Many thanks to all for the helpful insights.
Sure enough, the base (the
tilted anchor one) was moved from Brisbane to Fremantle, probably while I was taking a nap. But whatever, I was finally able to dock, and the relief from not having to endlessly wander the World's oceans looking for a home made my day. Kevin Costner would be happy for me (Waterworld).
Gotta love this game! It's a continual learning experience and just chock full of little clues, like the
tilted anchor, that the developers have been trying to keep secret. And gotta love the Subsim community for digging them all out and passing them along!