why is my seacocks connected/wired to my engine

MapisM said:
As I recall, I read a really techy explanation on why not bond everything together on Professional Boatbuilder, but that was some years ago and I can't find it online anymore.
Otoh, I found this article which also addresses your question, at least to some extent.
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Thanks Mapis. If you ever find the PB article please post it.

OK, Stan Honey set out a good reason not to bond seacocks. But let's be clear what he is saying. He is saying that IF you are in a marina that has stray DC current passing through the water, then bonding is not good becuase it provides a low resistance short cut for those currents with the result that the "out" skin fitting, the one a the end of the short cut, fizzes away. Now, if it were true, that would make good sense. But three comments:
1. I have no idea to what extent these "hot marinas" actually exist. Anyone know?
2. If he is right, prop shafts make for a much lower resistance "short cut" than a series of bonded seacocks, yet no-one sees anodic pitting at either end of their props shafts, sd they? This suggests the "short cut" theory is actually rare in practice.
2. He is not disputing that the multi-metal seacocks consist of little electrolysis cells themselves. And he is not disputing that one of the metals in the seacock must slowly fizz away as an anode. Her can't, because zillions of pages of science tells us that is so. Rather, he is implying that the corrosion in a hot marina is a worse evil than electrolytic corrosion within the seacock and so it is better to endure the latter to save yourself from the former.

Subject to my reservations in #1 and #2 above, his argument in #3 above makes sense. But please let's be clear that he is merely saying that the "stray current" evil, if it exists in your town, is a worse evil than electrolysis in unbonded seacocks. He is not disputing that bonding seacocks helps stop electrolysis in them. His advice not to bond applies only where there are stray currents.

I've no idea how you find out whether your marina has stray currents! Other than taking say 15m of cable, stripping the ends, and running it along your side deck with both ends immersed. Then looking to see if one end fizzes away.
 
Tranona said:
But they are not mechanically connected in any significant way, nor are they immersed in brine,
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I can't believe I'm reading this. The valve body is screwed several turns onto the skin fitting, and the ball is hung through the valve body on a shaft which passes through holes in the valve body. And it is all in the same pool of sea water on the wet side. You are saying that is not a significant mechanical connection, and not immersed in brine? Perlease... (The handle is indeed a red herring. We can ignore that)

Tranona said:
Still can't think of a rational reason for bonding seacocks
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It's right there. A seacock asembly is 3 different metals, touching each other hard, immersed in seawater (which facts I know you dispute so not sure if I'm wasting my breath). That's an electrolysis cell just like your stianless drive shafts and bronze alloy propellers. So that, prima facie, is the reason to bond to an anode. Now, there may be a more refined analysis that says the prima facie analysis is wrong, and we're trying to find that to understand this topic fully, and I'd love to hear it. But we most definitely START from the position we have two/three metals in seawater so your first-cut reaction is you need an anode

Tranona said:
Don't think there is any corrosion in this type of valve - suggest you cut an old one apart and have a look.
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I'm perfectly prepared to believe that in practice the RATE of electrolytic corrosion is so small that you do not get significant corrosion in 10 years or whatever. The low rate could be because of a very small difference in the nobility of the metals concerned. I am interested to find out if that is in fact the case. If so, it would mean that those who bond seacocks are guilty of being a bit perfectionist :-)
 
VicS said:
A mixture of copper copounds in particular basic copper chloride.

Are you sure the new seacocks are either bronze or DZR brass
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Vics - so what's causing this copper chloride to express itself on the outside of my unbonded bronze/dzr/bronze seacock assemblies?

Cheers
Jimmy
 
jfm said:
I've no idea how you find out whether your marina has stray currents!
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That's actually the point - in practice you can't.
I mean, even assuming that you could, in a specific marina and in a specific moment, the situation could be different the following day. And the boat is supposed to move, anyhow.
On balance, stray currents are a MUCH worse evil compared to electrolytic corrosion. Following your train of thoughts on the rate of corrosion (which btw I agree with), with stray currents the sky's the limit!
Bearing in mind that looking at my 15 yo unbonded seacocks I would expect them to last for another similar period (touch wood!), I tend to believe that the reason why some builders put seacocks under cathodic protection has more to see with the quality of the material used, which might suffer from a higher rate of electrolytic corrosion, rather than to being perfectionists.
After all, real perfectionists use sea chests rather than thru hull seacocks, to start with... ;)
 
jfm said:
I can't believe I'm reading this. The valve body is screwed several turns onto the skin fitting, and the ball is hung through the valve body on a shaft which passes through holes in the valve body. And it is all in the same pool of sea water on the wet side. You are saying that is not a significant mechanical connection, and not immersed in brine? Perlease... (The handle is indeed a red herring. We can ignore that)


It's right there. A seacock asembly is 3 different metals, touching each other hard, immersed in seawater (which facts I know you dispute so not sure if I'm wasting my breath). That's an electrolysis cell just like your stianless drive shafts and bronze alloy propellers. So that, prima facie, is the reason to bond to an anode. Now, there may be a more refined analysis that says the prima facie analysis is wrong, and we're trying to find that to understand this topic fully, and I'd love to hear it. But we most definitely START from the position we have two/three metals in seawater so your first-cut reaction is you need an anode


I'm perfectly prepared to believe that in practice the RATE of electrolytic corrosion is so small that you do not get significant corrosion in 10 years or whatever. The low rate could be because of a very small difference in the nobility of the metals concerned. I am interested to find out if that is in fact the case. If so, it would mean that those who bond seacocks are guilty of being a bit perfectionist :-)
Click to expand...

You seem to be hanging onto this idea that the bronze body and stainless steel ball is a problem - when in practice it isn't. Already agreed that the two are islolated by the PTFE bearing so they are not in ontact in sea water. This leaves the shaft that goes through the body. This is not in contact with seawater so is a dry bearing. Add to this, 316 and bronze are fairly close together (which is why they are used in this application) and the difference in mass and area is huge (large bronze, small stainless).

Suggest you read the explanations on www.corrosionist.com - easier than me trying to (mis)interpret it here. You will hopefully then see why using the two different materials does not cause a problem and anodes are not needed.
 
Tranona said:
You seem to be hanging onto this idea that the bronze body and stainless steel ball is a problem - when in practice it isn't.
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On the contrary. In my post which you quoted, and in other posts, I've conceded that prima facie there is an electrolysis cell but I'm perfectly happy to believe (and the evidence indicates) that in practice the rate of corrosion is vvv small, and that bonding of seacocks is therefore for geeky perfectionists only

Tranona said:
agreed that the two are islolated by the PTFE bearing so they are not in ontact in sea water. This leaves the shaft that goes through the body. This is not in contact with seawater so is a dry bearing.
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I totally give up. I can see I'll never succeed in getting you to understnad that a seacock is 2+ metals (a) immersed in brine on the wet side and (b) hard-connected on the dry side, even though it's patently obvious that that is so, and now you even accept that the shaft connects to the body. Best wishes! :-)
 
jfm said:
I totally give up. I can see I'll never succeed in getting you to understnad that a seacock is 2+ metals (a) immersed in brine on the wet side and (b) hard-connected on the dry side, even though it's patently obvious that that is so, and now you even accept that the shaft connects to the body. Best wishes! :-)
Click to expand...

They are simply not in contact in seawater. Have a look closely at one for real. If you read the site I directed you to you will find a bit on isolating the metals to prevent galvanic action - exactly what is done in this application. The shaft through the body is not in seawater.

You are having trouble "convincing" me of something that does not exist, so I could be making the same comment about your unwillingness to accept what I am saying. So probably best we both go on believing our own explanations!

When you think about, if what you are saying is right, every ball valve would come with a warning that it is made of incompatible materials and subject to corrosion in seawater - but they don't. So clearly the manufacturers don't see it as a problem. Not, of course that they are infallible, but leaving aside the issue of poor materials for the body, their confidence seems to be borne out in practice.
 
Tranona said:
They are simply not in contact in seawater. Have a look closely at one for real.
Click to expand...

You seem not to understand what an electrolytic cell/couple is. You have one when you have 2 different metals which are (a) both immersed in the same pool of seawater, and (b) which are also hard/mechanically connected to each other whether inside or outside of the seawater. There is no requirement for the point at which they are hard-connected to be within the seawater. If you don't understand this point, it's no wonder we have been disagreeing about whether a typical seacock is (in principle) an electrolytic cell

So with a seacock, you have the s/s ball and the bronze body both immersed in seawater, and both of those bits of metal are hard connected (behind the scenes, on the dry side) where the ball shaft passes through the valve body. All that amounts in principle to an electrolytic cell/couple, or a hundred years and zillions of pages of science are wrong. The ptfe seal is a complete red herring. (I do accept, as stated above, it might be a very weak cell with a quite tiny current and hence a tiny corrosion rate, but that's a different point)
 
Firefly625 said:
Tranona, I have appreciated your input as this issue and thread has been really informative. But... you kinda lost me at this bit... a seacock is not in contact with seawater??
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He didn't say "not in contact with seawater". He was saying that the point at which the two metals come into hard contact (namely, where the ball shaft passes through the valve body) happens not to be in seawater. That's a correct observation. But it doesn't lead to the result (namely, the absence of an eletrolytic couple) he thinks it leads to
 
Is it then this action that causes a green "copper chloride/something"?? deposit to appear on my non-bonded fittings or is that different? Should I be concerned about it? :confused:
 
Ripster said:
Is it then this action that causes a green "copper chloride/something"?? deposit to appear on my non-bonded fittings or is that different? Should I be concerned about it? :confused:
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I suspect that's something different. I suspect what you have is just oxidation (verdigris) of the metal surface on the inside of your boat. That's nothing to worry about because (absent something unusual) the rate of metal loss is tiny and you're talking 50 years before you have problem. You can slow this process down by wiping them in grease or spraying wd40 or whatever anticorrosion treatment you prefer
 
Ripster said:
Is it then this action that causes a green "copper chloride/something"?? deposit to appear on my non-bonded fittings or is that different? Should I be concerned about it? :confused:
Click to expand...

I need to get a scarier avatar. Asking this question with a picture of homer simpson elicited no answer. Asking it with a picture of a scary-ass toothless monster did the trick. Well done that man!

Cheers
Jimmy
 
jimmy_the_builder said:
I need to get a scarier avatar. Asking this question with a picture of homer simpson elicited no answer. Asking it with a picture of a scary-ass toothless monster did the trick. Well done that man!

Cheers
Jimmy
Click to expand...

Dyu mind, that is one of my better pictures after the new dental work. Anyway, I had to take it down as peops were being upset by it...;)
 
jfm said:
He didn't say "not in contact with seawater". He was saying that the point at which the two metals come into hard contact (namely, where the ball shaft passes through the valve body) happens not to be in seawater. That's a correct observation. But it doesn't lead to the result (namely, the absence of an eletrolytic couple) he thinks it leads to
Click to expand...

crumbs, that is indeed what was said, even speed reading I should be able to tell the difference between "with" and "in"... :o
 
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