Zinc guard

What are you going to coat with it? Nothing to do with preventing corrosion of bronze. It is a substitute or alternative to galvanising, for example on anchors or steelwork.
 
This is the best zinc rich paint available.
Its not galvanizing, and despite some suspect claims it doesn't perform as well as the documented 150 year history that galvanizing has.
But as for zinc rich paint, forget any others if you want performance.
 
So anodes are zinc, and so is this, I'm thinking greater anode like protection. Or am I missing something here? Is there a reason it will not do that? Will it bond to bronze even?
 
PabloPicasso said:
So anodes are zinc, and so is this, I'm thinking greater anode like protection. Or am I missing something here? Is there a reason it will not do that? Will it bond to bronze even?
Click to expand...

Yes, you are missing something. The basic principle of galvanic corrosion. This occurs in your prop because there is a mix of metals (a brass type alloy containing copper and zinc for the hub and blades and stainless steel for the pins). These two in seawater set up a galvanic cell and the zinc in the alloy leaches out. The anode is (almost) pure zinc and if electrically connected to the prop will corrode instead of the zinc in the alloy.

As I have said many times, the particular alloy in the prop you have seems to be more affected by this process than other alloys. So, if you don't renew your anodes the prop will dezincify. Typical signs are wear in the pins and gears and blades breaking up as the copper that is left after the zinc has gone has no strength.

There is no answer other than changing the prop for one of a different metal - but as you have discovered this is not cheap, unless you go back to a fixed blade aluminium prop. The main saildrive anode usually lasts longer and there are ways of adding additional anodes, for example wiring either a hull or hanging anode to the saildrive casing, but this will not deal with the prop as that is isolated electrically from the saildrive housing.
 
Tranona said:
Yes, you are missing something. The basic principle of galvanic corrosion. This occurs in your prop because there is a mix of metals (a brass type alloy containing copper and zinc for the hub and blades and stainless steel for the pins). These two in seawater set up a galvanic cell and the zinc in the alloy leaches out. The anode is (almost) pure zinc and if electrically connected to the prop will corrode instead of the zinc in the alloy.

As I have said many times, the particular alloy in the prop you have seems to be more affected by this process than other alloys. So, if you don't renew your anodes the prop will dezincify. Typical signs are wear in the pins and gears and blades breaking up as the copper that is left after the zinc has gone has no strength.

There is no answer other than changing the prop for one of a different metal - but as you have discovered this is not cheap, unless you go back to a fixed blade aluminium prop. The main saildrive anode usually lasts longer and there are ways of adding additional anodes, for example wiring either a hull or hanging anode to the saildrive casing, but this will not deal with the prop as that is isolated electrically from the saildrive housing.
Click to expand...

Ok so here are my questions. Why not fit bigger anodes to the hub? Is there a technical difficulty here in manufacturing them or some other issue? Could I drill and tap the hub to fit another anode, perhaps two, one either side to allow for balance when spinning? Or double up the three hub anodes piggy back style? Surely there must be a way or are the corrosion gods and anode/prop/hub manufacturers purposely conspiring against me to relieve me of more cash.

If this hub prop configuration is not fit for purpose due to corrosion issues won't I have some comeback against the seller?
 
PabloPicasso said:
So anodes are zinc, and so is this, I'm thinking greater anode like protection. Or am I missing something here? Is there a reason it will not do that? Will it bond to bronze even?
Click to expand...

Theoretically, that's correct - the zinc in the paint would act as an anode; that's exactly how galvanizing works as well (the zinc coating is sacrificial). But the amount of zinc in a coat of paint isn't going to be enough to operate in that way for any significant time when in contact with a dirty great lump of mixed metals.
 
I think you are doing well to get 12 months from one set on anodes, I get about 8 months and have two saildrives.
 
nigelmercier said:
If you can find a point that is electrically connected to the propeller, just run a wire from it over the side and hang a cheap anode on it.
Click to expand...

The volvo folding prop has a rubber hub, which isolated it from the leg, so connecting a hanging anode to it would require getting wet:eek:
 
PabloPicasso said:
So how about fitting bigger anodes? Is it possible to make them, or fit bigger easily available ones?
Click to expand...
Unlikely. If you have the prop with the small inset anodes there is no space for bigger ones.

Think you just have to accept there is nothing you can do to extend the life of your anodes unless you leave the boat out of the water! - Or buy a prop that does not corrode as badly as the one you have now.
 
Oh how happy I would be if someone made oversized anodes for a volvo saildrive hub. I would gladly trade a bit of hydrodynamics.
We're on a new to us Hamble Pile mooring this year
- Launched mid March
- Free dived to check mid June ... anode was 90% gone!
- 6x free dives (3x to remove + 3x to fit new anode)

- Checked again last weekend - I will be fitting a 3rd set to see the season out

I am seriously considering fitting the old fixed 3 blade for next season :-(
 
You must log in or register to reply here.

Share this page

Top