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  1. #1

    Sponson install question?

    So, I have taken on the task of installing a set of sponsons on my 97 SL780. Got all the accessories needed (I thought): rivet nuts, install tool, adhesive and of course a set of used sponsons. Looked up all the information here and printed off the posted instructions. All sounds like a simple job. BUT, as I drilled the 1st hole at the rear position and then the second one as well, I find that the material is much thicker than thought. Fiberglass hull thickness appears to be around 1" thick! The rivet nuts can not work with that thickness and I can't find any online that are 1/4-20 made to accommodate that material thickness. What now? Am I missing something in the way these work? It looks like they need to pinch up against the inside of the hull when drawn up in order to be secure. Please, has anyone else experienced this and if so what can I get that will work? Is this the standard thickness of the hull in this area? Does it get thinner the farther toward the front I go? Looking for advice, thanks!
    Troy


  2. #2
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Troy, where did you drill? There isn't anything that thick other than the rib support. Are you sure it's not styrofoam?

    Hull is only around 1/4" thick. You can see by removing your seat that the hull isn't 1" thick.

    Pic of the hole location please.

  3. #3
    I know, you can imagine my surprise when I saw how thick it was. And then the second hole was the same, and then I started on a third and it is the same. I picked around with a tool to see if it is styrofoam but is same hardness and density the full way through. I can feel the styro inside when I push my tool in there. I drilled the holes in the precise locations directed on the template and when you hold the sponson up there, it appears to be in the spot it should be. I can snap some pics if you think it will help.
    Troy

  4. #4
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Yes please.

  5. #5
    Here's pics I just took.
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  6. #6
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Holy cow.

    And that's totally solid all the way through? That hull would have to weigh a ton.

    If that's the case, I can only think an expanding concrete anchor might work on that.

    I hope others chime in with a better solution.

  7. #7
    My thoughts exactly! I have taken the water box out and am wondering how to remove the styro? Do you just have to break it out? It seems to be held in there with glue or something. As thick as that is, I figured I could just put bolts through with a nut on the inside? Only bad thing is I have such a large hole my bolts will be huge and how do I keep it from leaking? I can feel that there are ribs every so often but I can't believe that I have hit one every time I drill. What are the odds of that? If anyone else has advice, please chime in!
    Thanks,

  8. #8
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by tbaker View Post
    ...As thick as that is, I figured I could just put bolts through...
    There are other fastener types, such as the AVK A-L series.
    These expand inside the hole, rather than behind it.

  9. #9
    Ok, think I will try to order some of these A-L inserts. Also, what do you think about the A-W type? They are a brass type with specific applications for the fiberglass boat industry where they fill a hole and not really grip from back of material. Seems like this would work well also? What is the best adhesive to use when installing these? Also, would it be good to put some silicone on the bolt when installing in order to prevent leaking?
    Thanks,

  10. #10
    2000 pro 785 (son's) 1998 pro 785 (dads) old guy in mich's Avatar
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    ditto "blind" inset should work best. you can cut out foam with a hot knive, burns torch and an old serated steak knife work well. save pieces and glue back in latter.
    here a link on installing beach house sponson that have some pretty good info.
    http:/www.atlanticjetsports.com/install_bh_pol.htm

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