Anchor locker notch plate and bolt sizing

Discussion in 'Fiberglass and Composite Boat Building' started by fallguy, Feb 25, 2020.

  1. Rumars
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    Rumars Senior Member

    So I tried, please forgive my poor drafting skills.
     

    Attached Files:

  2. fallguy
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    fallguy Senior Member

    The problem with the concept is the core where you are running the bolt is NOT capable of dealing with the loads AH established. I did not anticipate this as a need and so only have 5# density core. I don't know the numbers, but my intuition is probably right.

    I have plywood on the sides and the plywood definitely is a strong enough core.

    Thanks for posting. Creativity requires many tacks.
     
  3. Rumars
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    Rumars Senior Member

    You could recore locally, it only needs compression strenght where the spacer block is. If I understand correctly you want to fit plates and screw them into the plywood sides? If so I would make sure the shear strenght of the bolts connecting plate to ply either side of the beam is higher then the expected total load. And of course that the plate does not buckle under the load.
     
  4. fallguy
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    fallguy Senior Member

    Yes. Will do.

    I am currenty looking at 1/4" plate and 3/4" bolts and believe they well exceed AH recommendations.

    The downside of the side metal brackets is if they are not built well; they could kink the masts/beams.
     
  5. Rumars
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    Rumars Senior Member

    Do you have the space to bend the top and bottom edges of the plate at 90° and turn it into a U channel? Or weld some bar to the edges for a full I-beam. That will make the bracket much stronger. I would keep the top of the bracket well clear of the beam to eliminate all possibility of pinching and corrosion.
     
  6. fallguy
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    fallguy Senior Member

    I will draw it tomorrow. Thanks for the support.
     
  7. rxcomposite
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    rxcomposite Senior Member

    Attach is the analysis of the forces involved. The pressure hitting the plate is a flat plate hitting the waves for which AH has calculated and gave you a safety factor.

    My quick assessment is that you should just put a removable flat plate to prevent the notch from opening up. Following the moment diagram, it might require a longer reinforcement at the knuckle of the tunnel. But that is only my guess as I do not know your laminate schedule. To prevent core crushing, consider putting anti compression bushings where the bolts are.

    To analyze in depth would require that you post the laminate schedule which might not be the right thing to do.
     

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  8. fallguy
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    fallguy Senior Member

    Unfortunately, I do not have confidence in the plascore core to plate the bottom beefy enough to deal with 100kN/m^2, and the top of the knuckle is only lightly bolted to the beam. The bolts holdong the cabin on would elongate and fail under AH's prescribed loads.

    Fortunately, the sides of the cabin are made of 12mm ply and laminated with 17 oz glass each side. I did so because I had concerns about this issue. So I can make a sturdy removable plate that also compresses the beam into the socket above. Then slamming loads are transferred to the entire craft instead of a weaker fitting. The main beam sockets are held in place by 4 per side 3/4" bolts and 3/8" stainless strapping. Those bolts are set in 9 layers of 1708 glass and epoxy. Based on my calculations; those 8 bolts are rated for 169,120 pounds or double or more than the slamming load. I did not calculate the 9 layers of 1708. The bolt heads are 2" square heads, so the loading is not on the heads of the bolts on the glass, but 16 square inches per side. 50/50 resin to glass. The glass is a little under 3/8" thick.

    I would use 12 3/4" bolts on each side of the plywood. This would also eliminate any concern of the knuckle shearing under a slam to just the leading edge of the cantilever.

    I still need to do something with the back beam as well. Probably some strapping from underneath. Those forces are probably not as strong, but 4 3/4" bolts and straps would get us in the ballpark at about 84,500#. That beam is held in place by a beam socket bonded well to the side of a bulkhead.

    I will draw up the plate tomorrow.

    Thanks to all who have posted. I am truly grateful.
     
  9. fallguy
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    fallguy Senior Member

    Not sure I fully follow again.

    I was planning to make a u shaped bracket that would be welded to the side plate. It would ise a rubber silencer and unfortunately; crevice corrosion would be a concern as the beam would have about a 20" contact area with neoprene silencing.
     
  10. rxcomposite
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    rxcomposite Senior Member

    For a quick analysis, do some comparison. The inboard side of the hull has a thinner laminate than the outboard hull because it is in a "protected" zone. It is the outboard hull that takes a beating due to transverse wave. The wet deck aft has usually the same laminate schedule as the OUTBOARD bottom shell. The forward part of the bow usually has reinforcement but since your drawing indicates it is 1 meter away from the bow of the hull, it won't be that great as it is no longer in the "unprotected" zone but rather lies deeper. It should have the same schedule as the wet deck. Just reinforce the area on the mating area of the cabin.
     
  11. fallguy
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    fallguy Senior Member

    The cabin bottom is made with one inch plascore. The plascore has very little strength alone. If you drill a hole in it and insert a bolt; it tears out on a force that is perpendicular to the honeycombs so easy that it is rather silly. The glass schedule for the plascore is 22oz triax. We doubled the triax on the inside; not out. I assumed a slamming load force woukd act more in tension on the inside. Then the seams were taped. We used two tapes of 1708 iirc inside. Then I overholed the plascore 2x the plate bolts which are only 1/4" diameter. We filled those holes; then taped the outside seam 3x 1708 tapes. Then we installed the plate. Then we removed the plate and installed small glass patches over the top holes to avoid a weak spot.

    So, the cabin bottom at the plate bolts is as follows bottom to top(iirc).

    1708
    1708
    1708
    22 tri
    Plascore 1"
    22 tri
    22 tri
    1708
    1708
    1708 patch.

    But the 1/4" plate bolts are too small for the loads.

    The cabin sides forward and atop the beam were made with plywood. The beam top was made 1" thick iirc. The cabin sides were made 1/2" thick.

    The aft backbone or top of the knuckle was made 1 1/4" thick plywood or maybe even 1 1/2" (forgetting at the moment), but very strong.

    The plywood cores are where I plan to reinforce.

    The aluminum plate we installed is only 3/16" aluminum. I was initially concerned with weight. This is a little silly now. The plate can be faired into the surrounding surface at this size. I am still a little concerned about the plate taking one hard and deforming, but the plate won't be doing the work of transferring loads to the main hulls. A side plate would do so. I will draw in a bit after I get some coffee.

    Let me know if you have concerns with my aluminum plate and small bolts after you see a drawing.

    I will also draw up a plan for the aft beam.

    Thanks.
     
    Last edited: Mar 1, 2020
  12. fallguy
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    fallguy Senior Member

    Here is my idea for a solution.

    I need to recheck the math on the bolts; they are probably too big. The nesting bracket would be made with 1/4" stainless and welded to the side plate that is bolted to the cabin ply sided core. The nesting bracket would be in contact with 5" of the beams bottom surface by 4" deep or a 20 square inch contact area. Gettimg a tight fit is important, but will subject to crevice corrosion. I have heard of anticorrosion padding; not sure.

    My drawings leave something to be desired. The plate will go all the way across the socker notch and installed last. I still have the notch cover in light aluminum not shown.
    9ACF8F2E-00BC-4669-9AB8-D27DDA2C349D.jpeg
     
  13. fallguy
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    fallguy Senior Member

  14. fallguy
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    fallguy Senior Member

    Please also note; the beam notch and all components are all fully glassed. There is no raw core anywhere here.
     

  15. Ad Hoc
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    Ad Hoc Naval Architect

    Is this beam purely to hold this extension part...or... is it part of the main hull connection?
     
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