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Old 19-09-2009, 06:09   #1
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Proper Thru-Hull Fitting Size

I own a 1975 C&C 27 Mk III

Just bought it and insurance wanted me to replace the Gate Valve Scupper with Ball Valve.

So in the process of removing and replacing I broke the seal of the Thru-hull fitting.

So took them off to re bed. Well one of them was awfully difficult to remove, especially when I don't have a step wrench and had to improvise.

So once I got it off I could see some of the threads are messed up.

So I believe I should replace.

The problem is it is a 1 1/4" flush Thru Hull fitting with a flang dia of 3 1/2"

I can't seem to see any on the internet with this large of a flang dia.

Why can't they standardize things? @#)((*%

Anyone have any ideas how I can find one with these dimensions?

The largest I've seen is with a 3" flang dia. So I guess I could use than and just fill the surrounding flang gap with more marine sealant
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Old 19-09-2009, 20:18   #2
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Try this:
Buy the thru hull you like. Put some saran on it. Put a bead of thickened epoxy around the hole left by the old thru hull. Lightly place the wrapped thru hull into the hole. When the epoxy is firm, remove the thru hull. You;ll now have a fitted hole for the new one ( they're all around 3") a little sanding when it's set up and then install the regular way.
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Old 19-09-2009, 22:13   #3
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Thank God for Wikipedia.... S&S means plastic wrap ;-) I agree with the method, don't use sealant. The best filler for this is colloidal silica because it prevents sagging. Make the mix very thick, like peanut butter.

ciao!
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Old 19-09-2009, 23:22   #4
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I did what SS suggested serveral years ago, but slightly different. I mixed some chopped fiberglass into the epoxy (used a great product called Fill-It from Smith & Co in Richmond, CA) to give it more strength. I also put numerous wraps of plastic around the threads when I put in the epoxy because I wanted room to put marine sealer on the threads (long story). When the epoxy set, I removed the thru-hull and pulled out the plastic (had used part of a gargabe bag. It worked very well.

Bill
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Old 20-09-2009, 08:19   #5
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Epoxy?

OK, not sure I completely follow. Sorry I'm new to owning a boat and have never done fiberglass, epoxy etc...

So hopefully I've explained things correctly. The hole itself fits a 1 1/4 " thread.

The recessed area on the outside of the boat is 3 1/2", where I'm told that a new fitting would be 3" So that would mean a 1/4" gap all the way around.

If I already have marine sealant under the new flange, in the treaded area, under the nut.

Pretty much I assume the excess will end up filling in that 1/4" gap like a caulking.

I thought I would just smooth out and leave it?

I'm not sure I follow putting in the fitting and try and fill?
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Old 20-09-2009, 08:37   #6
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Quote:
Originally Posted by outdoor View Post
OK, not sure I completely follow. Sorry I'm new to owning a boat and have never done fiberglass, epoxy etc...

So hopefully I've explained things correctly. The hole itself fits a 1 1/4 " thread.

The recessed area on the outside of the boat is 3 1/2", where I'm told that a new fitting would be 3" So that would mean a 1/4" gap all the way around.

If I already have marine sealant under the new flange, in the treaded area, under the nut.

Pretty much I assume the excess will end up filling in that 1/4" gap like a caulking.

I thought I would just smooth out and leave it?

I'm not sure I follow putting in the fitting and try and fill?
Outdoor, Your hull fiberglass is covered with gelcoat and hopefully an epoxy barrier coat to prevent osmotic blisters (delamination of glass below gelcoat). Blisters can be expensive to repair so a little extra caution is required when you do anything to cut through the gelcoat. I would not count on sealant to completely fill the void and keep the water from penetrating into your fiberglass (it is slightly porous). That's why other posters are recommending the epoxy filler. Epoxy gives more protection to keep water from delaminating your hull and is cheap insurance against a costly repair.

Check S&S's description of repair. You will be placing your new thru hull into the hole temporarily until epoxy cures and then removing it. The 1/4" void around the outside circumference of the thru-hull should then be filled with epoxy. Next sand down any high spots on the epoxy and install the thru hull with sealant. That should be a good fix.
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Old 20-09-2009, 10:03   #7
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Outdoor,

I can understand that the mixing of epoxy with fillers is intimidating when you never used epoxy before. So, I have an alternative which is really easy:

Wrap the fitting with plastic wrap like S&S described and mount it temporary with the nut on the inside. Visit you favorite hardware store and buy an "epoxy stick" for use on fiberglass (not the other type which is for use on metal). This looks like a 3/4" thick round stick. Using a knife, cut a small piece off the stick, like 1". The harder component is in the core of the stick so you must knead the cut off piece until it is mixed well (the two parts are a different color so it's easy to see when it's good). Now, form the mixed epoxy into a roll and push that around the fitting. Use a little water on your finger to smooth it out (this is the trick for using this product: it gives a very smooth finish). When you run out of mixed epoxy you can estimate how much more you need to cut off.

When done, let it cure, remove the fitting, sand a bit, cut the fitting to size and install the fitting with sealant. Let it cure and coat the epoxy and fitting with anti-fouling paint. Also, paint the inside of the fitting but take care to not put paint on the ball of a valve if that's installed already.

cheers,
Nick.
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Old 20-09-2009, 15:07   #8
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I might be starting to get it

Cut fitting to fit?

Why would I need to cut it? And how would I cut it?
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Old 20-09-2009, 16:39   #9
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You cut the threaded end with a hacksaw. The length is made so it fits most boats. If you fit a seacock (flanged valve) on the inside you must cut it short enough so that the flange of the seacock is tight to the hull so you can screw or bolt it down. If you fit an elbow and/or regular valve you must check clearances but the shorter the fitting, the better.

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Old 21-09-2009, 08:08   #10
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You cut the threaded end with a hacksaw. The length is made so it fits most boats. If you fit a seacock (flanged valve) on the inside you must cut it short enough so that the flange of the seacock is tight to the hull so you can screw or bolt it down. If you fit an elbow and/or regular valve you must check clearances but the shorter the fitting, the better.

cheers,
Nick.
What Nick says, but only if you have too may threads to snug down your seacock. ( I doubt your hull is 2" thick). Dry- fit your thru hull and go inside and see how many threads you have left. If you can't snug down your seacock on the end because the stub is too long, you'll have to cut it shorter.
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Old 21-09-2009, 09:49   #11
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What Nick says, but only if you have too may threads to snug down your seacock. ( I doubt your hull is 2" thick). Dry- fit your thru hull and go inside and see how many threads you have left. If you can't snug down your seacock on the end because the stub is too long, you'll have to cut it shorter.
But, your hull and backing plate might be (or made to be) as much as 2" thick.
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Old 21-09-2009, 09:54   #12
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If you have only 1/4" all around and it's probably what.... 1/8" deep ? I see no problem with just filling it with 5200 bedding that squeeezes out when you tighten the thru hull. Of course the epoxy mentioned above is great also.
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Old 21-09-2009, 11:22   #13
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But, your hull and backing plate might be (or made to be) as much as 2" thick.
But the fitting may be 4 1/2 (or more) inches long. Measure twice, cut once.
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Old 21-09-2009, 11:58   #14
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But the fitting may be 4 1/2 (or more) inches long. Measure twice, cut once.
Point taken.
FWIW: The threaded portion of Groco thru-hulls
at 1-1/4" ∅ is 3.31" long
at 1-1/2" ∅ is 3.5" long
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Old 21-09-2009, 12:09   #15
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Cheechako: the problem is (I assume but am pretty sure) that there's no gelcoat in that area. When you use sealant, it ends up butted against the gelcoat and that will leak quickly with water in the laminate as a result.

cheers,
Nick.
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