More Anodes and shorepower

[sr04]

I've been following the recent (and older) posts on anodes closely, as on lifting out our new to us fin keeler I noticed there were none fitted. She only has minimal electrical eqpt and was kept on a swinging river mooring previously.
I have fitted a fridge unit, small radar and chartplotter, and to compensate for the extra battery usage have fitted a wind generator.
I was going to fit a 12V 20A sterling charger/power supply for if we were in a marina and needed to run the fridge, but am now put off because of the worry of electrolosis/ galvanic attack, though I did read on another post that the alternator can produce the same effect as having shorepower connected.
As I have now fitted a wind generator am I increasing the risk of corrosion? And after visiting Anode manufacturers websites I have come to realise that the fitting of an anode on the hull or prop shaft is not straight forward as my marina is a Freshwater marina and I sail in saltwater, so does this mean I need to dry out the boat every trip so that I can fit the correct anode for the water conditions?

 

[fireball]

First question - is there any electrical connection between the battery -ve and any metal object in the water?
Check the propshaft/prop/pbracket, keel and skin fittings.

If there is and you are likely to spend some time in a marina on shore power then I would consider an anode.

If there isn't then you are only at risk from stray currents - this is current passing through the water that find an easier path through your boats metalic objects... this is one very good reason not to bond skinfittings together unless nessersary ...

For occasional visits to a marina I really woulnd't worry!

 

[sr04]

No there doesn't appear to be any electrical connection, there is no P bracket and the rudder is a skeg. I have been trying to find an anode on the engine but it doesnt appear that there is one. Its an MD11D and has been converted to indirect fresh water cooling so there will always be sea water in the engine/reverse gear which will be "connected" to the rest of the water in the marina, so the engine will effectively be underwater wont it??? and connected to the battery -

 

[fireball]

Electricity will take the least path of resistance - it is unlikely therefore to travel up the inlet pipe, through the water pump etc to get to your engine ... however, I would check to see if there is an anode on your engine - we have 2 on ours ... (Yanmar 2GM20 - raw water cooled)

 

[sr04]

If there is no other path, is up the intake not the path of least resistance??
The Volvo manuals and parts list show no anode for the MD11D or the MS2 gearbox. Anyone know better?

 

[Cloven]

We are in exactly the same situation of a freshwater marina with saltwater access. After much deliberation with MG Duff etc we have come up with the following solution which works well.

Hull and shaft anode are Aluminium. No point in fitting Zinc ones as in freshwater they would oxidise in a very short time and become ineffective and Magnesium ones would disappear in days when in salt water. Hull anode is bonded internally to P-bracket, engine & engine cooling water intake skin fitting. After one season, anode depletion is way less than 5%

When in the freshwater marina, the above Al anodes are backed up with a hanging magnesium anode and when in a saltwater marina/at anchor etc by a hanging zinc anode. I have set up an arrangement so that these hanging anodes can be connected to an external bolt (actually one that supports the wind generator pole) with a wing nut so they can easily be removed. Internally this bolt head is also bonded to the same points as above.

Out of interest, these hanging anodes are pretty expensive - £60 to £100 a shot but they do last a long time. I bought the Zinc one as such but for the magnesium one I bought a Mg hull anode from a narrow boat chandler for £16 and made up the hanging bit from some lightweight rigging wire etc.

The above should last for ages as when in the marina, the depletion of the Mg anode is very small and the Zn only comes into its own when at sea and at rest.

Hope this helps

 

[john_morris_uk]

Stop worrying!

Corrosion due to electrolysis (which is prevented or at least held at bay by sacrificial anodes) only takes place when two dissimilar metals on the nobility scale are in a conductive medium such as seawater AND are connected together electrically.

Some engines are not designed to have anodes fitted and last a lifetime without any problems. Our Volvo 2040 doesn’t have anodes - I don’t know yours personally, but it may not have or need them. Check with Volvo?

The problem with keeping your boat in fresh water and then moving to salt is that different anodes are recommended for both mediums. You could take advice from MG Duff, but remember that they are in the business of selling anodes!

The alternator DOES NOT have the same effect as plugging into shore power. The problem with plugging into shore power is that you can end up connecting (via the earth wire) to other boats near you and suffering from corrosion problems due to electrolysis. The simple answer is to fit a Galvanic Isolator in the earth lead. About £70 and simple to fit.

 

[VicS]

I think others have answered most of your questions.

I can confirm that the MD11 series do not have anodes fitted either to the engine itself or the gear box. Once converted to fresh water cooling the engine will be protected from corrosion by the antifreeze or inhibitor than you have in the fresh water side. There is no provision to fit an anode in the gear box cooler and I suspect the material used would not require one. The seawater side of the heat exchanger could have an anode though but again it depends upon the materials used as to whether it needs one.

The equipment you have fitted eg your windmill has no bearing on the need or otherwise to fit anodes.

If a shore-power connection left connected (not necessarily in use) for long periods then a galvanic isolator in the earth connection is a sensible precaution to guard against stray low voltage currents causing galvanic corrosion to underwater fittings especially excessive wastage of anodes.

 

[William_H]

You should have no worries with shore power charger provided you dn't leave it connected 24/7. So if you live on a swing mooring and use shore charger for just a few hours or even isolated days then you should have no problem.

There may be a misconception about galvanic isolator. No Gal isolator and no connection mains earth to ships negative/ engine water/ is the best isolation. But you need to ensure there is not an inadvertant connection ie charger body earthed to mains then also connected to negative output.
If you decide to connect mains earth to ships negative for safety from electric shock as done with ring mains sophisticated mains system then do so via a galvanic isolator. But I reiterate it won't do any good unless it is the only connection from mains earth to ships negative. good luck olewill

 

[VicS]

[ QUOTE ]
If you decide to connect mains earth to ships negative for safety

[/ QUOTE ] Rightly or wrongly the recommendation in the uk is that the shorepower earth should be connected to the ships earth, including the 12v -ve. Unless of course an isolating transformer is used.