Transom and stringer layup schedule

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

  1. rxcomposite
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    rxcomposite Senior Member

    There is nothing much in transom design except to watch out for few things.
    If you are going to hang an outboard into the transom, you must reinforce it. marine plywood is a good core. To bond marine ply, drill a few small holes to prevent trapped air, causing bond void. Use chopped strand mat or thickened epoxy to bond.

    The total thickness of the transom must not be greater than the bracket opening of the outboard, otherwise you will not be able to fit it.

    Reinforcement is minimum 3 layers of cloth + 1 initial mat for the plywood.

    The transom becomes the strongest part since the boat will be pushed from the aft.

    All corner joints must be reinforced, 1 1/2 x the cover laminate. Since the transom is a major structure, all longitudinals that will be attached to the transom must be bracketed, either a soft toe or straight bracket.

    I see two longitudinals and what looks like a center girder. It must be bracketed. The top end of the transom must be bracketed or connected thru a coaming. to increase stiffness.
     
  2. rxcomposite
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    rxcomposite Senior Member

    Reinforce this.
     

    Attached Files:

  3. SamSam
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    SamSam Senior Member

    I had noticed there were no knees and was going to say something, but then looked at the photo of the original boat in post #1 and figured all that construction probably works ok to reinforce the transom. It looks like the main deck and the two hatch builds solidify the transom pretty well as long as the corners of the motor well have enough reinforcement. If the deck and hatches aren't replaced, knees or some type of reinforcement is definitely needed.
     
  4. Aransas Flats Rat
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    Aransas Flats Rat Senior Member

    RX and Sam, thanks so much for the information sorry not to use the correct names and descriptions, the pictures shown do not include the final layer of core on transom, it is laminated and runs P to S completing the box section, then there is a deck installed taped and glassed to bulkhead and up and over hull side.

    Obviously I cannot tape the underside of the decks or is there a way? I was thinking of using thickened epoxy to seal off with a fillet
     
  5. Aransas Flats Rat
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    Aransas Flats Rat Senior Member

    RX, in the area you have marked red (above the tunnel there is a stringer to be taped in there. However there is no box section in that location, only laminated to the already attached core. Hope that makes since, does that area need knees if so how should they be built? Thanks
     
  6. fallguy
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    fallguy Senior Member

    You can reach in and fillet and tape the coaming to the transom box through the openings. I would use 6-8" tapes.

    They did not even run the original stringer back to the transom(ran short to BH), so I would be satisfied with bonding the coaming to the aft transom sections just like the box sides. I don't find the brackets needed.

    And the transom on this boat is tied via a center girder. Knees would be a bonus to push lateral forces into the hull.

    The OP also needs help to understand the amount of overlap needed in the 3 layers on the transom. I.e.... how many inches from each of the 3 layers onto the hull?

    Also, he could use some advice on stringer layup.

    He only had 6" tapes to start. I would guess something like 6-6-8 no common edges. And then the cap down to the bottom of the tapes. But how many layers in the cap and can he back each layer off say an inch?

    Thanks rx and samsam.
     
  7. rxcomposite
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    rxcomposite Senior Member

    You cannot tape the underside of the deck but you need to reinforce it. Make an angled bracket out of fiberglass and tab it to the bottom part of the hull. If the angle varies in relation to the surface of the floor, cut a thin marine ply to pattern and tack it to the sides. Finish with a bog for the sharp angle and 2 layers of mat. You now have a strong base for the floor to sit on.

    Tabbings usually start 2" per side then 1/2" wider every succeeding layer.
     
  8. rxcomposite
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    rxcomposite Senior Member

    The longitudinals you call stringers seems to be a little tall for the design and need no bracketing. Unless it doubles as a seat base. In design simplification, the main longitudinals forms part of the seat and the flat floor forms a triangle in relation to the v bottom. The side coaming attaches to the hull sides, continue horizontally forming the deck and turn down (in an opening) forming a "C". In effect, you have a box inside the cross section of the hull which makes for a very strong structure tied to the transom.
     

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  9. Aransas Flats Rat
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    Aransas Flats Rat Senior Member

    RX, thanks so much for the descriptions, I’m a novice so I will have to digest the drawings and recommendations to make sure I understand them as I am not familiar with all the technical names.

    The boat is a what they call a Tunnel Vee hull, it’s designed for running shallow as well as cutting a chop.

    So in short there is sharp Vee at the bow then flattens out at the stern, it is also a self bailing deck, I would guess this is why the sole is such elevated it also enables you to see better running the shallows. D8AF93A7-3757-4FE5-97AA-4C4DDBFBAD7B.jpeg 62AC602B-4AFD-4ABE-BB3A-1647E51F0B0E.jpeg
     
  10. rxcomposite
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    rxcomposite Senior Member

    You are doing right 90-95%. I just don't know the details. The drawings I provided should give you an insight where to reinforce.
     
  11. Aransas Flats Rat
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    Aransas Flats Rat Senior Member

    Can you explain this?
    “All corner joints must be reinforced, 1 1/2 x the cover laminate.”

    Thanks
     
  12. rxcomposite
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    rxcomposite Senior Member

    Section. More details.
     

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  13. Aransas Flats Rat
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    Aransas Flats Rat Senior Member

    Ok I got it now thanks.

    What’s a good layup for stringers, best width of tape and best number of layers. Thanks
     
  14. Aransas Flats Rat
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    Aransas Flats Rat Senior Member

    I have plenty of 6” wide 1708
     

  15. Aransas Flats Rat
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    Aransas Flats Rat Senior Member

    Please let me know what information on hull would better help you if any. Thanks
     
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