Electrolysis at Marinas?

[C08]

Having recently acquired a sailing club pontoon berth I am currently getting my head around pontoon matters as previously I have only had swinging or trot moorings, apart from marina visits.
I have noticed that some boat owners seem to leave their electrics plugged in when they are away from the boat although I am not sure whether there is stuff running such as de-humidifiers, pumps or heating. Anyway my question is how far away from a boat that has a water or earth leakage does my boat need to be to avoid electrolysis problems. My boat has only two "bronze" through hull fittings, head in and out but the rudder fittings are bronze. I do not have any anodes fitted.
I have heard a number of different discussions between other boaters debating whether this marina or that had a particular problem of corrosion caused by leakage from the pontoon electrics!

 

[KevB]

Firstly I believe you should always have anodes fitted regardless if you're onshore power or not to help stop interaction between metals. Secondly fit a galvanic isolator to help reduce any electrolysis whilst plugged in. Relatively inexpensive and easy to fit.

Having recently acquired a sailing club pontoon berth I am currently getting my head around pontoon matters as previously I have only had swinging or trot moorings, apart from marina visits.
I have noticed that some boat owners seem to leave their electrics plugged in when they are away from the boat although I am not sure whether there is stuff running such as de-humidifiers, pumps or heating. Anyway my question is how far away from a boat that has a water or earth leakage does my boat need to be to avoid electrolysis problems. My boat has only two "bronze" through hull fittings, head in and out but the rudder fittings are bronze. I do not have any anodes fitted.
I have heard a number of different discussions between other boaters debating whether this marina or that had a particular problem of corrosion caused by leakage from the pontoon electrics!

 

[maby]

And thirdly, what other boat owners do can only impact on you if you leave yours plugged into the mains supply.

 

[C08]

Firstly I believe you should always have anodes fitted regardless if you're onshore power or not to help stop interaction between metals. Secondly fit a galvanic isolator to help reduce any electrolysis whilst plugged in. Relatively inexpensive and easy to fit.

All my underwater fittings and rudder mounts are bronze so no disimilar metals so there should surely be no electrolyis due to disimilar metals. The proof of the pudding here is a 36 year old boat that has never shown any indication of electrolytic corrosion. Perhaps stray curents are a totally different mechanism and my questions are really to learn about that aspect of electrolysis and whether anodse help with stray marina leakages?

 

[C08]

And thirdly, what other boat owners do can only impact on you if you leave yours plugged into the mains supply.

Thanks for your reply but I do not understand your comment. Surely stray pontoon leakages from other boats may affect your boat whether or not you are plugged in.t Can you please clarify this?

 

[BoyBlue49]

A marina with shore power feeding electricity to boats that are in an electrolyte solution (sea water) will have the effect of being a giant battery.
All metallic fittings immersed in that solution will be subject to electrolysis. It is unlikely that your fellow berth holders are completely free of electrical leaks.
I suspect your previous moring has been in isolation where you have been free of the dreaded electrolysis, fit an anode just to be on the safe side.
To reduce your exposure, connect any electrical equipment directly to shore power rather than through the boat electrics, especially if leaving connected for any length of time.

 

[maby]

Thanks for your reply but I do not understand your comment. Surely stray pontoon leakages from other boats may affect your boat whether or not you are plugged in.t Can you please clarify this?

It's the interconnection of your boat with others via the earth wire that is responsible for the interaction. If your boat is not plugged up to the shorepower, it cannot be influenced by your neighbours. The problem, if there is one, is that some electical fault on your neighbour's boat results in a leakage current into their anodes or other metal work below the water line and this current is then transferred into your anodes with your earth connection closing the circuit. There can also be a problem if the shorepower earth floats up relative to the local earth potential because the cabling is long and possibly not in good condition - again a leakage current can be induced into the earth connection to your boat and through your anodes, resulting in increeased anode consumption. In both cases, it is dependent on your boat being connected to the shore power - if it is not, then the condition of neighbouring boats or the shorepower feed cannot impact on you.

 

[KellysEye]

>Firstly I believe you should always have anodes fitted regardless if you're onshore power or not to help stop interaction between metals. Secondly fit a galvanic isolator to help reduce any electrolysis whilst plugged in. Relatively inexpensive and easy to fit.

Agree. Stray current corrosion is normally caused by a bad earth on the marina power supply. Also a mix of salt and fresh water generates a stray current.

>Surely stray pontoon leakages from other boats may affect your boat whether or not you are plugged in.t Can you please clarify this? >Surely stray pontoon leakages from other boats may affect your boat whether or not you are plugged in.t Can you please clarify this?

I've never known that with GRP boats. There can be a problem if a Steel or Aluminium boat is parked nearby but there aren't many in the UK.

 

[Seajet]

This subject is close to my heart, the first ( galvanised and maintained ) steel keel on my boat corroded badly after about 20 years, and I found other boats and structures around there were suffering similarly.

I mentioned it to our moorings guy and a harbourmaster who told me the Marine Metalurgy dept at Portsmouth Uni' have a trials raft in langstone Harbour to investigate what seemed a local phenomenon.

I got onto them and they came like a shot to have a look; apparently there's something causing ' Accelerated Steel Corrosion ' in an area from Chichester to Portsmouth - so the navy are rather interested too.

They thought it might be ' steel eating microbes ' which excrete something which attacks steel, but agreed this wasn't the case.

It just happens my mooring is near a large marina and the power cables to Hayling Island.

I must say my new keel seems fine after 16 years, but I keep a careful eye on it, and note with interest the steel structures, buoys etc which used to be around are gone...

 

[Tranona]

Having recently acquired a sailing club pontoon berth I am currently getting my head around pontoon matters as previously I have only had swinging or trot moorings, apart from marina visits.
I have noticed that some boat owners seem to leave their electrics plugged in when they are away from the boat although I am not sure whether there is stuff running such as de-humidifiers, pumps or heating. Anyway my question is how far away from a boat that has a water or earth leakage does my boat need to be to avoid electrolysis problems. My boat has only two "bronze" through hull fittings, head in and out but the rudder fittings are bronze. I do not have any anodes fitted.
I have heard a number of different discussions between other boaters debating whether this marina or that had a particular problem of corrosion caused by leakage from the pontoon electrics!

If all your fittings are bronze and the fastenings are bronze then difficult to see how there can be any galvanic corrosion. It requires two dissimilar metals to be in contact with each other or the metal to be an alloy of dissimilar metals such as brass (copper and zinc). This does not seem to be the case with your fittings. However you may wish to think about your propeller and shaft if the latter is stainless.

 

[Andrew G]

As the proud owner of an aluminium 34’ yacht I am VERY concerned about people with power leads nearby. They can damage or sink my pride and joy – quite quickly. It’s against our marina rules to leave a mains lead connected when unattended - but it is not policed (I’m working on it). I have purchased a “Galvatest” (at vast expense) but by dangling it over the side I get a reading of any stray currents nearby – so far so good.
As to the OP’s question – I’d like to know too. Cheers Andrew

 

[C08]

If all your fittings are bronze and the fastenings are bronze then difficult to see how there can be any galvanic corrosion. It requires two dissimilar metals to be in contact with each other or the metal to be an alloy of dissimilar metals such as brass (copper and zinc). This does not seem to be the case with your fittings. However you may wish to think about your propeller and shaft if the latter is stainless.

Fortunately my prop is out of the water (OB) and raised when when leaving the boat.

 

[lustyd]

As the proud owner of an aluminium 34’ yacht I am VERY concerned about people with power leads nearby. They can damage or sink my pride and joy – quite quickly. It’s against our marina rules to leave a mains lead connected when unattended - but it is not policed (I’m working on it). I have purchased a “Galvatest” (at vast expense) but by dangling it over the side I get a reading of any stray currents nearby – so far so good.
As to the OP’s question – I’d like to know too. Cheers Andrew

I don't see how it makes a difference whether the boat is attended or unattended, surely if the boat next to yours is inhabited 24x7 and therefore plugged in it would be just as bad. I'm also unsure how you'd go about policing this without annoying boat owners. I would certainly not be happy if someone came banging on m coachroof at 7am to see if I'm on board, and probably less happy still if someone unplugged my boat without permission.

 

[maby]

I don't see how it makes a difference whether the boat is attended or unattended, surely if the boat next to yours is inhabited 24x7 and therefore plugged in it would be just as bad. I'm also unsure how you'd go about policing this without annoying boat owners. I would certainly not be happy if someone came banging on m coachroof at 7am to see if I'm on board, and probably less happy still if someone unplugged my boat without permission.

Fully agree - if our marina tried to ban leaving the boat on shorepower full time, I would be looking for another marina.

 

[vyv_cox]

There does seem to be an awful lot of confusion about corrosion in marinas. The basic truth is that if you are connected to the mains by a three-wire cable, one of which is the earth, then another boat similarly connected could form a cell with your boat. Both earths would need to be connected to the water and any underwater metallic components in the boats would also need to be connected, for example by having seacocks etc. bonded, engine, shaft and prop all earthed and suchlike. If all of this is true then there is a risk that a metallic fitting at the least noble end of the galvanic table could be corroded trying to protect something at the noble end. A galvanic isolator disconnects the earth if it sees current at a certain level, indicating that electrons are being passed.

The aluminium boat is a particular problem as an earth connection would almost certainly cause the hull to corrode. A galvanic isolator should prevent this but it might be better not to earth the mains supply to the boat. I guess that this problem is not unknown to the owners of aluminium boats, and no doubt there is a specialist solution that I am not aware of.

So far as 'stray currents' are concerned, what is the source of these? It is difficult to believe that electrons are buzzing about in the water looking for a home and I suspect some kidology.

 

[maby]

There does seem to be an awful lot of confusion about corrosion in marinas. The basic truth is that if you are connected to the mains by a three-wire cable, one of which is the earth, then another boat similarly connected could form a cell with your boat. Both earths would need to be connected to the water and any underwater metallic components in the boats would also need to be connected, for example by having seacocks etc. bonded, engine, shaft and prop all earthed and suchlike. If all of this is true then there is a risk that a metallic fitting at the least noble end of the galvanic table could be corroded trying to protect something at the noble end. A galvanic isolator disconnects the earth if it sees current at a certain level, indicating that electrons are being passed.

The aluminium boat is a particular problem as an earth connection would almost certainly cause the hull to corrode. A galvanic isolator should prevent this but it might be better not to earth the mains supply to the boat. I guess that this problem is not unknown to the owners of aluminium boats, and no doubt there is a specialist solution that I am not aware of.

So far as 'stray currents' are concerned, what is the source of these? It is difficult to believe that electrons are buzzing about in the water looking for a home and I suspect some kidology.

The cell effect of bonding two boats together is one problem - you are effectively letting your anodes be consumed in orderto protect someone else's boat. I'm not convinced that that is the real issue - most boats in the marina are going to have anodes, so all you are really doing is pooling them into one big galvanic protection pool - in theory it should all balance out reasonably well and there's no reason for anyone's anode to just fizz away. I think the bigger problem is when an electrical fault somewhere in the marina actually injects current into the network of devices. That might be on another boat or even somewhere in the marina infrastructure - don't forget that the earth wire coming into your boat is probably many tens of yards long, possibly more, back to the mains connection point where it is bonded to earth - and that earth is exactly that - "earth", not "water" - plenty of scope for differences in potential. Unlike the first case that you are referring to, which is just sharing your anode with a few neighbouring boats, this scenario could be actively pushing significant currents through your anodes and other under water metalwork.

 

[KellysEye]

>So far as 'stray currents' are concerned, what is the source of these?

As I said earlier stray current corrosion is caused a bad earth on the marina shore power. It is also caused when salt water mixes with fresh water. I would suggest every boat fits a galvanic isolator.

>The aluminium boat is a particular problem as an earth connection would almost certainly cause the hull to corrode.

We had a steel boat and the earth did not cause corrosion when we didn't have a galvanic isolator. I subsequently fitted one.

 

[vyv_cox]

Please explain. I have loads of electrical items that have no earth at all. Where does the stray current come from? How does mixing salt and fresh water generate current?

 

[lustyd]

How does mixing salt and fresh water generate current?

This would be amazing, water makers could power themselves and become a perpetual motion device

 

[vyv_cox]

I think the bigger problem is when an electrical fault somewhere in the marina actually injects current into the network of devices. That might be on another boat or even somewhere in the marina infrastructure - don't forget that the earth wire coming into your boat is probably many tens of yards long, possibly more, back to the mains connection point where it is bonded to earth - and that earth is exactly that - "earth", not "water" - plenty of scope for differences in potential.

I don't suppose every boat or marina power point has an installed circuit breaker but surely the majority do? An electrician friend tests them by touching the bare ends of wires to ensure the breaker trips, indicating to me that a relatively high resistance short will cause one to open. So I'm not too sure about your 'electrical fault injecting current into the network'.