In rules 16.6, it says that you must "remove the sea captain from the map". Is he "removed" to the turn track or the power card (giving him the option to return as a sea captain the same turn [or even the same impulse])? "removed from map" = to the turn track just as if in step 7 of 16.5; returning home after piracy attempt.
The latter would give him the possibility to circumnavigate twice the same turn.
The big thing to remember is that this is not optional after a circumnavigation; the moment that the captain arrives in the concluding sea zone, he's picked up....can't hang around to do more privateering, etc.