I bought my boat in NSW and it has two of these plates attached. One is on the transom and the other on a bulkhead below.
Questions:-

1. Are these plates relevant in NSW only or are they part of a national vessel I.D. system??

The number on the plate obviously corresponds to a file in an office somewhere.

2. What information would be in that file in regard to the details of the vessel?

I have been on the NSW Roads and Maritime web site and did not see anything about them there.

3. Which would be the office to contact in regard to these plates?

Thanks in advance.

Here we go...
www.rms.nsw.gov.au/maritime/registration/boatcode/index.html

cisco said..
So it is run by Roads and Maritime NSW and it's primary purpose appears to be identification of hulls and the ability to look up on the Personal Property Securities Register to see if there is a financial lien against the vessel similar to a REVS check on a motor vehicle.
Fees for these Boat Code Agents are a bit hefty

In Aus it Is run by the feds to meet www.iso.org/standard/22932.html but each state administers their own BoatCode providers and sets the maximum fees the agents can charge.

The RMS wont let you transfer a boats registration if it doesnt have this HIN or boat code installed ..

Its a massive pain in the arse when you just want to go for a cruise on your new toy but the owner won't let you until the transfer is complete and the rms wont transfer until you find a boat code agent and then you have to wait another week!!

Mobile boat code was really fast and easy once he was available.. all they want is to see a receipt and dont leave them alone with a drill!!! i had to stop the guy from fixing it with self tappers to my transom!!!