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

    Hi all,

    I'm doing my first restore of a boat (1969 slickcraft ss170v) and I have a question regarding the amount of glass needed for the stringers.

    The boat had been previously repaired by another owner and the stringers were glassed in with a very thick mat. I know it's mat because the fibers in the glass I pulled out are not woven or stiched.

    The only glass I have is 6oz cloth and 24oz woven roving. I am using West Systems epoxy.

    I have glued in the stringers with a thickened epoxy and tabbed them in with a single layer of the 6oz cloth. At the point where the stringers join the hull I built up the glass with 24oz roving extending 10" up the stringer and 10" onto the transom.

    How much more glass do I need on the stringers? Can I get by with say 3 more layers of 6oz completely enclosing the stringers? Should I use more of the 24oz roving or some combination of the two?

    And advice is much appreciated. This is my first time rebuilding a boat and I want it to be strong and safe.

    Thank you in advance.
     
  2. Lurvio
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    Lurvio Mad scientist

    Google is not very helpful in finding info on your boat. Could you post mearurements like LOA, Beam, Depth of hull, speed etc and maybe the professionals here can give you some figures.

    Lurvio
     
  3. Submarine Tom

    Submarine Tom Previous Member

    It depends but if in doubt, use more layers.

    -Tom
     
  4. ss170v
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    ss170v Junior Member

    Hey lurvio, thanks for the reply. I know what you mean about there being not much on google about this boat. I could hardly find anything.

    It's a 1969 Slickcraft SS170v built by Grew boats.

    LOA: 16'6"
    Beam: 76"
    Deadrise: 20 degrees at transom
    Speed: maxed out around 35 MPH with a 70HP 2 stroke. Original max rating for the boat is 100HP.

    The hull has 3 main stringers; Center stringer is 3/4" x 10", Outer stringers are 3/4" x 5". Transom is 2x 3/4" exterior grade plywood encased in woven roving and cloth. Deck will be 5/8 ext. plywood joined to hull with 24oz roving and covered with 6oz cloth.

    Hope that helps. thanks everyone.
     
  5. ss170v
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    ss170v Junior Member

    Also, to add to my first post I have now run a strip of 24oz roving along either side of the stringers to join them to the hull. (This is in addition to the 6oz cloth that's already there.

    I'm that will be good enough but I can add another layer of cloth if needed.
     
  6. Lurvio
    Joined: Jul 2009
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    Lurvio Mad scientist

    Well, I sure am not a professional, but i did a quick and dirty calculation based on Gerrs rules and got a result of a bit over 4 mm thick laminate. The rules define a square stringer so probably that number isn't much of use. 4 mm translates to 4 x 24 oz, combining roving and mat.

    Hope some of the actual professionals comment on these numbers. :)

    Edit: Nah, forget I said anything, that is a foam cored stringer so full strenght is from the laminate.

    Lurvio
     
  7. gonzo
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    gonzo Senior Member

    You should never use mat with epoxy. It has a binder designed to be dissolved by the styrene in polyester or vinylester resins. Are the stringers plywood.
     
  8. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    You can use mat with epoxy, the "binder" (sizing), is left in suspension in epoxy, so no harm is done. The reason you don't use mat with epoxy is two fold: first it wastes resin, a lot of resin, which makes the resin/glass ratio go way up, weakening the cured matrix and secondly it's not necessary with epoxy. Mat is a bulking and cross linking agent, used with weaker resins systems, such as polyester and vinylester. It's unnecessary with epoxy, but required with polyester.
     
  9. gonzo
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    gonzo Senior Member

    I agree you can use mat, but it is a waste of money.
     
  10. ss170v
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    ss170v Junior Member

    Thanks for the replies guys. I don't have any mat and I haven't used any. I'm using 24oz woven roving and 6oz E glass cloth.

    Stringers are made of 3/4" plywood.

    So I currently have the stringers bonded in place with an epoxy/microfiber paste. I've tabbed the stringers in place with 6oz cloth on either side. Bulked up the joints to the transom with 24oz roving and run a second tab of 24oz roving along the length of the stringer.

    Do you guys think this is enough? It's 30oz of glass the length of the stringer and 52oz at the joint to the transom.

    Should I completely enclose the stringers in the 6oz cloth or am I alright with what i've got?
     
  11. gonzo
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    gonzo Senior Member

    That seems like enought for tabbing. Did you build a radius at the joint?
     
  12. ss170v
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    ss170v Junior Member

    I used a plastic spoon to create a fillet with the thickened epoxy in order to lay the cloth over the angle. Then I layed the woven roving over top the cloth. Is that what you meant?
     
  13. gonzo
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    gonzo Senior Member

    Yes, you seem to have done it right.
     
  14. ss170v
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    ss170v Junior Member

    Thanks Gonzo. This is my first time but I read a lot before hand and got the book from West systems. I could just never find how much glass I needed for strength.

    It feels strong. I can stand on the stringers (250 lbs) and they are solid as a rock.
     

  15. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    On a high speed, 100 HP outboard boat, you'll want more then what you have down. You should also consider not using the heavy roving. It's much better (for several reasons) to use lighter fabrics (more layers). You'll use a lot less resin and the fabric will conform much better too. The heaviest tabbing I use is 18 ounce and more often I use 12 ounce (again multiple layers). I think you need to triple the amount of tabbing you currently have and Geer's scantling rules seem to support this according to Lurvio.

    If you have to error, it should be on the overly heavy side, not the too light side. In short the laminate you need should be engineered for the loads or you can mimic the previous laminate thickness with a similar, but new layup.
     
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