Originally Posted by goboatingnow
Tends to be only cost effective for large steel
boats and impractical on smaller boats with unsure power supplies. It in essence duplicates the activity of a zinc galvanic cell.
Quite correct, With a typical zinc to bronze/SS your getting about 250-300 mV between the zinc and bronze due to their natural galvanic values.
With impressed current you still have an anode, but it's not galvanic negitive to the other metals its protecting. A positive impressed current at +12V's DC is run through the anode(s) based on the amount of metal to protect.
Based on one design manual I read, you want ~50 mA per square meter of surface area being protected. For a typical non metal sailboat with solar
the load works out to ~ 3 watts. The reason its not made for small boats is its too simple and not enough money
OK, it's a bit more complicated then that from a calculation standpoint, but for a small sailboat <50 feet, there's just not much metal exposed.
Basically you run a wire from the + side of the battery
to a metal anode in contact with the water adjacent to the metal being protected. Could be SS, cast iron, really anything. Seawater has a 40 ohm resistance according to the manual I read here Designing Cathodic Protection Systems for Marine Structures and Vehicles - Google Books
As the minus side is most likely already connected to the engine
and prop shaft, that's about all there is to it. You could get fancy and add a shunt and DC mA meter and of course a fuse in the circuit would be required . But for the basic sailboat that's it.
3 watts with solar panels
is not a problem. I will be playing with this a bit I'm thinking.