Sealing up disused through hull - temporarily

[PANorth]

We eliminated the need for two through hulls by converting to a composting toilet. Each has a marelon ball valve. Is it best to take the valve off and put a cap on the threaded male through hull, put a plug in the valve (which would be kept closed), or simply close the valve? Or some other option? We don't want to remove the through hulls for now, because if we decide we don't like the composting toilet the option to reinstall the original system remains.

An anecdote: One of the through hulls had a brass fitting attached (along with some PVC). It broke right off when I tried to unscrew it. It was quite corroded. Very fortunate it broke while on the hard! I am sure it was very near to coming off by itself.

 

[peaman]

The valve is the "fire wall" against a broken hose, so the closed valve alone should be considered entirely adequate. A plug or cap, if secure enough (considering your broken and corroded fitting) might protect against unlikely accidental opening of the through hull valve.

Any "brass" fitting used with sea water should be either bronze (best) or red brass, which is available from better plumbing supply outlets. Common brass will deteriorate with loss of zinc, which is likely what happened with your fitting.

 

[PANorth]

I have had trouble finding a cap or a plug. I'd feel a lot better knowing that there is no chance of an accidental valve opening, even if unlikely. Any ideas about sources?

We have yet to put this boat in the water. We've been doing a bottom job for the past 20 months. We are within days of completing that, and, between bouts of fairing and sanding, we've been doing lots of other things on this 40 year old many owner boat. She has generally been well cared for, the corroded plumbing fitting being an exception. We expect to do some sailing on the Salish Sea this summer!

 

[Jerry VB]

I have had trouble finding a cap or a plug. I'd feel a lot better knowing that there is no chance of an accidental valve opening, even if unlikely. Any ideas about sources?

I bought a (3/4" IIRC) plastic plumbing plug at Home Depot. While I would not rely on it to keep the water out (that is what the valve is for), it does provide a secondary backup to the valve for when I am stupid an open the wrong valve.

 

[bigd14]

I added plugs to a couple unused thru hulls so I could exercise them regularly.

 

[Loren Beach]

Is it possible just unscrew the existing tailpiece and screw in a threaded plug? (or is the tailpiece cast into the valve body?)

 

[peaman]

I'd feel a lot better knowing that there is no chance of an accidental valve opening, even if unlikely.

One option is to use wire seizing to prevent the valve from being opened. Some valves are even made with lugs for the very purpose of locking it open or closed.

 

[Christian Williams]

This is all assuming you have the factory seacocks, not some substitute.

More on the topic here: https://marinehowto.com/seacock-thru-hull-primer/#:~:text=Flanged seacocks are considerably stronger,Marelon), Apollo and more.

I don't know how to spell through-hull. It isn't in the Shorter OED, the long version of which is the authority on English, or used to be. Through-stone is--a stone to bind a wall by going all the way through it. Or through-passage--a passage through. So probably the traditional spelling would be through-hull.

But that gives no joy in the typing. It seems pedantic and long, especially in a marine context. I dunno why, but it does.

The manufacturers all go with thru-hull, and I've decided to join them. Practical Sailor has an article the headline of which says Through-hull, and in the body copy it is spelled thru-hull every time. Now that?

That's just stupid.

It is too early for a drink but the evening will come eventually.

 

[Jerry VB]

I bought a (3/4" IIRC) plastic plumbing plug at Home Depot. While I would not rely on it to keep the water out (that is what the valve is for), it does provide a secondary backup to the valve for when I am stupid an open the wrong valve.

 

[Gaviate]

An anecdote: One of the through hulls had a brass fitting attached (along with some PVC). It broke right off when I tried to unscrew it. It was quite corroded. Very fortunate it broke while on the hard! I am sure it was very near to coming off by itself

I'm Not Alone!!!
Last week came splash day, while inspecting all thru (through) hulls upon setting in the water and b4 (before) leaving the lift, I discovered leaking at the galley drain fitting. Of course I grabbed the fitting (for no good reason) and the whole end broke off in my hand!!
Lifted the boat back out (slings still in place) and now intend to remove all through-hulls (I suspect they are all original) and fill in holes with fiberglass.
Galley drain never used, head through-hulls never used, and intend to go to composting system. In hind sight, I should've done this when first considered whilst re-doing bottom year before. 'That'll learn ya pilgrim' is what I'm thinking

 

[Christian Williams]

We need a photo of these fittings that break off.

 

[PANorth]

Is it possible just unscrew the existing tailpiece and screw in a threaded plug? (or is the tailpiece cast into the valve body?)

I am only guessing what the tail piece is. The valve is just a valve with female threaded ends.

 

[PANorth]

We need a photo of these fittings that break off.

Now I need to go find it.

 

[gabriel]

I use this in case one of my kids decides to see what the lever does.

 

[Gaviate]

We need a photo of these fittings that break off.

It'll be a couple of weeks before I can make it back to the boat and will gladly take some pictures. Description is; the pipe nipple that threads into boat side of gate valve, which is threaded on to actual through-hull. The break is flush with body of valve and came off with less force than needed to open the lid of a plastic pop bottle.
The valve was closed and leakage that I observed was between through-hull backing block and fiberglass hull. The condition of the nipple which broke off, on the other side of the valve, was not a source of the leak. The condition of the body of the through-hull is suspect, or things just came loose, as yet to be determined.

 

[PANorth]

Here are some pictures of my broken fitting. A close up and the whole assembly that was there when we bought the boat a short time ago.

Gabriel - Did you get that at a hardware store or is it a marine specialty part?

 

[Tin Kicker]

Here are some pictures of my broken fitting. A close up and the whole assembly that was there when we bought the boat a short time ago.

Gabriel - Did you get that at a hardware store or is it a marine specialty part?

The loss of thickness at the break strongly suggests a brass hardware store part, not a marine bronze one and it's why we avoid brass!

My boat has Marelon thru-hulls and when installing the composting head I went through the same question about what to do with the two thru-hulls for the black tank. My solution for each was to use an inexpensive Marelon tail piece to create a removable plug, so got two of these:

I deeply scratched up the inside with very coarse sandpaper,
used a torch to mostly crimp closed the hose end,
covered the hose end with tape,
stood it with the thread end up,
then filled it with JB Weld.

I dumped a bunch of valve grease on the ball then installed the tail piece. It's been well over a year and now & then I cycle each of the thru-hull valves just to keep them functional should I ever want to use one.

 

[Pete the Cat]

The loss of thickness at the break strongly suggests a brass hardware store part, not a marine bronze one and it's why we avoid brass!

My boat has Marelon thru-hulls and when installing the composting head I went through the same question about what to do with the two thru-hulls for the black tank. My solution for each was to use an inexpensive Marelon tail piece to create a removable plug, so got two of these:

I deeply scratched up the inside with very coarse sandpaper,
used a torch to mostly crimp closed the hose end,
covered the hose end with tape,
stood it with the thread end up,
then filled it with JB Weld.

I dumped a bunch of valve grease on the ball then installed the tail piece. It's been well over a year and now & then I cycle each of the thru-hull valves just to keep them functional should I ever want to use one.

Just make sure the fittings are Marlon. I understand that folks can use Home Depot fittings, but some of the plastics in non Marlon fittings degrade quite quickly under stress and torsion of a moving boat. I was disappointed to find that Ericson on my 1989 32-200 used non Marlon nipples on the head fittings-they shattered when I attempted to remove them. I mean shattered--there were no big chunks. I like Marlon through hull fittings, but the PVC stuff you can attach to it can create a hazard.

 

[Alan Gomes]

I was disappointed to find that Ericson on my 1989 32-200 used non Marlon nipples on the head fittings-

Ditto on my 26--also on the head fittings. BoatUS would only provisionally insure the boat, i.e., with the understanding that I had to correct it in a certain number of days (I forget now just how many) or I'd be cancelled. I didn't need their prodding; I corrected that immediately.

Those fittings did manage to hold together from 1984 until I bought the boat in 2012. Still a really, really bad idea.

 

[gabriel]

Here are some pictures of my broken fitting. A close up and the whole assembly that was there when we bought the boat a short time ago.

Gabriel - Did you get that at a hardware store or is it a marine specialty part?

I believe I bought it at West Marine, but it was a while ago so I could be wrong.