Epoxy/glass vs aluminum

Discussion in 'Materials' started by CBTerry, Feb 10, 2021.

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  1. fallguy
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    fallguy Senior Member

    To add a picture, use the upload a file link. I never use an album.

    I like the sprayable wax idea. It would allow some buildup. I was only trying to warn you about release potentially being difficult. If you consider all the variations in people we get here, many do not understand an epoxy laminate shrinks as it cures and would laminate over a simple layer of agent and then not be able to remove it.

    But extending the bottom of the mast is not wise.

    Laminating over a round item is not all so simple. Very hard to get it tight, then hard to get it released, but perhaps you are aware of some tricks since you are in the biz.
     
  2. fallguy
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    fallguy Senior Member

    Here are screenshots for picture uploading from iphone. You really at least need to provide or find the specs of the existing mast as a starting point I'd say.
    55707012-F27B-49EC-9855-1651AED893F6.png
     
  3. Rumars
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    Rumars Senior Member

    You have been given the official engineering way in post #6, but it seems you don't want to go that way.

    So just for you, my guestimating special:
    Mast extension to be of the same form as the original mast, wall thickness 3/8, butted perfectly to the Al mast. Sleeve or plug, perfect fit, thickness 5/8, straight walled 18 inches either side of the butt, tapering to 0 over another 12 inches. Total sleeve lenght, 60 inches. Sleeve to be glued with G-Flex to the Al, and riveted with monel or stainless in the straight area.
    Lamination by weight of dry fiber, 10% uni at 90° (hoop), 60% uni at 0°, 30% 45°biax. Start and finish to be a 10oz knitted fabric.
    If it breaks add more glass until it doesn't.
     
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  4. fallguy
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    fallguy Senior Member

    okay, kinda cool, but how does one build the extension the same size??

    I can see an extension that is bigger using the mast as a plug, but how to make a 3/8" thick same o.d. glass mast is tricky to do well as the mast is no longer the plug..

    any ideas?

    wow, 3/8 and 5/8...that 5/8 might catch fire...have to think about how to do that without overheating
     
  5. CBTerry
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    CBTerry Better, is the enemy of good enough.

    20210211_072758.jpg 20210211_072752.jpg
    This is a rotating mast for use on a home designed and built 28ft catmrn
     
  6. Rumars
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    Rumars Senior Member

    He obiously has to do a mold. Glue some XPS or EPS around a piece of wood and start sanding. The template to check the form is easy to make, transfer the mast contours onto a piece of ply and measure 3/8" from either the outside contour (for use with a sleeve) or the inside contour (for use with a plug), then cut to the new line. After laminating dissolve the foam with acetone or gasoline and remove the wood. Same thing for the inside plug, the sleeve can be laminated directly in place.
     
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  7. CBTerry
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    CBTerry Better, is the enemy of good enough.

    You are correct in saying that I have to use a mold, but only if I follow those instructions the gent was kind enough to give. I am much more inclined to use the mast, with mold release, as a plug and build it the way my diagrams have it. Most of which is because I already have the materials and it is quicker cheaper and easier. "Better is the mortal enemy of good enough."
     
  8. CBTerry
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    CBTerry Better, is the enemy of good enough.

    It is an older mast and my reading seems to indicate that the vast majority of older masts were 6061 , in the smaller boats there was more variability in Alloys it seems. Nowadays there are a larger Variety Inn play, or at least if the same variety of alloys there is a more even distribution amongst them.
     
  9. fallguy
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    fallguy Senior Member

    Your proposal will break. Perhaps harming someone.

    If that is good enough; go for it.
     
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  10. gonzo
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    gonzo Senior Member

    That is not good enough for an engineering analysis.
     
  11. CBTerry
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    CBTerry Better, is the enemy of good enough.

    it is about probability. Nothing is certain no matter how much you engineer stuff. Planes crash despite all of the engineering that goes into them. We even lost two space shuttles and each takes about a million discreet procedures to ready for launch. I will get a piece of 6061 2 inch wide plate, of same thickness as the mast and then lay up fiberglass similar size butt double the thickness and put each in a vise and test them. I will lay up the tube based on that....tapering the top one foot to ameliorate the stress riser.
    The Wright Brothers would never have flown had ....
    The Nina, Pinto, Santamaria would never have voyaged had...
     

  12. CBTerry
    Joined: Jun 2017
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    CBTerry Better, is the enemy of good enough.

    Everything will break given enough Force. Will it break at 4 knots of wind speed ? will it break at 10 knots of wind speed ? Perhaps 17.517 knots of wind speed? Since I am building the boat also from my own design, I will take it out in progressively harsher conditions and monitor a number of things closely. Many people have told me I will die from doing various things, and yet still, I have lasted on this Earth 58 years :) I will be tapering thickness of the fiberglass for the top foot or so
     
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