"No, his great genius is declared in his doing nothing particular to prove it"- The noble sperm whale

1/ Most of the chapter names are literal, i.e. tell us what the chapters are about: "The Chapel", "The Pulpit", "The Sermon", "The Ship", "The Cabin-Table", "The Mast-Head", "The Chart", "The Gam", "Brit", "Squid", "The Dart", "The Crotch", "The Tail", etc. 
Some chapter names, especially the anatomy chapters, are metaphorical: 
- "The Blanket" is about the whale's blubber. 
- "The Battering-Ram" is about the front of the whale's head. 
- "The Great Heidelburgh Tun" (I saw it on my trip to Heidelberg 2 years ago, by the way) is about the upper part in the whale's head called the case. 
- "The Prairie" is about the whale's "forehead". 
- "The Nut" is about the whale's skull and brain.
- "The Fountain" is about the whale's spout-hole. 
Ishmael wants us to see the whale, especially the sperm whale, clearly and does so through: 
- Descriptions. 
- Comparisons with human beings, and other animals: the whale in perspective. 
- Metaphors and similes. 

2/ Do I make it seem like Moby Dick is a tedious book filled with whale facts nobody cares about? Oh Melville is hilarious. I mean, read the passages where Ishmael praises the majestic look and superiority of the whale! 
From chapter 79 "The Prairie": 

"Physiognomically regarded, the Sperm Whale is an anomalous creature. He has no proper nose. [...] Nevertheless, Leviathan is of so mighty a magnitude, all his proportions are so stately, that the same deficiency which in the sculptured Jove were hideous, in him is no blemish at all. Nay, it is an added grandeur. A nose to the whale would have been impertinent. As on your physiognomical voyage you sail round his vast head in your jolly-boat, your noble conceptions of him are never insulted by the reflection that he has a nose to be pulled. A pestilent conceit, which so often will insist upon obtruding even when beholding the mightiest royal beadle on his throne..." 

Same chapter: 

"In thought, a fine human brow is like the East when troubled with the morning. In the repose of the pasture, the curled brow of the bull has a touch of the grand in it. Pushing heavy cannon up mountain defiles, the elephant's brow is majestic. Human or animal, the mystical brow is as that great golden seal affixed by the German Emperors to their decrees. It signifies—"God: done this day by my hand." But in most creatures, nay in man himself, very often the brow is but a mere strip of alpine land lying along the snow line. Few are the foreheads which like Shakespeare's or Melancthon's rise so high, and descend so low, that the eyes themselves seem clear, eternal, tideless mountain lakes; and all above them in the forehead's wrinkles, you seem to track the antlered thoughts descending there to drink, as the Highland hunters track the snow prints of the deer. But in the great Sperm Whale, this high and mighty god-like dignity inherent in the brow is so immensely amplified, that gazing on it, in that full front view, you feel the Deity and the dread powers more forcibly than in beholding any other object in living nature. For you see no one point precisely; not one distinct feature is revealed; no nose, eyes, ears, or mouth; no face; he has none, proper; nothing but that one broad firmament of a forehead, pleated with riddles; dumbly lowering with the doom of boats, and ships, and men. Nor, in profile, does this wondrous brow diminish; though that way viewed its grandeur does not domineer upon you so. In profile, you plainly perceive that horizontal, semi-crescentic depression in the forehead's middle, which, in man, is Lavater's mark of genius.
But how? Genius in the Sperm Whale? Has the Sperm Whale ever written a book, spoken a speech? No, his great genius is declared in his doing nothing particular to prove it. It is moreover declared in his pyramidical silence..."

From chapter 80 "The Nut": 

"... Now, I consider that the phrenologists have omitted an important thing in not pushing their investigations from the cerebellum through the spinal canal. For I believe that much of a man's character will be found betokened in his backbone. I would rather feel your spine than your skull, whoever you are. A thin joist of a spine never yet upheld a full and noble soul. I rejoice in my spine, as in the firm audacious staff of that flag which I fling half out to the world.
Apply this spinal branch of phrenology to the Sperm Whale. [...] For, viewed in this light, the wonderful comparative smallness of his brain proper is more than compensated by the wonderful comparative magnitude of his spinal cord..." 

From chapter 85 "The Fountain": 

"... But then again, what has the whale to say? Seldom have I known any profound being that had anything to say to this world, unless forced to stammer out something by way of getting a living. Oh! happy that the world is such an excellent listener!" 

Later in the same chapter: 

"... My hypothesis is this: that the spout is nothing but mist. And besides other reasons, to this conclusion I am impelled, by considerations touching the great inherent dignity and sublimity of the Sperm Whale; I account him no common, shallow being, inasmuch as it is an undisputed fact that he is never found on soundings, or near shores; all other whales sometimes are. He is both ponderous and profound. And I am convinced that from the heads of all ponderous profound beings, such as Plato, Pyrrho, the Devil, Jupiter, Dante, and so on, there always goes up a certain semi-visible steam, while in the act of thinking deep thoughts. While composing a little treatise on Eternity, I had the curiosity to place a mirror before me; and ere long saw reflected there, a curious involved worming and undulation in the atmosphere over my head. The invariable moisture of my hair, while plunged in deep thought, after six cups of hot tea in my thin shingled attic, of an August noon; this seems an additional argument for the above supposition.
And how nobly it raises our conceit of the mighty, misty monster, to behold him solemnly sailing through a calm tropical sea; his vast, mild head overhung by a canopy of vapour, engendered by his incommunicable contemplations, and that vapour—as you will sometimes see it—glorified by a rainbow, as if Heaven itself had put its seal upon his thoughts..." 

From chapter 86 "The Tail": 

"Being horizontal in its position, the Leviathan's tail acts in a different manner from the tails of all other sea creatures. It never wriggles. In man or fish, wriggling is a sign of inferiority. To the whale, his tail is the sole means of propulsion." 

Same chapter: 

"It is a little significant, that while one sperm whale only fights another sperm whale with his head and jaw, nevertheless, in his conflicts with man, he chiefly and contemptuously uses his tail. In striking at a boat, he swiftly curves away his flukes from it, and the blow is only inflicted by the recoil..." 

And: 

"... Excepting the sublime breach—somewhere else to be described—this peaking of the whale's flukes is perhaps the grandest sight to be seen in all animated nature. Out of the bottomless profundities the gigantic tail seems spasmodically snatching at the highest heaven. So in dreams, have I seen majestic Satan thrusting forth his tormented colossal claw from the flame Baltic of Hell. But in gazing at such scenes, it is all in all what mood you are in; if in the Dantean, the devils will occur to you; if in that of Isaiah, the archangels. Standing at the mast-head of my ship during a sunrise that crimsoned sky and sea, I once saw a large herd of whales in the east, all heading towards the sun, and for a moment vibrating in concert with peaked flukes. As it seemed to me at the time, such a grand embodiment of adoration of the gods was never beheld, even in Persia, the home of the fire worshippers. As Ptolemy Philopater testified of the African elephant, I then testified of the whale, pronouncing him the most devout of all beings. For according to King Juba, the military elephants of antiquity often hailed the morning with their trunks uplifted in the profoundest silence.
The chance comparison in this chapter, between the whale and the elephant, so far as some aspects of the tail of the one and the trunk of the other are concerned, should not tend to place those two opposite organs on an equality, much less the creatures to which they respectively belong. For as the mightiest elephant is but a terrier to Leviathan, so, compared with Leviathan's tail, his trunk is but the stalk of a lily. The most direful blow from the elephant's trunk were as the playful tap of a fan, compared with the measureless crush and crash of the sperm whale's ponderous flukes, which in repeated instances have one after the other hurled entire boats with all their oars and crews into the air, very much as an Indian juggler tosses his balls." 

3/ From chapter 85 "The Fountain": 

"Now, why should the whale thus insist upon having his spoutings out, unless it be to replenish his reservoir of air, ere descending for good? How obvious is it, too, that this necessity for the whale's rising exposes him to all the fatal hazards of the chase." 

What gives them life may be the very thing that brings them death. 
Just a short while ago Ishmael talked of the honour and glory of whaling, and described the skills, strength and bravery of whalemen, now: 

"For not by hook or by net could this vast leviathan be caught, when sailing a thousand fathoms beneath the sunlight. Not so much thy skill, then, O hunter, as the great necessities that strike the victory to thee!" 

Humble, hunters. 
Ishmael not only jumps from 1 topic to another, having an infectious enthusiasm for everything, but also constantly changes in his views and keeps contradicting himself. That's what makes him so fascinating.