I have recently done the same and designed the circuit which seams to work OK so far. If you want a copy of the curcuit diagrams PM me with an address as it is probably easier to print and post than email (unless you use Alcad)
Maybe I work differently but I think you are better off to devise your own diagram. Starting from what you want and proceed to the final outcome where you might make up your own drawings.
Anyway I would suggest that the boat be essentially 24 volt with a take off to a 24to12 converter for those services like electronics that need 12 volts.
This means all heavy current items must be 24 volt but it will give a good system. good lcuk olewill