why is my seacocks connected/wired to my engine

[MapisM]

It is in perfect working order with no sign of any corrosion on any parts except a bit of rust on the mild steel handle.

Agreed, I can confirm exactly the same for my seacocks (7 of them, 6 of which 15 yo as the boat is), all unbonded.
And some of them connected to electrical pumps (220V A/C, 24V toilets and anchor chain wash) , hence exposed at the risk of earth leaks which LS1 described. Which in principle I agree with, though I suppose that it should immediately become evident through a fault, or at least a major efficiency loss, of the pump involved.

As an aside, it's funny to see how in this recent article on seacocks the pic in the first page shows a badly worn out seacock, and it seems to be bonded with no less than two wires, for good measure...!

 

[jfm]

Would you then bond a bronze seacock installed with stainless bolts then?

(I recently refurbished my Blakes seacocks and reinstalled them with stainless bolts, as the phosphor bronze bolts were horrifically expensive and numerous posts I found seemed to reflect concensus that stainless was fine)

???

I'd never install it that way; I'd use a flanged seacock skin fitting with a big lock nut on the inside. But if I had to do it that way I'd use phosphor bronze bolts regardless of the cost - stainless steel is susceptible to crevice corrosion where it is deprived of oxygen at its surface

And if hypothetically I had to use stainless bolts for some reason then I'd prefer to bond it to zinc anodes but I wouldn't regard that as an urgent job because (in line with other comments on this thread esp Trnaona's) the RATE of electrolytic anode corrosion when the cell consists of ph bronze plus s/steel is very small, probably smaller than the crevice corrosion problem!

 

[jfm]

jfm, excuse my ignorance here, the reason for my post on Sunday was when I had my head down in my engine bay looking at my seacocks and the bonding wire the thought that I couldn't shake from my head was that I was bonding something that is a relatively soft metal to my engine; therefore what stops this from being an anode?

What stops it being an anode is the zinc anodes on your boat, which are even more anodic than the st/steel and ph/bronze in your seacock and skin fitting. Hardy have wired all three metal elements in your seacock (that is, the s/steel ball, the bronze/dzr valve body, and the bronze skin fitting) to this zinc anode.

 

[Tranona]

Can I ask a related question on this interesting thread. I will be replacing my Skin fittings and seacocks soon as I know two of them at least are CW617n brass, so taking no chances. But... is it OK to mix bronze and DZR. So a bronze skin fitting and a DZR cock? Or should it be one type only for each set?

Yes, that is quite common as the bronze skin fittings are reasonably priced compared with bronze valves. The last installation I did was like that.

 

[jfm]

The real;ity is that seacocks of this construction do not suffer from galvanic corrosion. the vast majority of boats do not bond their seacocks to an anode for two reasons. Firstly it is unecessary and secondly even if they are connected to anodes designed to protect stern gear at the rear of the boat they will be out of sight of the anodes.

I have never heard of seacocks failing because of galvanic corrosion of the ball valve - although as usual am quite open to persuasion if you can provide evidence of this happening. As I have already noted, the "experts" do not recommend bonding, most builders don't do it and not once in all the discussions and published articles on the subject has there ever been any mention of ball valves corroding - always fittings that are not bronze or DZR. They could of course all be wrong, but I don't think so.

Just to reinforce - sitting on my desk now is a 1/2" DZR ball valve I took out of my boat after 18 years because the new engine needed a bigger size. It was in seawater 50 weeks a year fully open, so totally immersed. It is in perfect working order with no sign of any corrosion on any parts except a bit of rust on the mild steel handle.

Tranona, I accept the evidence of course. What I deduce is as follows, though I'm happy to be corrected or hear alternative views:

1. There is no doubt, mechanically, that a seacock represents three metals mechanically connected, and immersed in brine. That means the most anodic metal will corrode and there is zilluions of pages of science to tell you that
2. However, the evidence you quote suggests that the RATE of electrolytic corrosion is incredibly small. So small that you don't even see any corrosion, even after many years.
3. For that reason it is ok not to bond to anodes, if you're not a perfectionist. You'll likely get away with it
4. Some more obsessive perhaps builders still choose to bond. Hardy, Fairline, some Ferretti brands come to mind. They could be accused of getting the perfectionist/pragmatic balance wrong(!)

To throw in a few further thoughts...

5. Plenty of web commentators comment along the lines "bonding could make things worse" but I haven't seen any good/convincing explanation of the science of that. (Well, if you put +ve voltage onto part of the bonding circuit making it +ve relative say to the P brackets that of course would make things worse, but you are not supposed to do that!)
6. I personally don't attach much weight to the MAIB report on the boat that had trouble in Brighton. The science in those reports is very lightweight
7. I don't know what proportion of boat builders do/don't bond. I'll look out for this more over the years. I'd be interested to know
8. It's moving the discussion to a different area, but I'm not a big fan of the oft-mentioned "line of sight" theory for the location of zinc anodes versus what they are supposed to protect. There is a distance consideration obviously, but I don't believe in the line of sight theory. It feels intuitively quite wrong doesn't it? I put it in the old wives tale category. Your engine plug anodes certainly cannot see everything they are meant to protect

All imho

 

[jfm]

Yes, that is quite common as the bronze skin fittings are reasonably priced compared with bronze valves. The last installation I did was like that.

I'd guess tranona that the relative anodic-ness of dzr vs bronze is nearly zero, so that the rate of electrolytic corrossion that occurs in such an installation is incredibly small, and unnoticeable even after say 20 years

 

[Firefly625]

What stops it being an anode is the zinc anodes on your boat, which are even more anodic than the st/steel and ph/bronze in your seacock and skin fitting. Hardy have wired all three metal elements in your seacock (that is, the s/steel ball, the bronze/dzr valve body, and the bronze skin fitting) to this zinc anode.

jfm, I understand that the boats main zinc anode would take the biggest weight of the job in hand, but what I didn't realise is that it must take 100%... until it drops off!

 

[EME]

A question for the "I dont need to Bond" group.

Why do zinc anodes disappear when you are away from the boat even when not connected to the metal they are protecting ?

 

[jfm]

jfm, I understand that the boats main zinc anode would take the biggest weight of the job in hand, but what I didn't realise is that it must take 100%... until it drops off!

Oh yes. If it fizzes away and you do nothing you are in trouble. Starting with your bronze alloy propeller bolted to your temet shaft. Part of the whole deal is you have to keep replacing your big hull anodes!

 

[Firefly625]

Oh yes. If it fizzes away and you do nothing you are in trouble. Starting with your bronze alloy propeller bolted to your temet shaft. Part of the whole deal is you have to keep replacing your big hull anodes!

well indeed that is a must every season.

 

[MapisM]

A question for the "I dont need to Bond" group.
Why do zinc anodes disappear when you are away from the boat even when not connected to the metal they are protecting ?

Not sure to see what you mean. Theft is the only answer which springs to mind...?!

 

[EME]

Not sure to see what you mean. Theft is the only answer which springs to mind...?!

Sorry ,, a tad perverse! I was thinking of "Transom Anodes"( and "Hanging Anodes" but a bit of a digression). By 'lose' I meant 'being sacrificed' ie 'fizzing'

 

[Tranona]

1. There is no doubt, mechanically, that a seacock represents three metals mechanically connected, and immersed in brine. That means the most anodic metal will corrode and there is zilluions of pages of science to tell you that
2. However, the evidence you quote suggests that the RATE of electrolytic corrosion is incredibly small. So small that you don't even see any corrosion, even after many years.

But they are not mechanically connected in any significant way, nor are they immersed in brine, and if the ball is stainless then the difference in potential is minimal. The handle is nowhere near brine - it usually rusts because it is in a damp environment in a bilge - but on many modern boats with dry bilges there is no rust problem. My 10 year old Bavaria valves have no rust on the handles - the 1/2" valve I mentioned was in a wooden boat with open bilges and always a bit damp.

Don't think there is any corrosion in this type of valve - suggest you cut an old one apart and have a look.

Still can't think of a rational reason for bonding seacocks - neither can the "experts" - although clearly some builders think it necessary, so it would be useful if they could explain why.

There are in fact many boats that have no anodes at all - my Bavaria only has the anode on the saildrive leg to protect the aluminium casing. Many boats with conventional stern gear also survive without anodes. Again my old wooden boat lasted 25 years with the original engine and no anodes, although the shaft was bronze. The next engine had a stainless shaft and I thought it prudent to fit an anode. Changed it once in 18 years and then mainly because the fittings leaked and caused some rot.

I am not for one minute saying anodes are a waste (?) of time, particularly on a boat like yours with big lumps of bronze and stainless in close proximity underwater, just not necessary for seacocks and through hull fittings.

If you feel happier with them bonded then fine - you won't ever be able to tell the difference because you won't get corrosion on them anyway.

 

[MapisM]

5. Plenty of web commentators comment along the lines "bonding could make things worse" but I haven't seen any good/convincing explanation of the science of that. (Well, if you put +ve voltage onto part of the bonding circuit making it +ve relative say to the P brackets that of course would make things worse, but you are not supposed to do that!)

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.

 

[EME]

MapisM The reason I've seen usually given is no more complex than that bonding everything could make problems worse and that individual (anodic) protection for every fitting is better. I can see that IF you have a problem with stray current in a hot marina (do they really exist?) and very dissimilar 'nobility' metals .. yet these are the same people who seem to suggest individual anodic protection for every metal fitting underwater.

 

[Scubadoo]

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.

and here is a more up to date May11 article stating not to bond http://www.yachtingmonthly.com/plus/527314/essential-seacock-checks

Certainly differences of opinion, but it would seem the more I look the more experts advise against bonding. To be honest it is a crazy situation that some boat builders do and others don't, then some like Sealine who have stated that they don't even use DZR/bronze and happy with the RCD directive that your covered for only 5years.

I know one thing for certain, I have learned a lot and whether I buy and new or used boat, that is one area that has my attention.

 

[jfm]

and here is a more up to date May11 article stating not to bond http://www.yachtingmonthly.com/plus/527314/essential-seacock-checks

I find it a shame that there is no attempt by the guy to justify the recommendation not to bond, other than a claimed "general concensus"

We start with the fact that in a seacock we have 2 or more different metals, mechanically connected, immersed in seawater. That is the basic recipe for electroylsis and the reason why those of use with bronze alloy props and s/steel shafts spend hundreds of €€€ on anodes every year. Now, it may be true that the prop/shaft situation is different from the seacock situation, but if so I'd like to hear an explanation of the science behind that. Surely not a lot to ask. And I will not do something just because a surveyor says I should with no further analysis offered!

 

[Scubadoo]

I find it a shame that there is no attempt by the guy to justify the recommendation not to bond, other than a claimed "general concensus"

We start with the fact that in a seacock we have 2 or more different metals, mechanically connected, immersed in seawater. That is the basic recipe for electroylsis and the reason why those of use with bronze alloy props and s/steel shafts spend hundreds of €€€ on anodes every year. Now, it may be true that the prop/shaft situation is different from the seacock situation, but if so I'd like to hear an explanation of the science behind that. Surely not a lot to ask. And I will not do something just because a surveyor says I should with no further analysis offered!

Fair point, I think it is time for some organisation like RYA to take this up and prehaps also RNLI as it is a safety matter as well.

 

[David of Essex]

There is a small percentage of boat owners that have the technical knowledge and experience to make there own decisions of such importance as discussed from this and other technical points about boating. Myself and I believe the majority of boating people are left with a choice of which is the right decision to make.
Excellent thread.
David

 

[rhumbunctious]

Perhaps a useful question to answer would be, which option represents the least risk. I.e. even if one argues that bonding seacocks and similar hardware is not necessary, is it harmful? I.e. does it harm if one does so, even unnecessarily, just to be sure?