Thru-Hull Valves frozen

Maine Sail · Jan 2, 2012

Euphoria2011 said:
Hello,

I have a 1983 Oday 28 and this spring I am gettiing the bottom done and while she is out of the water I need to replace two stuck sea cocks.

The one under the galley sink and the waste tank overboard discharge are both stuck. All I can see are the letters 600W0G on the both of them.
How do I find a replacement set?

Please see the pictures I took today.

That means 600PSI Water, Oil, Gas and is a very standard valve rating. You'll want to replace those with marine UL rated bronze valves and bronze male hose adapters NOT brass. PVC is not suggested for below water applications and you have a PVC male hose adapter in one of those pics.

You'll also want to double clamp below water connections. Groco ball valves are suitable for this application and Phil sells them here in the SBO Chandlery. These are marine UL rated valves and are intended for below waterline use.

Groco IBV Series Valves (LINK)

DO NOT let the thru-hull spin when you remove the valve or it will leak. You'll need a thru-hull spud wrench and two people to do this right. If the backing plates are "soggy" you'll need to remove the thru-hull and replace the backing block.

Maine Sail · Jan 2, 2012

Euphoria2011 said:
Oh, Ok thanks, so I just need to see what size to order.
I can base this off the hose size that they are connected to i guess.
Where do you see a PVC adapter?

In this photo. The gray thing threaded into the valve that the hose is connected to is PVC. It should be marine bronze.

Sunbird22358 · Jan 2, 2012

Let this be a lesson for all of us that Seacocks / Ball-Valves / etc (better not have any gate-valves though!) need to be kept active, periodically close and reopen the valves to be sure that when needed, they can be fully closed. I little grease in the good, old-traditional seacocks (the ones with a tapered barrel) will help as well. Good practice is to keep any shut-off closed when that thru-hull is not in use, just be sure to open before use! Keeping cockpit scuppers open always is good, but still periodically close/open those to keep them operable. Newer boats often have ball-valves with teflon seats and stainless-steel valve balls. They usually don't "freeze" up, but still need to be "exercised".

bria46 · Jan 3, 2012

Most thru hull fittings use straight threads. the easy way to tell is to look and see if your thru hull's have a nut on top of the backing block. In all three photos this looks to be what was installed by the OEM was a NPS threads (the "S" stands for straight). The IBV series suggested by Maine Sail uses NPT threads (the "T" stands for tapered). Although they appear to fit together, the Tapered threads do not seat firmly on the Straight Threads. That means that your threads will be mismatched requiring tons of pipe joint compond. However Groco has addressed this common problem in older boats their IBVF series. The IBVF thru hull fittings uses straight threads on the thru hull end and tapered threads on the fitting end.

Maine Sail · Jan 3, 2012

bria46 said:
Most thru hull fittings use straight threads. the easy way to tell is to look and see if your thru hull's have a nut on top of the backing block. In all three photos this looks to be what was installed by the OEM was a NPS threads (the "S" stands for straight). The IBV series suggested by Maine Sail uses NPT threads (the "T" stands for tapered). Although they appear to fit together, the Tapered threads do not seat firmly on the Straight Threads. That means that your threads will be mismatched requiring tons of pipe joint compond. However Groco has addressed this common problem in older boats their IBVF series. The IBVF thru hull fittings uses straight threads on the thru hull end and tapered threads on the fitting end.

Bria is correct. What you have, and many production boats have, is a thread mismatch between a straight threaded thru-hull and the tapered thread ball valve.. This type of installation does not meet ABYC standards.

If however your existing thru-hulls are in good condition and are not showing any signs of corrosion or dezincification (a pink coppery color when the green verdegris is cleaned away) then you can re-use them. If you can get a new valve on with plenty of both teflon tape and pipe dope, all without moving the thru-hull and iota, than you can often get it tight enough for many more years of service. While certainly not the preferred or ideal method, strength wise, thread match wise or current safety standards wise, it can work. Would I do it? Not on my own boat but there are many boats still floating using this rather poor installation technique......

Groco also makes a thru-hull fitting with "combination threads" cut into it. This is a band-aid at best as it is NOT a true tapered thread and only the tips of the thread peaks are shaved of in the hopes of getting a few more turns. The valleys however are no deeper as thes thru-hulls don't have the wall thickness to cut a real "tapered thread" into them without drastically reducing the strength.

This is a combination threaded thru-hull:

The big problem with this design is that you can NOT cut any length off the thru-hull and retain the "combination" threads. This makes your interior hard piped length quite tall/long and ultimately makes the thru-hull an even weaker link than it already is because of the long lever action of the valve and male adapters added height.

If you are getting to the level where the thru-hulls are removed than you'd be wise to use a flanged adapter on the inside. Even if you don't through-bolt it this is a much stronger installation and the threads all match. (See linked articles below)

This is why the ABYC disallows a thread mis-match:

Feel free to read the articles below on seacock and thru-hull installations.

Seacock & Thru-Hull Primer/Pre Information (LINK)

Replacing Thru-hulls & Seacocks (LINK)

bria46 · Jan 3, 2012

Thanks for the detailed explaination Maine Sail. When I installed my fresh water pump for my air conditioner Patrick at Groco told me all about the problem of mismatching threads. They also publish a service sheet explaining what Maine Sail stated. Thank you Maine Sail!! It is quite easy to shorten the over

bria46 · Jan 3, 2012

Thanks for the detailed explaination Maine Sail. When I installed my fresh water pump for my air conditioner Patrick at Groco told me all about the problem of mismatching threads. They also publish a service sheet explaining what Maine Sail stated. Thank you Maine Sail!! It is quite easy to shorten the over length of the NPS (straight) thru hull fitting, but Maine Sail is correct on NPT threads.

Barnacle Bill · Jan 3, 2012

And, the plastic or PVC "thing" as it has been referred to is called a tailpiece. Some are bent and some are straight. Yours is straight.

Maine Sail · Jan 3, 2012

Barnacle Bill said:
And, the plastic or PVC "thing" as it has been referred to is called a tailpiece. Some are bent and some are straight. Yours is straight.

It is not really a "tailpiece". A tailpiece by plumbing definition is the piece between a sink drain and the trap. The "thing", or as I called it in the first post "male hose adapter" is technically in the "pipe to hose adapter" family and more specifically, in the OP's case, would be called a male pipe to hose adapter. They also make female pipe to hose adapters and 90 degree male or female pipe to hose adapters.

If you asked for a tailpiece in a plumbing supply house you'd get a tailpiece for a sink drain and they'd ask you if you wanted it in chrome, PVC, brass and what drain diameter. You'd also likely get the retail pricing, not wholesale, once they realized you wanted a pipe to hose adapter not a tailpiece.....

The only marine product I know of referred to as a tailpiece was a straight threaded pipe adapter for older style Groco seacocks that had an NPS to NPS fit. Spartan Bronze makes the same part and they call it a hose adapter not a tailpiece. Groco's hose adapters are called PTH's or pipe to hose adapters as are Apollo/Conbraco and these are the two largest suppliers of marine UL bronze pipe to hose adapters. Apollo/Conbraco PTH.pdf

If you ask for a tailpiece at WM you might get a pipe to hose adapter and you might get a blank stare. Of course even if you asked for a pipe to hose adapter at WM you might still get a blank stare.

Thru-Hull Valves frozen

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