Even without getting anything from the slop chest, your share of the profits of a whaling voyage could be little or nothing, because there was no guarantee that the voyage would make a profit. If the ship came back full of oil in five months, well and good, but if it had trouble finding whales, and was out for two years, and it had to buy supplies along the way, then it wouldn't do as well. (Which sea song is it that ends with "You've slaved away two years of your life, and you've earned about one pound one"?)

As to current conditions for sailors: I served on a jury for a case in which a merchant sailor was suing his employer. It was the kind of case that I would have expected to be handled as a Workmens Compensation claim instead of coming to court: the sailor's feet had been injured in an accident, he had been able to return to work, but he was trying to recover the cost of his physical therapy. Since this did come to court, I take it that U.S. merchant seamen are not covered by Workmen's Compensation.