Captain Boomer, the commander of the English whaling ship the Samuel Enderby, is like Ahab’s reflection in a funhouse mirror: like Ahab, he lost a limb to Moby Dick, a limb that has been replaced by a prosthetic of whalebone. In Captain Boomer’s case, it’s an arm.
Unlike Ahab, however, Captain Boomer is able to put this incident behind him and leave Moby Dick alone. Captain Boomer is there to remind us how singular Ahab is—yeah, Ahab’s lost a leg, but it’s not every guy who, having had a traumatic accident, will then hold an obsessive grudge against the whale in question.
Wanting to know what separates Captain Ahab from Captain Boomer is like trying to figure out what makes a tragic hero different from a regular guy. It’s something intangible, but it’s definitely there.