Stray current in marina

[boatpoker]

Just FYI for your further corrosion education.

Bronze propellers are extremely rare and very expensive

The vast majority of propellers are "manganese bronze" , a misnomer as this falls clearly into the "brass" camp due to it's approximate 35% zinc content.

Some cheap Chinese props are known to have very active galvanic cells within themselves due to questionable metallurgy and impurities ...... i.e. they eat themselves
If your so called "brass" prop is turning pinkish it is losing it's zinc content due to galvanic corrosion (months/years) or stray current corrosion (days/weeks).

PS. The same thing can happen with cheap Chinese anodes. Buy only brand name, mil. spec anodes.
This alone could be your issue.

[Cadence]

It is not impossible you are providing ground for someone else or the marina. I don't know how it you are in no way connected to the shore? Possible someone with reverse polarity.

[boatpoker]

Originally Posted by Cadence

It is not impossible you are providing ground for someone else or the marina. I don't know how it you are in no way connected to the shore? Possible someone with reverse polarity.

Simply not possible if not connected to shore power.

[Cadence]

Originally Posted by boatpoker

Simply not possible if not connected to shore power.

Unlikely but the boat next door could be wired with +to his shaft or possibly a through hull. One never knows. Especially after reading about some electrical geniuses.

[boatpoker]

Originally Posted by Cadence

Unlikely but the boat next door could be wired with +to his shaft or possibly a through hull. One never knows. Especially after reading about some electrical geniuses.

One does know if trained in the issue.
Retired Certified Marine Corrosion Analyst.

[Cadence]

Originally Posted by boatpoker

One does know if trained in the issue.
Retired Certified Marine Corrosion Analyst.

But how many posts have you read with, well intentioned, people not being able to find their ass with both hands electrically?

[boatpoker]

Lots. but the last one was #34

[Cadence]

Originally Posted by boatpoker

Lots. but the last one was #34

You may be right. My degree is old. I haven't worked in electrostatic engineering in ages. So I maybe rusty.

[Rorzech]

Could you paint the starboard side hull with copper, and the port side hull with zinc and charge your battery while you're floating in salt water ?
Yes, I know it's a goofy idea , but has anyone tried it, to find out ?

[Cadence]

Originally Posted by Rorzech

Could you paint the starboard side hull with copper, and the port side hull with zinc and charge your battery while you're floating in salt water ?
Yes, I know it's a goofy idea , but has anyone tried it, to find out ?

It sounds goofy, but who knows. The barnacles may not like it either?

[senormechanico]

Originally Posted by glcalahan

Thank again!

Good point and thanks!* The boat went into the water May 18, '18.....3 weeks ago I moved the battery and spent several weeks with engine disconnected while I built/glassed a new battery tray for the new AGM 31.* Battery was and still is disconnected.*

By any chance does "disconnected" mean only the negative terminal?
If the positive is connected and the battery sits in salty dirt, it could mean a resistive path to seawater. Just a thought.

[CharlieJ]

#39

The galvanic potential between zinc and copper is less than 0.5VDC. Won't charge much with that potential.

[gulfislandfred]

When I was involved with the Port of Port Townsend, Washington, we had a "Hot" dock, where zincs went away (I'm avoiding technical terms to focus on my point) faster than they should, and props and shafts were ruined.



After years of consultation with experts, a fellow with experience suggested that we check the transformers on the docks to see if the cycles were in sync. Puget Power obligingly came down, and found that the "Hot" dock was out of sync with the other docks. They reversed the connection (I think where the 440V leads split into 220V), and it solved the problem.

[groman]

Thoughts on galvanic corrosion.
Items to watch out for in tracing excessive zinc wastage
1. Are your negative leads of the correct size for the expected current.
Any resistance will cause a voltage potential difference on you earth circuit.
2 The prop shaft should hae a separate earth connection to the engine.
Shaft goes to the gearbox.

All gears coated in oil. Oil being an insulator will prevent good earthing.
3. Ensure you have a suitable capacitor in the galvanic isolator to stop the diodes conducting on hi AC leakage currents.

[groman]

Thoughts on galvanic corrosion.
Items to watch out for in tracing excessive zinc wastage
1. Are your negative leads of the correct size for the expected current.
Any resistance will cause a voltage potential difference on you earth circuit.
2 The prop shaft should have a separate earth connection to the engine.
Shaft goes to the gearbox. All gears coated in oil. Oil being an insulator will prevent good earthing.
3. Ensure you have a suitable capacitor in the galvanic isolator (if used) to stop the diodes conducting on hi AC leakage currents. Check all appliances/instruments for leakage.