Plastic Through hulls at deck level

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Plastic Through hulls at deck level

Postby mike cunningham » Tue Dec 19, 2017 11:30 pm

Several years ago a boat yard broke all of my nylon through hulls at the deckline. The travelift slings broke the external hull flanges of all three fittings which were old and brittle. These through hulls provide an outlet for the bilge pump, the shower sump pump and a vent for the holding tank. They penetrate the hull just below the deck.

None of these is in any way threatening so I put off replacement for way too long. Today I finally got to replacing them and found that the hull core is fully exposed to the bodies of these thru hulls. There is no epoxy surround. If these fittings are not carefully sealed, you got a problem. So far I am good on the two I have replaced. One more to go. But beware, these fittings could be an entry point for water into your core if they are not properly sealed or the seal has been compromised.
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Re: Plastic Through hulls at deck level

Postby Mark K. » Fri Dec 22, 2017 5:01 pm

After removing the through hull I used a router bit in my electric drill to remove some of the balsa wood from the hole. It did a nice quick and easy job of it and left a uniform depth. I had to do it from both the inside and the outside to get all the balsa out. after that fill with thickened epoxy and install the new through hull. Now if it somehow leaks again there is no chance of water saturation into the core.
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Re: Plastic Through hulls at deck level

Postby katorpus » Sat Dec 23, 2017 1:16 pm

Rather than risk boogering up a router bit on the glass (or if you don't have one), your can use a bent over 8 penny nail (with the head cut off) or one of the thousand allen wrenches that are probably lying in the bottom of your tool box. I've done this quite successfully. If you're installing any kind of through hull "from scratch", drill a small pilot hole (from either the inside or outside) that completely penetrates the hull, then drill the hole the size you need through the inside glass/laminate first.

After you've done the core removal, it's a simple thing to cover the hole in the outer hull with a piece of tape before sealing the core from the inside. Drill out your final holes from both the outside and the inside (with your original pilot hole as the "locator" for the hole coming inward from the outside), meeting in the middle. This avoids chipping and tearout on either side.

I suggest using a battery powered drill (for at least the outside) to eliminate the chance of electrocuting yourself with the drill if the boat is in the water.

It's easier to get the core protected around the entire circumference of the hole if you thicken the epoxy just enough to "squeegee" it into the hole, pulling your plastic putty knife from bottom to top. (mask thoroughly around the hole first). You can then "stob" a dowel that's slightly undersized into the hole until it contacts the inner surface of the outside laminate. The excess will be forced out around the dowel and the masking will catch the runout. Pull the masking before the epoxy sets completely.

After it all sets up, grind the dowel and any remaining runout flush with the inner hull side, locate the center of the dowel (with the goal of leaving a flat surface for the through hull nut without digging into the original laminate) and drill it out to the proper size for the through hull. If you're going for a LARGE through hull, the dowel and the initial hole through which you remove the core can be quite a bit smaller than the through hull fitting, as long as you can get enough core out and enough epoxy in, that is. A 1" hole & dowel for a 1-1/2" final hole works pretty well if you remove 3/4" - 1" more core than that initial hole size.
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Re: Plastic Through hulls at deck level

Postby mike cunningham » Wed Jan 10, 2018 5:42 pm

I am pretty familiar with the process of replacing core with epoxy but thanks for the clarification on how to do it. I use the bent nail technique but only because it is really cheap equipment.

The real point of my post was to warn owners these thru hulls were not protected on my boat and may not be protected on other Freedoms. A bedding failure around these fittings could be bad news if left unattended for a number of years. So just a heads up.
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