Tri-hull restoration/wakeboarding pylon question.

Discussion in 'Boat Design' started by ssaumure, Jul 8, 2015.

  1. ssaumure
    Joined: Jul 2015
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    Location: Edmonton, Canada

    ssaumure New Member

    Have a question for the community, I'm in the midst of a reinell tri-hull restoration. One thing I would like to do is install a removable wakeboarding pylon. The thought I had was to attach three 2X6s between the stringers with a hole through the first two and the floor for the pylon. this would all be glassed in to repel water. I would also install a deck plate over it for when not in use.

    I would install cables to support the top of the pylon, though not sure yet how I will configure them.

    Does anyone see issues arising from this type of set up?
     
  2. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Welcome to the forum.

    It's difficult to picture exactly what you have in mind, though I have a clue. maybe you can post a picture and/or a drawing of your idea? Usually 2x4's aren't necessary for what you have in mind. Have you looked at the way other boats have rigged their tow arrangement? Often it's best to just steal a well engineered and setup idea, than to create a new one. Hell, I blatantly steal other folks good ideas all the time. As an example, I have a particular centerboard arrangement I use on sailboats, that I stole from a famous designer. It works so well, I can't bring myself to try something else and he's dead, so can't really complain too much about it. Plagiarism, it's the only way to go on this kind of stuff . . . ;)
     
  3. ssaumure
    Joined: Jul 2015
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    Location: Edmonton, Canada

    ssaumure New Member

    Thanks

    May not be the best picture but it should give an idea

    http://www.boatdesign.net/forums/attachment.php?attachmentid=101442&d=1436472212

    The three 2X6s are connected to the stringers, a hole through the first 2 to support the base of the pylon with the bottom 2X6 supporting the weight.
    The floor board would lay flush on the top 2X6 with a hole lining up then a deck plate over top when not in use.
     

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  4. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 477, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    I'll assume this will be bonded to the hull and existing stringers, under the sole. If this is the case, she'll be quite stiff side to side, but will not have a lot of stiffness fore and aft (assuming fore and aft parallels the 2 stringers). When working up a structure, it helps to try to picture where the loads are and how they can be transmitted to the hull shell and/or any existing structure.

    Your longitudinal structure does this fine, but the stack of 2 bys between, will have a cantilever force (the pylon) trying to twist them out. A quick and simple solution might be to place a 3rd longitudinal stringer on the centerline, so the 2 by stack can't rotate, without tearing it out as well.

    Personally, I'd use a different approach, treating it much like a mast partner. I'd have the two stringers just wide enough off the centerline, to permit the pylon to past between them or allow any pylon fasteners to land in them, with athwart bridging tying them to the existing stringers. I'd probably use a thick plywood pad on top of this new structure, that would get bonded to the underside of the sole, further spreading out the loads. A few more athwart bridges wouldn't hurt anything either.

    Shown is a typical grid, with the fore and aft longitudinals and the athwart braces, close to the pylon, bracketing it. The ends of the longitudinal should be tapered to prevent point loading (gray lines) and the athwart braces, bonded to the existing stringers (dashed lines). Not shown, but recommended is a plywood pad notched into the top of this assembly, at least a foot or more in area, where the pylon would be attached. I'd use a couple of layers of 1/2" plywood, but most will just opt for a single hunk of 3/4".
     

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