fiberglass over steel?

Discussion in 'Boat Design' started by boredman1, Dec 11, 2014.

  1. MikeJohns
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    MikeJohns Senior Member

    Sure there are various resin types and fillers with differing properties but all Polyesters and vinylester too, have hydrolysable ester groups in their molecular structures regardless.

    A good engineering guide to long term design composite strength is "Composite Materials in Maritime Structures" Vol 1 & 2 Cambridge University Press

    http://www.bookdepository.com/Compo...Aspects-Fundamental-Aspects-v-1/9780521451536
    http://www.bookdepository.com/Compo...ns-Practical-Considerations-v-2/9780521451543
     
    Last edited: Dec 23, 2014
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Needless to say, you can always "waterproof" the resin/glass with suitable paint, so that isn't a big deal.
     
  3. ondarvr
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    ondarvr Senior Member

    Probably some very good information in them about general polyester chemistry, effects of long term immersion and fatigue characteristics. The problem is they normally only cover the typical resins (resin chemistry) used buy builders, not the higher end products that very few use due to cost or other concerns, but are available and work far better.

    The cost of these high end polyester based resins is lower than epoxy, but higher than other polyesters, and typically polyester is chosen for cost concerns and to meet a minimal standard, not to exceed a spec or performance need. Cost and ease of use are frequently primary concerns when using polyester in most applications.

    Working for a very large global resin and gel coat manufacturer and working closely with the chemists and lab, allows me access to test results and resin formulations that the average commercial boat builder would never consider because his resin price would go up .20 cents per lb.

    Much of what I see in the polyester fabrication world are penny pinching designs and material specs, along with a low paid, minimally skilled work force with little supervision, trying to pull off some rather large projects that require far more attention to detail and skill than the fabricator (company) is capable of providing.

    This doesn't add up to a final product that has a great chance of succeeding long term.
     
  4. pdwiley
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    pdwiley Senior Member

    Or you can apply suitable paints directly to the blasted steel and save a lot of time, aggravation and mess.....

    PDW
     
  5. MikeJohns
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    MikeJohns Senior Member

    That's why I was defining waterproof earlier. It doesn't mean impermeable and a lot of these terms like waterproof are quite misleading.


    Water molecules will slowly permeate any paint, epoxy included. The underlying material will eventually saturate and there can be no loss of water molecules into the interior when it's over an impermeable barrier (in this case steel).
     
  6. MikeJohns
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    MikeJohns Senior Member

    They cover every formulation, fibre and fibre treatment. I think you should read volume 1, and the organisation you work for should certainly have it as a reference.

    Beware, dry coupon tests from the lab are next to useless for long term immersion properties. From memory, coupons boiled continuously for 4 days prior to testing give you the propereties of a fresh layup after 1 year immersion.
     
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  7. Mr Efficiency
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    Mr Efficiency Senior Member

    The only thing that might justify it is a steel hull that has been extensively compromised by loss of metal to rust, with pitting or pinhole perforations. It might extend the useful life, but the cost versus benefit would have to be weighed up.
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    As the saying goes, we are all dead in the long run, if it extends the life of the hull, it might have some merit. But not if it is going to accelerate corrosion.
     
  9. ondarvr
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    ondarvr Senior Member

    They can't cover every formulation, it would be impossible, every resin supplier has thousands. And there are many products available today that were not around for testing during the time period of this book.

    We also formulate and supply fiber treatments, coatings and binders,

    I was a fabricator making and testing panels with resins and coatings for continuos immersion for decades before doing what I do now, so I am more than a little familiar the process. I did real world testing in the environment that the product was going to be used. You also get a very good idea of how a product and or process works when you make the item and can follow it first hand over several decades of use in its intended application.
     
  10. ondarvr
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    ondarvr Senior Member

    Going back to what I said in an earlier post. I'm not saying that coating a steel hull is the correct thing to do, only that coating metals can in some situations work well.
     
  11. pdwiley
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    pdwiley Senior Member

    As a temporary repair somewhere remote, sure, I can see the advantages. Get home patch.

    For an ongoing repair to a compromised hull as above (rust) welding on a doubler plate (quick & dirty but effective) or cutting out the plate & welding in a replacement is the way to go.

    Steel is remarkably cheap as a raw material, the killer is the labour costs when it comes to repairs.

    I just don't see glass over steel being cost effective. First it needs to be damn near perfect as a water barrier when applied, second it has to STAY damn near perfect over the long term and third, it's going to be a right ***** to fair so cost a fortune in time. I hate fairing.....

    Where's the savings?

    PDW
     
  12. Mr Efficiency
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    Mr Efficiency Senior Member

    If you hate fairing, glassing overhead isn't much fun either ! I doubt glassing worn-out steel hulls will become a fad.
     
  13. MikeJohns
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    MikeJohns Senior Member

    Fair enough, although they are variants on the basic formulations.

    The more modern isophthalic variants such as isophthalic-neopentyl glycol are not common commercially available resins for the type of boatbuilding we are discussing here though. And they still have Ester groups that hydrolyse though they are much slower to break down, but expensive. You can probably give me the figures for saturation and absorbtion rate constants ?



    The epoxy modified polyester resins will be the best most people will afford to use.



    The fibre coatings have had a significant effect in reducing the effect of water absorbtion on strength loss in GRP. It's all quite interesting.


    Merry Christmas:)
     
  14. ondarvr
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    ondarvr Senior Member

    Frequently people make sweeping all encompassing statements, and form ideas about, a resin type from one or two experiences with it that may not be accurate.

    People say an ISO should be used for boat hulls, well, there are ISO's that work well in this application and ones that will fail in as little as a few months. They are both ISO resins and are typically looked at as being equal, but they aren't.

    I made products in the 1970's with ISO resin that have been immersed in water since the day they were put in service, other than the gel coat being faded they have no other signs aging or degrading and are performing at the same level as they did on day one.

    Water absorption into the laminate can have devastating effects, or very little effect, it all depends on the exact resin and how it was used. Just because one ISO failed has little bearing on whether a different one will.

    ISO's are not considered high end resins, while they are a step up from the lowest cost commodity products, they are mid grade when it comes to the range of resin choices for marine applications. The main reason more builders don't use better resins is due to cost.

    I have more to say on this topic but my battery is dying, so I'll check back in later.
     

  15. ondarvr
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    ondarvr Senior Member

    Using the correct resin in the wrong way can also result in failure. Using a very good VE with a chopper can build a good part, or a bad one, and may have nothing to do with resin. Over catalyze, under catalyze, or having the gun out of adjustment and the part could blister quickly. Yet use it correctly and it will last decades or more. Using bad glass in the chopper gun could create the same issues.


    The way Polyesters and VE's are used in production creates so many variables there are far more opportunities for something to go wrong when compared to epoxy.


    People using polyesters tend to make less money, have little training, entry level skills, be young, have no knowledge about or interest in what they are building and have high employee turnover. Even the supervisors may not have been trained or know much about the products and process, it's just a job. Polyesters tend to be used when cost is one of the main considerations, so less costly (lower quality) products are used.

    People on this site and most that use epoxy, either have a great deal more training or interest in the outcome. They tend to be older, higher paid, have an interest in the final product, want to use the products (resin & fabric) in the best way possible, read about how the products are supposed to be used, have better working conditions, etc. Epoxy tends to be used when long term higher performance is the goal.

    Now compare the two scenarios and which do you think has a higher likely hood of success. If epoxy was used in the same way polyesters are it would have a much higher rate of failure.
     
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