One clear advantage to setting his story on the open ocean in the context of a whaling expedition is the implication of a life-and-death conflict as a necessary part of the story.
This is true as an element of the purpose of the whaling expedition as whales will certainly die if the trip has even a little success. More importantly, perhaps, is the chance for people to die as they attempt to plunder this mysterious and elemental medium - the sea.
The voyage of the Pequod is no straightforward, commercially inspired whaling voyage.
Melville knew very well how dangerous whaling could be. Man's greatest fear, the fear of death, exists side-by-side with a very passionate mode of living, one that is physically demanding, competitive, and uncertain.
Viewing the Pequod’s voyage as a metaphor for life, the book seems to be saying that in following ambition or any far-off goal, an individual risks missing out on many of the good things in life, including home and domestic happiness.
Whaling provides the tension of conquest, the dangers of failure, and the heightened expectations of adventure.
Melville stated that the sea was his teacher: "A whale ship was my Yale College and my Harvard." The whale is a cosmic force upon the world of the ocean and acts as a symbol in this most of metaphysical compositions. The whale's power is magnificent, it is inscrutable to Ahab who wishes to break through its "pasteboard mask." Like the whale for Ahab, Melville felt evil in life, complaining that
the malicious Devil is forever grinning in upon me, holding the door ajar.
Moby-Dick is perhaps my favorite American novel -- the closest I think we have yet come to producing a true American epic. Melville knew the whaling industry from personal experience and thus could write with authority, but he also recognized in the industry a truly massive subject that would allow him to explore practically all facets of the human condition (except, curiously enough, relations between the sexes). The whale was, in the nineteenth century, the closest thing left to a true monster -- a kind of modern dragon -- and could thus be used in all kinds of symbolic ways. One reason people often don't like the book is that they think it's mostly about whaling, when in fact it merely uses discussion of whaling as an opportunity to discuss practically everything else as well. The book is powerfully written, and few people seem to realize how very, very funny it often is. Melville chose a subject that allowed him to give full expression to his knowledge and his imagination and to show that he was a deeply thoughtful man on many, many subjects besides the pursuit of whales.
One of the reasons he wrote about the whaling industry was his own experience as a sailor aboard the whale ship, the Acushnet. His sojourn as a sailor was prompted by a lifelong fascination with the whaling stories that his era heard and read of in plenty. One that particularly caught Melville's interest was the wreck of the Essex, which he read about in a first-hand survivor's account of the event. Another was the continual stories of encounters with a white whale called Mocha Dick that swam off Chilean waters near the island of Mocha.
I hate this book! I must say that it does have powerful imagery though. We now consider the whaling industry cruel and disgusting. However it was very important for quite some time. It also is a useful backdrop for a dramatic tale!
Let us remember for one moment that the United States as a nation has a rich history of being involved in whaling. It began its whaling industry in the seventeenth century, when the Massachusetts coast and the island of Nantucket were used as bases from which ships would launch whaling expeditions. Although initially the early whalers stayed close to land and only hunted whales who strayed close, in 1712 a whale ship was blown out into the deeper ocean thanks to a freak storm, and as a result encountered sperm whales. The capture of one of these sperm whales and the superior quality of the oil gained from this creature resulted in American whalers hunting down these creatures in deeper seas and during longer voyages. Such whalers would often travel extensively, even going into waters that had not yet been charted, and such voyages helped greatly in the development of cartography. This novel was written during the peak of the American whaling industry, thanks to the massive demand for products gained from whales at home. At this point in history, the United States possessed roughly three-quarters of the whaling ships in the world, making it the principal whaling nation.
In addition, critics pay much attention to the fact that in the same year that this novel was published, a whale seemed to assume the persona of the ferocious white whale in the novel in attacking a whaler and sinking it. Thus the contents of the novel do not seem to be too fantastic or beyond the realms of possibility.