How many layers of cloth for stringers

Discussion in 'Fiberglass and Composite Boat Building' started by ss170v, May 19, 2011.

  1. ss170v
    Joined: May 2011
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    ss170v Junior Member

    Thanks for the reply PAR. 3 times the current layup is a lot of glass!

    I may have to get some heavier cloth to use. Otherwise it will take 10 additional layers of the 6oz or 2 woven and two cloth to get the amount you recommend.
     
  2. Lurvio
    Joined: Jul 2009
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    Lurvio Mad scientist

    As I said nevermind what I said. Bear with me, I've just opened The Elements of Boat Stength a couple of days ago and I'm trying to learn something here. :)

    Bulkhead tabbing formula in the book gives a laminate of just 17 oz of fiber. This seems a bit thin to me. The number I posted earlier was for a foam cored stringer, not a plywood one, 4 mm translates to about 90 oz. I think the truth is somewhere in between.

    Lurvio
     
    Last edited: May 22, 2011
  3. ss170v
    Joined: May 2011
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    ss170v Junior Member

    Yeha, I'm having a hard time understanding what amount is needed. I've been reading other restores online and it seems pretty common to use 2 or 3 layers of 1708 with poly on stringers with similar size boats. That's about 36-52 ounces of glass.

    I'm using epoxy which on it's own has a tensile strength of 7,846 PSI and a flexural strength of 14,112 PSI. I would think that epoxy would allow for less glass to be used.

    I don't want to under do it and I can add more layers as needed.
     
  4. SheetWise
    Joined: Jul 2004
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    SheetWise All Beach -- No Water.

    I'm trying to learn here too -- but that statement confuses me. There's only one way I know of finding out you need more.
     
  5. ss170v
    Joined: May 2011
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    ss170v Junior Member

    Sorry, I guess that could be taken a few ways.

    I meant that if somebody could explain to me how much glass I needed I can add more.

    Either way, this afternoon I spent sanding the stringers in prep for the new layers of glass. I'm going to apply more, I just don't know how much more is going to be enough.

    I have enough cloth left to give the stringers another 2 layers and still have enough for the sole after that.

    I guess I will start with two more layers of 6oz cloth and wait to see if there are any more comments on this thread.

    Cheers and thanks!
     
  6. Lurvio
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    Lurvio Mad scientist

    Can you post pictures of your boat, from the stringers. I won't be able to give you a more specific answer, that is for the more experienced ones. :)

    Lurvio
     
  7. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Toss another layer of roving over it and call it a done deal. Without pictures and a whole lot of other information, determining how much you need, impact loading compensation, longitudinal stiffness, etc. then it's all just guess work.
     
  8. ss170v
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    ss170v Junior Member

    I only have pics of what the stringers looked like during the teardown process. My camera died from the dust while I was grinding later.

    These pics show what the stringer system looked like. I have been replicating what was there as far as structure.

    You can see that the previous owner did a horrible repair job. The stringers were in sections, joined together using braces and screws with no fiberglass covering.

    In my repair I did not use braces as shown; I used continuous lengths of plywood.
     

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  9. MyFlamingo
    Joined: Sep 2010
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    MyFlamingo Junior Member

    I have restored several similar boats of this vintage and style. In my opinion, Your useage of 24oz woven roving is WAY overkill. PAR is correct in LIGHT is RIGHT and mulitple layers. I would Highly Recommend Three Layers of 1700 Biax cloth and call it good. that is what I have use and NEVER had any issues. The Biax is super strong and easy to work with. The Woven....Not so much.
     

  10. ss170v
    Joined: May 2011
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    ss170v Junior Member

    Hey flamingo, thanks for the reply.

    I would agree that biax is the best choice and if there is a next time I will use it. As it is now, I've used the woven roving and cloth to finish this repair and I'm onto the sole of the boat now.

    The woven I actually found OK to work with as long as you don't try and wrap around 90 degree corners. The cured 24oz roving is really thick and strong. It sure soaks up the resin though.
     
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