Footnotes
Just a couple of footnotes to Christian's excellent list:
Joseph Conrad began writing after serving many years as a merchant seaman. Fans of Typhoon will probably enjoy my favorite: The Secret Sharer. It's actually a novella. Many other nautical novels and stories by Conrad, of course.
Erskine Childers, author of The Riddle of the Sands, was a soldier, sailor, parliamentarian and Irish revolutionary. In 1922, the British arrested him for possession of a handgun, and sentenced him to death. His last words were directed to the members of the firing squad: "Take a step or two forward, lads, it will be easier that way."
And now my own recommendation: The Last Grain Race by Eric Newby. The autobiographical story of a young university graduate who, in 1937, quits his first job in an advertising agency to ship aboard the giant four-masted barque Moshulu for a round trip from London to Australia.