The owners manuals
for boats are typically pretty worthless, that's if you get one at all. What is more important is to get all the manuals
for all the equipment
that was installed on your boat. Otherwise you can look up the PDF for that equipment
on the internet
. The panel on your boat looks custom to the boat manufacturer, so its doubtful there is a manual for it.
Have you looked at the gauge of the wire that leads to the breaker? Size the amperage of the breaker to the size of the wire leading to it.
Chances are good that if you unscrew that panel that you will see the amperage of the breaker on its backside. At the very least you will see the gauge of the wire leading to the breaker.
BTW, it's supposed to be a double pole breaker that shuts off both the Hot and the Neutral.