Well, now I look foolish!
The Spirit of Tasmania goes to Devonport, not Hobart, and Google Maps tells me it’s a four hour drive (or ride) from one to the other. Our bike is a 250cc single-cylinder bike, a type colloquially known as a thumper. The name is due to the vibration inherent in one quarter-litre cylinder banging up and down right under your groin… I was sore enough after a two hour ride from Springvale to Ballarat on the weekend. Four hours across the spine of Tasmania, while doubtless stunningly beautiful, does not sound butt-feasible.
So I will catch de plane, like a normal business zombie, and make use of free shuttle services wherever possible.