Anode wastage

[harstonwood]

Folks
Starboard leg ring anode is wasting significantly quicker than port leg. only about 20 % left, boat went into water beginning of March ( leg is VP290A on AQAD41B)

Have recently decided to disconnect shore power when away, hoping this will help. Normally leave batteries live.

Any thoughts as to reason, and how I could improve matters? If I put another sacrificial anode in water, where should I connect it?

All advice gratefully received

Ta HW

 

[Spi D]

Disconnecting shore power normally helps greatly on boats without separating power transformer.

Even helps the galvanic corrosion eating all other metal parts in connection with water or onboard power.

 

[Greg2]

First thing I would say is that the anode is doing it's job if it is corroding but it is strange that the other leg isn't wasting at the same rate. Worth checking that both are properly bonded to the legs e.g. a combination of anti-foul on the leg and grease on the securing bolts could isolate the anode.

On our last boat we had issues with props corroding (VP duo props) - turned out to be a faulty shore power cable that was causing the problem so worth taking the connectors apart to make sure that all is in order. We found that the live cable had some insulation missing and it was making contact with a bolt.

Other things we did along the way were to install a galvanic isolator (should reduce anode wastage), fit an additional bar anode to the transom between the drives (wired to the transom shields inside the boat - check that you have a circuit to ensure that it will work) and change to aluminium anodes. The later are claimed to last longer and work in fresh and salt water - our experience was that they did last longer. Think they were 'Red Spot' anodes and i would recommend them.

Personally I would check the shore power cable, check the bonding of the exiting anodes, install a galvanic isolator and switch to aluminium anodes. The additional anode may prove unnecessary so I would leave this to last.

It is worth saying that corrosion in marinas is a bit of a dark art, very complicated with lots of different theories and not many definitive answers (I did a lot of research in trying to solve our problems). It is entirely possible that the issue is not with your boat but with another boat in the marina. If you leave the shore power plugged in your boat is effectively another cell in a big battery so if there is a problem on another boat but yours is the weakest link then you will get the corrosion. Fitting a galvanic isolator effectively removes you from the circuit.

Finally, if you anode only has 20% left then it needs to be changed now.

Hope this helps.

 

[Spi D]

Agreed.
The large companies that work on galvanic corrosion solutions for commercial vessels, demand a huge deposit before even beginning to investigate.

It sure is a good idea to connect to shore only when needed.

 

[stuartwineberg]

Disconnecting shore power

I am sure there are proper experts on the forum who will correct or reinforce this but my understanding is that the reason for keeping the shore power on is to keep the main batteries under charge. If you let them dip down they will sulfate and have a much shorter life. Disconnecting your battery charger might solve the anode problem and create another one with the batteries.

 

[Spi D]

More philosophies about batteries, but if you disconnect on the main switch batteries should never drop between uses.

Keeping a constant charge at least calls for a so called intelligent charger as the batteries will otherwise suffer from the constant current, even after reaching 100%.

If you disconnect the batteries (both pos. and neg.) while charging constantly, they will have no connection aboard and the galvanic issue will not arise.

If you really need constant power for pumps etc., a separating transformer will be your security against unknown parameters in shorelines etc.

 

[harstonwood]

Many thanks for the replies thus far, I hope the anode will last until I lift out, first week of November. Will check wastage next week.

Have checked cable.........all ok

Only one set of batteries is charged with shore power (port eng and domestics), the starboard batt isn't.

I think the bilge pump is hot wired, but will check next week.

As a temp measure, I was considering an anode on a wire, but not sure best place to connect? shield/leg or engine?

Agree with comments about Aluminum anodes

Pwllheli is a difficult marina, as it has a river flowing through, so depending on where berthed, makes a diff. Some boats use magnesium, some zinc, some Ali

However as Pwllheli translates to salty pool ( from welsh) willl prob stick to zinc!

Boats eh!!

 

[Spi D]

Galvanic corrosion would but even Sherlock Holmes against the wall. If you consider water a transferring element, all that connects to the engine, drive or any seawater pump will be affected. Add to his all wired components..

Although separate battery banks there may well be a common ground somewhere.

Rule is to replace anodes at 50%. At 20% left visible the actual stuff left by weight may be close to zero.

Solar panels for slooow battery maintenance are becoming both better and cheaper. Lasts for many years and might cost less than one liftout and new anodes.

 

[RIN]

I am sure there are proper experts on the forum who will correct or reinforce this but my understanding is that the reason for keeping the shore power on is to keep the main batteries under charge. If you let them dip down they will sulfate and have a much shorter life. Disconnecting your battery charger might solve the anode problem and create another one with the batteries.

This is the problem I had with my batteries. The charger is not a modern one so I put a timer on the shorepower and leave it giving 15 mins charge 3 times a week.

As Greg2 did, I fitted a galvanic isolator as there was going to be a permanent earth connection.

I too fitted aluminium anodes but I have to say that I checked them this week and they were seriously worn. They were fitted at the relaunch on 5th May so that is not even 4 months! I was hoping to make it to November at the least.

Anyone else got experience of Aluminium anodes? These red spot ones http://www.force4.co.uk/6307/Performance-Metals-Aluminium-Anode-Kit---Volvo-Penta-Duo-Prop.html

 

[GrahamHR]

No experience with Aluminium anodes, I use zinc ones (boat is in salt water for 6 months each year ). Previously, the anodes were about 50% gone at the end of each season. My current boat has VPs Active Corrosion Protection system fitted (similar to Mercathode). Now my anodes last typically around 3 seasons before they are anywhere ner 50% gone (no, it doesn't mean that they are not working: I haven't painted them, continuity is checked before each season and I don't have corrosion of the drive ). Both boats had the same DPS type drive and stainless props. The ACP system seems to work. It has an indicator on the control box to tell you how hard it is working (1 green LED working normally, green and red LED working at maximum -maybe something wrong, red LED inadequate protection). It's permanently wired to the batteries, with only the green LED on it is drawing less than 3mA, so little or no effect on the charge.

If my next boat does not have one, I'll be fitting one.

Graham