When we wanted to sell our previous boat (also US registered), a 36 footer, here in Oz, we had to have it evaluated, done by a friendly yacht broker for a slab of beer
, then imported it. You need to investigate, with Australian Border Force (formerly Customs) about how it is done now.
In our case, the broker took a number of pictures, and said all the things that had to be changed for the boat to be sold in Qld. We had to provide an estimate of what the voyage sailing the boat out from the US had cost, in terms of charts
, etc. At that time, the way they did it was to subtract the costs of getting the boat here from the broker's evaluation, and then we paid the tax.
My understanding is that the parameters have changed since then. There will be forms to fill out. Pls. note, the used boat
market in Australia
is quite depressed now. Your boat, if she's in good shape and not needing major expenses, may still sell, but it is what I would call a "niche" boat, most people right now want bigger and showier, so good luck with it all.