Here in Aus we are controlled by a number of authorities.
Each State has its own authorities, Victoria, where I live, the main one is Marine Safety
Victoria - http://www.marinesafety.vic.gov.au/
Most private vessels are registered in their home state for local waters if they are not planning to sial or leave National waters.
Vessels leaving Aus need to obtain National Registration
For Nationally registered boats/ships the Australian Maritime Safety
maintains the Registra and controls such things as National SAR providing you have DSC
We do not have a National Coast Guard as you have in the States, local areas have their own Volunteer Coast Guards for small boating
All entry into Australia
by land or sea is controlled by the Australian Customs
Office and there are customs
offices at most major ports
Entry and berthing at public berths usually come under the control of the local Ports
and Harbours authorities.
Hope this is of help