Did you know that Patrick O'Brian wrote other naval historical novels before the Aubrey-Maturin series? Neither did I, but one of the reader guide emails I get from the Seattle Public Library recommended them to me, and I'm almost finished with the first one, The Golden Ocean. It follows a young midshipman on an actual voyage I gather I would've already known about were I as up on my naval history as I am my army, and if I knew the first three quarters of the 18th century as well as I know 1775-1815.
The book has the same lovely language and evocative descriptions as the Aubrey-Maturin series, though I'm not quite as engaged by Peter Palafox, the midshipman hero, as I am by Jack and Stephen. And I'll definitely seek out The Unknown Shore, which I gather is not exactly a sequel, but set during the same expedition.