Volvo prop anodes

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jackho

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Had 3 blade folding prop fitted two seasons ago. Changed saildrive anode at same time.
Boat kept in river (fresh water) when not at sea.
Lift out every second year. This year when lifted the the 3 prop anodes were "gone" except for powdered remains around the retaining screws. (Prop on close inspection looks ok)
Saildrive anode as is usual was hardly marked.
I believe I have read of similar incidences on this or other forums so respectfully await your comments, technical theories , recommendations and any other advice.

Jackho
 
Have a look on www.zincsmart.com There is loads of info on what type of anode you should be using in your circumstances.

They are also a very good source of resonably priced anodes, especially the more specialist ones.

No connection other than a satisfied customer etc, etc
 
Also information on MGDuffs website http://www.mgduff.co.uk/

Basically zinc anodes are suitable for salt water use only

Aluminium is suitable for salt or brackish water

In fresh water these anodes become passivated so magnesium must be used.

Magnesium however is too reactive for salt or brackish water use.

Something of a problem then for boats moving regularly between salt and fresh water.

Prop anodes are relatively small compared with the surface area of a propeller so cannot be expected to last long.

Don't let the anode on the sail drive leg become depleted. Be sure there is a good electrical contact with the leg.
 
We have Volvo 3 blade folders on our Broadblue 42 and the three part prop anodes last 6 months at best, the saildrive leg anode shows very little erosion and gets changed about every 4 years.

Our saildrive legs, gearbox, props etc are electrically isolated from any of the boats electrical system and earth connections. This is now standard practice for Volvo by means of insulating spacers and washers bolting the gearbox to the engine, together with the rubber cush drive to provide the electrical isolation. Hence it may not be a good idea to say the saildrive leg should be earthed, it probably should NOT be.

As already said the prob blade area is quite large compared to the anodes so life expectancy for the anodes is never going to be very long. We spend summers cruising and anchoring with winters in marinas but the anodes seem to last exactly the same length of time so stray electrical currents in marinas do not seem to make any difference.

It is not too big a problem for us because I can change the anodes while we are in the water so no lift out required, it may be more of an issue on a mono if you can't dive / snorkel under the hull so easily.

I have also recently tried the "pattern" anodes supplied by Keyparts instead of the Volvo item and they did not seem to last as long as the Volvo anodes, we got about 4 1/2 months from the patterns as opposed to 6 months from the Volvo anodes. No idea why this should be the case but that is our experience and I will stick with the Volvo anodes in future because they are only about £4 per set more expensive.
 
My VP three blade folder spends six months afloat in fresh water with usually about 3 expeditions to sea of about 3-4 week duration plus the odd weekend or daysail so magnesium is not an option. The prop anodes are zinc and degrade effectively and are almost gone when the boat is lifted ashore. The saildrive anodes are also zinc but passivate rapidly so are supplemented by a zinc hanging anode which is cleaned with coarse emery paper ever couple of weeks. I presume that the reason that the prop anodes degrade as expected and the leg ones do not degrade at all is because the rapid rotation cleans the surface.
So far (five years) the prop and leg look sound. The leg has never been antifouled but is coated with lanolin wax which is replaced every two to three years, the prop is polished as Propshield only last a few weeks on it.

If I had a conventional shaft with therefore a wider choice of anode and so did not have to use modified VP saildrive anodes (rope cutter) I would choose aluminium anodes which work well for the boats which are kept near mine.
 
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crisjones said:
I have also recently tried the "pattern" anodes supplied by Keyparts instead of the Volvo item and they did not seem to last as long as the Volvo anodes, we got about 4 1/2 months from the patterns as opposed to 6 months from the Volvo anodes. No idea why this should be the case but that is our experience and I will stick with the Volvo anodes in future because they are only about £4 per set more expensive.
Click to expand...


Bugger! guess what I have just fitted to my legs:(
 
We have 3 bladed folding Volvo props on our 38' cat anf find we get around 12 months from the prop anodes. Years ago we had the yacht in marinas for some time and on shore power and the anodes had a much shorter lifespan. The saildrive anodes last forever but ours are the old sort where you need remove the whole prop to replace them. We find that they wear where the stainless retain bolts are and inevitably are loose, and not in contact with the leg, when we slip. We have always used genuine Volvo anodes. This year we have 'overtightened' and used bolt adhesive to secure the bolts.

I would not change the prop anodes in the water, a bit fiddly, but we could simply beach. For the leg anodes it would be stupid to try to take the prop off in the water, we would inevitably loose something, I think there are 14 different components in each prop and beaching or slipping is the only way.

We had always used Al antifoul on the leg and for 30cm round the leg on the hull. But actually nothing works. This year we are trying Prop Shield on one prop (similar to Prop Speed but you can apply yourself) and a real leap of faith a product from Feldten Nano Extract Propeller and Drive Sealer. The prop and saildrive treatment has only been on for 1 month so far.

The props in the past have needed to be kept clean - so checking the anodes has never been an issue as we would beach.

We keep the yacht in the seawater all year and temps vary from around 16 to around 24 degrees C (Sydney).

Jonathan
 
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As an aside,

Because I've never seen it:

What does the effect of ineffective anodes look like on a prop or saildrive and where does it occur, anywhere, at the edges, top, tips etc. And if you were to find signs of corrossion other than be more careful with your anodes is there a remedial treatment?

Its not a subject I have seen aired.

Jonathan
 
Neeves said:
As an aside,

Because I've never seen it:

What does the effect of ineffective anodes look like on a prop or saildrive and where does it occur, anywhere, at the edges, top, tips etc. And if you were to find signs of corrossion other than be more careful with your anodes is there a remedial treatment?

Its not a subject I have seen aired.

Jonathan
Click to expand...

I lost a folder once when the shaft anodes detached themselves, the bronze was pinkish in colour and did not 'ring' when tapped, more obvious near the blade tips where the metal was thinnest. I would expect al. alloy to look dull grey and pitted but so far I have not seen that, touching wood!
 
Thanks Quandary,

I do wonder - many have their saildrives (and props) painted - Trilux 33 etc over copious coats of other stuff underneath. I wonder if corrosion shows through.

Because we have been using Prop Shield we have need to grind down to bare metal - I wonder what is hidden by paint?
 
We have 2 blade VP folding prop. The 3 ring anodes need changing every year. Shows they are doing their job! The larger anode only needs changing every couple of years.
 
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