Bronze V.S. Stainless

[Dharma]

Hi everyone,

Some of the plumbing attached to the (bronze) seacock of my boat need to be replaced. Is there any reason why I shouldn't use Stainless instead of bronze ? S.S. is about half the price of bronze and alot easier to find here...

Thanks

[Oscar]

Intuitively I say no, but I can't formulate an answer in a scientifically correct way. Someone will be along shortly to do just that, and I suspect the answer will contain the phrase "dissimilar metals". Oh, and then this thread will evolve into 27 posts on the pro's and con's of bonding......

[Chris Campbell]

Is there rigid plumbing attached to the seacock? I'm not sure I've ever seen that - I've always seen flexible tubing connecting things together. What plumbing are you replacing?

[Oscar]

I've seen rigid on industrial type boats, like fishing boats. It does limit your options re. routing.

[Dharma]

The plumbing I'm talking about is simply a 1 1/4'' T screwed on the ball valve (screwed on the seacock) with two insert adapter for the flexible hoses coming in. It was made like that to accomodate the two 1 1/4'' hoses coming from the cockpit drains. I have the same set-up on each side of the boat ( 2 seacock for the 4 cockpit drain).

I knew about the dissimilar metal issue (if there really is one with Bronze and S.S. ?) but I'm planning to change the seacock next year anyways (Then I could install S.S. seacock...) .

Can it turn out really bad in just 4 month in really cold (salt) water?

[Chris Campbell]

Stainless and bronze underwater do make a battery, which is why stainless prop shafts w/bronze props have zincs attached. And a zinc disappears (or nearly) in a season in many locations.The other thing is that stainless is not really a very good underwater metal, which makes me question using it at all for seacocks and through hulls. What about plastic? Is there a Marelon fitting that would do for this purpose? No problems with dissimilar metals, and is approved by ABYC.

This is just my opinion, of course, but I would stick with bronze or Marelon for all my saltwater exposed bits.

Cheers,

Chris

[Dharma]

If bronze and S.S. create a battery maybe I can use my new installation as an emergency power source!

Seriously, I think I will stick with bronze. It has worked fine for 31 year and it looks more "classic" than shiny S.S. ( Yeah, I know these seacocks are deep inside the boat where nobody see them, but still...)

Thanks

[bcooke]

Is there any reason why I shouldn't use Stainless instead of bronze ?

Dissimilar metal corrosion. The fitting will corrode from the inside and your first indication will be finding your boat underneath your mooring.

S.S. is about half the price of bronze and alot easier to find here...

Poor choices are always cheaper and easier. That's why people make them. Knitting is a reasonably inexpensive and simple hobby alternative.

(Then I could install S.S. seacock...)

They make stainless seacocks? Given the difficulty of machining stainless I would have to guess that a stainless seacock would be absurdly expensive. And then your boat would still sink since stainless corrodes underwater with no free air around it.

Stainless is great for above the waterline situations. Not good at all below the waterline.

Can it turn out really bad in just 4 month in really cold (salt) water?

Is it worth finding out the hard way?

The plumbing I'm talking about is simply a 1 1/4'' T screwed on the ball valve (screwed on the seacock)

What you are describing is not a seacock. The seacock is the valve. It sounds more like you have something that should never have been installed on a boat. I could be wrong. A picture would help.

[bcooke]

This is an example of a seacock.

[Dharma]

Actually, what I have is a bronce thru-hull with a bronze valve screwed on top of it. Like your picture, but in two seperate pieces. After the valve there is a close nipple (male-male) then a Te ( fem-fem-fem). On the 2 free openings of that Te, are the hose adapters (one hose comming on each side of the Te). IMHO this set-up is correct as long as I have the right material installed correctly, hence the first question.

A picture would be more clear but I don't have any right now....

[Dharma]

Another question....

While I was looking for new seacock I saw that some of them are in bronze with a 316 S.S ball. I will doubt the ball is perfectly insulated from the valve body (even more when they are full of salt water!) . Then they should have the same dissimilar metal problem ? Are good quality seacock are full bronze and only "cheap" ones have S.S. ball ?

[Ancient Race]

Another question....
While I was looking for new seacock I saw that some of them are in bronze with a 316 S.S ball. I will doubt the ball is perfectly insulated from the valve body (even more when they are full of salt water!) . Then they should have the same dissimilar metal problem ? Are good quality seacock are full bronze and only "cheap" ones have S.S. ball ?

Last question first: Many if not most quality seacocks are bronze with stainless balls and levers. While there is a dissimilarity of metals, regular maintenance - i.e. lubrication and actually opening and closing the valve regularly - limits the problem.

As to your first question: It sounds as if you don't actually have seacocks, which have flanges either as part of the seacock itself or as an intermediate component of the assembly, but rather have ball valves attached directly to the through hulls. Because through hulls have NPS (straight) threads, while ball valves have NPT (tapered) threads, attaching the ball valve directly to the through hull creates a thread mismatch and a strong possiblity of failure. Consequently it's considered a very bad, if not dangerous, practice.

By contrast, seacocks have NPS female threads to accept the through hull, and NPT female threads to accept hose barbs, tees, etc. at the upper end. In addition, seacocks also have the flange which is through-bolted to the hull and mounted on a pad internally, greatly reducing the possibility that errant objects - or feet - will snap off the valve and open a hole in the hull.

Greg

[Ryan]

Typcially the SS ball is isolated from the bronze body by a seal of some sort, teflon is common. As long as the two don't physically contact each other (the SS and bronze) then there is no dissimilar metal corrosion.

[Hirilondë]

As long as the two don't physically contact each other (the SS and bronze) then there is no dissimilar metal corrosion.

That's not true. It is less than if they were touching. Salt water is an electrolyte solution that connects everything under water together electrcally. Even fresh water conducts electricity, but less. But bronze and stainless steel are not that far apart on the galvanic scale, and when separated as well some think it is a safe thing to do. I can't really say where the line should be drawn.

[Ryan]

As long as the two don't physically contact each other (the SS and bronze) then there is no dissimilar metal corrosion.

That's not true. It is less than if they were touching. Salt water is an electrolyte solution that connects everything under water together electrcally. Even fresh water conducts electricity, but less. But bronze and stainless steel are not that far apart on the galvanic scale, and when separated as well some think it is a safe thing to do. I can't really say where the line should be drawn.

Dissimilar metal (or galvanic corrosion) cannot occur without a direct metallic path between the two metals AND an electrolyte (i.e. saltwater or freshwater). Certainly the two metals can corrode when immersed in an electrolyte without direct contact, particularly by electrolytic corrosion (stray current corrosion), but that is not dissimilar metal corrosion. While it makes no differance to the average boat owner which type of corrosion it is (although electrolytic corrosion is typically much more serious), I stand by the original statment as true.

[LazyGuy]

Many of us have a stainless shaft with a bronze screw. Doesn't seem to be an issue there.

[Tim]

Realistically, we all know that boats aren't going to sink instantly if you screw a stainless steel fitting onto something bronze.

There are numerous instances of differing metals in all places on board, both above and below the waterline. Sometimes issues arise; other times they don't. Sometimes the situation cannot be avoided.

In this specific case, however, the issue is more that it's best to avoid this when possible--which in this case it is. When fittings of the same metal are readily available, why push the envelope by knowingly choosing something different that goes against convention, common sense, and good advice, particularly with a below-waterline fitting? It is poor practice, even if no immediate harm comes from it.

Bronze tailpieces, valves, and all other common plumbing fittings for your boat are readily available at any number of marine retailers and Internet suppliers. In general, the cost of things like tailpieces is very reasonable and I can't imagine it being an issue.

[Ryan]

Many of us have a stainless shaft with a bronze screw. Doesn't seem to be an issue there.

As long as you have zinc anodes in good condtion, it shouldn't be.