Volvo Prop Anode question

[mattnj]

Hi,

Volvo 290 leg with stainless props and the behind prop anode, problem is that it had almost completely dissapeared and was new a the beginning of April this year. Is that a normal rate for one to corrode? Do i just need to get use to changing it 3 times a year or am i likley to have a problem elsewhere?
I have a galvanic isolator fitted already.
Can i fit more anodes? if so how, where and what type?
Are the Active corrosion prevention systems any good that Vovlo sell?
Can i buy a big fat anode and stick it in the water on a bonded wire when i am not on the boat? Or will that make it worse?

Thanks in advance.

Matthew

 

[spannerman]

We normally fit two transom anodes when SS props are used but you will need longer SS bolts, they do erode quickly with this type of prop as they act as huge cathodes, but its cheaper than a new drive.
The galvanic isolator just ensures that your shore power doesn't contibute to the problem, not sure if the Volvo Active system is good or bad, have seen it on a few engines I have installed and not heard anything negative about them.
I can't see that extra anode on a wire will make it any worse as the more reactive metal (zinc) you have the less electrolysis will be interested in your aluminium drive.

 

[mattnj]

Where exactly do you fit the anodes? On the leg itself or on the fiberglass part of the transom and bond it to the leg?

Matthew

 

[spannerman]

At the lower edge of the transom plate in front of the leg there is a large rectangular block anode, this is the one we piggy back an extra one to.

 

[mithril]

Re: Volvo Prop Anode question No 2.

I have similar problems with my anodes, they last 4 months. Difference is, my saildrive leg is fully isolated from internal electrics and has its own anode which lasts a couple of years, the prop is isolated from the leg so has its own anodes, 3 of then around the props hub. The anodes are obviously (?) protecting the prop but why has Volvo sized then to waste in 4 months. Realisticaly, Volvo is not that stupid so why do they waste away?

 

[ms1]

Re: Volvo Prop Anode question No 2.

Presumably you have anodes made of the correct material.
Magnesium for fresh water, Zinc for salt ?? I have also found that pattern anodes do not perform quite as well as good quality branded ones.
I would think at that rate of "sacrifice" the anodes would be absolutely fizzing .... I would suggest that something is not right. It could be a prob that you have .. it might be a prob on a neigbouring boat that is finding is way to earth through shorepower hook up to your ground system.
there is a view that all mains earthing should be connected to boat ground. There is an alternative view that suggests thats someone elses problem (or a marina wiring prob) might find its way to earth via your anodes.
You might be able to slow down the destruction of your anodes by fitting couple of 'danglies' .. extra anodes hung over the side and wired up to the inside of the outdrive transom shield.
If you try a dangly you can introduce a voltmeter and check what sort of voltage is evident ... then you can make changes .. unplug things etc and see what happens to the voltage by way of looking for a fault.
My experience suggest that not many electricians really know much about this matter. You could aleays talk to M G DUFF the anode experts.

 

[TonyS]

Re: Volvo Prop Anode question No 2.

You should have started this as a separate topic. You have added a sail problem with saildrive to a stinky problem.
Having said that I experience the same and have discussed it with Volvo who just say it depends on the boat and the environment. Some last a year and some 1 month. Mine last about 6 months but I was surprised today to see the anodes still there as I changed them before we went to S. Brittany in May. Normally, as in May, there is nothing left but that was after a year. If you want to read a big discussion look at the Halberg Rassey forum http://www.hroa.co.uk/discus/ and then at Saildrive prop -- rapid zinc erosion http://www.hroa.co.uk/discus/messages/1/63.html?1076532640

 

[mithril]

Re: Volvo Prop Anode question No 2.

I take your point Tony, exuberance I guess.

Thanks for the HR link, it seems many share the problem.

Dawing my own conclusions I believe the old solid hub props relied on the saldrive anode, plus any other connected hull anodes. But the new rubber hubs (so isolated from the saildrive) rely on 3 small prop anodes. THESE ARE SIMPLY INADEQUATE FOR THE TASK. The post above outline various sensible sticking plasters to mask the problem but the anodes are not big enough.