Corrosion, sacrificial anodes and galvanic isolation.

[bluetooth]

Evening All.
I know this topic has been covered so often but there has been a notable change in my anode corrosion this last 9 months I’m keen to be on the ball! After 9 years of mooring in the same berth the anodes on my trim tabs and outdrive are usually 35-45% corroded and I have often thought I could get 2 seasons out of them. I never do and change each year regardless.

Unfortunately I damaged a drive last May (previously posted here) and when the boat was lifted it was noted that the 2 month old new anodes had already corroded pretty significantly so I replaced them again. I never left the boat plugged into shore power that much and I was then even more careful except for over xmas when the heaters and dehumidifier and battery chargers were on (but no more than previous years).
The boat was lifted again last week and the anodes look 75% worn! So what to do now...

The marina is adamant that their electrics are fine – as other berth holders have also reported problems.
My boat was continuity tested last July and found to be in order.

So in my humble understanding of galvanic corrosion:
- No matter what you do the metals underwater are at risk of corrosion with salt water being the electrolyte
- The anodes are corroding and so doing their job but what if they corrode more and faster than sacrificial material exists. Should I add more anodes ?
- The shore power can be plugged in to the boat to charge the batteries but can also be plugged in bypass main electric board to power the heater/dehumidifier but not the batteries. I am alternating this option already depending on outside temperatures with my my rationale being cold weather can flatten the batteries
- My neighbours !! Is there a possibility an adjacent boats electrics could be at fault and increase the corrosion circuits? Should all boats have electrical tests of compliance before they can plug it. Is this something the marina should oversee given they all charge an ‘admin’ fee anyway to “read the meter”.
- I’m aware of galvanic isolators but do they really make a difference. Have heard that Galvanic isolation will only work if the stray current is below 3.7 volts if it is greater then the current will find the weakest link and the galvanic isolater is not effective. Any recommendations ?

https://www.safeshoremarine.com/assets/pdf/details/2.pdf
https://www.safeshoremarine.com/assets/pdf/InfoPack.pdf

There is no doubt something has changed affecting my anodes.
What else can or should I do ???

Many thanks, Simon

 

[QBhoy]

Hi
What outdrive do you have ?

 

[Portofino]

Somthing has changed .

Neighbours possibly current leak or depleted there anodes so yours are helping them now ( wasn’t before )

Or / and the “ cathode “ your metal you are protecting has got larger for your anodes in terms of size exposed. The drive paintworks integrity ? Not as good now ( age or repair/ repaint ) so anode sees a bigger cathode and has a party .

It’s a case of getting the balance of anode vs cathode sizes right so the depletion rate of the anode(s) fits in with your timescale.

 

[gjgm]

You should tell the marina to start a register of where people are reporting an issue, and you should demand to be moved to another berth.
Fit an isolator, not 100 pct cure, and yes, bypass the boat electrics with a dedicated lead to dehumidifier. I don't really get why people need to be charging batteries non stop for months on end, or powering dehumidifier all over winter. Half a day once a month ought to be enough,in my view if you are away from the boat anyway, assuming your boat is not actually a swamp and your batteries knackered.
So, I would move berth and get the boat tested again with the probe over the side in its new location- at least you will then know if you have the correct amount of an anode . There is not necessarily only a single cause. I think on drives in a marina, 6 months for the anodes is possibly almost a norm, these days.

 

[kashurst]

+1 something has changed. Assuming the marina electrics are OK (have they had any work done recently?) it's probably a near by boat with a problem - do you have new neighbours?
Definitely fit a galvanic isolator - it will prevent any external galvanic related electrical current (amps) travelling on the shore power earth connection unless the electrical potential (volts) is more than 1.2 Volts. This will prevent any neighbouring boat or marina component utilising your anodes. I have used the SafeShore unit on previous boats.

Check that none of your own wiring/switches are sitting in a puddle of water inside the boat.

 

[Scubadoo]

I had a similar problem, years of no problem at the same berth, then one year my bar anode was gone and the prop ring anode was just about hanging on. It cost me two trim rams!

Anyway, I noted the marina was rebuilding the crane lifting berth and large anodes being changed etc, also a new boat owner opposite liveaboard said he had electrical problems. Could not prove source of issue although marina did check electrics etc. I could see voltage leakage with a voltmeter (very small reading), so in the end fitted galvanic isolator, fitted two bar anodes, added an extra button anode to drive leg, and a triangle anode to the drive arm. Since then no problems and anodes last approximately two years(50% spent) although I always annually replace the prop ring anode.

I guess what I am saying it is hard find the exact issue, but took action to improve protection.

 

[Momac]

My near neighbour at the marina just had his boat lifted and his anodes were almost completely gone, as in nothing left other than some white crust.
Not surprising really as his boat not been out for an outdrive service in about 5 years . (He is from Yorkshire).
If you have a marina neighbour like him that would explain it.

 

[superheat6k]

Resolving your issue could be very difficult. Stray current corrosion is normally far more vicious, especially if it is a high voltage AC leak travelling through your binding circuit.

A GI will at least disconnect your boat from galvanic currents from any others nearby causing an issue via the shorepower Earth, but this won't resolve stray current or other issues.

On my last boat I had to deal with the following after I bought it until eventually the problem was resolved to an acceptable wear rate ...

1 Fitted a GI.
2 The reverse live neutral indicator was found disconnected, so I then reconnected it, but as the prior owner had fitted an LED and not a neon, it was effectively bypassing the GI along the neutral line. So
I disconnected the indicator and bought a polarity test plug to check any shorepower supply I might plug into.
3 Rewired two shorepower cables which the reconnected LED showed to have live neutral cross overs.
4 Replaced faulty bonding cables to the Port anode, which had caused one prop nut to dezincify.
5 Open +VE test showed I had a circuit to negative even with everything off. Disconnect the + VE terminal then with all services off but essential maintained circuits still on in standby (bilge pumps) measure the voltage between the terminal connector and battery post. It should be zero, any voltage at all means something is allowing DC current to flow. In my case a flappy type bilge pump switch, allowing DC directly into the trace level of salty water laying in the bilge and thence into the bonding circuit. This made the bonding circuit have a slightly raised potential just like a galvanic current would cause, with the result the anodes would then merrily fizz away. I fitted a Whale solid state switch, which resolved the problem. I now do the +VE open test every year.
6 I made a dangling anode from two old bar anodes bolted together with a stainless riser cable (NB only connecting to copper above the waterline), this was permanently wired to the GI boat side, so when using the boat the anode and its cable would be coiled up in a bucket in the same locker. I suspected the large steel pile by the boat might be attracting stray currents, so I used to dangle this by the stern gear to the pontoon side of the boat to take some of the zinc hit. It used to measure almost 1 volt between the wire and GI connection when disconnected, so was definitely picking something up.

Nigel Calder provides an excellent explanation of electrical corrosion in his wonderful tome Boatowners Mechanical and Electrical Manual.

 

[bluetooth]

My near neighbour at the marina just had his boat lifted and his anodes were almost completely gone, as in nothing left other than some white crust.
Not surprising really as his boat not been out for an outdrive service in about 5 years . (He is from Yorkshire).
If you have a marina neighbour like him that would explain it.

Great - I'm on this
Many thanks

 

[bluetooth]

Resolving your issue could be very difficult. Stray current corrosion is normally far more vicious, especially if it is a high voltage AC leak travelling through your binding circuit.

A GI will at least disconnect your boat from galvanic currents from any others nearby causing an issue via the shorepower Earth, but this won't resolve stray current or other issues.

On my last boat I had to deal with the following after I bought it until eventually the problem was resolved to an acceptable wear rate ...

1 Fitted a GI.
2 The reverse live neutral indicator was found disconnected, so I then reconnected it, but as the prior owner had fitted an LED and not a neon, it was effectively bypassing the GI along the neutral line. So
I disconnected the indicator and bought a polarity test plug to check any shorepower supply I might plug into.
3 Rewired two shorepower cables which the reconnected LED showed to have live neutral cross overs.
4 Replaced faulty bonding cables to the Port anode, which had caused one prop nut to dezincify.
5 Open +VE test showed I had a circuit to negative even with everything off. Disconnect the + VE terminal then with all services off but essential maintained circuits still on in standby (bilge pumps) measure the voltage between the terminal connector and battery post. It should be zero, any voltage at all means something is allowing DC current to flow. In my case a flappy type bilge pump switch, allowing DC directly into the trace level of salty water laying in the bilge and thence into the bonding circuit. This made the bonding circuit have a slightly raised potential just like a galvanic current would cause, with the result the anodes would then merrily fizz away. I fitted a Whale solid state switch, which resolved the problem. I now do the +VE open test every year.
6 I made a dangling anode from two old bar anodes bolted together with a stainless riser cable (NB only connecting to copper above the waterline), this was permanently wired to the GI boat side, so when using the boat the anode and its cable would be coiled up in a bucket in the same locker. I suspected the large steel pile by the boat might be attracting stray currents, so I used to dangle this by the stern gear to the pontoon side of the boat to take some of the zinc hit. It used to measure almost 1 volt between the wire and GI connection when disconnected, so was definitely picking something up.

Nigel Calder provides an excellent explanation of electrical corrosion in his wonderful tome Boatowners Mechanical and Electrical Manual.

Wow - that's some remedial action
Cheers

 

[bluetooth]

I suspected the large steel pile by the boat might be attracting stray currents, so I used to dangle this by the stern gear to the pontoon side of the boat to take some of the zinc hit. It used to measure almost 1 volt between the wire and GI connection when disconnected, so was definitely picking something up.

Did you know whether the steel pile was linked/earthed to the pontoons ?
My marina are interested to know
Many thanks