If he likes historical novels you might try the first Patrick O'Brian Aubrey/Maturin book "Master and Commander." The move "Master and Commander, Far Side of the World" was an adaptation of about 3 of the O'Brian books but never lived up to the potential that are in the books. There are 20 books in the series
Interesting fact is that the book's Jack Aubrey is patterned after Thomas Cochrane who was perhaps the most flamboyant and successful frigate captain in the British Navy through the Napoleonic Wars.
The battle where Aubrey's small brig takes on a much larger Spanish Frigate really happened:
"One of his (Cochrane's) most famous exploits was the capture of the Spanish frigate El Gamo, on 6 May 1801. El Gamo carried 32 guns and 319 men, compared with the 14 guns and 54 men on Speedy. Cochrane flew an American flag to approach so closely to Gamo that its guns could not depress to fire on the Speedy's hull. This left only the option of boarding, but whenever the Spanish were about to board, Cochrane would pull away briefly, and fire on the concentrated boarding parties with his ship's guns. Cochrane then boarded the Gamo, despite still being outnumbered about five to one, and captured her.
In the 15 month cruise of the Speedy Cochrane captured, burned, or drove ashore more than 50 ships
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If he likes non-fiction with a diving bent, then go to the library and get copies of Edward Ellsberg's books "On the Bottom" about the salvage of the submarine USS S-51 off of Block Island in 1921 (these guys were divers!) or "Under the Red Sea Sun" about the salvage work that Ellsberg and his team of divers did on the Red Sea in 1942. Both books detail incredible work done by Capt. Ellsberg under the most primitive conditions.