Originally Posted by Av8
My boat is wired 50a 125/250.
Not sure at this point...but I would check the neutral to the ground and see if I was getting 110...If so...as really what I think some have said...you might have one of the incoming hot legs somehow getting power to the neutral.
It should be the "other" leg from the one supplying the hot to that GFI.
If not obvious and you don't have the time but have the money...a pro may be able to track down the fault with specialized tools easier than I could.
If you like the work or just plain want to do it yourself...that's one direction.
Cant think of any other reason...but there are several ways /places the fault could be happening.