G10 vs 6061 Aluminum backing plates

Discussion in 'Boatbuilding' started by fpjeepy05, Jan 13, 2020.

  1. fpjeepy05
    Joined: Jan 2010
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    fpjeepy05 Senior Member

    We use enlay 1/2" aluminum into superstructures to tap and screw the legs of towers to. In many instances, it would be helpful to be able to use G10 instead. The concern is that over the life of the vessel the fatigue could cause the threads in the G10 to wear and fail. Has anyone ever seen any formal or informal test studies to see how G10 compares to aluminum in fatigue situations like this?

    I was thinking about making a crude test by drilling and tapping holes in the two materials then welding a screw to an old Sawzall blade and locking the trigger and letting it run for an hour and compare. Not the same, but maybe close enough to make a call.
     
  2. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    What life expectancy are you looking at?
    And if it is not suitable, then what is wrong with adopting a maintenance programme to assess them on a regular basis?

    What design data are you applying to this arrangement, to estimate/calculate your fatigue?

    Some data is noted
    here
    here
    and
    here
     
  3. kapnD
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    kapnD Senior Member

    I’d prefer to use G10, no corrosion problems.
    You can double or triple the backing plates for more thread embedment.
     
  4. Barry
    Joined: Mar 2002
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    Barry Senior Member

    Are you unable to just through bolt instead of threading?
    Or encapsulate a 1/2 inch stainless insert for threading?
     
  5. fpjeepy05
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    fpjeepy05 Senior Member

    I agree, but I have to make sure it is strong enough. It will be entirely shear on the screws so extra plates would prevent total failure, but as soon as there is any movement the owner would want it replaced so its still a failure.
    Again shear is the concern. I could count on adhesive on the foot to distribute the load to the outer skin, but I would prefer not to.

    Larger bolts would help, but that is more the tower guys job not mine.
     
  6. kapnD
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    kapnD Senior Member

    Tower mountings are subjected to forces in all directions, so sheer force is just a part of the consideration.
    I would think tensile stresses would be the major force involved.
    If you have doubts about the size of the bolts and their anchor plates, work with the tower builder, as you and he are the only two parties that really know what’s going on here.
    Such matters are rarely engineered to a fine degree, more usually determined by experience, and fortified by a generous dose of overkill.
    G10 is still my favorite choice for such items, as it is compatible with the layup, and can be an integral part of it, spreading stress over a larger area.
     

  7. fpjeepy05
    Joined: Jan 2010
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    fpjeepy05 Senior Member

    In this case, shear is what I am most concerned with. The back legs are mounting to the side of the house not on the deck.
     
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