Galvanic protection for boat engines.

[GILow]

In another thread I have been documenting an anode depletion issue with my new engine. That investigation is ongoing and will take some time to resolve. For simplicity, I’d like to keep that issue separate from the following discussion:

One possible solution would be to connect my engine to one of the two large sacrificial anodes that currently protect the propellor shaft and the rudder stock.

These anodes last years, and in the case of the rudder stock anode, anywhere up to six years.

My question is, are there potential pitfalls in connecting an engine with its own anode protection system to an external anode? Are there best practices in doing so?

(And just to keep this thread focussed on the question, please let’s not go down the “how to fix the problem” path, that’s a separate discussion that is already well documented on CF.)

Matt

[NYSail]

Fresh or salt water? Marina or mooring? I have a slip
in a marina and also gave a galvanic isolator but anchor a minimum of 3 days a week. My shaft / prop Bow thruster zincs last a season. Engine does not have zincs (yanmar). So you must have some big zincs on prop.... also unless you have a shaft saver (plastic), your engine is attached to your shaft zincs via the transmission.

[GILow]

Good points, so to clarify, I’m thinking specifically of engines in salt water and I assuming the engine is electrically isolated from the prop.

Trying to look specifically at external galvanic protection for just an engine, assuming no other protection other than the anodes that came with the engine.

I am concerned, for instance, that I might end up sacrificing the engine anodes to protect the rudder.

[tkeithlu]

Bond all your anodes together via the boat bonding connections. It should be one system. You can get an overview of the system with a silver reference electrode, such as this:

https://www.boatzincs.com/corrosion-...RoCU74QAvD_BwE

Yes, you do need to keep an eye on all of them; the zinc fingers in the engine may deplete, but one volt on the test anode means nothing is corroding but your zincs.

[rancher44]

FOR years I used a fish (zinc) that I used on my boat .
Buy them at West Marine .
Get the big one .
Use when you are at dock and connected to shore power

[MicHughV]

I agree with the fish zinc.....you have to wire connect it to the engine...I use a heavy gauge electrical wire...led from the engine to cockpit locker....open the locker, clip on the fish, good to go.
It's easy and simple to check, just pull it up. When you go sailing, just pull it up and lay it somewhere....it will likely get some marine growth on it....just brush it off from time to time....
If you don't have a fish.....you can make your own.....find somewhere you can buy a plate of zinc, bolt it to an electrical wire....solder on a clip....voila....done.

I have more problems with zinc depletion at a dock than at anchorage..