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Old 09-10-2015, 11:44 AM   #21
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Originally Posted by cardude01 View Post
So looking at these pictures, can I leave the existing through hull in place and just install the flange and a new valve?

How does that flange bolt to the hull?
You will have to remove the nut that holds the thru-hull into the hull. The thru-hulls screw directly into the seacock. Depending on the thickness of your hull it may be necessary to cut the length of the thru-hull down so that the seacock will fit all the way down on the thru-hull. As far as attaching the seacock to the hull there are several options. The easiest is to through bolt them using bronze flat head machine screws. Some people install a comparatively thick backing plate to the hull then drill and tap into the plate for bronze machine screws or bolts. If you do that be sure to epoxy the backing plates to the inside of the hull.

Another consideration is coring in the hull. If your hull is cored, the core should be removed where the seacock goes and that area built up with solid fiberglass, ideally to the thickness of the cored hull. This will strengthen the seacock attachment point and minimize the possibility of water getting into the core. A good builder will have already done this.

Personally, I would replace the thru-hulls at the same time that I did the seacock install. Thru-hulls are cheap.
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Old 09-10-2015, 11:46 AM   #22
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So looking at these pictures, can I leave the existing through hull in place and just install the flange and a new valve?

How does that flange bolt to the hull?

I think you can safely do nothing... until/unless you begin to see some sign of failure down the road, maybe 10-15-20 years from now. Sluggish rotation, for example...

Always good to get things "more perfect" of course, but if you've got other stuff to deal with -- things not actually working, for example -- it should be easy enough to establish reasonable priorities that don't cost you an arm and a leg replacing immediately serviceable stuff.

IMO, of course...

-Chris
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Old 09-10-2015, 03:31 PM   #23
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Cardude, I suggest that you use the Groco premade backing plates and the Groco flanged adapters. Inspect and clean your existing ball valves and thru-hull fittings. if they look ok, reuse them.

The backing plates are usually glued to the hull with epoxy. they have threaded inserts to which the flange is bolted.

Chris, the only combination threads I've seen were on a stainless thru-hull and I can't remember who made it. I read Groco's instructions for installing Seacocks and In-line valves on thru-hulls. (with flange it's a seacock, without flange it's an inline valve). The instructions do talk about combination threads but I don't think Groco (or Buck) thru-hulls have combination threads. I'll ask Groco about it and let you know what I find out.

The thru-hull that I saw with combination thread had a definite taper over about the last inch of thread. It was very obvious.
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Old 09-10-2015, 04:19 PM   #24
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Chris, the only combination threads I've seen were on a stainless thru-hull and I can't remember who made it. I read Groco's instructions for installing Seacocks and In-line valves on thru-hulls. (with flange it's a seacock, without flange it's an inline valve). The instructions do talk about combination threads but I don't think Groco (or Buck) thru-hulls have combination threads. I'll ask Groco about it and let you know what I find out.

Sounded nuts, to me, but then I have no clue about what manufacturing costs would be for two different lines of ball valves, one with NPS for use with thru-hulls, and one with NPT for use most everywhere else.

And apparently ball-valve/thru-hull installations are ubiquitous.

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Old 09-10-2015, 04:32 PM   #25
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Cardude, I suggest that you use the Groco premade backing plates and the Groco flanged adapters. Inspect and clean your existing ball valves and thru-hull fittings. if they look ok, reuse them.

The backing plates are usually glued to the hull with epoxy. they have threaded inserts to which the flange is bolted.

I relapped the old tapered cone valves during a haulout past winter and ended up replacing one "incorrect" through hull and valve and went with the backing plate and setup as Parks is suggesting. Thickened West to secure the backing plate. This made for a very robust set-up. I posted pics of the process on a thread at that time. I was encouraged to grind the existing mushroom head off on the outer hull- since unscrewing ANYTHING with NPT and NPS joined together is challenging.
It worked like a champ.



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Old 09-10-2015, 04:38 PM   #26
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I just replaced 13 below-the-waterline through hulls and seacocks on our boat (not all pictured below). Not a trivial job, but very straightforward if you follow the excellent step-by-step directions from Compass Marine (as previously posted). I used the Groco flanged adapters and backing plates epoxied to the hull. Great quality equipment and the installation is many times more robust than the original. I bought all the gear from Parks, whose prices were unbeatable.





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Old 09-10-2015, 06:00 PM   #27
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Wow. That's a lot of through hulls!
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Old 09-10-2015, 06:01 PM   #28
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Quote:
Originally Posted by HopCar View Post
Cardude, I suggest that you use the Groco premade backing plates and the Groco flanged adapters. Inspect and clean your existing ball valves and thru-hull fittings. if they look ok, reuse them.

The backing plates are usually glued to the hull with epoxy. they have threaded inserts to which the flange is bolted.

Chris, the only combination threads I've seen were on a stainless thru-hull and I can't remember who made it. I read Groco's instructions for installing Seacocks and In-line valves on thru-hulls. (with flange it's a seacock, without flange it's an inline valve). The instructions do talk about combination threads but I don't think Groco (or Buck) thru-hulls have combination threads. I'll ask Groco about it and let you know what I find out.

The thru-hull that I saw with combination thread had a definite taper over about the last inch of thread. It was very obvious.

OK. I get it now. I think I will tackle this project down the road during my next haul out.
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