Forrester's "Hornblower" series is outstanding. I read them as an adult and loved them, although they would be great for young readers, too. Hemingway thought Forrester to be the best storyteller he knew.
If you liked Hornblower, you will
love Patrick O'Brien's Aubrey & Maturin series. 21 books featuring Captain Jack Aubrey as he rises through the ranks of the British navy during the Napoleonic period; brilliant at see and less so on land, he never fails to delight. Characters are rich; battle scenes are excellent and realistic (as are the storm sequences).
Much of the material came directly from actual naval logs, and many of the exploits were taken from the true-life expereinces of Captain Thomas Cochrane. This series combines historical accuracy, enagaging and fast-moving plots, and well-developed characters. The first in the series (Master & Commander, which, by the way, is nothing like the movie of the same name) is a little slower-paced than the others, but it is worth the effort to get introduced to the characters.
I read these as an adult and introduced them to my then-8th grader, who also liked them. There are a few scenes in some of the books (including the first one) that may require some father-son discussions, however. We are talking about a young naval officer posted far from home, here.