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Thread: Need advice on Fiberglass please

  1. #1
    Join Date
    Dec 2016
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    Default Need advice on Fiberglass please

    Hello,
    I'm building a 17' CC and am getting to the point where I need to start getting fiberglass. The plans I have call for 2 layers of 6 or 10 oz cloth on the outside.
    I can get BIAXIAL MAT 1700 , 30" (standard 17 oz double Bias fiberglass cloth) for $2.50 a yard. Here's what I'm thinking.... first layer of 1700 followed by a single layer of 6 oz. I think it would save me money and make the hull stronger than just using 2 layers of 6 oz or 10 oz.
    My logic is the 1700 is the build up and the 6oz cloth as the second layer would be easier for me as a newbie to fairing as my understanding is the 1700 is not as smooth. I'm new to this and never fiberglassed before, so let me know your thoughts.

    Thanks!

  2. #2
    Join Date
    Jun 2000
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    Pleasant Valley NS Canada
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    Default Re: Need advice on Fiberglass please

    Please pardon my directness, but why - particularly as a novice boatbuilder - do you not want to follow the instructions of the designer?
    Hope for the best, but plan for the worst.

  3. #3
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    Dec 2016
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    Default Re: Need advice on Fiberglass please

    I'm not going to name the designer but he is pretty popular and sells a lot of ply on frame plans. He has very few stitch and glue plans... which I brought. He obviously never built this model because the plans have a few flaws in them, so I've lost faith in him. Wrong size frame, impossible bend at the bow... etc. Anyway, I am thinking that the extra fiberglass would only make the boat stronger.

  4. #4
    Join Date
    Mar 2007
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    East Quogue,NY
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    Default Re: Need advice on Fiberglass please

    The extra glass may make it stronger...but stronger for what? Two layers of 6 oz on top of 3/8" or 1/2" ( I'm guessing) plywood is already pretty freaking strong. Stronger than any normal use will see, that's for sure.

    Additionally, that extra glass will add time and money and increase the boat's weight as well as its fuel bill.

    But, its your boat. Have fun!

    Kevin
    There are two kinds of boaters: those who have run aground, and those who lie about it.

  5. #5
    Join Date
    Feb 2006
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    Pennsylvania
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    Default Re: Need advice on Fiberglass please

    The heavier cloth will be harder to finish well, not easier. Also, if 30" wide, you'll have more joins to deal with than with 60" fabric. So I agree with what's been said, stick to the plans.
    -Dave

  6. #6
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    Dec 2016
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    Default Re: Need advice on Fiberglass please

    Thanks for the advice.... nix the 1700

  7. #7
    Join Date
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    Default Re: Need advice on Fiberglass please

    Quote Originally Posted by glen65 View Post
    I'm not going to name the designer but he is pretty popular and sells a lot of ply on frame plans. He has very few stitch and glue plans... which I brought. He obviously never built this model because the plans have a few flaws in them, so I've lost faith in him. Wrong size frame, impossible bend at the bow... etc. Anyway, I am thinking that the extra fiberglass would only make the boat stronger.
    Re: additional strength of thicker 'glass sheathing...

    For an increase in 'glass & resin of 51% on one side of a 3/8" ply panel, stiffness increases 5%, strength increases 4%.

    In my world, such increases in strength & stiffness is not worth the increase in material costs and labour. YMMV, of course.
    Hope for the best, but plan for the worst.

  8. #8
    Join Date
    Aug 2006
    Location
    Rockford, IL
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    11,865

    Default Re: Need advice on Fiberglass please

    Saving money on fiberglass should not be your primary concern. The various sorts of "mat" are good for molded FRP hulls and major repairs involving considerable open area, but not for sheathing a plywood hull. BTW when mmd offers free advice, most of us take notes.

  9. #9
    Join Date
    Dec 2003
    Location
    Portland, Oregon
    Posts
    70,241

    Default Re: Need advice on Fiberglass please

    Quote Originally Posted by glen65 View Post
    Hello,
    I'm building a 17' CC and am getting to the point where I need to start getting fiberglass. The plans I have call for 2 layers of 6 or 10 oz cloth on the outside.
    I can get BIAXIAL MAT 1700 , 30" (standard 17 oz double Bias fiberglass cloth) for $2.50 a yard. Here's what I'm thinking.... first layer of 1700 followed by a single layer of 6 oz. I think it would save me money and make the hull stronger than just using 2 layers of 6 oz or 10 oz.
    My logic is the 1700 is the build up and the 6oz cloth as the second layer would be easier for me as a newbie to fairing as my understanding is the 1700 is not as smooth. I'm new to this and never fiberglassed before, so let me know your thoughts.

    Thanks!
    There's a lot to know about fiberglass & epoxy. Luckily, West System had published free downloads covering pretty much any question you have. Including the book that many of us regard as the 'bible' of epoxy and boatbuilding. And they have a tech services phone if you still have questions -- https://www.westsystem.com/the-gouge...-construction/

    The short version -- mat is too much fiberglass. And much of it - designed for use with polyester resin - comes with a binder that keeps the epoxy from working correctly. Sounds, offhand, like the original instructions for type and weight of glass are about right. And you can get what you need from a variety of suppliers. I've had good experience with these folks -- http://raka.com/

    Good luck, and have fun.
    David G
    Harbor Woodworks
    https://www.facebook.com/HarborWoodworks/

    "It was a Sunday morning and Goddard gave thanks that there were still places where one could worship in temples not made by human hands." -- L. F. Herreshoff (The Compleat Cruiser)

  10. #10
    Join Date
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    Norwalk CT
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    Default Re: Need advice on Fiberglass please

    Quote Originally Posted by mmd View Post
    Please pardon my directness, but why - particularly as a novice boatbuilder - do you not want to follow the instructions of the designer?
    Good question...

  11. #11
    Join Date
    Dec 2016
    Location
    Bethlehem, PA, USA
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    41

    Default Re: Need advice on Fiberglass please

    Quote Originally Posted by willin woodworks View Post
    Good question...
    Did you read my response to that question?

  12. #12
    Join Date
    Dec 2003
    Location
    Sound Beach, NY
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    4,413

    Default Re: Need advice on Fiberglass please

    I'm glad you got a good answer to your fg question.
    Good luck with your boat, keep us posted. We love to hear of launchings.

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