Tipping the GFI of the shore power outlet

[Swiss sailor]

Hi,
All of a sudden, the GFI on the shore power outlet is tripping when putting on even the lightest load. The boat sit‘s on the dry at the boat yard. To charge and maintain the batteries, a battery charger is always on. That was never a problem, until a few weeks ago. The boat is a 1999 Hunter 410 sailboat
There is a GFI equipped outlet from the yard I‘using. I have a 30Amp power cord plugged in. On the boats end, the cable and the boat are equipped with a smart plug.
I have tried many things to find out the cause, why the GFI tripps all the time:
- Changed the shore cable
- removed the battery charger (thought it might be shot)
- etc.

Sometimes, I get the 115VACdisplayed at the electrical pannel, sometimes it even tripps before I can read the instrument. Sometimes it does not trip, even with e load such as a larger dehumidyfier on (rated at 15 Amps 110 VAC)
I would highly appreciate any thought or hint.
Thanks.
Marco

[phorvati]

GFCI outlets can become more susceptible to nuisance tripping. Especially outdoors and ones that get abused. I would plug various power tools directly into the yard's outlet to see if that causes the trip as well. There might not be anything you can do. If the outlet has become more sensitive, than your extension cord alone could cause enough ground fault current via stray capacitance to cause the mismatch that triggers it. At yards approval, we ended up replacing the GFCI and problem went away.