Hose clamped onto threaded pipe - SailNet Community

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Old 02-29-2008
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Hose clamped onto threaded pipe

I recently replaced some old gate valves with brass ball valves along with all new thru hulls.

Originally, I'd been planning on attaching hard pipe fittings (meralon) to the male threads on the thru hull. But, it occurred to me weeks after the install, that I might be better off using a hose to attach directly to one of the new brass thru hulls that is a threaded male pipe. It's a very short space I've got to work with, and I don't have room to work in a coupling (threads to barb).

Is attaching the skupper drainage hose directly to a threaded brass thru hull a bad idea? There seems to be plenty of length on the brass threaded end to deal with (about 1.5"), so I guess it's just the question of whether the hose might get 'cut into' by the threads. Maybe there is a way to mitigate this to some degree with pipe tape or something else?

Thoughts anyone?

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Old 02-29-2008
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Marcusn-

First, I hope those ball valves are BRONZE, not BRASS. Brass has no place on a boat beneath the water line... Brass dezincifies very quickly and leaves you with a soft copper sponge that will fail under very little load.

If the through hulls are bronze, you should be using bronze fittings on it. Using plastic, even fiberglass reinforced plastic over male threads is a bad idea. The metal expands much more than the plastic will as it heats up later in the season, and the plastic will eventually fail with little warning.

If the space is limited height wise, then you might want to put a 90-degree elbow on the through hull and then attach the seacock to the elbow. Halekai has a good webpage on doing this, you can read here.

Using hose over threaded pipe is generally a loser of an idea. It is very hard to get the hose to seal properly, since capiliary action will wick water along the threads.

BTW, you shouldn't attach the ball valve seacocks directly to the through hulls. Please take a look at Halekai's web page on this for full instructions.
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Bronze they are

My mistake,
the thru hulls are in fact bronze. And, yes, they're integrated into the thru hull.

If I put a 90 on the end of the thru hull, it will put the open end in the wrong direction for a very short straight down drop. Unfortunately, this just won't work.
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Are the seacocks mounted directly on the through-hulls...they're not integrated, since they're two separate pieces that are threaded together. However, through-hulls are NPS thread and the seacocks are generally NPT thread, meaning that the seacocks are being held onto the through-hulls by very few threads, and not very securely at all IMHO.
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Last edited by sailingdog; 02-29-2008 at 07:34 PM. Reason: corrected typo... thanks Sway...
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Quote:
Originally Posted by marcusn View Post
I recently replaced some old gate valves with brass ball valves along with all new thru hulls.

Is attaching the skupper drainage hose directly to a threaded brass thru hull a bad idea? There seems to be plenty of length on the brass threaded end to deal with (about 1.5"), so I guess it's just the question of whether the hose might get 'cut into' by the threads. Maybe there is a way to mitigate this to some degree with pipe tape or something else?

Thoughts anyone? Thanks

Plenty of thoughts..

NEVER, NEVER, NEVER use brass ball valves on a boat!!!!! Bronze or Marelon are the only two SAFE methods. I'm hoping your post was just a typo as we all do it..

This brass ball valve was roughly a year old and the ball was totally GONE, VANISHED & EATEN AWAY! It came from Home Depot!! It was literally weeks away from catastrophic failure of the boat sinking type!




Read the two articles in the links bellow and it should give you an idea of what you need to do to do this job correctly.

Seacock & Thru-Hull Primer/Pre Information


Replacing Thru-Hulls and Seacocks
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marcusn,
You'll want seacocks on the thru-hulls regardless of their intended use.

What you're going to encounter is that the thru-hulls have a straight thread and your other fittings have a tapered thread. (NPS vs NPT) That's what dog was saying but he had a typo and I wanted you to be aware that you cannot just thread the two together.

Depending on your hose, you can slip it over the threaded end of a pipe and get it to seal. Usually you can only fit one size larger over. Anotherwords, 1" hose will fit over 3/4" pipe. Double clamp it and give a good tug on it to make sure it's secure. I see similar set-ups every day in my work and they're pressurized to 60 psi and not leaking. It's not the first choice of ways to do things, but sometimes.... You'll have to cut it off after it's been on a while but that's not unusual even with a male adapter (hose barb).
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Well, "proper seacock" police notwithstanding I used hose over threaded fittings on my boat.

The fittings are "marine brass" - whatever it is. One was purchased at West Marine, specified for, presumably, salt water connections, the other was already on board (and in the same place for about 10 years, looked pretty good though). I do watch them closely and plan to continue doing so.In any case similar marine fittings from other materials don't seem to exist.

To the point, what seems to help create a watertight seal is a teflon tape over the threads, and a good quality multilayer hose over that - plus double clamping. These are my cockpit drains and both of them are as dry as any connection gets - so far anyway. Certainly if there was any leakage, even the smallest amount - it would be very visible, as these thru hulls are never closed.

BTW, a recent BoatUS magazine has an article on thru hulls, and while they *recommend* flanged seacocks, they certainly don't say that that is the only right option, and in fact they do show a thru-hull mounted ball valve as an example of acceptable installation. This is acceptable to their insurance as well.
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