Swim platform/transom interface issue

Discussion in 'Fiberglass and Composite Boat Building' started by EStaggs, Jan 20, 2013.

  1. EStaggs
    Joined: Aug 2007
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    Location: Spokane, Wa

    EStaggs Senior Member

    Alright, I ran into a hiccup.

    Here's the existing transom on the Salty Pup:

    [​IMG]

    I planned on building it out with 5/8" of ply cored glass:

    [​IMG]

    I can't get those panels (mainly the center one) to lay flat on the transom's inside panel. It's got so many thickness changes between glass returns, buildups, fillets, etc., even after grinding, that I can't get it to lay flat period. We are talking gaps of up to 1"!

    I need a 24"-26" swim platform back there that's usable for up to 600lbs or so.

    What other solutions are out there?

    The glass is solid, somewhere in the 3/8" thick range, hand laid roving. It's in good shape for a mid 1960's layup. There will be a pair of boxes aft, and where those land on the transom I'll be laying some biax tape on the joints, and that reduces the full transom span down to 28" between the longitudinals and the sides, as well as across the center.

    Will I be asking for issues by just using beefy butt blocks in the 12" square range? Will be using brackets like most tournament ski boats so I can remove the step, something like this:

    [​IMG]

    I'm stuck right now, any help is appreciated. Photos are even better.

    E
     
  2. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    How big are the gaps in these irregularities? If less than 3/8", just use a notched towel and thickened (structural mix) epoxy. You can use screws from the other side to "suck" the panels down. You could also use braces or home made clamps too. If the gaps are bigger, use some fabric to fill the lowest spots, then the thickened epoxy thing. What are you using for the reinforcement panels?
     
  3. EStaggs
    Joined: Aug 2007
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    Location: Spokane, Wa

    EStaggs Senior Member

    The panels that I cut are 1/2" fir press laminated with 18oz roving and gelcoat on both sides. I ground the glued side down to glass for good adhesion with epoxy.

    The gaps are literally 1" and even a bit over that, so the amount of glass to build up would be more than the thickness of the sheet I'm trying to adhere to it.

    I tried lots of different clamp/brace combinations, and nothing would get it where it needed to be. Screws won't do the trick without severely deforming the exterior glass and possibly cracking the gelcoat (which I have plenty to repair on the gunwales).

    Thanks

    E
     
  4. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    It sounds like your reinforcement needed to be laminated in position. I'm not completely sure what "1/2" fir press laminated with 18oz roving and gelcoat" actually means, but the contact face doesn't need nor is it desirable to have gel coat. It also sounds like a polyester laminate, which doesn't stick very well to wood. Simply put, if you can bend it into place, you have limited options, none of which you're going to like very much.
     
  5. EStaggs
    Joined: Aug 2007
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    EStaggs Senior Member

    I'm looking for plan B right now, so ignore the fiber tech panels.

    What would one do with a solid glass transom of about 3/8" thick hand laid roving in polyester in order to put a 24" x 84" swim platform capable of supporting 600lbs? I'm trying to find another way than what I was doing.

    The panels you see are fir plywood that's been laminated on both sides with roving bedded in polyester and gelcoated, under pressure, on a large laminating table. I've done failure testing of it, and have yet to peel the glass away from the wood, the wood always fails. This is a very tried and true product from the transportation industry, and has a very long track record. The company is called Fiber-Tech that produces it, and makes everything from single thickness laminates to foam and wood core, aramid, etc etc.

    I ground off the gelcoat (as I explained in the post) so that I'd have good adhesion.

    Thanks!

    E
     
  6. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    I've done something very similar last spring on the boat of a friend. I made stainless vertical backing plates to distribute the load on the very uneven transom surface. Drilled holes through the transom and used long bolts and nuts. With everything in place and the nuts hand tight, we supported the platform, then removed the backing plates one by one and put a liberal amount of thickened resin on them before putting them back in place and tightening the nuts.
    The inside looks a bit funny, with resin coming out all around the backing plates. The plan was to cut it while it was still soft, but on that sunny day it cured a bit faster than we expected.
     
  7. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    1/4" plywood will likely bend to the radius you need. Can you put in two layers, bonding them together as you fit them? You don't need the heavy roving at the interface, though a healthy layer of mat will help conformity and bond issues.
     
  8. EStaggs
    Joined: Aug 2007
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    EStaggs Senior Member

    I wish it were a radius issue, but it's an extremely uneven flat surface.

    E
     
  9. alan white
    Joined: Mar 2007
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    alan white Senior Member

    Your main concern is to reinforce the area of attachment. No matter how you do it, the stress will go to the top and bottom of the transom. Therefore, you might think about a (pair?) of frames that carry the load down (compression) and up (tension) rather than thickening the whole transom.
    The boat's bottom is of course strong enough to take the compression but it may be the top edge of the transom will need to be beefed up with a bonded-in piece of say 1 1/2 x 2 or so. The vertical frames would be positioned at each bracket location. You might pad the transom1/2" with plywood where the holes will be drilled and the vertical frames (maybe made from 2 x 3s) could be just to the side of the holes to allow access to the nuts.
    Fillet (and round off) where needed to glass in the new wood.
     

  10. EStaggs
    Joined: Aug 2007
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    Location: Spokane, Wa

    EStaggs Senior Member

    I see what you're saying Alan, that's a very interesting way to think about it.

    I'll be putting in a pair of fish boxes that will give vertical structure, and could add a couple more to make that work. On top of that, I'll be bonding a 5/8" thick sole that will be taped in heavily, which ought to brace even more.

    Definitely some food for thought there.

    E
     
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