see he is evil and intimidating. His sailors are petrified of him. He has a wild look, he stomps about the ship on his wooden leg, and everyone runs (if they can) when they hear him coming. He has no regard for his men and cares little about the danger he may be leading them into in pursuit of Moby Dick.

As to the second part of your questions. If people are unstable, they often have obsessive qualities when they are wronged. Mentally healthy people may be hurt, but they either confront the person and try to work things out, or move on. Ahab's obsession over catching up to and killing Moby Dick is madness. He defies every known logical fact (regarding weather, how far out of the way it will take the ship to catch up with Moby Dick, the fact that he is captain of a whaling vessel and should be fulfilling his contract to obtain whale products, etc.) in his obsession.

One way of looking at Ahab's "monomania" is to place it in the context of the larger ontological crisis he seems to be suffering. That is, Ahab believes that the world, as it is, is false, a kind of deception, a "pasteboard mask" as he says in chapter 36. His quest to destroy the whale is more than just revenge. It is by killing the whale that he can obliterate this false world and enter the true one.

To put it very crudely, in Lacanian terms, we can say that Ahab desires to return to the "pre-Oedipal" state. The pre-Oedipal is a kind of pre-linguistic union of the child with the mother, or "other." This union is destroyed by the imposition (by the "father," or society) of language, which destroys the unity with the mother and forces the child to recognize its separateness from other things and people.

Using this formulation, we can see the whale as symbolic of the father (or the "phallus"). That is, the whale is the thing that separates (or "dismembers") Ahab from his pre-Oedipal connection to the mother (nature). This is literally true for Ahab, who has lost a leg, but also true in a Lacanian sense, in that the phallus/whale has replaced Ahab's phallus/leg as the center of the mother's desire.