What metaphors are used in The Big Sea: An Autobiography by Langston Hughes?

Hughes uses the Big Sea as a metaphor both for life, and as a metaphor for literature. The sea represents freedom to travel the world as a man, and the day Langston first embarks on his first voyage, he feels that it is the first day of his adult life. He muses, "I wanted to be a man on my own, control my own life, and go my own way. I was twentyone."