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Old 20-02-2015, 09:09   #1
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Thru Hull and Seacock Installation

I recently contracted someone to do various work on my boat and among these things was the removal of and installation of all new thru hulls and seacocks, of which there are 9 total. I had two of them permanently closed up but the others were put in with just the threaded thru hull and backing nut.

This contractor, even with 20 years of experience, was dumbfounded at the suggestion that he use flanged seacocks with backing plates instead of simply screwing a valve onto a thru hull with only the backing nut. He is a motor yacht type, not an offshore sailor. The thru hulls were installed professionally, he used 5200, and they are strong, clean, and look good but they are still only held in with the backing nut that's included with the thru hull. He also prepped, dried, and epoxied the existing holes in the hull so that they are strong as well.

Here is my question: Since this person no longer works for me, and I am going to add backing plates and flanges to all of these thru hulls, do I need to completely remove them all and start from scratch or can I (would you) gingerly screw on and seal a flange adapter to the existing thru hull? They have been in for a number of weeks now and the 5200 is completely cured.

I will remove them and start over if I have to. I'll be finishing this project myself. But I am concerned about breaking loose the thru hull seal as they are when I screw down a flange and seacock. Are the thru hulls strong enough to withstand the torque of adding a flange and valve? Would you have someone outside holding the mushroom head with a spud wrench while making these additions?

Currently I am leaning towards just adding the flanges and valves to the existing new thru hulls. Any advice on this would be hugely appreciated. I really don't want to break all these things out and start over.

We sail extensively and cruise full time with children. Although we don't currently cross oceans we do make hops from the Bahamas to the USVI.

Thanks!
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Old 20-02-2015, 16:17   #2
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Re: Thru Hull and Seacock Installation

IMO you have a mess on your hands. I wouldn't have used 5200 and I would have used 4200 with proper flanges and backing plates.


If it were my boat I would do it all over again.
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Old 20-02-2015, 16:51   #3
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Re: Thru Hull and Seacock Installation

Remove and re-do... Backing blocks of G-10 epoxied to hull, re-seal with 5200 or 4200. Using the correct tools to remove the t-hulls and seacocks, the 5200 will allow for removal. Do it right for the kids and a good night's sleep.
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Old 20-02-2015, 18:07   #4
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Re: Thru Hull and Seacock Installation

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IMO you have a mess on your hands. I wouldn't have used 5200 and I would have used 4200 with proper flanges and backing plates.


If it were my boat I would do it all over again.
+1
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Old 20-02-2015, 18:56   #5
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Re: Thru Hull and Seacock Installation

Depending on the thickness of your hull plus backing plate, there may be too much thread on the thru-hull sticking out to tighten the flanged seacock all the way down. The normal procedure is to measure and cut off the excess length from the through hull so the remaining length matches the threads in the valve. That may be difficult with it already in place. Another problem will be drilling the holes for mounting screws and installing them with the boat in the water.
Neither is an insurmountable problem, but you might be better off hauling the boat and starting over properly.
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Old 21-02-2015, 08:26   #6
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Re: Thru Hull and Seacock Installation

I'd redo it too but can't help but wonder how many boats are out there without backing plates and flanges. Backing plates seem reasonably common but when I was shopping for a boat I didn't see any with flanges and few with backing.
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Old 21-02-2015, 08:30   #7
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Re: Thru Hull and Seacock Installation

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I'd redo it too but can't help but wonder how many boats are out there without backing plates and flanges. Backing plates seem reasonably common but when I was shopping for a boat I didn't see any with flanges and few with backing.
Flange-less ball valves were pretty common on production boats, and the vast majority of boats with them are still floating.
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Old 21-02-2015, 09:01   #8
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Re: Thru Hull and Seacock Installation

Personally, "if it ain't broke, don't fix it." If there're no leaks and everything is working fine.... leave it alone. Most modern boats don't come with the backing plates and flanges. Get an extra set of bungs for $20 if you're worried about leaks which are much more likely to originate from old hoses than a failed thru hull to hull joint.

Leave it alone....
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Old 21-02-2015, 10:07   #9
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Re: Thru Hull and Seacock Installation

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Quote:
Originally Posted by bcboomer View Post
I'd redo it too but can't help but wonder how many boats are out there without backing plates and flanges. Backing plates seem reasonably common but when I was shopping for a boat I didn't see any with flanges and few with backing.
Flange-less ball valves were pretty common on production boats, and the vast majority of boats with them are still floating.
My boat was built in 1981 and was setup like this. It has a thru-hull and ball valve with a wood backing board. None of the previous owners ever replaced them. I replaced one for the engine raw water intake and used G10 backing. Now I'm going to work on a refit and replace the rest (7) with flanged seacocks and G10 backing. One or two I might just close up all together. At least now I know what to look out for when looking at other boats.
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Old 21-02-2015, 12:09   #10
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Re: Thru Hull and Seacock Installation

What are the thoughts about Marlon flanged seacocks?

This fall I took all the brnze seacoks apart on our Cal2-46. I polished and cleaned the cone and seat on all. Applied a light coat of grease and reassembled. one broke the shaft where the with the lock nut. Upon inspection I believe the was some electrolysis that weakened the shaft. The thru hulls are all bonded which make me think they may all be subject to electrolysis.
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Old 21-02-2015, 23:07   #11
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Re: Thru Hull and Seacock Installation

I think Trudesign are much better. Of course I may be prejudiced because that's what I used.
That said, the Marlon valves have a reputation for seizing up.
Trudesign have a number of certifications and are designed not to seize up.
For the smaller valves they now have a reinforcement that gives them an ABYC spec. The larger ones are tough enough on their own.
Their strength and immunity to corrosion from stray current lets me sleep better.
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Old 22-02-2015, 13:44   #12
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Re: Thru Hull and Seacock Installation

Quote:
Originally Posted by Kenomac View Post
Personally, "if it ain't broke, don't fix it." If there're no leaks and everything is working fine.... leave it alone. Most modern boats don't come with the backing plates and flanges. Get an extra set of bungs for $20 if you're worried about leaks which are much more likely to originate from old hoses than a failed thru hull to hull joint.

Leave it alone....
Yes I think I'm going to leave them in. The more research I do and with everyone's thoughts here, I'm slowly realizing I can remedy the current situation.

While I won't use a valve on a straight thru hull, I will add a backing plate and one of those new bronze adapter flanges. Then I'll 5200 and glass the whole thing in so its a permanent part of the hull. Either way it'll be solid.

The boat is a 1980 Gulfstar 50 and the hull is pretty thick as it is. The flange and backing plate will just be added insurance.
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