Do you have muliple breakers or is this the boats main breaker? If you have multiple breakers, try rewiring the circuit to another breaker and see what happens. Otherwise, this something you just need to chase down.

Note what's "on" now (battery charger and drawing any load). Turn-off ALL the AC, then see if it trips all by itself. You should see no current with everything off... Then you start down the chain to figure-out what it is.

Something is going on.