How we cite our quotes: (Chapter.Paragraph)
Quote #1
[And] all the time the dual working of my mind distracted me almost to the point of insanity. (1.11)
The captain hints more than once at his feelings of insanity. Sure, he might just be exaggerating, but there's definitely something deeper going on with the "split mind" he keeps referring to. He constantly feels like he's in two places at the same time, and that doesn't really sound all that sane.
Quote #2
My nerves were so shaken that I could not govern my voice and conceal my agitation. (2.82)
The captain doesn't like surprises, and a lonely life on the sea has left his nerves so frayed that he can barely deal with even the teeny tiniest bit of anxiety. This is definitely not what you want in a captain.
Quote #3
This was the sort of thing that made my terrifically whiskered mate tap his forehead with his forefinger. (2.82)
The captain can't stand the way his chief mate is always tapping his head in the captain's presence. He's not entirely sure what the gesture means, but he assumes the chief mate is saying that he is stupid, drunk, or insane. Then again, the captain might just be paranoid.