Blocking a thru-hull

I have a couple of unused through hulls as the two heads are plumbed directly into the holding tanks (Great Lakes). They are blocked by the original ball valves, which are themselves plugged at the exit orifice for safety. I don't want to glass over the holes in the hull because the boat could eventually end up on one of the Coasts where overboard sewage is authorized. However, I would prefer a solid thru-hull type plug (no water passage drilled in the center) in those holes. I've been searching for them on-line with no success. Is there such a thing?

I asked the same thing of Forespar who make Marelon products, they thought it was a great idea but have not done anything about making solid plugs.

We live on the west coast, I had mine removed and glassed over last year as everything goes to the holding tank which has the capability of being pumped of if needed. Now I don't have to worry about those thru hulls anymore.

An engineering firm should be able to machine up a solid replacement from a material of your choice. You could cut the cost by having it threaded to fit an original nut.

I doubt you will find a thru hull that doesn't have a hole in the center. What would be the point?

If the thru hulls and valves didn't leak before, why would they leak now? You don't say how they are plugged but you have the valve turned off and the outlet plugged. That would seem to be sufficient.

I had a head thru hull valve fail, by cracking around the stainless ball. I temporarily stopped the leak by pounding a wooden taper in from the outside. You might do this as a safety. Cut off any excess, and when it is time to remove them, screw on a pulling line.

koliver said:

I had a head thru hull valve fail, by cracking around the stainless ball. I temporarily stopped the leak by pounding a wooden taper in from the outside. You might do this as a safety. Cut off any excess, and when it is time to remove them, screw on a pulling line.

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Good idea. I'll do this if I can' find an off-the-shelf solid bronze plug.

I plugged a thru hull on my sailboat that I thought I might want to reuse with a Groco thru hull with the combination thread and a bronze cap and sealant. Installed and forgot about it.

I don't see why you couldn't install what would basically be a 1/2" thick backing plate with not center hole drilled. Seal the raw fiberglass inside the hole in the hull copious epoxy. Seal the backing plate with 4200 and bolt it down. At worse, you will have a dimple in the hull that will either be hard to clean growth out of or it is ignored and allowed to fill in...

I have plugged holes by installing a new thru hull that is pipe thread and not barbed and filled it with thickened epoxy and after installing it I capped it with a bronze cap with 5200 on the threads. If need be I can remove the plugged through hull and install a new one with a sea cock.

Comodave beat me to it. Pack it with a thick epoxy putty. If you use Zspar Splash Zone I bet you could do it with theoat in the water.

For my blanked thru hulls, I drive a wood plug from the outside and as all of mine are threaded, a cap on the inside. They still need to be zinc protected or bonded to something that is. For a hose barb type you could solder in a plug.

Doesn't the wood rot out being in the water all the time?

I suggest you not save the hull openings unless you are certain the boat will end up somewhere they can be used. Being on the coast is fine but you still have to be three or more miles offshore to legally "straight shoot" black water. Spend your money to close up the holes instead of finagling a work around. If direct overboard discharge is needed down the road install new hardware and have confidence in its condition and reliability.

Are you saying these through hulls are just that with ball valves and not true seacocks?

If true seacocks, why do anything other than leave shut with the top plugged or with a piece of hose thats plugged.

If you have ball valves screwed onto through hulls and you are going through the effort to remove them, I would just epoxy up the holes correctly and be done with it. Nothing else is really safer unless you install a real seacock.

By the time you want an overboard discharge directly from the toilets which isvwhat I am guessing you have, hardly anyone has a system set up like that anyway these days of type 1s and the growing number of no discharge areas.

bglad said:

I suggest you not save the hull openings unless you are certain the boat will end up somewhere they can be used. Being on the coast is fine but you still have to be three or more miles offshore to legally "straight shoot" black water. Spend your money to close up the holes instead of finagling a work around. If direct overboard discharge is needed down the road install new hardware and have confidence in its condition and reliability.

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I agree 100%. Plus the bronze is probably old enough to resent a future liability.

I've got two which I've turned off and capped. I've got about 4 unused transducers which I intend to have removed and the holes properly 'glassed-in.

I moved two throughhulls on the sailboat, removed a dead transducer and 'glassed the holes.

Seems a happier thing to have the hull pierced only as necessary and not looking like a pin cushion.

I just intalled a thru hull transducer, hated to do it but the technology strongly suggrsted it...especially after glassing in 2 transducer holes and 4 through hulls a few years back.

Filling and drilling new holes is really no big deal.

psneeld said:

Are you saying these through hulls are just that with ball valves and not true seacocks?

If true seacocks, why do anything other than leave shut with the top plugged or with a piece of hose thats plugged.

If you have ball valves screwed onto through hulls and you are going through the effort to remove them, I would just epoxy up the holes correctly and be done with it. Nothing else is really safer unless you install a real seacock.

By the time you want an overboard discharge directly from the toilets which isvwhat I am guessing you have, hardly anyone has a system set up like that anyway these days of type 1s and the growing number of no discharge areas.

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They're seacocks, which are blocked at the discharge end. The boat originally had three discharge holes...one for the single holding tank macerator, and one each for the two heads. There were/are also seacocks for the raw water flush intakes. All are currently closed and the output openings are plugged and clamped. The heads are now fresh water flush and discharge directly into the original forward(common) holding tank and the new aft holding tank.

I want to retain the aft opening in the event I or the next owner wants to plumb a macerator/overboard pump to the tank. Same for the original forward tank....retain option of a macerator pump, which was removed when I modified the system for Great Lakes operation. That leaves the forward direct head discharge, and the two raw water intakes. The forward water intake hole is in a good location for a second depth finder, so I want to retain it.

So, two holes could be glassed over, I suppose. Three might have future application. The boat comes out of the water every year, so I have annual access. I was thinking a solid plug in the three "future use" holes would be more safe than the seacocks with plugs.

Anyway, I now have some great advice and will make a plan. By the way, I just completed a self survey for my 5-6 year insurance renewal, and they asked that a wooden plug kit be on board in the event of a leaking seacock. This is what got me thinking about "hardening" the thru-hull setup. By the way, my insurance company is Markel, and they are to be applauded for moving toward self surveys. Y'all might want to suggest to your company to eliminate the "surveyor" tax. In this age of digital photos, it is quite ridiculous. (Or switch to Markel).

If you dont trust the seacocks, get rid of them and glass the holes.

As I said, later or the next guy may want them in a different location anyway.

If you really want to keep them, and you trust them, keep them and just screw in a nipple, fill with sealant and screw on a cap as others suggested.

A hole simply filled with epoxy paste with a couple of layers of GRP with epoxy inside as insurance would be a 5 min job to remove if ever desired.

I vote for keeping them in place. My old Hatteras had a bunch at one point as a result of a PO replacing the seawater heads, each with individual intake and output through hulls, six in all. But then, they started getting used again... a raw water wash-down, an air conditioner for the aft deck, additional macerator for the holding tank... and so on. Guy who bought my boat put in a second generator. And so on again. Just maintain them and monitor them like anything else.