Drilling holes below the waterline.

Discussion in 'All Things Boats & Boating' started by Duane P Wetick, May 12, 2013.

  1. Duane P Wetick
    Joined: May 2013
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    Location: Erie, PA

    Duane P Wetick Junior Member

    I don't like the idea of drilling holes below the waterline on fiberglass boats to mount transducers, trim tabs, swim platforms, etc. Some boaters I know have had to have their entire transoms rebuilt because of water seepage. What's the right way to mount things below the waterline?

    Cheers, DocWet [Everything has limitations...and I hate limitations.]
  2. michael pierzga
    Joined: Dec 2008
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    Location: spain

    michael pierzga Senior Member

    The hole must be made watertight !

    Have a look at the Gougeon Brothers book on boat building

    Its free on the West site



    The concept is to remove the core in the area of the fastener then refil with thickened epoxy to prevent water from contacting the core and to act as a compression sleave to keep the core, sandwich from compressing when you torque the fasteners.

    Bed the fitting into epoxy to assure that its mating surface is true. Remove fitting, then rebed into 5200 or a bedding of your choice.
  3. alan white
    Joined: Mar 2007
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    Location: maine

    alan white Senior Member

    Bed those things in polysulphide. Most hulls aren't cored but some are. As said, use epoxy to seal any core. M<ake sure the epoxy has some purchase on both inner and outer skins. In cases of a solid hull where the fiberglass is thin (as it might be on a stern quarter), a plywood backer bonded in epoxy thickens the hull, strengthening the base the fitting is being attached.

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

    PAR Yacht Designer/Builder

    Use polysulphide on wood or if the bedding comes in contact with wooden core material, use polyurethane on 'glass.

    Thru hulls are a necessary evil and shouldn't be a concern. They're used extensively throughout the industry and if appropriately maintained, they'll cause no issues. The real issue isn't the thru hulls, but their neglect. If you leave bedding and fasteners unchecked for years, you're going to find out why you shouldn't have placed them out of mind.

    Backers are a good idea, though I prefer inert materials for these, such as G-10 or simply a build up of additional laminate in the area.
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