Like countless Gloucester fishermen before and since, Howard Blackburn and Tom Welch were trawling for halibut on the Newfoundland banks in an open dory in 1883 when a sudden blizzard separated them from their mother ship. Alone on the empty North Atlantic, they battled towering waves and frozen spray to stay afloat. Welch soon succumbed to exposure, and Blackburn did the only thing he could: He rowed for shore. He rowed five days without food or...