Race plays an enormous role in The True Confessions of Charlotte Doyle since Zachariah, one of the book's most significant characters, is black. Zachariah's race, he tells us many times, is one of the reasons he finds such a connection with Charlotte. Zachariah is an older black man and Charlotte is a young girl: thus they're both outcasts on the society of the boat. Also, though the book doesn't include any slaves or slaveholders, many of its scenes suggest that we should at least have that topic on our mind. For example, the images employed to describe Zachariah's whipping by Mr. Hollybrass and the captain (Chapter 11) should immediately make us think of depictions of slavery we've seen before. We thus align the captain with a tyrannical slave master – and begin to see the larger implications of his cruelty.
The alliance between Charlotte and Zachariah suggests that sexism and racism are more similar than dissimilar.
Though he's a free man, Zachariah's race still prevents him from receiving a fair trial.