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Old 29-01-2015, 15:07   #16
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Re: Boats coming apart at the toerail...

Pretty interesting when you stop to think about it:

On one hand, the scientific studies showing that FRP degrades with age, and to a surprising degree even with perfect layup, etc.

On the other hand, we have hundreds of older FRP boats sailing successfully, with no particular signs of the hulls falling apart... and this with the common knowledge that early manufacturing processes were far from perfect.

What are we to conclude? Either the scientific studies don't really apply in the case of FRP boats, or the older boats really were "overbuilt", and that the overbuilding protected the structure from excessive flexing and fatigue damage, etc. I'm tentatively in the latter camp, for the studies seemed to be fairly rigorous and I tend to believe in science.

Now I'm wondering just what may be the implications of this for newer FRP builds, where much thinner "highly engineered" shells are used. There are far too many reports of hull flexing in these boats for me to believe that they are as rigid as the older, less engineered boats were. Does this relative flexibility explain the Cheeki Rafiki (sp?) type failure ? Will we start seeing more FRP structural failures as the current generation of lightly built boats start to age? I dunno, but it would not surprise me.

A sobering thought in any case.

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Old 29-01-2015, 15:56   #17
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Re: Boats coming apart at the toerail...

Jim,

The other option is that the number of cycles a boat experiences is too low to lead to this type of degradation.

Keep in mind cycle fatigue has two components, the number of cycles and the magnituge of those cycles. I don't know the expected magnitude of the stresses a fiberglass hull will absorb (as a % of UTS), but at 50% fiberglass is shown to absorb 10^6 cycles. My guess is that a hull is designed to keep loads below 20% and none of the S/N curves I could find model stresses that low.
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Old 29-01-2015, 17:00   #18
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Re: Boats coming apart at the toerail...

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Jim,

The other option is that the number of cycles a boat experiences is too low to lead to this type of degradation.

Keep in mind cycle fatigue has two components, the number of cycles and the magnituge of those cycles. I don't know the expected magnitude of the stresses a fiberglass hull will absorb (as a % of UTS), but at 50% fiberglass is shown to absorb 10^6 cycles. My guess is that a hull is designed to keep loads below 20% and none of the S/N curves I could find model stresses that low.
Good points! Considering the complexity of analysis, I doubt if many FRP boat builders do actual calculations like this... perhaps the giants like Bennie do? But for smaller producers, I suspect that a lot of the design is fine tuned seat of the pants on the part of the NAs. I surely could be wrong about this, and if someone with current knowledge cares to chime in, I'll listen and learn.

At any rate, the obvious longevity of FRP boats in general is encouraging! And my strip planked composite hull shows no signs of decay, delam, or degradation after nearly 25 years and >100K miles, so I'm smiling!

Cheers,

Jim
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Old 29-01-2015, 17:10   #19
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Re: Boats coming apart at the toerail...

When boats spend 95% of their time at the dock, not much stress involved, a few storms a year maybe.
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Old 29-01-2015, 17:45   #20
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Re: Boats coming apart at the toerail...

Just to throw in a counterpoint: http://www.ericgreeneassociates.com/..._Longevity.pdf

I have no dog (or cat) in this race....
but I hope this report is closer to the truth when compared to the scarier degradation reports.
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Old 29-01-2015, 18:40   #21
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Re: Boats coming apart at the toerail...

Every time a newer production boat suffers a structural failure there is always a group that chimes in on obvious past damage that no one new about that caused the problem. Maybe that's the case here or that the boat did indeed strike something when it was rolled as the area that failed is a real odd ball place for a failure.
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Old 29-01-2015, 18:54   #22
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Re: Boats coming apart at the toerail...

Jim, I'm fully in agreement with your second "overbuilt" option. "Overbuilding" is another word for "safety factor". All engineering uses safety factors, ranging from small safety factors in critical applications like aircraft design, to very large ones. Small safety factors require high grade design, quality materials, quality construction practices, heavy maintenance, etc. Large safety factors let you get away with a lot.

On a boat it is difficult (or practically impossible) to know what all the loads will be. There's so much variety in what the boat may see. Collisions, uncontrolled jibes, a heavy storm, etc etc. So the take away is that big safety factors cover a variety of sins in design, construction and maintenance. And they increase the chances of the boat surviving the "Oh ****" moments which happen every once in a awhile.

There's a lot to be said for strongly built boats.
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Old 29-01-2015, 19:09   #23
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Re: Boats coming apart at the toerail...

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Originally Posted by leftbrainstuff View Post
Fibreglass doesn't age as such. That being said it's time to put our propellor caps on.

Any composite is composed of a matrix (fibreglass in this case) and something to fill all the voids and mechanically key the matrix as a single homogeneous unit. (Resin)

Failure modes include physical (abrasion, impacts, fatigue, thermal, erosion and overload and chemical (UV, chemical attack, etc).

So to answer this question we need to answer some questions.

Was the failure of the resin matrix itself or the joint? You mentioned failure at the toe rail. Is it screwd, bolted, bond3d or glassed together.

Finally any delamination failure will usually be traced to a manufacturing defect. This is not a failure of the composite but a quality issue.

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FRP definetly degrades with age. In essence it never stops curing. At some point it gasses off all of it's plasticisers and becomes brittle. Depending on the quality of layup and resins this may take decades. Some boats Willard made for the USN actually tested stronger after 20 years (See this months edition of Professional Boat Builder magazine) but eventually the Willards too will degrade.

I see this off-gassing issue often in fire damage claims. Often the neighbouring vessels show no more than soot but the structure is seriously degraded and brittle due to super fast curing induced by the heat.

My opinion .... we are just entering the age of brittle, degraded FRP and will see much more of this in older boats.
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Old 29-01-2015, 19:18   #24
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Re: Boats coming apart at the toerail...

Everybody that thinks "over built" should read Gerr's book, Elements of Boat Strength. There are tried and true formulas for boat scantlings based on years (centuries?) of boat building experience. The engineers at our mass production boat builders probably could learn a lot from that book.
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Old 29-01-2015, 19:28   #25
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Re: Boats coming apart at the toerail...

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Everybody that thinks "over built" should read Gerr's book, Elements of Boat Strength. There are tried and true formulas for boat scantlings based on years (centuries?) of boat building experience. The engineers at our mass production boat builders probably could learn a lot from that book.
Couldn't agree more ! You must also remember that boats are no longer built by boat builders, they are built by accountants.

Anyone who thinks these paper thin Beneteaus, Hanse, Bavaria or jeanneau's will be around in 40 years is out of his mind.
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Old 29-01-2015, 21:55   #26
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Re: Boats coming apart at the toerail...

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Fiberglass loses a lot of strength through cycle fatigue. A excellent describtion and lab tested results are in the Gougeon Boatbuilding book available as a free download from the WEST epoxy site. Chapter 3 "Wood as a Structural Material" has these figures graphed for wood, steel, aluminum and glass and carbon. Briefly after a million cycles, accrued over about 4 years of weekend use and cruising, wood has 60% of its strength left, aluminum 40% and glass 20%.
You need to put these test results in context. Simple lab tests to failure don't correlate well with complex structures in service. These tests also exclude other in service effects. Those quoted values are meaningless other than in a lab.

Miners law gives far more reliable correlations. But you need to know the in service fatigue loadings and frequencies.
Most fibreglass hulls built before the manufacturing cost down engineers optimised the hulls wiil outlast most owners.

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Old 29-01-2015, 22:01   #27
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Re: Boats coming apart at the toerail...

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I think this is a common misconception. A polyester resin layup immersed in water certainly loses significant strength with time. Any cycle loading will produce additional losses.
The degradation due to water immersion is at best a second order decay.

Any loads, static or cyclic, that are less than the threshold predicted by miners law will not degrade any material in service.

Fibreglass is also used as tank linings for a wide range of very noxious chemicals. Done well lifetimes of many decades is common.

Failures occur far more frequently from misuse and manufacturing defects than material failure.

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Old 29-01-2015, 22:44   #28
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Re: Boats coming apart at the toerail...

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Fibreglass is also used as tank linings for a wide range of very noxious chemicals. Done well lifetimes of many decades is common.
Yes, but there is fiberglass and then again there is fiberglass. There are different types of glass in use, different weaves, different weights, etc. and there are also many different types of resins in use. I don't think it is useful to compare tank linings to common boat building materials or techniques which use mostly polyester resin with maybe several layers of vinylester resin. There are of course custom or semi-custom boats built with very strong, flexible and long lasting e-glass and either epoxy or vinylester resins.
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Old 29-01-2015, 23:00   #29
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Re: Boats coming apart at the toerail...

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Originally Posted by noelex 77 View Post
I think this is a common misconception. A polyester resin layup immersed in water certainly loses significant strength with time. Any cycle loading will produce additional losses.



This is why proper barrier coating and a dry hull is so important. To prevent hydrolysis and resulting degradation of the laminate. In essence, a properly coated hull is no longer immersed in water, as no water touches the laminate.
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Old 29-01-2015, 23:23   #30
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Re: Boats coming apart at the toerail...

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Originally Posted by leftbrainstuff View Post
You need to put these test results in context. Simple lab tests to failure don't correlate well with complex structures in service. These tests also exclude other in service effects. Those quoted values are meaningless other than in a lab.

Miners law gives far more reliable correlations. But you need to know the in service fatigue loadings and frequencies.
Most fibreglass hulls built before the manufacturing cost down engineers optimised the hulls wiil outlast most owners.

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Keep telling yourself this stuff. Time will tell and you may may get lucky!

Most boats do spend most of their time at the dock so they won't be experiencing many cycle loadings, just the degredation from immersion and sunlight. Bigger waves = more cycles as do stronger winds. Saying results of tests are meaningless doesn't make them so. The seas will be providing the unbiased tests in the long run, not a class I'd like to skip the homework in.
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