Jfc. This book took me a year and one month to read (possibly due to my poor attention span and the onslaught of whale/maritime data that I have to make sense of) I ended up finishing the book instead of abandoning it out of pure spite. 

The first part (around ⅓) is interesting and Melville's humor is hilarious. The second part is dry and the plot moves slower than before, it's just pure whale facts– Melville basically bludgeons you into submission with an encyclopedia. The latter part of the book (thankfully), the action picks back up. 

Also, the prose can sometimes cause a headache or two so you may need to list down (and search) some of the maritime terms used to avoid future confusions.