@Lee Hadjiosif you also should check your power cord is pin correct (you said you reversed hot & neutral in post 1 above). if the reverse is at the marina end it will be fine at your dock but cause big problems when you dock elsewhere. If the problem is in your boat wiring then loaning you cable to someone else would be a problem
I think you’ll find there is a big DC component on one of the lines. This can be your “fault” or some one else in the marina. To check see if the DC voltage is on you power cord when not plugged into your boat.
Don’t delay on this, you could be eating up your prop, thru hulls, shaft.....
Galvanic Issolators help your boat be isolated from power issues like this.
Les