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Old 06-08-2009, 14:08   #1
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Gate Valve Replacement Problems

I have recently purchased a 33' boat and will be replacing three gate vales with ball valves. The valves look like they "JUST" screw into the threaded thru hull. Now, on a 26 year old boat, I suspect nothing is just "JUST" and there may be some complications.

Using a pipe wrench, is there a possibility of cracking the hull or loosening the thru hull? Do you have to secure the thru hull before applying pressure? Anything else to be concerned about?

I am on the hard so don't have to worry about sinking, at least not just now.

Thanks, Dave

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Old 06-08-2009, 14:23   #2
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When I replaced the gate valves, I just replaced the through hulls as well. They are much cheaper than the seacocks anyways. Why not just have everything be new? In one case there was no separating the gate valve from the through hull requiring a bit of work with a grinder and some minor glass work.

I find it's rare those projects are as easy as they first seem they might be.

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Old 06-08-2009, 14:26   #3
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The thru-hulls you have are incompatible with simple ball valves. The threads are different, that is why they won't thread correctly. One has straight teeth, and the other not.

Check this out from our member Maine Sail, to see what I mean:

Replacing Thru-Hulls and Seacocks Photo Gallery by Maine Sailing at

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Old 06-08-2009, 14:50   #4
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When removing a valve, from a through-hull intended to remain; you must restrain the through-hull, from breaking free of it's bedding and turning.
Groco, for instance offers a Step Wrench, which fits multiple sizes of fittings, for the purpose (see pic below).

As noted, Main Sail has an excellent photo-tutorial at
Replacing Thru-Hulls and Seacocks Photo Gallery by Maine Sailing at
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"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"

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Old 06-08-2009, 16:56   #5
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How big are those gate valves??

Its a 5 minute job to remove the old thru hulls and valves if you are planning to replace the thru hulls. Don't fight the frozen threads, but take a 4 inch grinder and grind off the flanges on the outside of the thru hulls and drive the remainder back into the boat.

While the thru hulls have straight threads and the valves are tapered (NPT), Loctite makes a special goop which seals everything and holds the valves from turning.
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Old 06-08-2009, 17:38   #6
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Replace the whole shebang....It will allow you to sleep better at night.
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Old 06-08-2009, 18:08   #7
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I completely agree with Chief. You are asking for problems by doing it any other your boat sinking. Never take the cheapest route with thruhull fittings.


Life begins where land ends.
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