A sailor comes uneasily to a tortured tale of survival at sea, the conditions for it being both his worst nightmare and his suspected greatest challenge. A sailor doesn't want to read this book, but he is drawn to it partly to prepare for his own sea survival, a dark fear always slopping around in the bilge of his consciousness.

Sitting back in a chair far from the hypnotic sounds of water slapping against a hull, a sailor is made more uneasy that this struggle seems to have been so unnecessary: Our hero, apparently looking for some meaningful test in his life, thinks his self-designed and self-built tiny wooden boat, all of 21 feet, has a reasonable shot at navigating the Atlantic Ocean.

He was obviously wrong, and one has the nag that he should have known better. Having made it across the ocean to England, able to pick and choose the weather and helped by a companion, he decides to enter a single-handed race on the way back, a race that starts in a gale, with waves predicted to be 40 feet high. Before the race, a skipper asks: "Isn't it lunacy to start a transatlantic race in these conditions?"

A sailboat is a strikingly dynamic craft, constantly twisting and bending and flexing and working. When it is working too hard, it says so: a snapped halyard, a rudder that breaks a gudgeon, a mast that tumbles from the deck to the sea, any number of minor disasters that say, "too much." Warnings, one way or another, are given.

Callahan alludes to some anxiety about whether his boat, Napoleon Solo, could take it. He tried to insure it before he left, and he writes a bit defensively about its abilities. And he did have a warning: Several days into the transatlantic race he hit something in the water, probably a half-submerged log. The hull cracked open, pouring water into the cabin with "every passing wave." Callahan made a temporary repair and dropped out of the race, heading slowly and cautiously for the Spanish coast.

Several months later, the hull repaired and his boat now much farther downwind in the Canary Islands, Callahan left hastily for the Caribbean, sailing alone. It was the middle of winter, not the best time to go, and he knew that. During his first major storm, after one week at sea, he awoke in the middle of night to a loud "bang," and the boat was almost completely filled with water within 30 seconds.

The sinking of Napoleon Solo is a dramatic dividing line in this book. The haunting questions about how Callahan got himself into this fix become less important with each passing day. Life for Callahan begins anew in a round rubber raft about six feet across that drifts at less than 25 miles a day toward the nearest shipping lanes 450 miles downwind and the Caribbean islands 1,800 miles away. Water and food aboard the raft are good for about two weeks. To survive, he might need 90 days' worth. No one had ever survived alone on an inflatable raft for more than 40 days.

Callahan's survival requires a grind of desperate lifesaving tasks: jabbing at sharks day and night to keep them away, coping with a deteriorating raft that must be repaired often and pumped up at least four times a day, keeping the balky salt-water stills at work producing their meager ration of about a pint of fresh water each day, fishing and fishing and fishing, bailing, struggling with storms, and keeping a constant lookout for a passing ship. There is rarely enough fish to eat -- none of it is cooked and most of it will be so dry that it must be put in water for an hour before it is chewable. There is never enough water, and there is the constant threat that the stills will fall apart. There is never enough strength in Callahan's muscles, eaten away by his own body, which loses a third of its weight.

The raft is constantly vulnerable to attack from sharks, the water stills do wear out, the many contraptions devised for the spearing of fish fail, the raft is ripped open and nearly sinks, hundreds of infectedsalt-water sores eat away Callahan's flesh, and loneliness constantly works its curse. The physical struggle to stay alive is beyond describing, though Callahan succeeds in bringing it clearly to mind.

If all that there was to learn here was about survival, and survival at sea, it would be enough. But Callahan, in the midst of panic and desperation, is able to re-create the world of half-consciousness that a starved, dehydrated, lonely human roams in when left in a desert of sea. The real discoveries to be made in this tale turn out not to be about sailing, or surviving, or endurance. The real discoveries are about the human mind. Physically, a man alone at sea in a raft is totally outgunned: the wrong wave, the wrong shark, the wrong germ floating on a piece of seaweed; it is all simply a matter of time before something gets him or he is saved by raw dumb luck. Mentally, the battle is much more even, the odds really in the man's favor. Callahan's mind is his own savior.

It is a terrible, arrogant and even controversial cliche' that man is separate from other life forms on this planet because of his mind, but it is undeniably true and rather marvelously proven in Steven Callahan's case.