I was under the impression that there is no duty to pay between the US and Oz since the free trade agreement a couple of years ago. Only GST which is calculated on the price paid for the boat plus the costs of getting the boat to oz either by shipping or by the most practicle comercial route inc crew wages ,victualling (except grog), etc . I'm not sure but I have heard duty is still payable if the boat is not built in the US. check out , www.customs.gov.au/site/page.cfm?u=4365
I was also told by the US embassy that you need to go further than CANADA or MEXICO to apply for a new visa. This was in june.
This is all probably pointless at the moment with the recent decline in AUD to USD value.