Rapid anode wear?

[GDPR150987]

3 months ago I changed the prop anode and hull anode. Used the same MgDuff stuff I do every year. Each year I change them not because they have worn down more part of my yearly service routine. I could have probably got another year out of them in the past but they are cheap so didnt mind changing them.

However 3 months ago put new ones on, put boat in water for 7 weeks (marina), left the shore power on with fridge and battery charger on, took boat out of water and yikes 50% already gone! Never seen that before so took a crash course in anodes for dummies. Decided to buy a galvanic isolator with status alert warning lights AC & DC. https://www.ebay.co.uk/i/2919000242...3D710-134428-41853-0%26rvr_id%3D1242722921456

Put boat back into water (diffrent pontoon this time) again for 2 weeks and plugged in new GI to shore power. It did not indicate any faults so I was happy in thinking no issues with my electrics. Just as a precaution I did not connect upto shore power this time for the 2 weeks.

Just pulled boat out yesterday and now both anodes are almost down to 25%!

Things I have changed to boat electrics this year are Ive brought 2 new house batteries (only 1 originally) and connected them and the engine battery to a smart meter to show the state of charge etc. Its wired as per instructions from smart meter.

So any ideas why the increased anode wear is now taking place. At this rate I will probably be changing the pair 3 or 4 times a year compared to the once a year.

Thanks in advance

 

[jrudge]

Some questions

1 whilst not turned on was the shore power physically connected ?

2 are any other noticing any change ?

3 you now seem to have three batteries in parallel is that correct engine and 2 new house. If not in parallel how are they connected

4. When you left for 2 weeks were the batteries on for any reason or physically disconnected ?

I am no expert in anodes. I understand the theory just fine, but in essence the anodes are finding a cathode I pass a charge and he shore power is he most likely candidatec

 

[kashurst]

+1 what Jrudge said
are you close to a steel boat or any metal piles or metal work in the water? If you have a galvanic isolator fitted correctly and your anodes are still fizzing away you are indirectly protecting another big lump of metal
get the shore power connection checked out - especially the earth - sometimes its not "earthed" properly

if your seacocks are bonded check the quality of the connection and make sure you do not have a current leak from a bilge pump switch or similar.

with the shore power connected measure the voltage across the galvanic isolator - use AC and DC measurement. It should be zero in both modes. If more than 0.5V the shore power is iffy.

If not sure what to do disconnect shore power and isolate your batteries so everything is off. the anode erosion should stop then

edit check your galvanic isolator is working use a multimeter to check diode voltage drop in both directions

 

[GDPR150987]

Thanks jrudge

1. Shore power was physically disconnected

2. Not sure as when I asked the marina manager he was quick to say all shore power had been recently tested and was fine

3. 4 batteries, 1 engine, 2 house and a bow thruster. Engine battery is wired in to just engine and has its own dedicated isolator as has the bow thruster batt. The 2 house batteries again have their own dedicated isolator and are both connected in parallel together.

4. All batteries were isolated. The house batteries have an Eber connection which remains live and is also connected to smart meter. Engine batt has just smart meter live connection.

Hope that all makes sense

 

[GDPR150987]

Thanks Kashurst,

The GI is an inline version that plugs into end of shore cable and then into boat connection point. I put a link in in my OP to the type of GI I brought. Not sure how I would carry out the voltage check with this type of GI. I was hoping if there was any issues then the status system built into the GI would have alerted me?

Seacocks are not bonded but the P bracket is and so is a section of the drive shaft.

In the last 2 weeks in the marina the boat batts were all isolated and boat not connected to SP. Anodes still wearing fast.

 

[superheat6k]

I would turn off all 'normally turned off when boat is left' electrical services.

Disconnect the 12 v supply +VE cable from each battery bank.

Measure the voltage between the terminal on the cable and the battery post from which it has just been disconnected.

If the reading is anything other than 0 volts start finding out where the circuit is being created, starting with the bilge pump float switches.

If everything is turned off then there should be an open circuit down the cabling from these connection points. Therefore there should be no voltage difference to measure.

Even a small voltage will allow vastly more electrical energy to dissipate, and if this finds the bonding circuit and the anodes it can waste away significant quantities of zinc, and once that has gone the other underwater metalwork can start to follow it.

Don't ask me how I know about this !

 

[GDPR150987]

Thanks superheat. Appreciate the help.