No one knows anything as NOTHING has been published to the Royal Thai Gazette. everything is speculation. do yourself a favour and READ the Australian - Thai tax treaty, then ask a qualified person to interpret that document and what it means to your situation. IF, IF, IF something ever gets in the the Royal Thai Gazette, then you have something to ask a qualified person about.
Facebook is social media, not qualified to advise on YOUR situation.
This isn't the right forum. He needs to be talking to the marina manager at yacht Haven marina in Phuket. Rules will be tied to him being skipper of foreign vessel.