i surf and paddle skis out here alot, so i find this actual question of some interest
i did a few quick google searches, it seems that NSW law is very open to interpretation but doesn't actually appear to state sups in any of their legislation
Victoria puts sups in under kiteboards or sailboards, being more than 400m from shore you need a life jacket, where NSW just states kiteboards or sailboards,
maritimemanagement.transport.nsw.gov.au/lifejackets/lifejacket-law/index.htmlwww.wearalifejacket.vic.gov.au/lifejacket-lawsthe above are what i was going off
it is interesting as you are crossing a channel and a bar, but technically there aren't any rules or laws against doing it on a surfboard, as long as you don't paddle in front of the ferry or get a really fussy maritime officer you shouldn't have any issues
i welcome feedback if i am wrong or have missed anything
Jarryd