Transom and stringer layup schedule

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

  1. fallguy
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    fallguy Senior Member

    He actually would be able to glass the coaming in...not saying it is best...just that he could through the hatches. The best way would be to follow the old design; so if it were bolted to provide flanges to bolt...etc.

    Taping makes future removal of the cap cutting required....
     
  2. Aransas Flats Rat
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    Aransas Flats Rat Senior Member

    Fallguy, there was nothing but glass (outside only) holding the box tops, there was actually a gap underside and you could feel were the cut a 45 on edge. No glue or tape underneath
     
  3. Aransas Flats Rat
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    Aransas Flats Rat Senior Member

    1EC470A2-3525-4D92-920F-9DB59E22C9C4.jpeg In your drawing you described a seat(triangle) in the original build they did have a partial floor in the bottom of the box as shown in drawing, I thought it was just a floor bottom, do they need to go back?
    I am just checking because you discussed it as bracing
     
  4. fallguy
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    fallguy Senior Member

    The knee portion of the insert would probably be good as the transom is only 3/4" there.

    Did you go two or three layers of 1708 on the transom?

    I had advised three originally, but then said two might suffice. I would be inclined to take the knowledge of rx over pretty much anyone. So of he says three; go three.

    Top taping would work, but inside taping would make it rock solid.
     
  5. Aransas Flats Rat
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    Aransas Flats Rat Senior Member

    Two layers, will add another when materials get here.
     
  6. rxcomposite
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    rxcomposite Senior Member

    AFR, Fallguy- The 1.5X thickness is the minimum. You can go to 2x. Say the core (plywood) is 2 layers per side. 1 layer 4" tape will work but it is best to lay up 4" tape then 5", 2 layers. In single skin laminate, if it is 4mm thick continous (or whichever is greater) , add 2 more reinforcing tape, making it a total of 6 (or 1.5X).

    In plywood core, it is best to go by weight. If it is 12.5 mm. thick, need 1800 gr/m2 per side, 20 mm thick -2250 gr/m2, 25mm thick- 2700 gr/m2. Sorry for the metrics. Looking at Lloyds.

    Tape is always biax. -45+ 45 degree
     
  7. Aransas Flats Rat
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    Aransas Flats Rat Senior Member

    Dan, the cap was not bolted or flanged only taped and glassed over the outside skin by 3” 60B4CBE2-E6B1-4145-A9FC-5DED4E79CBE9.jpeg

    Grey area taping/glass overlapping
     
  8. fallguy
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    fallguy Senior Member

    1708 tape is 600g/m2 &45s

    His ply core is 20mm at the stern and 60mm at the front of the transom box after applying the bulkhead via epoxy glue. In a transom repair, you can only tab one side. This would mean he needs 4 layers at the stern and something ridiculous at the 60mm box.

    My transom was 40mm corelite, not ply, and I applied 1600. The clamping area on top was wrapped over the top, so would have 3200 on top, but would be well short of Lloyds. I considered adding one or two extra layers of 600 on the clamping board bonded to the motorwell. I digress, but only for example.
     
  9. fallguy
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    fallguy Senior Member

    I realize that now. I am just saying a single layer even of tape on the inside would be nice and help support if that area is ever stepped on and it would serve as the bracket rx showed atop the stringer (and thus that bracket is unneeded.

    If you don't do it; it won't be the end of the world..I probably would.

    Rx is in Phillipines, so he is asleep while we are awake ftmp. Be patient for his replies. He is by the book smart.
     
  10. Aransas Flats Rat
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    Aransas Flats Rat Senior Member

    No problem, I’m trying to learn but I need translation as I am way out in left field on the proper names and what they mean.

    If I get what he is saying, I did add tape, two layers to all transom hull skin corners before putting in core then added two more after installing core then two overlapping layers of glass,
     
  11. Yellowjacket
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    Yellowjacket Senior Member

    What you have done so far looks nice and properly done. What is more important now is how you replace the "cap" that was at the transom. The top needs to be "boxed" similar to what you show in the photo that you've called "original". Although it is most likely that what you have in that photo was not how the boat was originally built. The reason I say that is that the holes cut in the top of the transom "boxes" are not finished but are just cut out with a saw and doing that significantly reduces the structural integrity of the transom. If they were smaller and "flanged" then it would be less of an issue, but it's pretty clear that those holes weren't there when the boat was first built. Just as importantly cutting them exposed the plywood core in those areas and it was rotting since the wood was getting wet. The cap is important because it transmits the transom bending loads into sides of the hull. Without that cap the transom becomes very flexible and you'll eventually crack the hull from the flexing. If you want some kind of wells in the transom you need to replace that stiffness with something to carry the bending loads on the transom to the sides of the hull. As noted above the caps AND the slanted area ahead of the caps that becomes the front wall of the transom also is important in "closing the box" and making this a stiff structure. If you do this properly then you don't need any "knees" or other structure down at the bottom to support the transom. Also note that you've cut back the inner lip of the cockpit opening and that needs to be replaced and tied into the structure that you use to "top" the transom area for the hull to be as good as new. What a lot of people don't realize is that the back of the hull needs to transmit the loads to the sides of the hull and this requires beam stiffness in the plan view. Big thick transoms work, but are structurally inefficient. The best way to get that stiffness is to have some beam stiffness in the plan view and that is what the cap originally did.
     
    rxcomposite likes this.
  12. Aransas Flats Rat
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    Aransas Flats Rat Senior Member

    Thanks Yellowjacket, the pic “original” came from the factory that way, all that were built came that way. So far I have put it back as it was originally, changes made are extended the stringers to reach the transom as originally they stopped 12-13” short of stern/transom bulkhead as well as bow deck bulkhead. Also the original transom core was just taped in and the inside of the box was only gel-coated. Current pics don’t show the final 3/4 layer/bulkhead that will be installed after stringers.

    Pics are how it was originally built
    C5C74334-59EC-4E77-BDAF-0B38203A3BC6.jpeg F46EEC6D-8862-46D9-95C1-CE1309566DEB.jpeg 38311C36-56F6-4BE5-B095-E72A0866F510.jpeg
     
  13. Aransas Flats Rat
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    Aransas Flats Rat Senior Member

    I also agree with the hatch size and can clearly see were it would cause an issue structurally, I planned on reinstalling access hatches there but wasn’t sure what size when I got to that.
     
  14. Aransas Flats Rat
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    Aransas Flats Rat Senior Member

    Can you please explain, I am not sure I’m understanding what you are saying.
     

  15. fallguy
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    fallguy Senior Member

    I think he is referring to the need to glass the cap back on and over the hull exterior which I believe you plan.
     
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