You'll need an "Recreational boat operator licence". Seeing you are in Victoria - VicRoads administers the recreational boat operator licence test and issues the licence to the applicant. If you wish to sit the test you must make a booking with VicRoads either in person or on 13 11 71.

Alternatively, you can attend a approved training course and take the completion certificate to VicRoads to gain your licence. More details at: transportsafety.vic.gov.au/maritime-safety