Dante's little boat

In a number of places the image of the skiff comes up as one travels the heavens:

In Dante's Divine Comedy

In Tiger's Fang 

In Greek Mythology

Summary The poets are approaching the great tower when two flames shoot from its top, and immediately, another flame replies from the other side of the marsh of Styx. Soon after the signal, a boatman, Phlegyas, arrives, eager to take more damned souls deeper into Hell. The sight of the poets angers Phlegyas, however, and he begins raging. Virgil chastises him, and the poets enter the boat. As the boat makes its way to the other side of the swamp, a soul rises from the slime and accosts Dante. The soul is Dante's Florentine enemy, Filippo Argenti, one of the Wrathful in the marsh. Dante and Argenti exchange words, and Dante wishes that Argenti receive further punishment. Virgil praises Dante for his comment, and says that Dante will get his wish. Shortly, other shades descend upon Argenti and tear him to bits. The boat approaches the shore, and Dante sees the City of Dis where the fires of Hell glow. Phlegyas lets the poets off the boat, and they are immediately accosted by a group of shades that question Dante's appearance in their realm. The shades refuse to let Dante pass, though they say that Virgil may enter but not return to his own circle. Dante is afraid that he will never be allowed to leave Hell, and he cries to Virgil to remedy the situation. Virgil goes alone to the gate of the City to see if he can open it. He returns unsuccessful in his task, but assures Dante that a Great One is on his way to open the gate. 

On page 65, Twitchell says they came to the River Stix and "an old, old man appeared in a boat and bade us to step into it. We boarded the little skiff ...."