Their wives, it should be said at the outset, do not entirely approve: Bob and Ralph Brown, two 50-something brothers, are planning to steer their 21-foot flats boat—a motorized fiberglass raft—across the Atlantic Ocean to honor three Marines who died for their country nearly 30 years ago.

The boat has a canopy roof, but no cabin. Crowded with gas cans and water bottles, it looks like a kind of floating bachelor pad—the brothers themselves have the demeanor of overgrown frat boys. Genial and straight-faced, they plan to live on fruit cocktail and “hand snacks” (potato chips, energy bars) for the next 48 days. They have fishing rods, but no cook stove; there’s cereal in case of emergencies. They will take turns sleeping, outfitted in foul-weather gear and lashed to the boat, on a child-size air mattress. “The air mattress really makes it a lot better,” says Ralph, a former Marine himself. “You just go ahead and lay down and get wet.”