Removing and fiberglassing over through hull fittings.

Discussion in 'Fiberglass and Composite Boat Building' started by HCB66, Jul 28, 2020.

  1. HCB66
    Joined: Oct 2017
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    Location: USA

    HCB66 Junior Member

    Looking to remove very old through hull fittings below the water line. I want to remove and glass over them. To me it seems pretty strait forward mostly but can the average person do fiberglass work that will stand the test of time? To me it seems like if I just follow instructions the fiber glass work will hold fine. I've also seen videos where both the inside and outside edge of the hole are ground so they have an incline rather than just filing the hole up, which makes sense. Any advice?
  2. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    Fiberglassers have special magical powers and mere mortals can't do the work!

    Of course you can do the repair yourself

    Working from the inside is often easier than working over head (or turning off the underscore). How much room is there inside of the boat?

    Definitely grind a ramp. 8 to 1 is the typical scarf slope.
  3. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Obviously using a taper both inside and outside, you can arrange a plug that is trapped, and can't fall out, or in. I'd say it depends how large the holes are, and how thick the hull is, as to how you go about it, small holes could be managed by a bog made of epoxy and glass fibres mixed with a thickening agent. Larger ones, a glass lay-up.
  4. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Not sure if you have a core, but a core changes things a bit. And I'd use epoxy.

    I like to use plastic and a sharpie to help me size the glass pieces. And chop strand works fine even with epoxy. Biggest piece first. Keep going until the repair is largely fair. Sand out a bit for fairing a/o gc.
  5. fredrosse
    Joined: Jan 2005
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    Location: Philadelphia PA

    fredrosse USACE Steam

    First of all, what is the material of your hull? Wood? Fiberglass? HDPE? Aluminum? Steel? The hull material needs to be known, along with the hull thickness in the area of the thru-hull penetration, and how big is the thru-hull penetration. This is probably an average size hole in an average size boat?

  6. missinginaction
    Joined: Aug 2007
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    Location: New York

    missinginaction Senior Member

    About 10 years ago I removed a couple of thru hull depth sounders and relocated a raw water intake. I'll explain how I did it. These were in the bottom of the bilge. Work from inside the boat. First I cleaned up the area with some acetone. Took an angle grinder to the area and ground to clean laminate and scuff up (I have no core). Didn't go crazy, just cleaned things up. Vacuumed everything up and cleaned again with acetone. Went outside. Wiped down and gently sanded the bottom paint around the holes. Cleaned up with acetone. Placed clear plastic packing tape over the holes to keep the epoxy resin from running out. Went back inside. Mixed a small quantity of neat epoxy (just an ounce or two). and filled the holes, just even with the laminate in the bilge. As soon as the epoxy in the hole started to kick off I began laying up fiberglass cloth inside the bilge. I used some 1708 biaxle stitchmat that I had laying around. You could use woven roving of just some heavy fiberglass cloth. The 1708 is pretty thick so I used 5 layers. I wanted to replicate the thickness of the hull where I was working, more or less. I started with a small piece and placed increasingly larger pieces as I went. I used slow harder with the resin so I had time to work and get a good , solid, resin rich laminate. Went outside. Peeled off the tape and found a small void on the outside of the boat where an air bubble had formed. Mixed a little thickened epoxy and filled it in with a putty knife. Sanded, put a little bottom paint on it and I was done.

    I see Mr. Efficiency went from a larger piece of cloth to smaller and that worked, so I suppose you could go either way. My repair has a slight rise in the center where the old fittings were and the new laminate is thickest.

    Not to difficult.

    Last edited: Jul 29, 2020
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