"The Republic"
This boat is a symbol for the human soul, because it's namesake, The Republic, by Plato, uses the same metaphor, except that instead of a community on a ship, it is a community in a city in Plato's version. But basically, the name of the ship is a clue to the wise reader that the plot can be interpreted as a metaphor for enlightenment.
The blackmailed marriage proposal
This genius plot device is actually symbolic. It represents Calhoun's disenfranchisement, because his girlfriend (who allegedly loves him) is willing to bribe his debtors into forcing Calhoun to marry her. That is worse than blackmail, because she is paying a white man for the right to "own" a black man, so Calhoun knows instantly that she doesn't understand what his life is really like. He leaves her.
The reunion and marriage
When Isadora discovers Calhoun has singlehandedly saved a boat full of people by being powerful, reliable, and reasonable, she learns what exactly he really is as a man. She realizes that such a powerful man could never have been blackmailed, and they are reunited. This scene is an allegorical symbol, because they get married which is a clue to the reader that what Calhoun earned from all his suffering was a wife who truly appreciates him.
Captain Falcon
This man is a mean, powerful man, but then when he finds out that he has lost power of the ship, he commits suicide during the storm. This is the allegorical inverse of Jonah in the Bible who voluntarily sacrificed himself to appease a storm, but for good reasons, to save the people on board. Falcon represents the selfish interests of a tyrant.
The motif of slavery
Although slavery is illegal by the time this plot occurs, it still happens illegally. That goes on in America for a long time, and Calhoun knows the limitations of American "freedom" for a newly freed slave. In Calhoun's journey, he experiences many types of slavery.
The best part of the slavery motif is that when Calhoun stows away and the captain says he must die or work without pay, Calhoun is humble enough to work, even though it looks like slavery, but when his girlfriend tries to buy him in marriage, he knows instantly that he's worth more than that.
In other words, although we typically associate slavery with hard work, Calhoun teaches us that true slavery is being controlled by others. Hard work turns out to be an important part of the human experience, but as long as it is being done voluntarily.
