Galvanic corrosion

Galvanic corrossion in boats/ships occurs because of the voltages created by the dissimilar metals of props, rudders, shafts soaking in an electrolyte, with the "earth" return of the shore power completing the circuit.

The trick is to break the earth return by using a galvanic earth isolator. These are readily available commercially.

As for your situation using a gen set, it may not be an issue if the genset is not grounded on shore. However best practice is to use a galvanic isolator.

Thanks for your input. Galvanic action is certainlycaused by dismilar metals, generator windings being more noble than an aluminum hull. I know about galvanic isolators but the regulations that I deal with require a gen. neutral disconnect for the purpose of meggering. BV is a regulatory body that mentioned that the neutral (grounded), be disconnected when on shore power. My thoughts are that the generator windings may induce galvanic current?

It is difficult to see what effect it would have.

Galvanic protection is applied to metal parts immersed in water. Google "sactificial anode" for more information.

Connection of shore-based supplies to a boat is covered in British Standard 7671. Equipment installed wholly within the vessel falls outside the standard.

Most U.S. Navy pierside power connections use 3-p delta to avoid that very problem (imbalanced phases causing current flow on the neutral and potentially through the ships hull to utility ground on shore). Ship's hull is not used as a return path for power and a separate conductor is used for safety ground isolated from the power systems and ideally only connected to the hull at a single point. (Easier said than done, but that's the goal anyways.)

You might want to start with MIL-STD-1310, Standard Practice for Shipboard Bonding, Grounding, and Other Techniques for Electromagnetic Compatability and Safety. Also be sure to look at MIL-STD-1399, Section 300, Electric Power, Alternating Current and MIL-STD-2003, Electric Plant Installation, Standard Methods for Surface Ships and Submarines.

You can access these mil-specs at http://dodssp.daps.dla.mil/

Good luck with your quest.

If there is any current in the shore power neutral to ground there will be two parallel current paths. One the ground connection between the switchboard ground and the shore ground and the other the path from the hull through the water to the shore.

The path from the hull through the water will cause "stray current corrosion" NOT "galvanic corrosion". Stray current corrosion can cause hull pitting and loss of hull coating.

Thanks John (even though I didn't know there was any difference) What my ghost is at this point is will a 4 wire generator, while stopped with it's neutral connected to the swbd ground bus and an aluminum vessel create "stray" or galvanic currents?

Yes, an aluminum vessel can be damaged by stray current or galvanic corrosion. If either condition exists it will be more damaging to an AL hull than a comparable steel hull.

Who's bright idea was it to build a ship from what is usually a marine sacrificial anode? What are you using for the sacrificial anode and I hope you don't say aluminum.

I agree 100% with comments referring you to standards for shipboard grounding, bonding, etc. I also agree to "ground" the ship neutral at a single point.

Good luck.