By today's standards your AC service appears to be wired incorrectly. Not uncommon for older boats.

#1 AC White / Neutral and AC Green / Grounding should not be connected on-board the vessel, only at the source of power or back on land. The only exceptions are a new power source such as an inverter in operation or a generator, in operation.. If you have continuity between AC white and AC Green this is not correct.

#2 Paneltronics made IP panels and the three pole breaker is usually what Paneltronics refers to as "smart" breaker. They are made by Airpax IIRC (I don't think Carling makes them any longer). The problem is that yours is bussed together between white and green on the load side. For a replacement (Panaletronics has them in single front toggle) you would need their "cap" (they call it a surge arrestor) that runs diagonally from the supply Neutral to the load side of the green end box. The jumper you have should not be there with a replacement the breaker.

#3 AC Green/Grounding is not to be "switched" and I can't see where the stacked green wire disappears off too. I suspect it is not switched elsewhere but need to mention it. The third box on that breaker should be for reverse polarity but many times builders simply used a 240V three pole breaker and that would make it incorrect. A simple test is to toggle it on & off and test continuity on the end green wire box.

#4 AC Green/Grounding and DC ships ground should be tied together on-board for safety reasons. I also can't see that. IP normally did this...

#5 What does the front of that breaker look like? How many toggle positions? Most older Paneltronics were single toggle but some were double..

I have the part numbers for the breaker and "surge arrestor" at home. Drop me an email and I can dig them up. compassmarineservices at gmail dot com