Some of the older Chinese boats used red and black ac wiring. Black was the neutral red the load. l have seen black to black connections shore power to ship effectively reversing polarity of the whole boat. I can see that happen on a generator installation as well.Should be easy as >swapping a couple of wires,<
However I would get a second opinion to weather it is actually reversed ,as it is hard to contemplate reverse polarity on board for a long time.
You may have used an idiot surveyor
If you are a boat owner, paying someone to fix your problem is ok if you can afford it, but I maintain that ignorance is more dangerous than electricity, so you need to get in there (power off) and learn how your system works!