Transom and stringer layup schedule

Discussion in 'Fiberglass and Composite Boat Building' started by Aransas Flats Rat, Dec 17, 2018.

  1. Aransas Flats Rat
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    Aransas Flats Rat Senior Member

    Thanks Fallguy, in the pictures I show how original inside were. D28F27C0-CC44-416C-AAF1-C9BB60EB9646.jpeg



    The area circled in green was as a floor/shelf. Should they be replaced? F22DABDB-F6D4-4832-AC6D-3337A895F907.jpeg
     
  2. fallguy
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    fallguy Senior Member

    Yup.

    Goes behind the Bulkhead.
     
  3. rxcomposite
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    rxcomposite Senior Member

    Thanks for the nice words, it encourages me. We built hundreds of boats in an LR approved facility hence my inclination to cite LR often.

    Don't worry if you are a little bit "smallish" than LR rule. You are not building to Class anyway. ISO would require 300 gr/m2 for light sheating on wood. But that is only for the skins. All others require calculations using section modulus. But that is beyond the scope of the topic.

    The layup for plywood core is a very general rule and is mostly for major structures. LR list more guidelines for different parts/structure/location.

    Attached more LR rules as a reference.
     

    Attached Files:

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  4. rxcomposite
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    rxcomposite Senior Member

    AFR- Do you have more pictures of the hull before you gutted it. Seems something wrong/inadequate with the design as Yellowjacket also noticed.

    For example, the bottom lattice/herringbone stiffener design is something that is sometimes discussed but rarely used. There are other more sound fundamental engineering practices. The gunwhale seems to be a cantelever design. I am looking for a rubstrake or wood stiffeners. There are discontinuties in the transom structure.
     
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  5. Aransas Flats Rat
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    Location: Florida

    Aransas Flats Rat Senior Member

  6. Aransas Flats Rat
    Joined: Sep 2018
    Posts: 190
    Likes: 10, Points: 18
    Location: Florida

    Aransas Flats Rat Senior Member

  7. Aransas Flats Rat
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    Aransas Flats Rat Senior Member

    Hope this helps
     
  8. rxcomposite
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    rxcomposite Senior Member

    Ok. It is clear to me now. The main longitudinal and center girder is oversized as it forms part of the sunk deck. The deck is connected to the sides and forms a box frame, enough to stiffen the gunwhale. My only comment is that the main longi should be connected to the transom (post #66, encircled green). For this design, the transom is the strongest part and all points emanates from where the motor is attached. The deck forms part of the structure that reinforces the transom. Keep it that way.
     
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  9. Aransas Flats Rat
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    Aransas Flats Rat Senior Member

    RX, thanks and that makes sense. By longitudinal, is that the stringers? If so they stopped 14+” from transom on original build, when I cut the new ones they run from bow deck bulkhead to the transom
    A1EE1C13-9CC0-45D0-86CD-F2AA94013327.jpeg
    7D9EF8D2-84C3-46EF-BB13-822971BDF635.jpeg
    Is this what your explaining?
     
  10. Aransas Flats Rat
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    Aransas Flats Rat Senior Member

    I have two layers of 1708 cloth on the transom now should I add another layer, asking prior to installing stringers. And I am still unsure of taping for the stringers?

    Thanks
     
  11. rxcomposite
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    rxcomposite Senior Member

    Yup. That's it.
     
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  12. rxcomposite
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    rxcomposite Senior Member

    Generally, all are called stiffeners, major or minor (primary or secondary). Stringers implies minor stiffeners but can also be used but not as a major.
     
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  13. rxcomposite
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    rxcomposite Senior Member

    Two layers would suffice but the 1 1/2 x follows the tabbings and caps. Follow the weight rule and thickness posted.
     
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  14. fallguy
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    fallguy Senior Member

    Can you give an example of how to apply these numbers? I think if I met these standards my boat would weigh an extra ton and never make her lines.
     

  15. Yellowjacket
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    Yellowjacket Senior Member

    Ok, these pictures of the original boat offer a lot more info. The deck essentially supplies stiffness to the transom and motor mount, with the deck in place you don't need as much stiffness in the "cap" area. Think of the deck as a stiffening plane that keeps the transom from moving. what is important is how you construct your replacement for the deck and how you install it, because that is the element that is stiffening the transom. In the earlier pics you didn't show the deck and the assumption was that the deck was much lower in the hull. Since the deck is high up, it provides the stiffness to the whole system.

    You will need to reinstall the small bottom stiffening elements. One other thing that you may think about would be to replace all of that stuff with a couple inches of closed cell foam, or you could foam the entire inside of the area under the deck. That would not be cheap, but it would make the boat impossible to sink. Since once the deck is installed there is no access to the area under the deck, you have to make sure that you don't get any water under there, or you have to make sure that you totally seal all of the wood that you put down there or you'll eventually have rot.
     
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