NavList:

...The navigation in the boat after the mutiny would have been essentially identical to the navigation of Joshua Slocum a century later. Bligh used dead reckoning for longitude, and Noon Sun sights for latitude.

Dead reckoning in higher latitudes involves the mathematical complexity of dealing with the differing sizes of latitude and longitude degrees, but in the tropics where Bligh and his compatriots were sailing, it's simple: longitude and latitude are just like x and y on a basic graph. You work out how many miles you've travelled west and how many miles north and you add (or subtract as appropriate) directly from the previous day's latitude and longitude. Dead reckoning usually requires a simple timepiece to keep track of the number of hours spent on each heading, if there is any change of heading. Bligh, like Slocum, had a simple watch. I've also seen speculation that Bligh could have kept track of elapsed time using time sights for local time. I consider that an improbable fantasy.