In Jean Lee Latham's novel Carry On, Mr. Bowditch, Nat Bowditch goes to sea for the first time as a clerk and second mate on the Henry. He decides to take a bit of risk on a venture of his own, with some cargo to sell at the ship's destination. He has $135 of his own money (earned by his work as a surveyor), and he invests in shoes, boots, and half-boots. His venture pays off. Nat comes home to Salem with nearly $500!

The next few times Nat sails, he does not invest in cargo of his own. On his first voyage on the Astrea, the ship carries a mixed cargo, quite successfully, to Lisbon and Manila. Nat serves this time as supercargo (the man responsible for the safe transportation and sale of the ship's cargo) and second mate. On the second Astrea voyage, Nat is relieved of his second-mate duties and focuses on his roles as supercargo and navigation teacher. We are not told what kind of cargo the ship carries this time, only that it is bound for Cadiz and the Mediterranean.

Nat sails as supercargo on the Astrea a third time, now bound for Batavia to pick up a load of coffee. The ship “sails in ballast” on the way out, with a hull filled with gravel or sand for stability but no cargo. Rather, the captain carries money to purchase the coffee. However, there is no coffee to be had in Batavia, so Nat convinces the captain to sail to Manila and pick up a load of cargo there (we are not told exactly what).

Nat makes one last voyage, this time as both supercargo and captain on the Putnam. He carries specie with him to purchase pepper from Sumatra and nearby islands, but Nat encounters difficulties in obtaining a load of pepper. While he waits longer than he wants in the sweltering heat, he finally gets part of a load for the right price. He refuses to delay any more, however, and decides to round out his cargo with coffee. Then, with his courage and mathematical talent, Nat manages to successfully guide his ship with its mixed cargo home to Salem even through the densest fog.