Excessive annode corrosion

[Miken]

Lifted the boat out yesterday, She has been on a mid stream pontoon in portsmouth Harbour since April, Very pleased with the amount of fouling on the hull (green slime only) having used Cruiser UNO for the first time. Not so pleased with the prop though used prop shield and the results were not good very heavily growth and lots of barnecles. Anyway the real issue was the state of the Annode. It's fitted with a Volvo Sail drive and folding prop. Annode was replacedwhen she was relaunched (It only has one ) and it's fitted between the Leg bearing housing and the prop (It's an early Volvo Folding prop so does not have any annode on the prop itself). The annode has almost gone completely is this right ?

She has only been connected to shore power on a couple of overnights in marinas.

There is a Grounding cable (Looks like it's been added)between the Engine block and the Keel but no annode on the Keel.

Is this amount of annode errosion normal or is something wrong

Any advice would be apreciated

Regards

 

[MarkGrubb]

That sounds normal compared with my experience. I use a single collar anode on the prop shaft immediately behind the prop. Its only there to protect the prop, there are no other metal fittings close enough for them to be protected: the surveyor said that anodes only protect metal that is within line of sight. If that's the case then strictly speaking I don't need the bonding across the prop shaft coupling, but its there anyway.

Put the boat in the water at the end of March, lifted it out for a week in July to do a quick job below the waterline and the anode was half eaten, so replaced it. Lifted it out again at the end of October for the winter and the new anode was half eaten by then. So an anode a year sounds normal. My boat sits on a mooring bouy in Poole Harbour.

 

[Bajansailor]

I wonder if it would be feasible / practical to install another anode next to / within 'sight' of the saildrive leg?
For example, one of those conventional anodes with two studs going through the hull, like the ones from M G Duff.

You could then connect it via a bonding cable inside the hull to the engine. Logic would dictate (?) that the rate of consumption of the special (read expensive) saildrive anode should hence be reduced (?).

 

[pvb]

[ QUOTE ]
You could then connect it via a bonding cable inside the hull to the engine. Logic would dictate (?) that the rate of consumption of the special (read expensive) saildrive anode should hence be reduced (?).

[/ QUOTE ]Don't think that would work - Volvo saildrives are usually electrically isolated from the engine.

 

[VicS]

Large area of a copper alloy prop, in close proximity to a small anode = rapid dissolution of the anode. That's the basic electrochemistry I'm afraid.
More anode surface area would give the appearance of helping but at the end of the day the actual amount of material lost from the anode(s) will be unchanged.

 

[oldsaltoz]

G'day Miken,
We have twin Volvo Sail drives and the anode next to the prop will just last a season, we have 3 bladed stainless steel props too.

Make sure the new screws that come with the new anode are tight and add a dob of loctite to the threads, also insulate the screws, we a drinking straw on the threaded section and a conical washer under the head or the screw, these anodes have a habit of coming loose.

If you can add another anode close to the leg, do so. Never use a copper based antifoul on the leg, it will eat it.

Avagoodweekend......

 

[Piers]

It's doing its job by being eaten away in preference to the other metal bits. If it's going quickly, add another or make the replacement larger. Don't be upset - it's only the anode!

 

[jb2006]

We are in the Hamble - Volvo saildrive - bronze folding prop - seems to be 2 saildrive anodes a year

 

[ytd]

we have the volvo saildrive with folding prop. It has the 3 little anodes on the prop as well as the collar anode on the shaft. The prop anodes never last the season but the collar one makes it through the year

 

[MAURICE]

Hi
I used to have a Bav 34 in Spain it had a Volvo 2030 with sail drive. I added a anode beween the prop and rudder connected to the sail drive. The engine is isolated from the drive so provided you connect to the sail drive it will be OK.
The anode was a Mcduff with two studs it lasted 3 years and was about half worn when i sold the boat. The ring anodes on the leg were lasting much longer probably two years worth.

Hope this helps