What is the boatman's description in "Divine Punishment"?

This is a
good question. 

Charon, as you know, is the ferryman who takes people across
the river in the underworld.  Dante was familiar with Charon from Virgil's Aeneid  (6.298-304
and 384-416). You might want to look up the references to compare and contrast. Knowing from
where an author got his material is impressive. 

As for his description,
Charon is depicted as an angry old man (who has a lot of threats), with blazing eyes of fire and
white hair. 

Inthree, there are two descriptions of him. I will quote both
for you.

And behold coming toward us in a boat an old man,
white with the hairs of age, crying: "Woe to you, wicked souls.

Charon
the demon, with eyes like glowing coals, making signs to them, gathers them all in; he beats
with his oar whoever lingers.

He also objects to taking a
living man (Aeneas, Dante) on his boat.