"Space Captain" is a science-fiction novel written by veteran author Murray Leinster, and published in 1966 as one-half of an Ace Double, with the other side being "The Mad Metropolis" by Philip E. High. The book is a "space navy" story where faster than light starships are treated like 20th century ships. Also, I found it surprising that the book was titled "Space Captain" because much like with Dean Koontz' Star Quest, I am surprised no one had used that name before.
This book leans into the comparison between spaceships and naval ships, stating that the protagonist, Captain Trent, came from a long line of ship captains, through centuries of space colonization, and going back to Captain Trents who commanded sailing ships. After making this introduction, it establishes his current predicament: he is the captain of a merchant ship in a sector of the galaxy menaced by space pirates, and he must use his wits to combat and overcome pirates...in space. This story is only 105 pages long, so there isn't a lot of character development. The story, like so many other Ace Doubles, has a romantic subplot (Captain Trent rescues a space princess and falls in love with her for no discernible reason, besides it provides some motivation when she gets captured again). Other than that, this story is straight-ahead space combat, with very little that is original. Of course, in being a straight-ahead science-fiction story, it also eschews some of the cliches of Ace Doubles at the time: there is no magic or sword fights. In fact, the fact that this volume was backed by "The Mad Metropolis" makes this one of the few Ace Doubles I've read where both stories were hard science-fiction without fantasy elements.
There is one problem with criticizing this story for lack of originality: Murray Leinster published his first science fiction story at the age of 23, in 1919. This book was published in 1966, a full 47 years later. This book decribes the physics of space travel, the social organization of planetary government, and talks about the geology and biology of extrasolar planets in some detail. So as someone who grew up with Star Trek and Star Wars and spaceship battles being big business, this might seem unoriginal---but that is because Murray Leinster literally was one of the inventers of these ideas. For that matter, while the idea of planetary systems around other stars might be established science now, it was not until the last few decades that these things were confirmed by science. It seems a little stale to me today, but that is no fault of the author's.