Seacock - Mixed metals?

[Tim Good]

See photo below. These are the main outlets for my forward and aft heads. At some point in the boats history the previous owner appears to have had the valves replaced with stainless.

As you can see the main valve is stainless but the elbow is bronze. Is this:

A: Not good. Change the elbow or ball valve to match

B: Not great but not the end of the world. Keep an eye on it for the next few years.

 

[GrahamHR]

Why or why aren't the plastic Marelon and their ilk ones not widely available; very tough, immune to corrosion and when you find them, they usually aren't more expensive than bronze or stainless steel. It's one of those applications when "plastic", the right plastic is best.

 

[sailorman]

You would be wise to remove that bonding wire soonest.

 

[Tim Good]

You would be wise to remove that bonding wire soonest.

Why so?

 

[sailorman]

Why so?

The valves are isolated & do not need to be connected to an anode

 

[GrahamM376]

Why or why aren't the plastic Marelon and their ilk ones not widely available; very tough, immune to corrosion and when you find them, they usually aren't more expensive than bronze or stainless steel. It's one of those applications when "plastic", the right plastic is best.

They're off the shelf - TruDesign composite - http://www.leesan.com/index.asp?m=3&b_idno=23&t=Tru+Design+Plastics

I also agree with sailorman, remove the bonding wire.

 

[macd]

Why so?

As you can see the main valve is stainless but the elbow is bronze.

The weight of opinion is that skin fittings are best not bonded. Plenty of threads detailing why. I daresay VicS will pop by with a learned explanation.

What makes you think the yellow metal fitting is bronze? It could be, but could equally be some form of brass. If it bears the letters 'CR;, it's DZR brass which is much better than normal leaded brass for marine use (although not all DZR brass is marked in this way). Brass and 316 stainless (if that's what the ball valve is) are some distance apart on the galvanic scale and are best not used together.

 

[vyv_cox]

I cannot see your photos well enough to tell but are you sure the valves are stainless? One has a distinct look of copper-based corrosion about it. There seems to be plenty of sealant, which will help to eliminate corrosion at the threads, but internal components may be susceptible.

Modern thinking is that corrosion-resistant valves and fittings are far better off looking after themselves, rather than relying on anode that may not be able to 'see' them to provide questionable protection. The major risk is that unless such fittings are absolutely identical one will corrode preferentially to protect the other. My research suggests that the USA insistence on bonding is more to do with dissipating lightning strikes than it is for corrosion protection.

 

[Tim Good]

So lets assume I remove the wires and assume the valves are stainless on a bronze elbow and skin fitting.

Should I really be considering dismantling and replacing with all bronze or is that a bit OTT?

 

[VicS]

The weight of opinion is that skin fittings are best not bonded. Plenty of threads detailing why. I daresay VicS will pop by with a learned explanation.

Nothing more learned than not necessary to bond them or protect them with anodes if they are of corrosion resistant material

It should be noted that bonding skin fittings to the anodes etc was seen as one of the contributing factors to the near loss of the F.V. Random Harvest some years ago.

Also a bond between a skin fitting and DC negative, combined with an electrical defect, was probably responsible for electrolysis of the fitting and sinking of a forumite's mobo in its berth a few years ago.

 

[jfm]

Also a bond between a skin fitting and DC negative, combined with an electrical defect, was probably responsible for electrolysis of the fitting and sinking of a forumite's mobo in its berth a few years ago.

Are you referring to Seahope's boat Vic? If you are, then that is not a correct description of what happened and there is absolutely nothing in that episode whatsoever to support the "don't bond seacocks" camp. I have all the intricate detail, which isn't pertinent to this thread, because I handled the insurance claim on it (and won)

More generally, I'm firmly in the camp of bonding seacocks as are many boatbuilders. I'd use a thicker wire than that yellow one and all my seacock are OEM bonded by the builder with very thick cable (and all are in "sight" of the anodes, though that is a somewhat urban mythy point imho). Seacocks are not "isolated", because they usually contain more than one immersed metal themselves and therefore are their own galvanic cell. But let's not have the argument again as we have done it to death!

@OP, I would find out what the ball valve is. Could be s/s, but could be nickel plated bronze. If the s/s I would change it all to bronze or DZR, but there is no information in your post to suggest this is urgent - can wait till next haul out.

Of course, you might want to check which ins policy you have too as they differ where galvanic activity is concerned, but that's a whole different topic

 

[Tim Good]

but there is no information in your post to suggest this is urgent - can wait till next haul out.

No not urgent as they appear in very good condition. But I am prepping the boat for a circumnavigating in April 2016 and the boat is currently out of the water for a new prop shaft. As such I'm just getting everything "just so". Whilst I'm out the no1 priorities are seacocks, rudder, stern gland and prop shaft. Latter two I'm not doing myself so might as well do what the best I can on the others for the next 6 weeks.

 

[macd]

Could be s/s, but could be nickel plated bronze.

Or plated brass, in which case almost certainly not DZR.

 

[VicS]

Are you referring to Seahope's boat Vic? If you are, then that is not a correct description of what happened and there is absolutely nothing in that episode whatsoever to support the "don't bond seacocks" camp. I have all the intricate detail, which isn't pertinent to this thread, because I handled the insurance claim on it (and won)

More generally, I'm firmly in the camp of bonding seacocks as are many boatbuilders. I'd use a thicker wire than that yellow one and all my seacock are OEM bonded by the builder with very thick cable (and all are in "sight" of the anodes, though that is a somewhat urban mythy point imho). Seacocks are not "isolated", because they usually contain more than one immersed metal themselves and therefore are their own galvanic cell. But let's not have the argument again as we have done it to death!

@OP, I would find out what the ball valve is. Could be s/s, but could be nickel plated bronze. If the s/s I would change it all to bronze or DZR, but there is no information in your post to suggest this is urgent - can wait till next haul out.

Of course, you might want to check which ins policy you have too as they differ where galvanic activity is concerned, but that's a whole different topic

sorry I don't remember whose boat it was. Just that there was connection between the skin fitting or seacock and the negative connection of a piece of electrical equipment, bilge pump IIRC, which was known not to work correctly.

It seemed likely that the connection to the skin fitting coupled with a poor connection somewhere in the negative supply to the pump, or whatever, could have resulted in electrolysis of the fitting when the bilge pump was running or at least attempting to run. It must, I am sure, have been something more serious than just galvanic corrosion.

I only base my conclusions on what we were told on here. If that does not agree with your expert examination of the boat, assuming we are talking about the same incident, it would be useful to know your explanation and diagnosis.

I am very surprised by your opinions on bonding seacocks as it seems to fly in the face of current thinking and contrary to the recommendation of the MAIB following the Random Harvest incident.

 

[jfm]

sorry I don't remember whose boat it was. Just that there was connection between the skin fitting or seacock and the negative connection of a piece of electrical equipment, bilge pump IIRC, which was known not to work correctly.

It seemed likely that the connection to the skin fitting coupled with a poor connection somewhere in the negative supply to the pump, or whatever, could have resulted in electrolysis of the fitting when the bilge pump was running or at least attempting to run. It must, I am sure, have been something more serious than just galvanic corrosion.

I only base my conclusions on what we were told on here. If that does not agree with your expert examination of the boat, assuming we are talking about the same incident, it would be useful to know your explanation and diagnosis.

I am very surprised by your opinions on bonding seacocks as it seems to fly in the face of current thinking and contrary to the recommendation of the MAIB following the Random Harvest incident.

I think you must be referring to Seahope's boat as that is the only Seacock fizzing case I can think of on mobo forum. It was a freak set of facts and wholly irrelevant to the stuff in this thread. It doesn't form any basis for arguing seacocks shouldn't be bonded. The full facts were never posted on the forum because it got litigious with the insurer and there was info Seahope wouldn't want publicised. So unfortunately any conclusion based on the stuff on here is likely to be wrong. I realise of course you can only go on what you've been told! We did win fully with the insurer - full payout of the boat's value. And I didn't examine the boat btw because I didn't need to. I beat the insurer just by using the report from the insurer's own surveyor; it's always nice to see a playing-badly insurance company hoisted by their own petard

The Random Harvest MAIB report said that bonding seacocks in a boat with a crummy electrical system could be a bad idea. It didn't say that bonding seacocks in a properly constructed boat was a bad thing. If you want to assume people's boats are electrically crummy then perhaps it is good advice to tell them not to bond seacocks and compound the crumminess. But let's not lose sight of the fact that a crummy boat is an essential ingredient in the harm that follows from bonded seacocks. There is no such harm in a properly sorted/constructed boat.

Fact is most seacocks are made of more than one metal. On the dry side the different metals are touching, and on the wet side they are in the same puddle of brine. That's a galvanic cell obviously. Worse still if you have, say, a seawater pump that fails to earth ie its 24v supply is leaking to its body then you'll have a current going down the water in the pipe to the open sea and for the last 6 inches it will use the seacock assembly as its conductor if there's no bonding. Random Harvest just didn't think all the scenarios through (nor did it need to) and so should not be taken as conclusive on the merits of bonding generally on a well found boat as opposed to a crummy boat. Frankly Random Harvest has got too much credence on internet forums imho.

Anyway I think you may be overstating things when you say "current thinking" Vic. Most builders whose construction techniques I've seen, including the UK big players like Oyster, Fairline, Princess, sunseeker, bond all their seacocks. The instructions with a Groco say "The seacock base has a bonding screw. Use at least 14 gauge marine grade stranded copper wire to connect the seacock to the vessel bonding system." I honestly think the "don't bond" movement is a bit internet urban mythish, fuelled by a slightly uncareful reading of Random Harvest. I'm firmly in the camp of retaining my builder's OEM bonding with heavy gauge wire (and of course isolation transformers on the shore lines)

 

[Heckler]

I think you must be referring to Seahope's boat as that is the only Seacock fizzing case I can think of on mobo forum. It was a freak set of facts and wholly irrelevant to the stuff in this thread. It doesn't form any basis for arguing seacocks shouldn't be bonded. The full facts were never posted on the forum because it got litigious with the insurer and there was info Seahope wouldn't want publicised. So unfortunately any conclusion based on the stuff on here is likely to be wrong. I realise of course you can only go on what you've been told! We did win fully with the insurer - full payout of the boat's value. And I didn't examine the boat btw because I didn't need to. I beat the insurer just by using the report from the insurer's own surveyor; it's always nice to see a playing-badly insurance company hoisted by their own petard

The Random Harvest MAIB report said that bonding seacocks in a boat with a crummy electrical system could be a bad idea. It didn't say that bonding seacocks in a properly constructed boat was a bad thing. If you want to assume people's boats are electrically crummy then perhaps it is good advice to tell them not to bond seacocks and compound the crumminess. But let's not lose sight of the fact that a crummy boat is an essential ingredient in the harm that follows from bonded seacocks. There is no such harm in a properly sorted/constructed boat.

Fact is most seacocks are made of more than one metal. On the dry side the different metals are touching, and on the wet side they are in the same puddle of brine. That's a galvanic cell obviously. Worse still if you have, say, a seawater pump that fails to earth ie its 24v supply is leaking to its body then you'll have a current going down the water in the pipe to the open sea and for the last 6 inches it will use the seacock assembly as its conductor if there's no bonding. Random Harvest just didn't think all the scenarios through (nor did it need to) and so should not be taken as conclusive on the merits of bonding generally on a well found boat as opposed to a crummy boat. Frankly Random Harvest has got too much credence on internet forums imho.

Anyway I think you may be overstating things when you say "current thinking" Vic. Most builders whose construction techniques I've seen, including the UK big players like Oyster, Fairline, Princess, sunseeker, bond all their seacocks. The instructions with a Groco say "The seacock base has a bonding screw. Use at least 14 gauge marine grade stranded copper wire to connect the seacock to the vessel bonding system." I honestly think the "don't bond" movement is a bit internet urban mythish, fuelled by a slightly uncareful reading of Random Harvest. I'm firmly in the camp of retaining my builder's OEM bonding with heavy gauge wire (and of course isolation transformers on the shore lines)

OK,with respect to your knowledge. Why did Bene not bond the seacocks on my 351 and 381? If I was to bond them now and something were to happen due to seacocks fizzing, who would be to blame? Would the best advice be, keep the system as the manufacturer made it?
S

 

[GrahamM376]

I honestly think the "don't bond" movement is a bit internet urban mythish, fuelled by a slightly uncareful reading of Random Harvest. I'm firmly in the camp of retaining my builder's OEM bonding with heavy gauge wire (and of course isolation transformers on the shore lines)

I've been advised by three surveyors over the years that bonding is a bad idea and I'm sure their advice is not based on "urban myth". If bronze or dzr are used for the through hulls, seacock and tail, all materials are the same with the exception of the valve ball which is insulated from the body by a "plastic of some sort" seat.

Slightly off track, there have been various reports by owners of twin keelers which had one keel bonded at build, that the bonded keel suffered far more rust/corrosion than the unbonded one.

 

[VicS]

I think you must be referring to Seahope's boat ...............................

It's a pity that the full facts have not been made known. It seems from what you say that Seahope even withheld relevant information when he posted his tale of woe on here but I guess at the time he was looking for advice on which way to go to resolve his problems with the insurers while my interest was really in knowing the exact reasons for what happened and how a repetition could be avoided

I was never happy with what we were told of the surveyors report, or at least of the way it was being interpreted, so its good to learn that you were able to actually use it to your advantage.

The MAIB report on the Random Harvest makes great play of the fact that the seacock(s) fitted were of an "unsuitable" material but their measured corrosion rates exceeded the rates which would normally have been expected.

They point out that expert opinion is that a hull anode is not as effective at protecting the "out of sight" inside of a fitting as it is at protecting exposed areas. They go on to point out that the general opinion of experts in the field of cathodic protection is not to bond skin fittings etc to the cathodic protection system!

One of the recommendations was to disconnect all though hull fittings from the cathodic protection system. This is quite separate from a recommendation to have the wiring system inspected and upgraded.


I will, if you like, withdraw my reference to "current thinking" but I will replace it with the words "expert opinion".

 

[jfm]

It's a pity that the full facts have not been made known. It seems from what you say that Seahope even withheld relevant information when he posted his tale of woe on here but I guess at the time he was looking for advice on which way to go to resolve his problems with the insurers while my interest was really in knowing the exact reasons for what happened and how a repetition could be avoided

I was never happy with what we were told of the surveyors report, or at least of the way it was being interpreted, so its good to learn that you were able to actually use it to your advantage.

The MAIB report on the Random Harvest makes great play of the fact that the seacock(s) fitted were of an "unsuitable" material but their measured corrosion rates exceeded the rates which would normally have been expected.

They point out that expert opinion is that a hull anode is not as effective at protecting the "out of sight" inside of a fitting as it is at protecting exposed areas. They go on to point out that the general opinion of experts in the field of cathodic protection is not to bond skin fittings etc to the cathodic protection system!

One of the recommendations was to disconnect all though hull fittings from the cathodic protection system. This is quite separate from a recommendation to have the wiring system inspected and upgraded.


I will, if you like, withdraw my reference to "current thinking" but I will replace it with the words "expert opinion".

Vic, come on, you are better than that. That MAIB report was a poor job. All those statements about "expert opinion" and "general opinion of experts in the field" were utterly unsubstantiated and no authority was cited. On that score, it was slapdash. Perhaps that's to be expected: the reality is that the world's best engineers and weigher-uppers of evidence do not faff about doing reports on sunken 25 foot fishing boats in which nobody died and seacocks. When you have your own knowledge and perhaps a degree plus lots of experience in engineering matters you take a report like RH with a healthy pinch of salt.

 

[jfm]

I've been advised by three surveyors over the years that bonding is a bad idea and I'm sure their advice is not based on "urban myth". If bronze or dzr are used for the through hulls, seacock and tail, all materials are the same with the exception of the valve ball which is insulated from the body by a "plastic of some sort" seat.

The shaft is not insulated in its bearings by the sealing ring. I've got a new seacock here with a perfect ptfe seal and my continuity meter tells me the ball is connected to the valve body.

How are you "sure"? Do you really think that the best engineers in the world would be in business as small second hand boat surveyors? The fact they are small boat surveyors is frankly a strong indication that they are not the sharpest tools in any box. They might even have read Random Harvest and not read it particularly well! The world's best yacht makers bond their seacocks.

This isn't life or death so I'm happy to agree to disagree . (Except on the "insulated" point - that is factually incorrect). I only gave the "bond your seacocks" view to balance this forum, which had collected several statements saying it was widely accepted that seacocks shouldn't be bonded.