One example of what we mean when we argue that the style of Moby-Dick is convoluted is to read the third paragraph of Chapter 42 ("The Whiteness of the Whale"), which, you might notice, is a single, 471-word sentence.
But just in case you wanted to learn about the novel’s style and you don’t have an hour or two to hand, we’ll look at a slightly shorter sentence from the paragraph before that:
Aside from those more obvious considerations touching Moby Dick, which could not but occasionally awaken in any man's soul some alarm, there was another thought, or rather vague, nameless horror concerning him, which at times by its intensity completely overpowered all the rest; and yet so mystical and well nigh ineffable was it, that I almost despair of putting it in a comprehensible form. (42.2)
If you’re not ready to just read that and agree with us by saying, "whoa, yes, that’s convoluted," think about it this way: the basic barebones of this sentence are the words "There was another thought." The subject of the sentence is "thought" and the verb is a conjugation of "to be" – what could be simpler?
But Melville embroiders this basic structure with lots of other words, until we have this elaborate verbal edifice with six different, interrelated clauses. And don’t get us started on the joke that Ishmael uses this incredibly contorted and complicated sentence to say that it’s going to be hard for him to phrase his thoughts in a way that’s easy to understand.
Apart from just being complicated and highly wrought (that is, elaborately crafted), Melville’s style in Moby-Dick is ornamented by really complex diction: "He was intent on an audacious, immitigable, and supernatural revenge" (41.23). Even when Melville’s sentence structure is straightforward, Melville uses complex, ornate vocabulary to generate a sense of grandeur and magnitude, elevating the dignity of the novel.