FWIW, our current
boat was Aussie built, and was a registered ship. We had to de-register her, not being Aussie citizens, and she is now registered in Illinois in the USA. The first time we went offshore
with her, Customs
insisted on exporting her (this was later determined to be in error, but too late to do any good). When we returned, we had to import her. There was no duty nor GST due because of her origin, but there was a fee of <100$ involved (this in 2003). On subsequent trips offshore
, we've simply cleared in and out like any other vessel.
I'm not sure if your situation is the same, but it sounds similar. I'd check directly with Customs
(oops, I mean Border Force), since they are the folks the new owner would have to deal with.