Moby-Dick Questions Chs. 43-46: How does ch. 43 move the narrative forward

How does ch. 43 move the narrative forward?  What does it add to the novel?  In ch. 44, where is Ahab taking the ship, and why?  How is the end of ch. 44 deepened by Ishmael’s analysis of whiteness at the end of ch. 42?  What is Ahab without Moby Dick?  Why does Melville title ch. 45 “The Affidavit”?  What is the purpose of Ishmael making the “special point” on the bottom of page 224 [173] about the ship Essex.  Note that the story of the Essex in 1820 is a true story.  Why does Ishmael include a footnote about Owen Chase; what is the purpose of this footnote?  What does Ishmael surmise about Ahab in ch. 46?  What is meant by the “charge of usurpation”?