Ishmael's Changing Narration

Because I never got to take American Literature II and I'm pretty sure Moby Dick was a required reading, I started reading it myself.  I'm almost certain that I'm missing out on things that would have been covered had I read it as part of a class, but I have noticed one thing about the narrative voice.

At the very beginning, Ishmael is clearly a first-person narrator.  The novel starts with his finding a room at a hotel and trying to find a ship to sail on.  But as the novel goes on, he becomes less and less of a first-person limited narrator.  Some scenes are written more like plays.  And I'm a bit dubious that Ishmael would have been present at them all, especially because some of those scenes occur at the same time.  Chapter 121 occurs at midnight at the forecastle bulwarks and is a conversation between Stubb and Flask.  Chapter 122 also occurs at midnight, but it's set aloft with Tashtego talking about the weather.  I don't see how Ishmael could have overheard both conversations at the same time.

He also starts referring to the crew as "the men."  Yet, since he is part of the crew, it would make more sense for him to say "us."  Because he describes the crew as something separate from himself, he doesn't seem to be physically present anymore.

So throughout the novel, the narrative voice changes from a first-person limited to a more third-person omniscient.  And I think that part of the reason that this changes may be Ahab's determination to catch Moby Dick and - more importantly - the crew's determination to go along with him.  In a way, the crew becomes less of a collection of various men and more of an extension of Ahab and his determination.  As the change in Ishmael's narration indicates, the men sort of give themselves up in order to help Ahab in capturing the whale.

EDIT (13 Sept. '13):  I finished reading the book to-day, and what I had vaguely described is explicitly stated in the book.  In Chapter 134, Ishmael writes, "They were one man, not thirty... and were all directed to that fatal goal which Ahab their one lord and keel did point to."