I don’t know the title of the book.
I believe it was published in the 1940s or 1950s, but I’m not certain of this.
The overall plot is a sailing voyage from the East Coast (Boston, I think) around the tip of South America to San Francisco.
It is definitely NOT the Richard Henry Dana book Two Years Before the Mast.
The main character is a young boy in his teens going to sea (as an apprentice deckhand or cabin boy or some such) for the first time on one of the new, fast clipper ships and he’s got to learn all about shipboard life and work, furling and unfurling sails, coiling ropes, tying knots, etc. He somehow makes an enemy of an older seaman who confronts him at the climax of the story, while a shipboard fire is raging, with the intent to kill him. The boy somehow escapes, but his injuries are extensive enough that he is unable to complete the voyage.
That’s about all I can tell you. I remember it being a ripping good yarn. I hope this description is enough.
Could this have been one of the Tod Moran series by Howard Pease? It sounds like the first one in the series…but all the titles sound the same to me, so I can never remember which one is first.
I don’t know if this would be helpful, but someone has made a long list of fiction titles involving adventures at sea:
http://cs.brown.edu/people/jhughes/boats/FAQ/node58.html
The Howard Pease novels mentioned by the last commenter can be found here – if yours isn’t one of them, perhaps it may be on the list as well.