With roughly 100,000 large merchant ships in the water at any time, scores sink, burn, break apart, run aground, or explode each year—often with toxic consequences. It is Captain Nick Sloane's job to board troubled vessels and salvage what he can. Against heavy odds, he recently refloated the doomed cruise ship Costa Concordia. William Langewiesche explains why Sloane may be the most valuable man on the seas ... Every ocean voyage involves risk. This has always been, and will always be. Currently about 100,000 large merchant ships sail the seas. If past patterns hold, during the next 10 years some 25,000 of them will be categorized as insurance casualties. Another 1,600 will be lost—roughly one ship every two and a half days. Some fraud is involved, but most of the losses are real. Though safety is said to be improving, it is evident that the oceans remain wild and will not soon be tamed. ... In that light one of the greatest seafarers at work today is neither a naval commander nor an old-salt merchant mariner but a certain marine salvage master with a taste for chaos and a genius for improvisation. He is a burly South African, aged 53, by the name of Captain Nick Sloane. His job is to intervene where other captains have failed, and to make the best of ships that are sinking, burning, breaking apart, or severely aground. Usually those same ships are threatening to leak bunker fuel—the sludge that powers them—along with crude oil or other toxins in quantities that could poison the environment for years to come. Sloane boards the ships with small teams—by helicopter from overhead, or by Zodiac from oceangoing tugs—and once he arrives he stays aboard and fights, sometimes for weeks at a stretch. ... He is tenacious in part because of the financial stakes involved. By well-wrought tradition, rescuers are not recompensed for saving lives at sea, but those who save a ship have a claim to a large part of its value, including its cargo. The final payout involves calculations not only of the ship's total value but also of the difficulty and danger involved in making the save. Today the payout is usually determined through Lloyd's of London, after the work is done, and on average amounts to perhaps 12 percent of the assessed value, except in disputed cases referred to arbitration, where the payout may climb higher. Such cuts amount to millions of dollars. On the other hand, expenses have to be paid out of pocket, and if the salvors fail to save the ship, they may win nothing at all—not even a thank-you for trying.