Anchor locker notch plate and bolt sizing

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

  1. fallguy
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    fallguy Senior Member

    I did email Richard after posting here and he suggested I could use lashings. I still think a strapping plate under the beam and on the sides will achieve the best result and is pretty easy to implement, just heavy.

    Not sure what I would lash to...probably need some hardware for lashing.
     
  2. Ad Hoc
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    Ad Hoc Naval Architect

    Im trying to understand better what is going on and what is what...as there are so many trees I can't see the wood!

    In your dwg:
    upload_2020-2-28_9-3-59.png

    1. What is the total weight acting as shown by the arrow?....that is weight of the structure and whatever is the max weight it shall carry/support etc....and the distance of its CoG to the notch.
    2. The blue ellipse, is this just side shell laminate that connects the main hull with the extension
    3.. The beam you note above the notch.. what is the purpose of this beam?
     
  3. fallguy
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    fallguy Senior Member

     
  4. fallguy
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    fallguy Senior Member

    Here is a picture that shows the crossbeam in the hull socket and the cabin socket sitting atop the beam. This is the starboard side. The cantilever is to the left in the photo. The section of plywood above the beam notch socket is about 7" high and this and the socket do all the work supporting the cantilever. I can stand on the front of the cantilever section with no notable deflection. I am only worried about a slamming load; not so much the loads from above. I just don't want the cabin to crack if we hit a breaking surf head on at speed. 239CD668-5BC1-4978-AA69-0C636C105B55.jpeg
     
  5. Ad Hoc
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    Ad Hoc Naval Architect

    Ok.. so 500lbs = 225kg. and a level of 0.50m.

    It's gonna bounce, so 1g = 225x 2 = 450kg. But then you want a reasonable FoS = say 3 = 1350kg = 13.24kN.

    At that lever your BMmt = 6.62kNm, and shear of 13.24kN.

    But im not clear how this bit connects to the hull?... lots of nice piccies... but the connection and thus load path is not clear to me, a dwg is far better to avoid any misunderstanding.
     
  6. fallguy
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    fallguy Senior Member

    yes, the notch seats on the crossbeam; it was moulded in place and then remoulded off the boat more perfectly; we used ground san and epoxy for the material; in addition; there is 1/8" neoprene silencing between the seat and the beam when assembled
     
  7. fallguy
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    fallguy Senior Member

    A8D43755-E2DB-4BF7-B74D-40AE2728542C.jpeg The crossbeam is attached to the hull with strapping; red arrow. There are two straps on each hull; one is not seem in the picture.

    The blue arrow shows a bolt. There are 5 bolts that hold the cabin onto the beam. They are rated at 14 tons. During this process of evaluating things; I am wondering if I need more of them as well.

    The neoprene silencing was cut back a bit to allow us to tape the external area. That is the black square in the picture. We probably moulded a bit farther than we needed to is all...
     
  8. fallguy
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    fallguy Senior Member

    These forces are not a worry for me.

    I am worried about hitting a head sea at speed. Those forces would be much greater (when the cantilever section would be in tension I believe).
     
  9. Ad Hoc
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    Ad Hoc Naval Architect

    Im getting confused.

    You're showing a beam ... and the bolts..... and yet you're also showing this extension part....

    What is the concern - the two are different issues - structurally.
     
  10. fallguy
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    fallguy Senior Member

    Fixed the drawing...a bit 94018A96-D26B-42C5-AB9E-45B4B7D7746F.jpeg
     
  11. Ad Hoc
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    Ad Hoc Naval Architect

    Ok.. getting somewhere now.

    So..what is the issue/concern:
    The beam you show -its strength and connections?
    or
    The overhang and its connection to the main hull?
     
  12. fallguy
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    fallguy Senior Member

    I am worried about hitting a head sea at speed and cracking the cabin or elongating the bolts that hold the cabin onto the beam.

    I apologize for confusing anyone. The boat has been my life for 3 years and I know it back n forth; so easy for me to assume others would comprehend it easy. But it is a bit complex.

    Adding to this is my inability to draw well or reference post numbers on a mobile device..
     
  13. fallguy
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    fallguy Senior Member

    I am considering moving to an area where heading out into a breaking sea is often and don't want to worry about what I perceive as a weakness in the design. Not a hope to punish the vessel, but to know it can take it.
     
  14. Ad Hoc
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    Ad Hoc Naval Architect

    Apologises not necessary.
    You know you're boat inside out, we all think and analysis differently - thus just clarification needed, on my part. Sorry for asking what may appear endlessly simple and obvious - to you - questions.

    Ok, understood. But after running the numbers and if you're satisfied you have sufficient support, it comes down to QA... of the material layups linked to the load paths available.
    That is all any designer/engineer can do - and trust their calculations and trust the quality of the materials have the property values used in the calculations.
     

  15. fallguy
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    fallguy Senior Member

    If I hit a head sea at 25 knots; my intuition tells me the forces acting on the cantilever section would be more than the vessels weight which is 4 tons.

    I already went beyond the design using ply for the core here. This is because we only have 7" of core above the beam.

    Is my intuition wrong?
     
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