Prop anode confusion - please help

[cpedw]

My Volvo saildrive prop needs a new anode every year - nothing left at the end of each season, even though the saildrive anode seems to be almost as new after 3 seasons in use.

My problem is where to get a replacement for Volvo part 3858399-R. There are 2 issues: the material and the supplier. I can find Aluminium parts generally cheaper but some e.g. Solent Anodes say suitable for saltwater, Yachtboatparts say Zinc has been replaced by Aluminium but SVB24 say Zinc for saltwater, Aluminium for brackish. Are these different aluminiums?

Another problem is the significantly cheaper options from places I've never heard of: jfedua at £14 for zinc or Waveinn £12 for a Tecnoseal brand but they don't specify what material. Does anyone have experience or views of these sites?

Thanks,
Derek

 

[vyv_cox]

Aluminium anodes are suitable for all waters. There has been considerable development of the alloy, that now has the same galvanic potential as zinc. I had an article on this in YM a couple of years ago, will put it on my website when I have a spare moment.

 

[Neeves]

There are 2 anodes on a sail drive prop, the segmented one that comes in 3 identical parts and the one that fits between the prop and sail drive leg. The one that fits to the leg can also come in 2 parts, or 2 halves.

If you buy the correct parts for your prop and leg they are not expensive and they will fit.

Based on the costs you quote they cost Stg1 per month but I think you are saying the sail drive prop lasts for 3 years, that's 35 piece a month and only the prop anodes cost stg1 per month.

Life is too short to worry - buy the genuine part and sleep well.

Jonathan

 

[Tranona]

Just a couple of observations. First the Volvo prop with its 3 little anodes is well known for the short life of anodes. This is for 2 reasons, first the material of the hub and blades is not the best and second the bulk and surface area of the anodes is small in relation to the "bronze" of the hub and blades. If it is any consolation at least they are cheap in comparison with anodes for other folding and feathering props. Second as Vyv says the move is toward using an aluminium based alloy rather than a zinc based one because it is cheaper, has the same potential and is equally effective in brackish water - important for Volvo with their sterndrives which are commonly used in such waters in their major market the US. On a saildrive there is no connection between the ring anode on the leg and the anodes on the prop and the former tend to last longer because the bulk and surface area are higher in relation to the small amount of unpainted and exposed aluminium of the housing. I changed the one on my 130 drive after 4 years in the water all the time because it was over 50% worn by weight, but would clearly have gone another 2 or 3 years.

 

[vyv_cox]

I have added an anodes page to my website at Anodes It explains the reasoning behind the move from zinc to aluminium anodes and gives a brief mention to magnesium.

 

[migs]

The small anodes on our three blade folding Volvo prop used to waste away entirely in a year, but last year I Veloxed the prop for the first time. This time, after one year in the water the anodes were only about 1/3 used up. Even better, there was almost no fouling on the prop and only a few tiny spots of Hammerite special metals primer showing though the Velox. A quick rub down and a recoat with Velox was all that was needed for another year. I agree with Tranona that the saildrive anodes don't seem to wear at all...

 

[oldgit]

A conumdrum. ?
Since the dawn of time the locals , both commercial and fishermen, have traditionally used zinc anodes, in the past even not unknown for the fishermen to resmelt recycle old anodes. They seem to have survived.

Our club moorings on the Medway would tend towards salt on the flood, brackish on the ebb and possibly neat fresh with groundwater from above the lock.
Fish which would be considered a freshwater species have been caught by net within a mile of our moorings (Pike) and salt water fish just below the tidal lock.
Some brave adventurous souls have changed to aluminum , but the majority have stuck to Zinc.
No real price differences from local smelters between zinc or aluminium.
No tales of disaster from either choice, so far .

 

[vyv_cox]

No real price differences from local smelters between zinc or aluminium.

The compositions of zinc and aluminium anodes are precise and complex, not something that local smelters are likely to deal with. There are good reasons for going to aluminium, which my article explains. We are currently in the change-over period but I suspect it may not be too many years before aluminium is first choice.