SVAphrodite said..
Is it work keeping the Australian registration?
I think its is very easy to maintain it in practice, there are some details to be aware of:
You need to fill in a form if you change your address, and post back the certificate by registered post, and they will send you out a new certificate for the new address (there is no fee for the change of address).
If you paint the boat then you need to paint the boat name, home port and registration number in the same places using letters of a certain minimum height and font (described in division 3, section 20 of the Shipping Registration Act 1981).
If you want to change the home port or boat name, then there are forms with fees and of course you would have to change the markings on the boat.
If you change the engine, there is a form for the new engine number.