Bravo 3 Anode life

Can anyone give me some idea how long a set of anodes (original equipment on a brand new installation) should last?
The leg is a Bravo 3 and is (supposedly) covered by a Mercathode system.
There is no stray current in the immediate area. The props are stainless steel.

 

With the Mercathode system active, the zinc anodes last at least 5 years. Of course they will look bad because they are pitted, but as long as at least 50% of the mass is still present, they need no replacement.

Unfortunately many installations are not wired correctly, fuses become corroded and the controllers are not as reliable as they should be.

 

Thanks CDK.
I haven't had any experience with the Bravo 3 before. My previous Bravo 2 went for a number of years (moored in the salt water, as this one is) without having to change anodes, but it had an aluminium prop.
This new unit has been in the water for only about 4 months and I would estimate that the anodes are already approaching 50% degradation. At this rate I would be having to replace them twice a year!

 

The system is supposed to cope with steel props as well. With that much decay of the anodes it probably isn't working at all. Unscrew the 12V wire at the controller and measure the current, there should be approx. 10-20 mA.

 

Look at it this way, if they are eroding then they are working.

 

Do check your mercathode system - they made a special idiot-light tester for these but checking with a multimeter should work fine. I've seen the mercathode systems turn into nonfunctional bricks on a couple boats; I've seen one bad fuse cause the mercathode to be off while the owner thinks its working meanwhile the drive is turning to swiss cheese unnoticed! If it's the condition of the dock/water and you can't fix that, changing zincs frequently is CHEAP preventive medicine (or is the problem that you don't have a trailer and don't want the difficulty of changing them underwater?)