Zachariah tries very hard to befriend Charlotte at the beginning of the voyage, saying, “I can assure you, Zachariah can be a fine friend.” He feels they have something in common—their differences.
“Miss Doyle is so young! I am so old! Surely there is something similar in that. And you, the sole girl, and I, the one black, are special on this ship. In short, we begin with two things in common, enough to begin a friendship.”
Since Charlotte is the youngest and Zachariah is the oldest, he feels they should be friends. He also thinks the distinction of being the only girl and the only black man will create a bond.
Charlotte disagrees and states that she doesn’t need a friend. However, Zachariah is undeterred and states that, “One always needs a final friend.” He explains that a final friend is the companion who sews a hammock and wraps it around his friend’s body when the sailor is put to rest at sea. So, Zachariah is basically saying that he would be a good friend to have in case she dies on the voyage.
Charlotte is disgusted by this idea and tries to leave. It is at this point that Zachariah offers her the dirk for protection.