibreglass boats on sydney harbour. lol.

Bananabender
QLD, 1538 posts
26 Jun 2019 4:14PM
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Good read.
www.sailnet.com/forums/543126-post2.html

LooseChange
NSW, 2140 posts
26 Jun 2019 4:42PM
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The better question to have asked would have been "Do GRP boats weaken over time?". The short answer is yes they do, while maybe not the actual glass fibres as much but certainly the loads and stresses they subjected to will have an effect on them. The resin is definitely another culprit in the equation. Both polyester and vinyl-ester are set by the addition of a catalyst and catalysis continues on for ever, it never stops catalysing. Epoxy resin on the other hand is set by a hardener which if combined in the correct ratios will set and that will be the end of any chemical reaction, the downside of epoxy is it softens under heat and is not UV stable.

In both systems the glass fibres can still fail due to internal movement within the laminate caused by high stress and fatigue. Every time you change tack you are loading and unloading the structure by all the systems on the boat, whether that be the keel exerting forces into the hull or the shroud wires relaxing and then tensing up again. Up to this point in time no boat has just 'fallen apart' due to old age but there is definitely a finite age limit.

MorningBird
NSW, 2644 posts
26 Jun 2019 5:20PM
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I don't know the answer to this specific question but offer two related issues.
An over engineered yacht like the S&S34, Brolga 33, Valiant 40 or Currawong will not suffer as much from cracking and stress fracturing than say a lightly built modern racer. I have seen minor cracking in S&S34s, all of them older and much raced hard offshore.
The relative age of the particular yacht in a class or series of yachts is important. E.g. Because MB is the youngest Swarbrick built S&S34 and has been lightly used since launching (I'm only the 2nd owner) I will have plenty of warning of major failures. As the Association has a pretty good knowledge of many of the boats I should learn of any major failures.

Tamble
194 posts
26 Jun 2019 3:32PM
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Other factors may come into play to, but the bottom line is that flexing weakens fiberglass - a lot.
The more a structure flexes, the faster it weakens; thus the Laser example. It's not necessarily a case of badly built; all solid fiberglass dinghy type boats will suffer the same as their structure is not thick enough to eliminate panel flexing.

Foam cored dinghies suffer less from this because, for the same weight, they flex much less.

Heavier structures may not suffer such obvious panel flexing, but rig and sea loads can still flex the structure in less noticeable ways.

And if you have a balsa cored structure you have another world of problems because if water penetrates into the balsa, it quickly rots, levaing very flexi (usually) decks.

Kankama
NSW, 604 posts
26 Jun 2019 7:32PM
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I am not an engineer but there is a fair bit of this on the web and in composite books.

Like most of the above posts have said - it depends. If your laminate is loaded closer to its ultimate failure load then it will take fewer fatigue cycles to propagate cracks. Polyester laminates seem more susceptible to micro-cracking. We see this as soft laminates in Lasers, Hobie 16s and Endeavours or other old yachts with single choppy laminates.

The answer is to back off the stress by making the laminate thicker, which we often don't want to do - so we accept less life and go lighter.

Fatigue is a tricky beast. The DC 3 plane has basically no fatigue limit because they over designed the plane. It is so low stressed that the number of fatigue cycles is still way into the future. Yet more modern planes, made lighter and therefore more susceptible to fatigue, have been retired.

www.boatdesign.net/threads/material-strength-and-fatigue.13174/

So a thicker, lower stressed old boat, can have a longer and stiffer life than a newer but more highly stressed laminate. Or you could just build it in wood which is really good for fatigue which is why they build trees out of it. Pair with epoxy and you have great fatigue resistance.

www.mjmyachts.com/images/stories/pdf/sp%20advantages%20of%20epoxy%20resin.pdf

Shanty
QLD, 487 posts
27 Jun 2019 11:51AM
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Thank you for your replies. Tell me if I'm incorrect but this is my understanding. GRP does not weaken purely because of age. If a boat was built then put in a dark shed with no access to sunlight. It will not have any ware. If your boat is sitting in a marina or on a swing mooring, it is having VERY minimal Uv damage done to it. Other Than that the hull is only really damaged by not maintaining it properly or excessive use over many years.

i will also add i remember being told by my dad about wooden boats. I asked him how long wooden boats last when I was about 11. He told be "Well Mick, Depends who owns it. A wooden boat that's well built and well looked after will out live both you and I". Later on in life who also told me providing the boat doesn't rot first. The fittings will let go first.

Interesting stuff. Thanks for your answers again.
Regards,
Mick

troubadour
NSW, 317 posts
27 Jun 2019 12:58PM
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Select to expand quote
Kankama said..
I am not an engineer but there is a fair bit of this on the web and in composite books.

Like most of the above posts have said - it depends. If your laminate is loaded closer to its ultimate failure load then it will take fewer fatigue cycles to propagate cracks. Polyester laminates seem more susceptible to micro-cracking. We see this as soft laminates in Lasers, Hobie 16s and Endeavours or other old yachts with single choppy laminates.

The answer is to back off the stress by making the laminate thicker, which we often don't want to do - so we accept less life and go lighter.

Fatigue is a tricky beast. The DC 3 plane has basically no fatigue limit because they over designed the plane. It is so low stressed that the number of fatigue cycles is still way into the future. Yet more modern planes, made lighter and therefore more susceptible to fatigue, have been retired.

www.boatdesign.net/threads/material-strength-and-fatigue.13174/

So a thicker, lower stressed old boat, can have a longer and stiffer life than a newer but more highly stressed laminate. Or you could just build it in wood which is really good for fatigue which is why they build trees out of it. Pair with epoxy and you have great fatigue resistance.

www.mjmyachts.com/images/stories/pdf/sp%20advantages%20of%20epoxy%20resin.pdf


Love the timber quote
Timber and plywood is a very underrated material as long as it is built right and yes lots of epoxy

Bananabender
QLD, 1538 posts
27 Jun 2019 3:04PM
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Whenever I hear about the longevity of Timber Boats it reminds me of the fact that the original Sea Clocks built by John Harrison and so accurate seafarers were able to establish accurate Longitude sightings with a sextant were built of wood in the early 1700's and are still going at the Maritime Museum whereas the metal clocks are dormant in fear of wearing out.
Mind you each part of the wooden clock has been replaced by carpenters many times through wear etc. but it's still original!

boty
QLD, 685 posts
27 Jun 2019 3:29PM
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hull shape is also very important in composite hulls as more modern shapes with large flat panels flex more where as more traditional shapes ie ss 34s have more compound curves which flex less causing less cracking of the resin and therefore longer lifespan this gas been changed in more modern designs by better engenereing of the layup with better cores and better resins and fibers

TopHat 25 Mk2
ACT, 91 posts
27 Jun 2019 6:59PM
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Majority glass boats are moulded using polyester resin, its perfectly fine, later done repairs more likely to lift then the original glass, there pretty well bombarded when moulded, people bang on about osmosis, never seen in 35 years of glass boats and ive had alot.

Bananabender
QLD, 1538 posts
27 Jun 2019 7:07PM
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Select to expand quote
TopHat 25 Mk2 said..
Majority glass boats are moulded using polyester resin, its perfectly fine, later done repairs more likely to lift then the original glass, there pretty well bombarded when moulded, people bang on about osmosis, never seen in 35 years of glass boats and ive had alot.


Your a lucky fella albiet it was not a huge deal to fix even though it scared the sh.. out of me when I saw it for the first time and the burst blisters weeped

2bish
TAS, 805 posts
27 Jun 2019 7:21PM
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TopHat 25 Mk2 said..
Majority glass boats are moulded using polyester resin, its perfectly fine, later done repairs more likely to lift then the original glass, there pretty well bombarded when moulded, people bang on about osmosis, never seen in 35 years of glass boats and ive had alot.

Yeah I guess you've been lucky... I've just watched my mate do an extensive osmosis repair on his mid 80's Adams 40. It was riddled with osmosis. The job took 3 months and lots of $.

In the yard, where I'm up on the hard at present, there's a largish motor cruiser, 45' or so, that's been undergoing a similar extensive osmosis treatment. They are about!

Jolene
WA, 1554 posts
27 Jun 2019 5:52PM
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Select to expand quote
boty said..
hull shape is also very important in composite hulls as more modern shapes with large flat panels flex more where as more traditional shapes ie ss 34s have more compound curves which flex less causing less cracking of the resin and therefore longer lifespan this gas been changed in more modern designs by better engenereing of the layup with better cores and better resins and fibers


That's a critical point, Look at a UFO 34, or a Cole 32 from behind and they look like a tractor tube with a stick in the middle, Very tube like although the cole borders a bit on being a bit slabby forward of the beam due to the design of the flush deck, with more freeboard trying to maintaining head room in the cabin

Shanty
QLD, 487 posts
27 Jun 2019 8:26PM
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Another question for y'all. When Jessica Watson writes in her book about strengthening the hull. What would of happened there? Surely putting up more fibreglass on the in/exterior wouldn't of done anything for more hull strength?

Jolene
WA, 1554 posts
27 Jun 2019 7:04PM
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I think she removed the anchor well /chain locker, glassed in a collision bulkhead and filled it with floatation.
She sealed off the lazzerets to stop water ingress from them into the main hull ( made independent storage with own pumps) and glassed over the cockpit drain though hulls.
And most probably much more on the deck.

Shanty
QLD, 487 posts
27 Jun 2019 9:08PM
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Select to expand quote
Jolene said..
I think she removed the anchor well /chain locker, glassed in a collision bulkhead and filled it with floatation.
She sealed off the lazzerets to stop water ingress from them into the main hull ( made independent storage with own pumps) and glassed over the cockpit drain though hulls.
And most probably much more on the deck.



I meant to the actual hull superstructure. Yes she filled the anchor locker and under the V berth with flotation foam. Apparently they spent over 350,000 on it. Jesse Martin wouldn't have spent 110,000



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"Does Fibreglass Weaken Over Time?" started by Shanty