To save costs, the Hispaniola from Treasure Island (1950) was reused and renamed Lydia but now the ship was rocked instead of the horizon, this caused many problems due to the combined weight of ship's crew and equipment.
The rights to the novel were originally acquired by Warners with Errol Flynn in mind, but after the financial failure of Adventures of Don Juan (1948) and growing difficulties with the actor, he was not cast. Warners was already building up Burt Lancaster as its new swashbuckler, but the role of a British sea captain seemed out of his range, so Gregory Peck was ultimately cast.
The ship Bush and Hornblower board to meet the admiral at the end of the movie is the actual HMS Victory, currently dry-docked at Portsmouth, England. As Admiral Horatio Nelson's flagship at Trafalgar, she still commissioned as an official vessel of the Royal Navy, and the only surviving, original ship of the line still in existence.