On the subject of Matthew Flinders (August seems to be SSM's Matthew Flinders Month), I didn't manage to find originals of either Palmer's or William's reports to the authorities in Bombay. Apparently the reports were recorded in a journal called "The Orphan", but the BL doesn't hold it. Yale University, of all places, does though. Sometimes you can get the story from other newspapers, but although the BL holds a lot, the newspapers published in India in 1803/04 are missing across the board. Rather bizarre that, and unfortunate. Still, you never know, there may be something in the Admiralty or Colonial office files at National Archives.
Well, the details are recorded in a long footnote in Flinders' Book (and I'll give you the title in all its full glory):
"A Voyage to Terra Australis; undertaken for the purpose of completing the discovery of that vast country, and prosecuted in the years 1801, 1802, and 1803, in His Majesty's ship the Investigator, and subsequently in the armed vessel Porpoise and Cumberland schooner. With an account of the shipwreck of the Porpoise, arrival of the Cumberland at Mauritius, and imprisonment of the commander during six years and a half in that island." The copy on my desk has a little handwritten note in the flyleaf: "Presented by the author 25th july 1814". I know it's booky-geeky, but I love that stuff.