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Thread: Hatch flange bolted only to top deck skin on 1991 Privilege 39

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  1. #1
    Join Date
    Oct 2018
    Location
    Saint Petersburg, FL
    Posts
    4

    Default Hatch flange bolted only to top deck skin on 1991 Privilege 39

    I've been refurbishing the Goiot Tradition 50.50 hatches on Cyclops by replacing the lenses, gaskets, handle O-rings, and re-bedding the deck flanges. The hatches above the living spaces are attached with machine screws and nuts, visible after removing the headliner.

    I found that the deck flange of the hatches covering the forward storage compartments in each hull was installed with machine screws through only the top skin of the deck. The hinge plate (attached to the hatch frame containing the lens) was bolted through the entire deck as expected. Inside the storage compartment, I found a smooth ceiling, with no nuts to loosen, under the deck flange. That left me wondering if maybe wood screws had been used, or if there were nut plates embedded inside the deck. Turning any of the screw heads produced no upward motion. I cut an exploratory hole to discover that machine screws attach the deck flange, and only through the top skin.

    I had to cut access to reach all of the nuts from inside the storage compartment. I'll be replacing the foam core and lower skin over that area, then re-attaching the deck flange with longer machine screws through both skins.




    Also, if you ever need to replace a hatch lens, don't bother trying to buy an OEM part. It's unthinkably expensive compared to having one made locally. I found several shops within a half hour drive, in St. Petersburg, FL, that will clone an existing hatch lens. The cost was similar between the local shops, around $70. They'll make them while you wait, versus waiting to have one shipped and paying several hundred dollars per lens for an OEM part.

    I had no such luck sourcing the gasket material locally, because of its trapezoidal cross section, and had to order it from France.



    The nearer hatch is one I refurbished, before I installed the latches. The hatch forward of the gangplank ramp was only attached to the top deck skin.

    I used DowSil 795 to glaze the lenses into the hatch frames, 3M Black Weatherstrip Adhesive to attach the gasket. I used 3M Marine Adhesive Sealant 4000 UV to bed the first hatch I refurbished, and switched to butyl tape after that for less mess and no limit on working time.
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  2. #2
    Join Date
    Jul 2009
    Location
    Gosport
    Posts
    349

    Default Re: Hatch flange bolted only to top deck skin on 1991 Privilege 39

    Well done - that is a lot of work but worth doing!
    Bit scary about how those front hatches were fitted on. Imagine that with waves breaking over the bows

  3. #3
    Join Date
    Sep 2017
    Location
    Boat: Croatia; Living in Tokyo during the months not on the boat
    Posts
    25

    Default Re: Hatch flange bolted only to top deck skin on 1991 Privilege 39

    Thanks for your report with all the details.

    I also think that the machine screws through only the top deck skin sounds bit weak.

    However, what is the thickness of the "top deck skin"?
    Is the top deck skin only gel coat or has it glass fibers inside?

    One can also start thinking about the forces which will be applied to the hatches. The screws (originals) only have to press down the top element to ensure a proper sealing.

    Waves washing over the bow, will IMHO only have very small sheering force (height of the frame is about 2-3 cm / 1 inch but much more force (weight of the water), which presses the hatch down.
    Thus the major force of a wave will support the screws.

    Other opinions?

  4. #4
    Join Date
    Jul 2009
    Location
    Gosport
    Posts
    349

    Default Re: Hatch flange bolted only to top deck skin on 1991 Privilege 39

    I have had paint stripped from the side of a hull due to waves in a storm (Wharram) which also
    broke the front cross beam so I wouldn't underestimate the potential forces in waves

  5. #5
    Join Date
    May 2012
    Location
    Oslo area
    Posts
    45

    Default Re: Hatch flange bolted only to top deck skin on 1991 Privilege 39

    Thanks a lot for sharing this report and the pictures with us. It seems you are doing a thorough job, which can not be wrong. The other comments lead me to thinking of what is commonly done in the industry? On our boat, there are no through bolts. But the Lewmar hatches have an aluminum base frame, which is attached with many screws to the upper surface. Looks similar to yours. In addition the frames are glued. The hatch hinges themselves are screwed on top of the base frame. Again, only to the top surface of the sandwich construction. The top surface does not yield when walking on it, so it is fairly solid. I have had no second thoughts regarding strength. Someone might know the standard of other manufacturers?

  6. #6
    Join Date
    Oct 2018
    Location
    Saint Petersburg, FL
    Posts
    4

    Default Re: Hatch flange bolted only to top deck skin on 1991 Privilege 39

    I haven't measured the thickness of the top fiberglass skin, but we can assume that it's nothing unusual. My primary concern was gaining access to the nuts, so that I could renew the sealant between the flange and the deck, which had been in place since 1991.

  7. #7
    Join Date
    Oct 2008
    Location
    Worcester, U.K., Moraira, Spain
    Posts
    567

    Default Re: Hatch flange bolted only to top deck skin on 1991 Privilege 39

    It doesn't sound like normal Privilege practice. On my, admittedly later generation boat, anywhere where equipment was fitted was either solid laminate or fitted with stainless backing plates behind the outer skin. It wouldn't be usual to through bolt all the way through a foam cored section for fear of crushing the foam through over tightening.

  8. #8

    Default Re: Hatch flange bolted only to top deck skin on 1991 Privilege 39

    Quote Originally Posted by Jeannius View Post
    It doesn't sound like normal Privilege practice. On my, admittedly later generation boat, anywhere where equipment was fitted was either solid laminate or fitted with stainless backing plates behind the outer skin. It wouldn't be usual to through bolt all the way through a foam cored section for fear of crushing the foam through over tightening.
    It is usual practice to create epoxy bolts to prevent this from happening. Drill through the upper skin, then using a special tool, Allen Key, in the drill and rotated to remove the foam, or balsa, between the skins around the hole. Pore in epoxy and allow to set. Re-drill hole through both skins. The epoxy forms a sealed cylinder around the bolt hole and prevents crushing and water ingress.

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