Too much excitement

[Kubcat]

We had a bit of ‘excitement’ on the boat.

Turned on the air conditioning and after about half an hour or so the bilge alarm went off.

The boat was filling fast and I had no idea what happened.

To cut a long story short a 20 year old Guidi 90 degree elbow in the raw water circuit corroded and fell off the thread.

It was located under our bed with many panels removed. Some with a screwdriver.

The location is difficult but it appears the elbow screwed into a stainless tube that runs under the tanks. It is also below the waterline.

Dissimilar metals was my first thought. There appeared to be a thread tape that came out as string.

Should I buy another one and be done with it or look at a different material?

 

[Kubcat]

Is there a better place to post a raw water plumbing issue?

 

[lisilou]

PBO section might get you some helpful advice.

 

[jfm]

Buy a bronze one and it will be fine. Best to earth it to the node circuit too (though many argue against earthing them, for reasons I don't agree with).

 

[Hurricane]

Buy a bronze one and it will be fine. Best to earth it to the node circuit too (though many argue against earthing them, for reasons I don't agree with).

Yep - I agree with you but Princess didn't bond any of our seacocks and they are all fine.
We even have one identical to the OPs one and thats fine too.
I do check them regularly though.

 

[Portofino]

Buy a bronze one and it will be fine. Best to earth it to the node circuit too (though many argue against earthing them, for reasons I don't agree with).

It’s what I did ^ Earth them to the transom anodes .
In my ER I noticed the green/ yellow Earth wires connecting the tanks , the underwater exhaust metal hardwhere ( the bits glassed in ) .
Had all my cocks replaced circa 2015 shortly after getting it .There was nothing wrong with them except the main engines were stuck open .Suspect the PO never closed them .

They are now regularly exercised , but I started to notice on the main engines some 2 1/2 inch valves they were stiffening up .
Now is it just creatures / barnacles etc or is it basically corrosion, or both ?

So seeing as the boats earthing strips for the engines (MAN ) are only inches from the main seacocks I bonded them in .
Guess what they run very smoothly now , hardly any effort to open / close .

As I said as well as the main engines there already are other metal bits connected in so a couple of seacocks more …..

I realise reading around the subject…..almost like anchor threads bonding polarises opinions.



Exhaust box Earth wire for the metal work glassed in .^



The main anodes ^ they are connected by a large copper Earth strap running back from the ER .The MAN s are connected too , the main anode protection.Thus no silly hidden hard to get pencils .In the med you can easily snorkel change theses and monitor them .They do easily last 12/12 btw .

The rudders + ram are connected inside under a bunk .



Other side of the transom.You can see one ( Stb ) copper strip and its bolt to the anode , the L shaped partially painted thing under the waste tank to pump out pipe

Note the “ Chiller inverter “ I was a pioneer , early adopter of this air con tech when it burst out on the scene circa 2014 .

In essence it Uber quiet , but being DC the motor never stops , just varies it’s speed being dc .This means you avoid AC current start spikes .Sure theses days there are soft start AC but nether the less they draw far more current and might exceed the boats or more likely in a busy marina the shore powers headroom = your AIr con faults .
Or @ anchor your geny has more head room with one one of these. It’s current draw is a fraction of a trad AC compressor.

Note JFM s new boat the SL has a this inverter tech .I suspect the rest of the field of boat air con has caught up with Frigomar . Esp in Italy !
Note Henry’s new Priny , or Princess hasn’t.Still old fashioned AC motors = spiky and heavy on consumption FWIW .

That unit sat under his bunk kicks out up to 42000 btu and maintains an ice cool boat on 3 A - 5A .Silently.


Sorry for the TD ….saw the unit in the pics and thought it needs further description.

 

[Kubcat]

I ran off to our local Stainless Shop that sells bronze as well and they said that there is no real way to see if it is bronze or brass but by the fact it lasted 20 years it was most likely bronze.

As it screws into a stainless steel fitting that is in perfect condition, they suggested I use a stainless steel replacement elbow so no dissimilar metals are joined together.

On another forum the moderator who sounds extremely knowledgeable said that my fitting must have been brass and that the photos show zinc demineralisation.

I guess if going bronze gives me another 20 years, then that is a good alternative.

The boat has a very extensive bonding system and I found it odd that it wasn’t bonded. Perhaps being attached to stainless steel changes things, I have no idea.

 

[Tranona]

I ran off to our local Stainless Shop that sells bronze as well and they said that there is no real way to see if it is bronze or brass but by the fact it lasted 20 years it was most likely bronze.

As it screws into a stainless steel fitting that is in perfect condition, they suggested I use a stainless steel replacement elbow so no dissimilar metals are joined together.

On another forum the moderator who sounds extremely knowledgeable said that my fitting must have been brass and that the photos show zinc demineralisation.

I guess if going bronze gives me another 20 years, then that is a good alternative.

The boat has a very extensive bonding system and I found it odd that it wasn’t bonded. Perhaps being attached to stainless steel changes things, I have no idea.

That is brass which has dezincified because of the saltwater running through. Classic case. Bonding to an external anode will not do anything. The whole point of bonding to an external anode is to protect items that are dissimilar metals underwater such as yellow metal propellers on stainless shafts . Your elbow is not underwater. What is happening is that the seawater is creating a circuit between the stainless steel elbow and the zinc in the elbow so that the zinc disappears (dezincification) and leaves you with just copper which crumbles away as clearly shown in your first photo. An anode in the tubing would reduce this (as is common in engines with similar mixes of metal in the raw water circuit) but a faff to install one.

If you can get a stainless elbow use that. If you can't then try to isolate the brass from the stainless. Actually brass will eventually dezincify in seawater even if not in contact with another metal (think of the brass screws often used in wood on boats). There is a lot of misunderstanding about the nature of galvanic action on boats and often "bonding circuits" are created that are totally unnecessary. The golden rule is to identify where two dissimilar metals that have different potential are in contact in an electrolyte (seawater) and then look at either isolating them or using an anode to protect the lower potential metal. seacocks, for example in a grp or wooden hull do not need bonding to anything as they are self contained and not connected to any other metal underwater. Propellers and shafts do usually require anodes as do aluminium drive housings, trim tabs and often rudders because they are made of a mix of stainless and yellow metal.

Hope this helps

 

[Kubcat]

That is brass which has dezincified because of the saltwater running through. Classic case. Bonding to an external anode will not do anything. The whole point of bonding to an external anode is to protect items that are dissimilar metals underwater such as yellow metal propellers on stainless shafts . Your elbow is not underwater. What is happening is that the seawater is creating a circuit between the stainless steel elbow and the zinc in the elbow so that the zinc disappears (dezincification) and leaves you with just copper which crumbles away as clearly shown in your first photo. An anode in the tubing would reduce this (as is common in engines with similar mixes of metal in the raw water circuit) but a faff to install one.

If you can get a stainless elbow use that. If you can't then try to isolate the brass from the stainless. Actually brass will eventually dezincify in seawater even if not in contact with another metal (think of the brass screws often used in wood on boats). There is a lot of misunderstanding about the nature of galvanic action on boats and often "bonding circuits" are created that are totally unnecessary. The golden rule is to identify where two dissimilar metals that have different potential are in contact in an electrolyte (seawater) and then look at either isolating them or using an anode to protect the lower potential metal. seacocks, for example in a grp or wooden hull do not need bonding to anything as they are self contained and not connected to any other metal underwater. Propellers and shafts do usually require anodes as do aluminium drive housings, trim tabs and often rudders because they are made of a mix of stainless and yellow metal.

Hope this helps

Helps a lot. I was leaning to stainless, now confirmed.

Thank you.

 

[Portofino]

Think what TTH ( through the hull ) fitting the stainless sea cock screws in to = dissimilar metal scenario + sea water . In which case the valve will need bonding .The SS cock might survive the lesser metal electrolytically ie the TTH fitting will start to fizz .
The pair better the same material .

1- Inside stuff bonded to an external zinc ( without any protection from other zinc )work’s protectively only if theres a seawater circuit , some electrical continuity.

Like the MAN , MTU manufacturers who do not use pencil anodes scattered around the engines ancillaries.Any dissimilarity between engine components ( the various wet sea water coolers ) is taken up by the zinc depletion instead of component.As long as there is continuity ie seawater left inside to form the other side of the circuit the earthing strap to the zinc ( see my pics in post # 6 )

2- With individual pencil anodic protected stuff eg your geny , air con chillers , and certain engine manufacturers you need to ( hassle as it is disassemble time and eyeballing ) regularly check and replace them if they are below a certain meatiness .
Some fresh water flushing if the item is standing for months years might be beneficial .More so the greater dissimilarity of the components or the tiny size in terms of longevity of the pencil zincs .

Fresh water flushing of the items mentioned in para 2 with be detrimental because you are diminishing the return side of protective circuitry back to the transom zinc .That’s why MAN , MTU don’t fit a bodgeflow TM systems…….and go for yrs decades without any engine corrosion issues clocking tens of thousands of hrs up .


For the OP try and get the TTH and valve the same materials * if not consider bonding to a external submerged zinc of suitable mass .


* Even then “ same materials “ is to get a neutral electrolytic potential .Fine in theory and exactly achievable if the stuff is poured out of the same melting cauldron at the foundry .
If the two component s are cast up from different melts ( highly likely) then there will be slight differences of potential .
Wether significant differences I very much doubt it .How ever not unknown and accounts for examples rare as they are of un bonded matching pairs later corroding .A connection to an external zinc , bonding would have extended the longevity

 

[Tranona]

Think what TTH ( through the hull ) fitting the stainless sea cock screws in to = dissimilar metal scenario + sea water . In which case the valve will need bonding .The SS cock might survive the lesser metal electrolytically ie the TTH fitting will start to fizz .
The pair better the same material .

1- Inside stuff bonded to an external zinc ( without any protection from other zinc )work’s protectively only if theres a seawater circuit , some electrical continuity.

Like the MAN , MTU manufacturers who do not use pencil anodes scattered around the engines ancillaries.Any dissimilarity between engine components ( the various wet sea water coolers ) is taken up by the zinc depletion instead of component.As long as there is continuity ie seawater left inside to form the other side of the circuit the earthing strap to the zinc ( see my pics in post # 6 )

2- With individual pencil anodic protected stuff eg your geny , air con chillers , and certain engine manufacturers you need to ( hassle as it is disassemble time and eyeballing ) regularly check and replace them if they are below a certain meatiness .
Some fresh water flushing if the item is standing for months years might be beneficial .More so the greater dissimilarity of the components or the tiny size in terms of longevity of the pencil zincs .

Fresh water flushing of the items mentioned in para 2 with be detrimental because you are diminishing the return side of protective circuitry back to the transom zinc .That’s why MAN , MTU don’t fit a bodgeflow TM systems…….and go for yrs decades without any engine corrosion issues clocking tens of thousands of hrs up .


For the OP try and get the TTH and valve the same materials * if not consider bonding to a external submerged zinc of suitable mass .


* Even then “ same materials “ is to get a neutral electrolytic potential .Fine in theory and exactly achievable if the stuff is poured out of the same melting cauldron at the foundry .
If the two component s are cast up from different melts ( highly likely) then there will be slight differences of potential .
Wether significant differences I very much doubt it .How ever not unknown and accounts for examples rare as they are of un bonded matching pairs later corroding .A connection to an external zinc , bonding would have extended the longevity

All just about completely irrelevant to the OP as his issue was a yellow metal elbow attached to a stainless pipe in the cooling water circuit for his A/C INSIDE the boat. An external anode will be of no use whatsoever. It has to be in the seawater that surrounds the metals in this case the cooling water circuit.

Basic lack of understanding of the principles of galvanic action.

 

[Kubcat]

Think what TTH ( through the hull ) fitting the stainless sea cock screws in to = dissimilar metal scenario + sea water . In which case the valve will need bonding .The SS cock might survive the lesser metal electrolytically ie the TTH fitting will start to fizz .
The pair better the same material .

1- Inside stuff bonded to an external zinc ( without any protection from other zinc )work’s protectively only if theres a seawater circuit , some electrical continuity.

Like the MAN , MTU manufacturers who do not use pencil anodes scattered around the engines ancillaries.Any dissimilarity between engine components ( the various wet sea water coolers ) is taken up by the zinc depletion instead of component.As long as there is continuity ie seawater left inside to form the other side of the circuit the earthing strap to the zinc ( see my pics in post # 6 )

2- With individual pencil anodic protected stuff eg your geny , air con chillers , and certain engine manufacturers you need to ( hassle as it is disassemble time and eyeballing ) regularly check and replace them if they are below a certain meatiness .
Some fresh water flushing if the item is standing for months years might be beneficial .More so the greater dissimilarity of the components or the tiny size in terms of longevity of the pencil zincs .

Fresh water flushing of the items mentioned in para 2 with be detrimental because you are diminishing the return side of protective circuitry back to the transom zinc .That’s why MAN , MTU don’t fit a bodgeflow TM systems…….and go for yrs decades without any engine corrosion issues clocking tens of thousands of hrs up .


For the OP try and get the TTH and valve the same materials * if not consider bonding to a external submerged zinc of suitable mass .


* Even then “ same materials “ is to get a neutral electrolytic potential .Fine in theory and exactly achievable if the stuff is poured out of the same melting cauldron at the foundry .
If the two component s are cast up from different melts ( highly likely) then there will be slight differences of potential .
Wether significant differences I very much doubt it .How ever not unknown and accounts for examples rare as they are of un bonded matching pairs later corroding .A connection to an external zinc , bonding would have extended the longevity

About a year ago we replaced the seacocks from bronze to stainless. I wonder if that hastened the demise of the brass/bronze fittings.

I did reattach the bonding after installation.

I also replaced the seawater pumps with bronze, also bonded. Attached to the seacocks by rubber hose.

Then we have more rubber hose, then the stainless pipe with brass/bronze fittings at each end, that disintegrated.

Then more hose and off to a stainless manifold, bonded, then more hose and to the air conditioners.

 

[Tranona]

You don't need to bond seacocks, either stainless or bronze in a GRP hull as they are not attached to any other metal underwater (conditions for galvanic action). Downside of using stainless is the possibility of crevice corrosion particularly in the threads. This is different from galvanic action and anodes wont do anything to help.

 

[jfm]

You don't need to bond seacocks, either stainless or bronze in a GRP hull as they are not attached to any other metal underwater (conditions for galvanic action). Downside of using stainless is the possibility of crevice corrosion particularly in the threads. This is different from galvanic action and anodes wont do anything to help.

Age old debate, that I don't want to re-ignite, but I just want to record that what you write isn't universally accepted or even "majority" accepted. There are TWO metals in a seacock, touching each other on the dry side, so the conditions for galvanic corrosion do exist. I always bond them, and the couple of boat builders I have worked with plenty bond them as standard practice. I don't want to debate it - just recording that there are 2 opposing PoV here.

 

[Tranona]

Age old debate, that I don't want to re-ignite, but I just want to record that what you write isn't universally accepted or even "majority" accepted. There are TWO metals in a seacock, touching each other on the dry side, so the conditions for galvanic corrosion do exist. I always bond them, and the couple of boat builders I have worked with plenty bond them as standard practice. I don't want to debate it - just recording that there are 2 opposing PoV here.

But bonding will not help. Thousands of production boats are built , many with several seacocks with no bonding whatsoever and don't see a rash of failures.

Failures are almost always the skin fittings or hose tails which are often made of brass which dezincifies (and an anode does not help). Ball valves rarely fail and if they do it is the mild steel spindle which rusts and the latest DZR valves have stainless spindles in DZR bodies which are similar potential so removing the weak point. As you say the spindle and the body are on the "dry" side so where is the electrolyte to create a galvanic circuit?

I know some boat builders persist in bonding, but the vast majority don't because it is simply unnecessary.

My current boat was built in 1979 and has no anodes except the one on the new feathering propeller. My last boat was 2015 and had one anode on the saildrive and one for grounding the 240v circuit. next time you go to a boat show have a look at sailing boats and count the number of anodes you see apart from on saildrives and maybe for the propeller on a shaft drive. None for seacocks.

Suggest it is a majority view not to bond skin fittings or seacocks to anodes.

 

[jfm]

As I said, I don't want long debate/thread drift and and am happy to agree to disagree. I merely want to record for the forum that the position you put forward isn't a settled point, so any reader can check for themselves.

Just to answer your Q "where is the electrolyte?" it's the seawater. This is relevant in 2 ways. First galvanically: the ball and the body of the seacock are from different metals, both connected electrically on the dry side, and both immersed in the sea - that's unarguable i think, though the quantity of galvanic current is pretty small. Second, electrolytically: if a DC pump/valve/sensor developed a failure in its 0v connection the motor/sensor could "earth" through the seawater being pumped which would in turn cause the seacock to be at a positive voltage relative to the sea and fizz away electrolytically if unbonded; if the seacock is bonded that won't happen.

Your "vast majority" view statement isn't verified. Of course the vast majority of boats (a different thing from views) are at the cost-caring end of the market so don't care to do anything to protect vs the two risks mentioned above. Counting boats doesnt give you a reliable answer. If you ask knowledgeable people "if money were no object and you were building/speccing the best boat you could, would you bond seacocks?" I suggest the vast majority view will be "Yes". Look at high-end and money-no-object boats: very many (and imho a vast majority, though I don't have data) have bonded seacocks.

 

[jfm]

That unit sat under his bunk kicks out up to 42000 btu and maintains an ice cool boat on 3 A - 5A .Silently.

Just to be clear, because you said "up to" , and not wishing anyone to be mislead, it does not kick out 42000 btu/hr at 3-5 amps. There is no a/c technology that does that. It needs 10-12 amps (at 230v AC) to make 42000 btu/hr. If it's pulling 3-5 amps, then it is making about 15,000 btu/hr not 42000. Not disagreeing that inverter motor a/c compressors are a good thing, but just correcting some simple maths/laws of physics.

 

[Portofino]

Just to be clear, because you said "up to" , and not wishing anyone to be mislead, it does not kick out 42000 btu/hr at 3-5 amps. There is no a/c technology that does that. It needs 10-12 amps (at 230v AC) to make 42000 btu/hr. If it's pulling 3-5 amps, then it is making about 15,000 btu/hr not 42000. Not disagreeing that inverter motor a/c compressors are a good thing, but just correcting some simple maths/laws of physics.

Correct it runs at partial power my 3-5 amps because it’s over specced size wise “ ice cool “
Sure berthing up when it’s 40 * C outside in a stinking hot marina on shore power I assume it is working hard for the first 30 mins .
When it’s like that ( for those not familiar with the Med scene ) ie even in the shade under a Bimini you only last 30 mins before having to jump into the sea to cool off , we start the geny on the run back to the home berth , while the mains are on , to start chilling the boat down .
Once tied up and plugged in using the 3 way switch I just move it from geny to shore and the AC carry’s on seamlessly .
Then I turn the geny off .

It means by then the cabins have cooled nearly “ice cool “= handy on those stinking hot days . Thus we only need 3-5 A from the dock to “ maintain “this .Which in untried visiting marinas or busy rammed marinas with dodgy pedestal’s the AC keeps running .Cos we are not asking the dock infrastructure for a lot of amps .



Additionally If you look at the pic there is a “ ECO “ button which iirc half’s the power consumption or maxes out at a very low amps ? Never use it as it’s under that bunk to access .

Agree with your writing on anodes thus far above .Again not wanting to start arguing, but the op has just stated a dissimilar metal thingy as I suspected with the skin fitting and SS valve . I have nothing more to add on this and won’t be drawn .
He hasn’t imagined or fabricated his pic in post #1 .