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Old 26-12-2010, 10:25   #1
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Fiberglass Fatigue ?

Is there such a thing? Our 125' Delta is 20 years old and we are starting to see many cracks at every level. Seems like everytime I fill one and patch it, I discover 2 more. Has the industry tracked just how long fiberglass can be reliable? Any input or opinions would be appreciated. BTW, I posted this on a thread, but then figured out how to start a new thread, hope that don't mess anyone up.
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Old 26-12-2010, 10:48   #2
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Fiberglass fatigue is generally something more prone to high speed performance boats that are subject to a lot of pounding and can start to break down the actual glass fibers, slow moving sailboats usually not so much. That being said the construction layup and how a boat is used will also play a factor.

In your particular case it should be determined if what you are seeing is gelcoat cracking or an actual breakdown of the cloth. Cracking of the gel is a very usual occurance and can be a result of several issues.
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Old 26-12-2010, 10:49   #3
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Fiberglass fatigue is a definite possibility. Anywhere that there is flexing and a hard spot can be the cause of fatigue and cracking.

You may just have gel coat cracking though. The gel coat will crack and craze when it gets older and there is flexing of the fiberglass underneath. You might want to get your ship surveyed by a good surveyor to find out what is really going on.
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Old 26-12-2010, 10:53   #4
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Now I could be wrong but as far as I'm aware fibre glass fatigue usually comes in the form of delamination... not external cracks, as stated above thats gel coat cracking through stress points like deck fittings, stanchions etc...
But.. if someone knows better I'm open to education...

PS. Does your hull 'Crackle' as it cools down at night...?
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Old 26-12-2010, 10:53   #5
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cburger, I read an article a while back of a couple that saved their sailboat (a cruiser) from sinking from a large crack in the hull caused by a hard edge of a wooden stringer. So you are absolutely right that construction and layup can play a big part in the longevity of any boat.

Delamination can also be caused by stressing the fg by any stresses that cause flexing. I doubt that you would get much delamination without it showing up as stress cracks though.
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Old 26-12-2010, 11:03   #6
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Are the cracks in the glass laminate or just in the gel coat?? Most boats will develop crazing/cracks in the gel coat over time. It's because the gel coat is a relatively inflexible medium over a relatively flexible FRP laminate. Somethings got to give when the boat flexes, and all do, and it's the gel coat which develops cracks.

Another problem is thickness of the gel coat. If the gel coat is too thick, it will crack faster and easier. Our old boat had the deck layed up on a cold day in Costa Mesa. To keep the gel coat on the cabin sides they kept spraying the cabin sides as it ran down the sides onto the cabin top, deck was laid up upside down. The cabin top ended up with very thick gel coat that was constantly cracking. I tried grinding out the cracks and filling them but the cracks kept coming faster than I filled them. Finally just bit the bullet and ground the cabin top to bare laminate and painted with LPU, no more cracks.

Another problem is design of the boat. The Tartan 34 classic had very sharp turns where the cabin met the deck. Many of these boats show a crack radiating out from where the forward and cabin sides meet. The only solution is to grind down to bare glass and coat with a more flexible surface medium. FRP likes easy turns to spread out the stress area. It's not that the FRP is going to fail but that any inflexible paint/gel coat won't be able to handle the flexing. In most cases this isn't a structural problem but purely cosmetic. That's not always the case, however. If the bulkheads are right up against the boat hull, they will make a hard point causing the hull to flux at these hard points. Some boats have experienced cracking of the laminate in such highly stressed areas. Anything glassed to the inside of the hull should have at least a small space away from the hull to prevent this hard point and attachment/reinforcing laminates extending out a good ways to spread the load.

In a 125' FRP boat, there is bound to be a lot of flexing. It's inherent in the material. Would be willing to bet you've got gel coat problems, not FRP laminate problems. The first resin reinforced boats weren't FRP (fiberglass) but CRP (cotton). These first plastic boats were built in the late 40's and some were still in surface in commercial applications when we were building our W32 in '70s. I'm sure someone has done scientific longevity testing but I'm not aware of it. In any case, would bet a properly designed and built FRP boat protected from UV radiation by a surface coat will outlast any of us. My first boat, a Columbia 26, was not a well built boat. Managed to bust the bulkheads loose sailing between the islands in the first year. That boat is still sailing between the Islands 40 years later with the bulkhead fixes that I did almost that long ago.
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Old 26-12-2010, 11:19   #7
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Fiberglass is very flexible so more than likely you are experiencing gel-coat cracks. It is a good idea to keep records of where you are finding the cracks. Here is the web link for a gel coat / marine composites expert in the USA: Home.
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Old 26-12-2010, 11:23   #8
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Any material, whether it be metal, wood, plastic, etc. will suffer from some sort of 'fatique' if it is subjected to changing loads or flexing over time. I'ts all down to the original design that determins if/when it will fail.

With GRP boats, the old adage "they don't make 'em like they used to.." applies. In the early days, the matterial was not as well understood and so everything made out of it tended to be over engineered. Classic GRP boats from the '60s and '70s tend to have VERY thick and strong hulls and for that reason, the vast majority are still in active use today.

However, as better understanding of it came about, the hulls and decks started to get thinner and thinner for weight saving and cost reasons. This thinner GRP will allow it to flex more and so you'll see much more modern boats with stress cracks, crazing, etc.

So, it's all down to three basic things. Design, Maintanance ans Use. If one of those has been poor in the past, there will be problems.
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Old 02-01-2011, 15:22   #9
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I believe that the Delta's are not gel coat, but painted construction. If your in the PNW, I would ask them to evaluate it. They have a very competent repair division if work is needed.
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