New to Fiberglass, very basic questions...

Discussion in 'Fiberglass and Composite Boat Building' started by science abuse, Jun 15, 2010.

  1. AndrewK
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    AndrewK Senior Member

    science abuse, placing a layer of glass between the foam is not making best use of the reinforcement. All the glass should be only on the outer surfaces, just glue the foam together.
    Use the lighter weight glass that you have, all other things equal its the total weight of glass that will determine the strength.
     
    1 person likes this.
  2. tunnels

    tunnels Previous Member

    So the core is not contributing anything to the strength ??:confused:
     
  3. apex1

    apex1 Guest

     
  4. Herman
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    Herman Senior Member

    All I will add at this moment, just to help the topic starter (remember that he is a beginner, we should not overwhelm him with all kind of information which mostly can be regarded periferal), anyway, what I would like to add:

    -use your light cloth, which is what you have, and which is cheapest for you at this moment. Make sure you laminate it nice and evenly, no resin puddles, please.

    periferal:
    I can supply you with both polyester, vinylester and epoxy resins which will easily drain out on vertical surfaces. It all comes in different variaties, which might be thixotropic, the version which is most suitable for hand laminating.

    I guess tunnels used a thixotropic vinylester, and perhaps encountered an infusion polyester or epoxy.
     
  5. rxcomposite
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    rxcomposite Senior Member

    Science A,

    Thicker cloth, or more commonly known as "boat cloth" builds up thicker because of the larger undulations of the threads. This gets to be filled up with resin.

    Thinner cloths, or aerospace type cloth are thinner. More layers are needed but the resin needed is much less resulting in a stronger product. it is also less stiff.

    in a laminate, the center part, or the core is not subjected to compression or tension but shear. This is where the chopped strand mat works better (and cheaper too).

    When the center part is substituted with a core of foam, thickness increases quickly, resulting in a much stiffer product than a single skin laminate.

    Density is a function of strength. Thickness a function of stiffness. The structural engineer tries to balance both properties and do so by carefull choice of materials.
     
  6. mark775

    mark775 Guest

    I believe you meant strength is a function of density. Stiffness a function of thickness.
     
  7. apex1

    apex1 Guest

    Sure Mark,

    but he was right in general!:)

    We sometimes have to remember that some of the most valuable members are NOT native english speakers! ***

    Regards
    Richard

    *** no I did not refer to me.
     
  8. missinginaction
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    missinginaction Senior Member

    Hey, where did science abuse go?:confused: Hope he's still around.

    Science, not to long ago I had questions similar to yours. Keep in mind that you are building a canoe, not a yacht and not a hydroplane and certainly not an airplane. You want to do a nice job, but you're not going to experience 5 G's or be out in a hurricane, right?

    FWIW I think that you are on the right track with the light weight cloth. For your purpose I don't see any advantage in using something like a biaxle stitchmat where you have cloth stiched to a layer of chopped strand mat or anything similar. For what you are making I'd suggest taking a look at a book called:

    The Nature of Boat Strength by Dave Gerr.

    Mr. Gerr will explain the relationship between various types of composite layups and their strengths. Armed with his book you should be able to determine what type of material is best for your canoe and how heavy your glasswork should be. You'll be surprised I think at how light you can make it. FWIW I'd agree with most of the advise you have gotten here except for the advise about using chopped strand mat. I'll agree with Apex1 that CSM is not advisable for your canoe but I think you already know that.

    Go get Gerr's book and take a look, you'll be able to figure it out. You're allready on the right track.

    MIA
     
  9. rxcomposite
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    rxcomposite Senior Member

    Yes Mark 775. That is correct. Thanks Apex 1 for understanding.
     
  10. mark775

    mark775 Guest

    I certainly intend no slight. Native English speakers, as a rule, are among the least likely to show the respect of learning other's languages. In fact, I was correcting it as if it were a typo - The English here is quite good, generally, and I hope never to come across as nitpicking. Carry on...and thx.
     
  11. science abuse
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    science abuse Junior Member

    Still around, but lately I've been quite busy. I'm actually a mechanical engineer by trade, and "knowing what I don't know" brough me here asking questions. :) True she's essentially a canoe, but do plan on being very rough with her. This boat will be beat by waves and undoubtably rolled repeatedly.

    And for what it's worth, you're English is quite good, and I appriciate all of the advice!
     
  12. afella
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    afella New Member

    Hello all. I am new to the forum. The following is the way I assumed layup of a hull or deck was performed. After the gel coat has cured you use 3/4 to 1 oz.csm for the skin coat. You roll the skin coat material making sure there are no air bubbles between the gel coat and skin coat.After this is completed you allow the skin coat to cure. Then you place a heavier weight csm and woven roving (when dealing with a hull) and use the same procedure as previously stated with the addition of "squeezing" all excess resin from the roving/csm. Please feel free to correct/advise me concerning these processes.
     
  13. Herman
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    Herman Senior Member

    Yes, afella, this is indeed how it is done in general.

    After skincoat you can build up a laminate. There are different flavours, the CSM /woven roving combo is one of them., but there are others as well, including lots of CSM, CSM with stitched fabrics, and all option with or without a core material, which can be foam, coremat, balsa, and some other but less used options. (Cork, for instance)

    Actually today I will be visiting a consulting office to help them converting a CSM/woven roving combo laminate into an infusable laminate. (LLoyds approved).
     
  14. afella
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    afella New Member

    Is It ever too hot for a layup

    Thank you Herman for such a quick reply. I have a question concerning temperature. It is very hot in south Carolina. Is there a maximum temp at which you can layup a part. I am speaking about the catalyst percentage and the environmental temp.
     

  15. Herman
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    Herman Senior Member

    No not really, but do work inside or at least in the shade. Avoid the very hot part of the day.

    If bought locally, the polyester resin should be able to cope with the conditions. There are many types of polyester, some are better handled in cold environments, some better in hot environments. You are more likely to run into stuff that can be used in your environment.
     
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