Anodes

[Grajan]

Changed from Zinc anodes to Alloy this year on our 36' twin screw diesel motor yacht only to notice seven weeks on that trim tab anodes are already 30% gone and the larger ones showing erosion, previously could run for two years with zinc before renewing.
It was my belief that the alloy anodes as well as being a "greener" product was also longer lasting. Boat hasnt moved during this period as waiting for repairs to be completed. Engines have been run up on a weekly basis and she is connected to shore power.
was advised by manufacturer to speak with retailer and not to contact them direct which I found strange when it is such a specialised subject.
Anyone else have any observations?

 

[vyv_cox]

No explanation that I can think of. The galvanic potential of aluminium anodes is equal to that of zinc and they have greater capacity. Do you have their specification?

 

[B27]

Aluminium is similar to zinc on the electro-chemical scale, but Aluminium oxide is an insulator, while Zinc Oxide is a semiconductor.
I'd need convincing about aluminium.

 

[Rappey]

I'd need convincing about aluminium.

Mcduff...

Why Aluminium?
Aluminium alloy anodes have been in use for many decades, primarily on larger cathodic protection projects such as Port and Harbour sheet & pilling installs. This was due to the better performance of aluminium compared to Zinc which outweighed the cost difference on bigger projects. However, over the last 10 years the cost of the special high-grade Zinc required has doubled, meaning Zinc is no longer the cheaper anode material.

Aluminium is now used as standard by the UK's major boat manufactures as aluminium has a higher driving voltage, meaning it can be used for brackish water as well as salt. Aluminium also has a higher Amp-hour per Kg rate, meaning that the same sized anode will last up to 20% longer. Aluminium anodes also contain no Cadmium, unlike Zinc anodes, producing a more environmentally friendly product.

Aluminium
AD77
Salt Water Use
Brackish Water Use
Made in the UK
Used by leading UK Boat Builders
20% Longer Life
3x Lighter
Higher Output
Environmentally Friendly
Costs less than Zinc

Zinc
ZD77
Salt Water Use
Made in the UK
Traditionally used for over 60 years
Widely Available


Ive been seeing mcduff ads on fb for a few months now and they basically say "why are you still using zinc" ?

 

[vyv_cox]

Aluminium is similar to zinc on the electro-chemical scale, but Aluminium oxide is an insulator, while Zinc Oxide is a semiconductor.
I'd need convincing about aluminium.

Anodes

 

[B27]

So an aluminium anode needs to be an Aluminium-Zinc alloy.

Zinc seems to be cost -effective and I've got a choice of brands.
Alloy anodes may be technically more cost-efficient but there's no sign of the savings being passed on to the small boat owner.

It's easy for me, I have a drying mooring so check the anode often, if you can't do that, then paying a small premium for something that lasts a bit longer may be a good idea.

I've changed my prop recently, the old one was painted, the new one is not, so I might look at that. But Zn anodes are cheap and prop paint is not.

 

[vyv_cox]

So an aluminium anode needs to be an Aluminium-Zinc alloy.

Zinc seems to be cost -effective and I've got a choice of brands.
Alloy anodes may be technically more cost-efficient but there's no sign of the savings being passed on to the small boat owner.

It's easy for me, I have a drying mooring so check the anode often, if you can't do that, then paying a small premium for something that lasts a bit longer may be a good idea.

I've changed my prop recently, the old one was painted, the new one is not, so I might look at that. But Zn anodes are cheap and prop paint is not.

Where aluminium anodes score particularly well is in mixed waters, e.g. berthed in fresh but sailing on the sea. Also brackish water of course. The hydroxide layer that forms on zinc anodes inhibits their operation.