Marina Ground Fault Circuit Interrupters

[Rufus]

Last week a transient great loop boat tied up next to us in our relatively old marina. He had moved here from a newer marina that has dockside GFCI, which kept kicking off his cords. He said the boat has had a persistent problem in all GFCI equipped marinas. When he arrived here, he contacted the local yard whose owner spent half a day looking for the problem. No luck. So, they decided to install an electrical device that isolates the boat from the shore-based AC and permits dock side power feed to the boat. I believe it's a transformer of some sort. (He already has an installed galvanic isolator.

My first question is whether the boat could be leaking potentially lethal stray current into the water even with the device?

A second question (and probably unrelated) is in regard to galvanic corrosion. Is it correct that this is strictly a DC current issue or can leaking AC also contribute to this problem. I've wondered about this for years given the aged electrical system in the marina (and probably some of the old jalopy boats in it).

 

[syjos]

A correctly installed isolation transformer will prevent current leaks into the water since it does not use earth for ground.

Any current leak, AC or DC is not desirable on a boat.

 

[tiltrider1]

The yard used a portable Isolation Transformer. The boat is still leaking but all the leakage is returning to the boat which makes it safe for swimmers. There could still be possible electrolysis issues but if the yard could not find the leakage then it is not likely to be any electrolysis issues.

Galvanic is dissimilar metals, electrolysis is electrical.

 

[rslifkin]

ELCIs and GFIs can trip for reasons other than leakage. Improperly wired neutrals on a boat with 2 shore power inlets will do it as well.

 

[Rufus]

Thanks for the info regarding isolation transformers.

I'm still not clear if dock to boat AC current issues could result in the "pink prop" problem for nearby boats over extended periods (not in the case of this transient). From what I've read...it's a DC related phenomena...

 

[O C Diver]

Thanks for the info regarding isolation transformers.

I'm still not clear if dock to boat AC current issues could result in the "pink prop" problem for nearby boats over extended periods (not in the case of this transient). From what I've read...it's a DC related phenomena...

Pink prop is the result of your prop shaft anode / zinc being eroded away. Typically stray AC current from another boat near you will attach your underwater metals that are protected by anodes. When the anodes are eaten up, then in can effect the metals such as your prop and prop shaft. While it's best not to have long exposures to boats leaking AC into the water, properly maintained sacrificial anodes should keep your underwater metals safe.

Ted

 

[mvweebles]

Good article by Steve D on the topic, though makes my head swirl a bit. Goes into stray current facts and myths.

https://www.cruisingworld.com/keep-corrosion-at-bay/

Peter

 

[Rufus]

Thanks all. The Steve D. paper clarifies it for me....I think. The part I was missing is that the AC grounding wire is tied in with the boat bonding system. Hence, plugged in boats on the dock are interconnected. Not a good situation on a dock full of neglected junkers that are always in the circuit.

 

[diver dave]

ELCIs and GFIs can trip for reasons other than leakage. Improperly wired neutrals on a boat with 2 shore power inlets will do it as well.

very true. Even more, these devices don't measure leakage. They measure L minus N current. From any unbalance, it is assumed that there is a hazard. But, it is an indirect way to measure dangerous leakage.

 

[phillippeterson]

Do steel hull boats have the same issues with nearby boat stray currents?