Thru Hull Modification - Page 2 - SailNet Community
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post #11 of 21 Old 04-22-2019 Thread Starter
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Great idea. Thanks
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post #12 of 21 Old 04-22-2019
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Re: Thru Hull Modification

Presuming that your backing plate is permanent (i.e. not wood) like G10, you just seat the backing plate with the new outer threaded fitting tight into the inner seacock fitting... all with epoxy mush. Once cured for a hew hours, grind off the proud outside part. i.e. grind off the protruding thru hull flange and the hardened epoxy that oozed out around it. All smooth and strong as the hull itself or stronger.
This type/model of seacock can be rebuilt from the inside, BTW.
We replaced all of our 80's Marlon originals like this in the 90's, when these new-generation Forespar products had replaced their earlier Marlon ones.

No worries about electrolysis and waaaaay stronger than the ABYC minimum spec for seacock strength.

The base mounting mounting system is clearly visible in this blog. Note that the epoxy was smoothed around the backing plate. Strong and water proof. Gotta say... that Forespar winterizing thru-hull fitting is really great, too. Use it every season.
Coupler, Shaft Seal, and Antifreeze - Blogs - EY.o Information Exchange

1988 Olson 34, by Ericson Yachts.
Sail # 28400
Betamarine 25 (new 2018)
RCYC, Portland, Oregon

Last edited by olson34; 04-22-2019 at 11:30 AM.
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post #13 of 21 Old 04-22-2019 Thread Starter
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I think I'm with you except for the hull side. The new skin is much smaller than original. Are you saying that the new thru hull will hang below the hull and to apply epoxy around it. Then when cured grind off excess? Thanks for your imput
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post #14 of 21 Old 04-23-2019
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Re: Thru Hull Modification

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I think I'm with you except for the hull side. The new skin is much smaller than original. Are you saying that the new thru hull will hang below the hull and to apply epoxy around it. Then when cured grind off excess? Thanks for your imput
If it is the same (or a tad less) diameter as the hole, it will suck up tight with thickened epoxy all around the thread, against the G10 backing plate, and oozing out around the outside of the head (no matter what style of head). Once hardened all the 'proud' part outside gets ground flush with the rest of the hull. Basically the thru hull part has become (Zen alert...) one with the frp hull.

1988 Olson 34, by Ericson Yachts.
Sail # 28400
Betamarine 25 (new 2018)
RCYC, Portland, Oregon
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post #15 of 21 Old 05-30-2019
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Re: Thru Hull Modification

There is a 2" gap between my West Marine Perko and Groco 1-1/4" Thru-Hull and the Seacock
Who here has a 2" thick hull.
West Marine doesn't sale anything smaller and i can't find anything online
Our hull is 1" solid glass, do i really need a 1" thick backing plate to make it fit?
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post #16 of 21 Old 05-30-2019
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Re: Thru Hull Modification

Get your hacksaw out and cut the through hull off.
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post #17 of 21 Old 05-31-2019
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Re: Thru Hull Modification

Thanks roverhi.
Just to make sure i'm hearing you right, what your saying is to cut the brand new Thru-hull in half to make it fit the brand new Seacock? All because my hull isn't over 2" thick like a shrimp boat.
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post #18 of 21 Old 05-31-2019
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Lightbulb Re: Thru Hull Modification

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Originally Posted by Whalerus View Post
There is a 2" gap between my West Marine Perko and Groco 1-1/4" Thru-Hull and the Seacock
Who here has a 2" thick hull.
West Marine doesn't sale anything smaller and i can't find anything online
Our hull is 1" solid glass, do i really need a 1" thick backing plate to make it fit?
It might be helpful to harmonize our terminology in such a thread, too.
What you describe is a "valve screwed onto a threaded thru hull" and not actually a "seacock". The later sits lower and is a one piece casting incorporating a valve (usually a ball valve these days) and the hose is clamped directly onto the tailpiece. This is very very strong compared to a valve screwed onto the thru hull fitting.
And, a seacock also sits low against the hull inside surface. If your hull's layup is actually one inch thick in the installation area, yes, you already have the equivalent of a 'backing plate'. Of course that is just an opinion flung out from the internet - worth 'bout what you paid!
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1988 Olson 34, by Ericson Yachts.
Sail # 28400
Betamarine 25 (new 2018)
RCYC, Portland, Oregon
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post #19 of 21 Old 05-31-2019
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Re: Thru Hull Modification

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Originally Posted by Whalerus View Post
Thanks roverhi.
Just to make sure i'm hearing you right, what your saying is to cut the brand new Thru-hull in half to make it fit the brand new Seacock? All because my hull isn't over 2" thick like a shrimp boat.
Yes, cut the thru-hull to whatever length works with your hull thickness. You could put an over thick pad under the valve but it wouldn't be needed for strength. If you go the thick pad route would not use plywood. Used plywood when we built our boat and most of them delaminated over time. You could saturate the plywood with epoxy but that's not a guarantee that water still will not play havoc.
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post #20 of 21 Old 06-03-2019
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Re: Thru Hull Modification

I suggest you give Marinehowto.com a visit and read the entire article he wrote on thru hulls.
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