Thru-hull/valve choices

[dcruz99801]

Apologies in advance if this has been covered -- please point me there.




We are in Guaymas, Sonora, Mexico buying a boat (not our first, also selling our tri) and the broker just mentioned it has gate valves that should be replaced; it's a 79' Perry design, probably built in Taiwan, surprised the original gate valves are still there.



Where we are, the options are costly and limited; a 1-1/4 bronze Groco ball valve is $91 + 134 shipping. 304 Stainless is available for less, but probably Chinese (read 'quality unknown') and I just saw a few $200 Marelon valves on Amazon. All will cost time & shipping.



The big questions:

* Is 304 SS an acceptable substitute for bronze?

* I have my doubts about SS corrosion, out of sight in the bilges, especially in a boat that sinks (tri owner prejudice). Is it viable for 5-10 yrs?

* What about Marelon? It will never corrode -- is grounding relevant anymore?

[Cheechako]

Sounds like you need to go to San Diego and return with good valves. Bronze is best in my opinion. Tapered bronze real seacocks are the best of the best if you ask me.
So you probably have a through hull fitting with threads extending into the boat with a nut? Then Gate valves are screwed on to that?

For ease you could just screw on new valves. In the long run I'd rather see proper seacocks with a flanged base against the hull or pad.

But first: what are your plans? While everybody disses gate valves, in reality they often last a long time if they were any good to start with. I have seen ball valves come apart also. Marelon type have handle breaking issues if you dont buy the right style (there are 2 or more styles)

Should you just put new ball or gate valves on for now and rebuild later when you can get good seacocks?

[xxxxx]

I had to change all my through-hulls and seacocks. I went with Bronze.

304 Stainless is not a good option for constant immersion in water (salt or fresh). SS corrodes in the absence of oxygen--we know this. This is confirmed by SS manufacturers ("304/L grade of stainless steel is one of the more popular grades for making components that will hold up well when exposed to salt water but not submerged in it." https://bit.ly/3rl3IFL )

I found Marelon to be expensive and its primary selling point was of dubious benefit in my eyes. Yes it's very resistant to corrosion, but it's moot. We know how to prevent corrosion of bronze. There are bronze through hulls that have been in service for decades.

Bronze is also much physically stronger than Marelon. That was important to me. The chance of it being sheared off are much lower.

That was my rationale for choosing bronze.

Answers to your questions:

1) In my view SS 304 is not an acceptable substitute for Bronze in this use case.
2) I don't know. Why risk it? These are critical failure points.
3) No bonding is required.

[Manateeman]

Bronze real flanged seacocks with backup plates...Groco or Apollo. Please read the article in marine how to.
Boatbuilders will not often talk about mistakes but after 50+ years, I’m pulling out all the Marelon Forespar “seacocks” and going with Groco.
There are other “supported ball valves” in plastic but not in any yacht I build.
Plastic...never again.
Happy trails to you.
Captain Mark and his crew of Professional Boatbuilding Manatees

[Orion Jim]

Originally Posted by Cheechako

Sounds like you need to go to San Diego and return with good valves. Bronze is best in my opinion. Tapered bronze real seacocks are the best of the best if you ask me.
So you probably have a through hull fitting with threads extending into the boat with a nut? Then Gate valves are screwed on to that?

For ease you could just screw on new valves. In the long run I'd rather see proper seacocks with a flanged base against the hull or pad.

But first: what are your plans? While everybody disses gate valves, in reality they often last a long time if they were any good to start with. I have seen ball valves come apart also. Marelon type have handle breaking issues if you dont buy the right style (there are 2 or more styles)

Should you just put new ball or gate valves on for now and rebuild later when you can get good seacocks?

Tapered bronze are what I’ve had for 36+ years as original equipment on my Cape Dory. As good now as the day they were installed. You can’t do better than Spartan in my opinion.
https://www.spartanmarine.com/seacocks-thruhulls

[alaskanviking]

I replaced almost all of my seacocks and thru hulls a year and a half ago. Just installed the last remaining ones tonight. I went through a similar selection process.

Stainless is not a good metal underwater. I never got a warm fuzzy about the strength of Marelon for a seacock. Bronze is really the only option that you can rely on for underwater use.

Theres some things to watch out for. Not all brands have the same bronze alloy. There are a lot of fittings, calves and seacocks that are red brass, that you have to watch out for. The zink in brass alloys gets eaten out leaving the remaining metal brittle and isn't much better than stainless underwater.

Groco uses a good alloy so I try and get their seacocks and valves. They have 3 different types of seacocks. Thier BV line is rebuildable while in the water, and have considerably more metal than other types and brands, which means they also cost about double. They have a standard seacock that's reasonably priced. And lastly they have an flanged adapter that accepts the straight thread of the thruhull on the bottom and has a male NPT thread on top for a valve. I like these because it's easy to install a new valve without removing the thruhull, and they are as strong as the BV seacocks at the threads.

There are different reasons for the different types. I originally got mostly BV seacocks. I got some of the flanged adapters in some of my more tight fit areas. I think I prefer the flanged adapters better, as it's easy to replace with a new valve, and essentially you never have to remove the thruhull again. Including the valve and hose adapter, They're about half the price of the BV seacocks which is an advantage.

I don't really use or like the standard seacocks. You can't repair them and you'd have to pull the thruhull to remove. For a close to the same price I can get the triflange adapter, valve and hose barb which can replace the valve. But they're strong and made if good materials so if I had a financial cap I'd use them.

Be careful you don't put the flanged adapter to close to anything that could prevent the valve from twisting on. Was my f-up last week. Was 1/4" to close to the seacock next to it and I wasn't able to install the valve. Had to pull the seacock so I could install the valve and reinstall the seacock. Messy . Sealant everywhere.

[alaskanviking]

Compass marine/marine how to is a good source of info on seacocks.

I also found that you have to spend extra effort to make sure all the bolts and holes are straight. If the hole is slightly off it will make it difficult to install the thruhull.