why is my seacocks connected/wired to my engine

[Firefly625]

A bit of help needed please, my toilet outlet seacock is connected to my engine block, surely this is wrong?

Had my boat for a couple of years and just poking around seen this and for the first time questioning this!!

 

[VicS]

There was at one time a tendency to bond all the underwater bits and pieces together and to the anodes with a connection also to the engine block to provide a link to the stern gear.

It would not now be recommended to include seacocks or other skin fittings in such a bonding arrangement.

 

[Seahope]

A bit of help needed please, my toilet outlet seacock is connected to my engine block, surely this is wrong?

Had my boat for a couple of years and just poking around seen this and for the first time questioning this!!

Good thing to check this.

 

[andy59]

So is the wisdom of the forum saying that metal skin fittings do NOT need bonding ?

 

[VicS]

skin fittings and seacocks should be made of corrsosion resistant materials such as bronze or DZR brass.

One of the recommendations of the MAIB into the near loss of the FV Random Harvest 9 or 10 years ago was that the skin fittings should not be bonded to the anodes etc.

 

[Firefly625]

Thanks for replies that has confirmed what logic said should be the case. Bonding a bronze seacock to the engine just didn't make sense, but when you look and see that both toilet outlet and engine intake are bonded you just start to question your own mind...

 

[jfm]

Hmmm

In the case of a skin fitting made of a single material, eg a simple skin fitting pick up or drain with the fitting and backing nut made of the same material, then I agree bonding makes no sense in grp boat. But if the fitting is made of two metals (ie every seacock) then one of those is cathode and t'other anode relative to each other, and such a fitting should be connected to the ship's anode system imho to create the result that the ship's anodes become the anode relative to both metals in the seacock, so that neither will corrode. This is the practice of many reputable yards, including Hardy, and is how my sq78 is done. If I were commissioning a new boat this is how i'd insist it be done (though most good yards would do this anyway)

It makes perfect sense

As VicS says, the maib report on Random Harvest questionned this practice and suggested that thru hull fittings and seacocks should not be bonded. I gotta say, that was one lightweight report and it dumped 2-metal seacocks and one-metal thru hulls into the same discussion, which is totally lacking in science. Just cos MAIB say it doesn't make it right...

 

[aquatom]

I have seen many non bonded seacocks corrode and start to leak. But have had no issues with bonded ones. To bond seacocks would only be a problem if very cheap anodes were used or if the anodes had wasted away and not been replaced, then the next most reactive metal in the bonded system would be under attack!

 

[Firefly625]

Hmmm

In the case of a skin fitting made of a single material, eg a simple skin fitting pick up or drain with the fitting and backing nut made of the same material, then I agree bonding makes no sense in grp boat. But if the fitting is made of two metals (ie every seacock) then one of those is cathode and t'other anode relative to each other, and such a fitting should be connected to the ship's anode system imho to create the result that the ship's anodes become the anode relative to both metals in the seacock, so that neither will corrode. This is the practice of many reputable yards, including Hardy, and is how my sq78 is done. If I were commissioning a new boat this is how i'd insist it be done (though most good yards would do this anyway)

It makes perfect sense

As VicS says, the maib report on Random Harvest questionned this practice and suggested that thru hull fittings and seacocks should not be bonded. I gotta say, that was one lightweight report and it dumped 2-metal seacocks and one-metal thru hulls into the same discussion, which is totally lacking in science. Just cos MAIB say it doesn't make it right...

Thanks for reply jfm, very interesting, and that of course does make sense. Got to say I am totally ignorant to MAIB report on Random Harvest.... so thanks for your steer on situation.

My little Hardy only has 3 seacocks, engine intake, heads inlet and outlet. All are bonded, hardly visible as bonding wires run underside of pipe work and jubilee clamped to neck of seacocks under joined section, certainly factory done. While I have been away on the boat for the last 2 weeks I had noticed a small weep from toilet outlet , so small in fact that all I can see is a some salt crystals forming round the base which is what got my attention. I wiped them away and after a few days they re-appeared, started to worry that it was actually seacocks fizzing away. But had a much closer look after posting first thread and seacock looks totally sound.

 

[Tranona]

Hmmm

In the case of a skin fitting made of a single material, eg a simple skin fitting pick up or drain with the fitting and backing nut made of the same material, then I agree bonding makes no sense in grp boat. But if the fitting is made of two metals (ie every seacock) then one of those is cathode and t'other anode relative to each other, and such a fitting should be connected to the ship's anode system imho to create the result that the ship's anodes become the anode relative to both metals in the seacock, so that neither will corrode. This is the practice of many reputable yards, including Hardy, and is how my sq78 is done. If I were commissioning a new boat this is how i'd insist it be done (though most good yards would do this anyway)

It makes perfect sense

As VicS says, the maib report on Random Harvest questionned this practice and suggested that thru hull fittings and seacocks should not be bonded. I gotta say, that was one lightweight report and it dumped 2-metal seacocks and one-metal thru hulls into the same discussion, which is totally lacking in science. Just cos MAIB say it doesn't make it right...

Not sure it makes sense at all. Seacocks, if they are bronze or DZR are all one metal. In a GRP or wooden boat there is no need to bond them. I have bronze seacocks nearly 50 years old in my boat with no signs of corrosion. I have just removed a DZR ball valve after 18 years on the same boat - just like new. Despite what you say very few builders bond seacocks, and those that do probably do it out of habit rather than any rational reason.

Perhaps you could give examples of "two metal seacocks" and examples of where corrosion takes place if they are not bonded.

Have just looked at the MG Duff site - not a single mention of bonding through hulls or seacocks, only stern gear - shafts, props, rudders to anodes.

 

[Latestarter1]

These posts highlight different views on cathodic protection, however they are all based on theories which if they were perfectly understood, would all be in agreement with each other.

The reality is, that the mechanisms which actually create a cathodic or anodic cell have not been scientifically explained yet. Radom Harvest report is typical example.

Groco sea cocks, in my book some of the best, have bronze housing with bonding connection point with stainless ball valve with PTFE seal.

If one balances the relative risks, then its a no-brainer really. Bonding the shaft and prop and all the thru-hulls means that everything metallic below the waterline is protected in the event of unexpected failure. Say 12/24 volt seawater pump developes an earth leak, the powerful current will discharge to earth through the seawater in the hose, because seawater is electrically conductive. You need to choose whether you would prefer the current to exit the boat via your sea cock or your anode.

I know of certain marinas where there are a large number of vessels on significant shore power load, stray currents are rampant. On a professionly installed system, the corrosion meter, or earth leakage device would alert you to a problem. It is not possible to have a corrosion meter unless your thru-hulls are bonded.

Nobody is right or wrong in this discussion, if you are unhappy with bonded sea cock, simply disconnect it.

 

[Tranona]

You are confusing electolysis with galvanic corrosion. The two are quite distinct and anodes are primarily used for galvanic corrosion where two connected dissimilar metals are in seawater. Such conditions do not normally exist in a seacock and through hull in a GRP boat. Therefore bonding to an anode is not required. The anode - if it is needed also has to be close and in line of sight to the item that it is bonded to - so bonding a seacock at the forward part of the boat would need an anode close to it (if it needed one at all - which it doesn't).

Corrosion caused by electrics (your unexpected failure) is a very different animal and the Duff site has some suggections for dealing with it - that do not involve anodes.

 

[jfm]

Seacocks, if they are bronze or DZR are all one metal...Perhaps you could give examples of "two metal seacocks"

As far as i have ever seen, seacocks use different metals for the body and the ball, and possibly for the shaft too. My post above was based that "two metals" premise. If in fact seacocks are made entirely of one metal then my post should be ignored, But I don't think that is the case

I do not have examples. On my boats seacocks are always bonded and I wouldn't have it any other way. But I don't need to give examples: if you place two different metals in seawater and electrically connect them inside the hull then one will be an anode and the other a cathode. Surely no-one disputes that? The rate of corrosion of the anode will depend on many factors and might not be significant, but that is dependent on the specific case and I cannot comment generically on the rate

 

[Scubadoo]

This is all very interesting and quite worrying to read. I would go on recent evidence, that there seems to be a few boat recently that have sunk and nearly sunk because of bonding wires issues. Then there are boaters here that have had seacocks with no bonding wires for over 20years or more without any sign of problems.

On my boat, I noticed that my Sealine seacocks (toilet) are not bonded and the conditions of the seacocks look fine, I've had the boat for 12years from new.

Check your seacocks reguarly and any sign of problems double check which is what firefly has done. I also as a precaution keep wooden bungs nearby.

 

[Ripster]

This is all very interesting and quite worrying to read. I would go on recent evidence, that there seems to be a few boat recently that have sunk and nearly sunk because of bonding wires issues. Then there are boaters here that have had seacocks with no bonding wires for over 20years or more without any sign of problems.

On my boat, I noticed that my Sealine seacocks (toilet) are not bonded and the conditions of the seacocks look fine, I've had the boat for 12years from new.

Check your seacocks reguarly and any sign of problems double check which is what firefly has done. I also as a precaution keep wooden bungs nearby.

Agreed. Alarm bells rang with me earlier on in the year, so I checked mine out and found that one of the cooling Seacocks that had been replaced by a well known Hamble dealer about 18 months ago (it had seized up) was now brass - unsuitable for Seawater! When I checked the heads group - same issue - the originals looked ok but a replacement fitting and cock were brass too - CW617n to be precise. So on lift out later this year - all the below WL skin fitting and seacocks are being renewed. BTW - as you might expect on a janneau - none are bonded.

 

[Tranona]

As far as i have ever seen, seacocks use different metals for the body and the ball, and possibly for the shaft too. My post above was based that "two metals" premise. If in fact seacocks are made entirely of one metal then my post should be ignored, But I don't think that is the case

I do not have examples. On my boats seacocks are always bonded and I wouldn't have it any other way. But I don't need to give examples: if you place two different metals in seawater and electrically connect them inside the hull then one will be an anode and the other a cathode. Surely no-one disputes that? The rate of corrosion of the anode will depend on many factors and might not be significant, but that is dependent on the specific case and I cannot comment generically on the rate

But the two metals are not connected. The balls run in a composite bearing and are isolated electrically from the body. When you do get corrosion in seacocks it is usually because the metal is brass and not DZR or bronze. There really is no need to connect seacocks to an anode.

The bonding of seacocks is a hangover from the days when seacocks were often connected by metal piping to engines. Now they are almost always isolated by plastic piping, and the metals they are made of are compatible with eachother.

Not arguing with your basic principle about dissimilar metals and seawater - just pointing out that seacocks do not fit that description.

 

[Firefly625]

This is all very interesting and quite worrying to read. I would go on recent evidence, that there seems to be a few boat recently that have sunk and nearly sunk because of bonding wires issues. Then there are boaters here that have had seacocks with no bonding wires for over 20years or more without any sign of problems.

On my boat, I noticed that my Sealine seacocks (toilet) are not bonded and the conditions of the seacocks look fine, I've had the boat for 12years from new.

Check your seacocks reguarly and any sign of problems double check which is what firefly has done. I also as a precaution keep wooden bungs nearby.

I was bought up on the basis that you always close the seacocks when you leave the boat or go to sea (apart from engine sea cock of course!!!), so that is what I do.... all my seacocks have double jubilee clamps and the appropriate size wooden bung tied to it... but I only have 3 to worry about. However the toilet outlet (which is the one I had a concern with), along with the engine intake are both in the engine bay and I can only get my head within about 2 foot of them if I lie on top of the engine (a position that Volvo paul is very accustomed) so I cannot inspect them easily or as closely as I would like.

I have found this thread very interesting and thank all you knowledgeable chaps for you responses but I am not certain I am much the wiser. I am glade to say my seacocks are bronze (as I think you would hope to see on a Hardy) and as they have been bonded for the last 10 years I don't think I am now going to change anything.....??

 

[jfm]

But the two metals are not connected.

If that statement were correct, there would be no point bonding seacocks, I agree. But I think that statement is wrong. I haven't studied the design but I'd expect they will be connected by the shaft where it passes through the body, and I'll put a Fluke on one next time I get the chance to test this. But regardless of that, the balls/bodies of seacocks for loos and black tanks are certainly connected very nicely by the pool of urine that sits on the inside when the seacock is closed

 

[VicS]

the balls/bodies of seacocks for loos and black tanks are certainly connected very nicely by the pool of urine that sits on the inside when the seacock is closed

The pool of urine is just the electrolyte, It only forms half of the circuit. The half which is missing and which is necessary for galvanic corrosion to occur is the solid connection between the two metals.

 

[jfm]

The pool of urine is just the electrolyte, It only forms half of the circuit. The half which is missing and which is necessary for galvanic corrosion to occur is the solid connection between the two metals.

I see your point VicS. I have briefly thought about whether, as far as electrolytic corrosion on the seawater side is concerned, the urine can serve as the "solid connection" but then you get into complexity about electrolysis going on on the urine side too. I don't know, and will happily back down on the "pool of urine" argument

I still suspect there is an actual solid connection where the shaft passes through the body and where the shaft's retainer nuts contact the body. Do you think differently? Do you think they are fully isolated by plastic components, so they never touch? I thought the seal was made only by the contact of the ball with the plastic material whose edge you can see if you look up the pipe, and that there was no sealing required where the shaft passes through the body. In other words, it's metal on metal where the shaft passes through the body, I think. I'll be corrected if you know better but that's how I recall the standard form of seacock construction