Hard Top Attachment - Will This Work as Planned?

Discussion in 'Fiberglass and Composite Boat Building' started by fly186, Mar 7, 2017.

  1. fly186
    Joined: Nov 2016
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    Location: Florida

    fly186 Junior Member

    OK, I guess I don't have a clue but I'm not sure you do either.
    How can this top "oil can" with all the support from the frame as shown in the picture below? You can do chin-ups on any of that tubing and it doesn't move. In addition, there's two layers of 10 oz and then 1708 on the top as well. It's not exactly "flimsy".
    If it rips off I guess you can say "I told you so" but I'm using the Sikaflex 221 with the 205 primer. I'll also have 4 attachment points.
    Wish me luck.
    20170311_101603_resized.jpg
     
  2. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    Thanks for the picture. There is plenty of framework there. That's what I meant by "bows underneath". I didn't know what the T top frame looked like. All that framework often is built inside the hardtop.
     
  3. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    I don't think your top will oil can (seems too well built for this), though I do think you'll have a "zipper" failure in the bedding, without significant hard mounts, regardless of what this might be. These sealant/adhesives are great for some plastics and in locations where high elongation is required, such as dissimilar materials, but once you get them started, they tend to zipper along until something stops them. A good example of this behavior is the little rubber strip on the back of a gift card, that attaches it to the cardboard it's sold on. To remove this little rubber strip, you pull on one end and it stretches out, pulling more and more until the whole thing releases. Another example is the picture hanging strips they now sell. You apply them to a wall and they have a little hook imbedded in the adhesive, they hold fine, but to remove them you grab the tab and pull, where it then comes off cleanly. The adhesive deforms, stretches and peels right off.

    My previous comment about a bonded hard point is simply bonding (directly to the laminate, not the paint) a "T" or other shape (metal of course), that can be physically attached to your top cage. I understand your not wanting penetrations in the nicely built top, which is why I suggested this approuch. I'm assuming the top has a perimeter frame, probably of aluminum? Even if it doesn't and the top is stiff enough a plate with a bolt or perpendicular welded to it could be bonded, then attached to the cage. There is a stainless piece for this used on binimi's and windshields. It's designed to be machined screwed, but could be bonded as well. Picture a length of pipe, cut in halve or nearly so.

    [​IMG]

    If you made these up yourself, they could "capture" the top without bonding, assuimg it couldn't flex enough to release itself from the containment.
     
  4. missinginaction
    Joined: Aug 2007
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    Location: New York

    missinginaction Senior Member

    That's a nice fitting PAR. He could use stainless steel structural washers under the head of his machine screws to spread the load a bit and make a nice looking top as well. I used these structural washers all over my boat where I needed additional strength to bear heavier loads. All of my cleats, the attachment points on the swim platform and railings were done with these washers and nylocks. I've never had an issue with anything loosening up or crushing.

    I understand that you don't want to drill through your top fly, but if you have a change of heart........well these would serve you well.

    https://www.albanycountyfasteners.com/Fender-Washer-Extra-Thick-18-8-Stainless-Steel-s/767.htm
     

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  5. rasorinc
    Joined: Nov 2007
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    Location: OREGON

    rasorinc Senior Member

    Question? Was saying use aluminum bolts (no corrosion or adhesives ) Bad advise?
    Or am I missing somthing here. On a trailer there is going to be great lift and I would
    not trust adhesives.
     
  6. fly186
    Joined: Nov 2016
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    fly186 Junior Member

  7. jorgepease
    Joined: Feb 2012
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    jorgepease Senior Member

    I fastened my hard top down by first putting rubber weather stripping. Then about 6 selftapping screws around the edge directly into the tube. It's what the metal shop told me to do.

    I used Sika on fiberglass, it's incredibly strong, used it to bond the base for my rubrail's but I put it on heavy, it's relatively cheap, also use the black primer first if you go that route. I didn't think it would work too good on the top with limited area to glue to but never tested that.
     
  8. fly186
    Joined: Nov 2016
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    fly186 Junior Member

    Thanks. I did some testing last weekend with the Sika 221 and various materials including anodized pipe, PVC, etc. on smooth fiberglass, not even scuffed, and with no primer of any kind. A 12" piece of aluminum pipe with a 1/4" bead, on one side of the pipe only, could not be pulled apart by hand after 24 hrs. To get it off I had to pry it up from one edge with a large screwdriver. It is strong stuff. I'm not using the black 206 primer because it will make a mess. I'm using the Sika 205 clear primer just to achieve the very best bond possible between the paint and aluminum.
     

  9. jorgepease
    Joined: Feb 2012
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    jorgepease Senior Member

    cool! Yeah it's as good as any I have ever used including, I think, better than the plexus which is like 4 x more money.
     
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