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

    RX, thanks for the information and documentation.
     
  2. Aransas Flats Rat
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    Aransas Flats Rat Senior Member

    Yellowjacket, thanks for the confidence that it wasn’t a lost cause.

    Just for thought the original system was attached to nothing with the exception of the tabing/glass to the hull sides. The original builder had everything attached with sheet rock screws, no adhesive and of course they failed. They had 3”wide 3/4 ply strips laying P-S on top of the stringers so the deck was essentially floating and pounding on the stringers
    BC6D941B-1CFB-46CE-A8A8-53526FE46943.jpeg
    Towards the stern there was a stack of plywood just sitting under the deck/sole.

    As for now I am stuck on whether or not I need more glass on the transom area before I install the stringers and the stern bulkhead, at the moment I have two layers of 1708 tabes to hull bottom with 18”tape. I explained complete lamination so far above.

    I am also stuck on the laminations for the stringers, I could really use some guidance on that
     
  3. Aransas Flats Rat
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    Aransas Flats Rat Senior Member

    Yellowjacket, I definitely planned on reinstalling the stiffeners, they were all rotted/saturated and attached with chopper, it didn’t take much to remove them.
    When reinstalled I planned on using 3” x 3/4 ply core glue them with thickened epoxy and tape over with three layers of 6” 1708 tape, if there is a better or more correct way please advise.

    Thanks
     
  4. Yellowjacket
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    Yellowjacket Senior Member

    That is certainly one way to do it. OTOH you could just put down 3/4 of an inch of foam sheet and put a couple layers of glass on top it and be done with it. Not sure what would be easier. There really is no easy way to do it. Putting the foam down and getting it properly bedded is easier in small pieces, but glassing over the top will be easier to do in a larger sheet. The original builder had a good design, but it looks like he probably didn't follow what the designer planned when he started making the boat. Most production boats are made as cheaply as possible and yours is no exception. What you need to consider with the transom is how much power are you putting on it, and what do you have compared to the original hull. Make sure you've got as thick a wood as the original and make sure the glass is as thick and go with it.
     
  5. Aransas Flats Rat
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    Aransas Flats Rat Senior Member

    Thanks Yellowjacket, the transom is already more solid than it was with the core glued in and glassed, I think I will add another layer of 1708 and one more round of tape to the hull after the explanation of how the transom is the strong point of the design.

    The original deck/sole was 3/4” I planned on going back with 1/2”, build it as one piece. Triple tape butt seems one layer of 1708 underside and two to three layers topside overlapping the hull sides and transom.
     
  6. Aransas Flats Rat
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    Aransas Flats Rat Senior Member

    The boat came with a Yamaha 115 and the hull as was is rated for a 140.

    However right now I’m stuck on how to install the stringers, I don’t know how many layers of what to install them with. So hopefully someone can give a recommendation I’m starting to wonder if there is an answer?? I’m not trying to hold anyone responsible just trying to get it done right. Thanks
     
  7. rxcomposite
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    rxcomposite Senior Member

    What is the depth of the center girder (the middle one)? Depth of longitudinals (adjacent)? What is the spacing in between?
     
    Last edited: Dec 30, 2018
  8. rxcomposite
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    rxcomposite Senior Member

    Don't follow the numbers. This is LR and the numbers are default value intended for boats up to 24 meters. I posted the figures just to give you an idea how it varies depending on the location.

    Ok. To answer your Q, the table list 3850 gr/m2 for bottom outboard laminate and 2850 gr/m2 of laminate for the inner skin on a sandwich laminate. The difference in numbers is because the outboard laminate is in compression and the inner is in tension. Composite is weaker in compression hence it needs to compensate by making it thicker.

    The only way to arrive at the exact thickness and material to be used is by stress analysis as there are many variables to be inputted. It won't follow the default but will assure you that the laminate will not fail. Both ISO and LR uses the same method of analysis.

    PM me if you have any specifics in your mind and I will run the calculations.
     
  9. Aransas Flats Rat
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    Aransas Flats Rat Senior Member

    RX, the center stringer is at its tallest 17” and averaged 11” as it runs strait down the keel, P&S stringers tallest 10.5” at the stern and tapers down to 3.5 at the bow bulkhead. Thanks
     
  10. rxcomposite
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    rxcomposite Senior Member

    AFR- Attached lam schedule for the longitudinals. My first computation for 2019.

    You have to tab the plywood longitudinal first then make up a 90 degree form and wet tab it to the longi and reinforce as shown. The ends are heavily reinforced as it is failing at 5.5 inch depth. The height is too shallow. I assumed you have 8 feet of unsupported span as I do not see any bulkhead or major transverse along the length. The top lamination takes up the tensile stress and support also your deck. If you have Uni lying around, you can substitute it for the WR. 2x UDR 600 will do. This will prevent any delamination of the flooring in the future.

    It might appear complicated but if you take the time to understand it, everything will fall into place.
     

    Attached Files:

  11. Aransas Flats Rat
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    Aransas Flats Rat Senior Member

    RX, I hope you and yours had a wonderful Christmas and a Happy New Year, thank you so much for the explanation and For the time you took in making the detailed drawing. That makes It very understandable and is much appreciated.

    I got a couple questions on the abbreviations, I am sorry but I’m not familiar with them such as WR maybe (Roven Woven?), UDR or DBM

    Can you explain the center drawing (red, tan and brown) I would assume the tan is the ply core, brown is glass and red is thickened epoxy?

    Is the number example:
    web= 6x dbm1708 (does this mean the number of layers in the specified area?)

    Can you spell out please, sorry for my lack of understanding.

    Travis
     
  12. Aransas Flats Rat
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    Aransas Flats Rat Senior Member

    Also I think you are showing 1/2” ply deck core (correct)
    If I am understanding correctly you show 3/4” ply core for stringers, this is what was in originally. The new stringers are two sheets of 1/2” ply laminated together with offset butt joints. No sure if it makes much difference just wanted to make sure I understood the drawing. Thanks
     
  13. rxcomposite
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    rxcomposite Senior Member

    WR is standard run of the mill Woven Roving, UD or UDR is unidirectional roving or just plain uni. DBM is double bias with mat backing as we have been discussing in the previous post.

    The center drawing is the web lamination schedule as shown by the arrows and corresponding number of layers (2times, 3times, 6times). The core is plywood, originally 3/4" thick.

    The deck I assumed 1/2", laminated on both sides. I just made an assumption since the deck is supported by many transverse stiffeners and it has less load than the bottom. Naturally, it can be made thinner.
     
  14. Aransas Flats Rat
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    Aransas Flats Rat Senior Member

    Thanks, yes the original deck was 3/4” and I planned on using 1/2 glassed on both sides. If you thank that is sufficient?
     

  15. Aransas Flats Rat
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    Aransas Flats Rat Senior Member

    Can you specify tabing to the hull bottom, I’m not not understanding layers.


    How much overlap onto the hull bottom?
    I think you show 1 layer 2” overlapping then a 3” layer overlapping by a 1/2”?
    I’m a little confused on the layers all the way around, sorry
     
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