How long lasts Fiberglass?

Discussion in 'Materials' started by Vega, Apr 26, 2006.

  1. Roly
    Joined: Jul 2005
    Posts: 508
    Likes: 23, Points: 18, Legacy Rep: 222
    Location: NZ

    Roly Senior Member

    No better adhesion with epoxy? What about cores that are nearer the density of the resin?With a less fragile transition interface. And,structural cores, with a cyclic "life" greater than foam.i.e. noble timbers.

    Forget the crap poly putties & fillers in the production boats.

    Little distinction at all?

    I cannot get my head around that.

    Roly

    ps I know little about steel boats but the prospect of emersing them in an electrolyte
    does not ring any bells for me.

    Life is a trade-off. Risk free-spice free.
     
  2. Guillermo
    Joined: Mar 2005
    Posts: 3,644
    Likes: 185, Points: 63, Legacy Rep: 2247
    Location: Pontevedra, Spain

    Guillermo Ingeniero Naval

    Yes, the use of not proper resins is one of the reasons. But unproper workmanship also, I think in a bigger proportion. All FRP laminates and gel-coats allow water to migrate trhough them at a higher or lower rate (Even epoxies). Water in the laminate is not the problem by itself, but, as you mention in your later post, its reaction with encapsulated styrene.
    My nowadays 35 years old boat, duly laminated with isophtalic resins, presented hydrolisis due to a poor bonding of the 3d layer with the adjacent ones. It seems a 520 gr/sqm very tight woven roving was used, and the resin did not fully impregnated it, leaving voids where styrene accumulated instead of vaporizing out.
    I'd say most GRP old boats, even those with isophtalic resins and gel-coats, develope hydrolisis problems in a bigger or lesser extent, specially if boats are kept the whole year afloat (worse in warm waters), because it is almost imposssible to 100% guarantee hulls without styrene voids unless post-cured in ovens, which is not the case of commercial production hulls. The incidence of the problem will vary from almost undetectable for well manufactured ones to fully 'rotten' hulls with extensive delaminations in the worst cases.
     
  3. Vega
    Joined: Apr 2005
    Posts: 1,606
    Likes: 26, Points: 58, Legacy Rep: 132
    Location: Portugal

    Vega Senior Member

    You seem to diminish the problem, but even if the studies regarding prediction of aging and life time of submersed composites are few, all show an existence of a major problem:

    “Although the stress-corrosion behaviour of bulk and fibrous glasses has been extensively studied, the extension of the corresponding theories to the prediction of the fatigue behaviour of aged glass/epoxy composites has been the object of a limited number of investigations.”

    “These investigations demonstrated that the fatigue life of the material is controlled, at the microscopic level, by the progressive accumulation of broken fibers on the tensile side of the specimens. After hygrothermal ageing, the weakening of the reinforcement fibers induces a dramatic reduction in the endurance properties of glass/epoxy systems.

    The observed enhancement of the delayed fiber failure processes was attributed to the subcritical growth of cracks from fiber flaws under the combined action of stress and moisture. These stress corrosion cracking (SCC) mechanisms were found to be strongly sensitive to the physico-chemical changes induced at the fibre/matrix interface by the hydrolytic degradation of the matrix. “

    "These results demonstrate that the moisture content of the material is not the relevant parameter to describe its damage state after hygrothermal ageing. The residual lifetimes are dependent upon the whole hygrothermal history of the composite"

    http://www.mdi.espci.fr/~chateau/Fatigue/fatigue.html

    The last paragraph is very important. It shows that you can not reverse the Osmosis effects in a boat. Sure, you can dry the boat and prevent major water absorption, but the effects of the high content of the water in the fiber have already weakened the fiberglass substantially.

    Regarding also brittleness:

    “Furthermore, comparing lifetimes after ageing …it can be conclude that the ageing duration in immersion has more influence than the temperature level on the fatigue properties of the composite.

    All changes can be related to the following issues:

    Changes in the thermo mechanical properties of the polymer-matrix as a consequence of moisture diffusion.

    …the irreversible chemical degradation may be enhanced in immersion due to the leaching and the hydrolysis of a residual amount of Dicy hardener remaining unreacted in the epoxy network after cure.

    …in both cases, it is clear enough that ageing in immersion will induce stronger drops in the composite thermo mechanical properties due to higher water uptakes.[/B] The fall in the glass transition temperature could also favour physical ageing which in turn may increase DGEBA/Dicy-matrix brittleness.

    ….The creation of hygrothermal defects in the bulk composite due to water sorption processes was found to induce drastic decreases in lifetime.”



    http://www.mdi.espci.fr/~chateau/Papers/CST2.pdf
     
  4. Roly
    Joined: Jul 2005
    Posts: 508
    Likes: 23, Points: 18, Legacy Rep: 222
    Location: NZ

    Roly Senior Member

    Obviously the most important factor in this study is that water vapour migrates through epoxy at a significantly high rate and accelerates individual fibre failure by plasticising the matrix.
    The migration is already documented in the old mme test.
    http://www.seqair.com/skunkworks/Glues/WestSystem/Thinning/Thinning.html

    Thinning or no thinning. Sad, but true. Whether the butyl epoxy barriers improve this ,who knows?
    So much for epoxy paints keeping water away from a steel hull.
     
  5. Guillermo
    Joined: Mar 2005
    Posts: 3,644
    Likes: 185, Points: 63, Legacy Rep: 2247
    Location: Pontevedra, Spain

    Guillermo Ingeniero Naval

  6. Vega
    Joined: Apr 2005
    Posts: 1,606
    Likes: 26, Points: 58, Legacy Rep: 132
    Location: Portugal

    Vega Senior Member

    Well, I want to know.

    As you know all boat manufacturers apply three of four coats of epoxy barriers in the new hulls, before Applying the anti-fouling (of course it is an extra and you have to pay for it:rolleyes: )

    I guess that it offers a protection for some time, but I suppose that that time is a lot less than most people think.

    I want to ask you, and Mikejonhs (you guys look to be the more experienced members on the issue) how long that would be.

    My local boatyard says that if it is a professional boat (working boat) you should apply a new protective epoxy barrier each three years, and for a pleasure boat each 5 years.

    I don’t see why a working boat should be treated more frequently than a pleasure boat:?:

    Any comment on those numbers?
     
  7. Vega
    Joined: Apr 2005
    Posts: 1,606
    Likes: 26, Points: 58, Legacy Rep: 132
    Location: Portugal

    Vega Senior Member

    Thanks, your observation made me see that I have made an error regarding the links. I quoted two times the same link (the one you have posted).

    Now it is correct and the correction is important because the more interesting is this one;):
    http://www.mdi.espci.fr/~chateau/Papers/CST2.pdf
     
  8. Guillermo
    Joined: Mar 2005
    Posts: 3,644
    Likes: 185, Points: 63, Legacy Rep: 2247
    Location: Pontevedra, Spain

    Guillermo Ingeniero Naval

    I would like to know essays more close to the real thing. What I can say after surveying several isophtalic resins hydrolyzed hulls, is they become 'softer' and not brittler (as far as I understand the terms). Hydrolyzation eliminates isophtalic resins from laminates, so they give way easily when under load, at least in macroscopic scale. I've seen some extreme cases with almost no resin remaining throughout big areas, just barely damaged fibers. You could easily pass an screwdriver through them...!
     
  9. MikeJohns
    Joined: Aug 2004
    Posts: 3,176
    Likes: 198, Points: 63, Legacy Rep: 2054
    Location: Australia

    MikeJohns Senior Member

    Roly
    The issue with steel boats and epoxy is different, the steel doesn't absorb the water available in the epoxy, in places where the epoxy has not bonded well to the hull you will get some blistering but this is an application issue. The Epoxy does provide a good electrical barrier and this is what prevents the corrosion...preventing ion exchange. ( Note that the water in the epoxy is close to pure and pure water is a very good insulator )

    Vega
    You would like an absolute prediction.... so would I.....:).....

    If you built the boat in ideal conditions with very controlled material application and used water resistant resins and epoxy coated the result (Sealing the inside eg in the bilges is just as important.) then you will significantly slow the ingress of moisture but there will still be a significant moisture level after 10 years in the water. What happens after that is a bit of a lottery as it is with all GRP boats.

    Crack propogation is the crux in material brittleness, the plastic component of GRP cracks readily and the crack propogates until it reaches a glass fibre (on a microscopic scale) the fibre stops the crack propogating further. However the fracture collects water and leads to further failure of the fibre resin interface which is now under stress, the fibre can let go or fail under tension and the crack then propogates further. This process carries on minutely with every stress cycle...... No wonder the GRP hull loses stiffness with age.

    Note that the resin gets more brittle with age ie cracks more readily but the net result is a softening of the GRP composite

    The heavier you build the lower the stresses but heavy built boats are still prone to osmosis.
     
  10. Roly
    Joined: Jul 2005
    Posts: 508
    Likes: 23, Points: 18, Legacy Rep: 222
    Location: NZ

    Roly Senior Member

    Wish I was. I have talked to a lot of people on this issue but have no quantative conclusion to offer. Many boats seem to be in pristine condition but with only anecdotal numbers (and crew opinions) to compare their performance
    to when they were new. (Stiffness) I am not privy to surveyors case histories
    and do not know any personally that can quote cases and their particular construction in terms of failures.
    Perhaps Mike could help here. (Specifically epoxy composites, as GRP, (polyester) failures are well written on.)


    Mike,
    In timber, what approximate percentage have you found in epoxy/timber composites where there is no breach to the sheath,and they have been subjected to long term immersion?
    And how thick was the laminate in this/these case(s)?

    Ya can tell me to naff off if I am breaching doctor/patient privledge. ;)

    Roly
     
  11. MikeJohns
    Joined: Aug 2004
    Posts: 3,176
    Likes: 198, Points: 63, Legacy Rep: 2054
    Location: Australia

    MikeJohns Senior Member

    Sorry Roly I dont have statistics I can give you.
    Well saturated sheathed wood epoxy composite construction is robust and more durable than the foam core FRP, however I have not had enough to do with vessels constructed this way to form any hard conclusions. They do have their problems (what construction doesn't), but there are to few here to get a good cross section to note trends ( and no industry here producing such vessels) .

    If you are interested in the wood epoxy construction then a good start would be to read:

    The Gougeon Brothers on Boat Construction, 5th Edition
    by Meade Gougeon This book certainly takes the "hype" out of wood epoxy products .
     
  12. Vega
    Joined: Apr 2005
    Posts: 1,606
    Likes: 26, Points: 58, Legacy Rep: 132
    Location: Portugal

    Vega Senior Member

    Sorry, perhaps I didn’t explain well.

    What I have been told by local specialists is that each five years, I should scrap all anti-fouling, clean the hull, let it dry and apply a new three layer epoxy barrier, like the one that they have applied in the factory.

    They say, and it seems logical to me, that the old epoxy barrier loses efficacy till it become useless.

    What I was asking is if 5 years is the right time to put a new epoxy protection. I have some doubts because they do that every 3 years in the fishing boats.

    What is the normal practice regarding this around there?
     
  13. Guillermo
    Joined: Mar 2005
    Posts: 3,644
    Likes: 185, Points: 63, Legacy Rep: 2247
    Location: Pontevedra, Spain

    Guillermo Ingeniero Naval

    Do they? I'ts the first time I hear something like that. I'd be indeed surprised if they in fact do that every three or five years for fishing boats or whatever. Unbelivable! Aren't they pulling your leg...?
     
  14. MikeJohns
    Joined: Aug 2004
    Posts: 3,176
    Likes: 198, Points: 63, Legacy Rep: 2054
    Location: Australia

    MikeJohns Senior Member

    Vega
    What sort of hull (layup) do you have?

    We leave the epoxy coatings on unless they fail an adhesion test . I have heard of 10 year life spans for the effectiveness of epoxies in immersed situations but I have never seen any data to back that up.


    Three years sounds like scare tactics to create work. Beware of urban myths .......they abound in the marine industry.
     

  15. Vega
    Joined: Apr 2005
    Posts: 1,606
    Likes: 26, Points: 58, Legacy Rep: 132
    Location: Portugal

    Vega Senior Member

    Guillermo, I am positive that they have said that to me. It is not a fancy shipyard, it is the main one in Nazaré. As you know the port has a small Marina, but is mainly a fishing port.

    Mikejonhs, I now well the owner, and I will ask him to provide me the information that backs up that procedure.

    I have searched on the internet and I could not find any indication regarding the durability of an epoxy barrier, but it seems to me that if : “there will still be a significant moisture level after 10 years in the water”, it is probably because that barrier have lost its efficiency.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.