If Timothy and Dorothy Severin have their way (or rather find it), Columbus has had his day. The couple is convinced that America was really discovered by a leaky boatload of Irish monks—and nine centuries prior to 1492. Neither of the Severins is a Gaelophile or some other kind of nut. He's a British author-historian, she's an American-born medievalist, and they've produced 11 highly respectable books between them. But labeling Tim Severin an author is like kissing off Clark Kent as a reporter.

More aptly, perhaps, Severin is an Evel Knievel with a classical education and an intellectually questing lady. In researching two earlier works, he retraced the route of Marco Polo by motorcycle and explored the tricky 2,348 miles of the Mississippi River by canoe. Now, at 35, Tim is undertaking his greatest adventure: an odyssey from County Kerry to Boston in a 36-foot oxhide-hulled replica of a medieval currach. In just such a boat, according to legend, a Benedictine from Tralee named Brendan reached "the promised land" of North America in the sixth century A.D. It was Severin's wife, Dorothy, who first pointed out the Navagatio, an account of the exploits of St. Brendan (he has since been canonized), and questioned the accepted scholarly view that it was so much blarney. "The voyage was common knowledge in medieval Europe," points out Tim. "Putting it crudely, Columbus read about America in a book." So, "though it seemed a flight of fancy," Tim found that after intense further study, "its feasibility did check out uncannily right down the line. It was thrilling."

Dorothy will, reluctantly, leave the thrill of corroborating their thesis to Tim and a crew of four men. It's not sexism, she concedes, but the need for more muscle on the oars and the lack of a private cabin for her "to hide in." A further consideration, of course, is their 4-year-old daughter, Ida, since, as Dorothy perhaps understates it, the five-month passage is "not entirely without risk." But, at 34, she suffers from no secret widow wish, doesn't need an insurance windfall (she comes from Texas oil money) and has verified to her own satisfaction her husband's seamanship. Tim skippered a shakedown cruise last summer, taking her and Ida from England to Istanbul in their 27-foot sloop. So with the Severins' heightened sense of history, the vessel is scheduled to set forth from Brandon Creek on May 16, which the Irish just happen to celebrate as St. Brendan's Day.

"It wasn't hard to become a romantic," Tim confesses. "It was the easy option, and I had success at it." He was born a Watkins in India where his father managed a tea plantation. He later romantically adopted his present surname to keep the name of his mother's family—"a long line of mercenaries"—from dying out. Tim was polished in boarding schools in England and the U.S., and calloused as a cowhand in Montana before returning to Oxford to study historical geography. He bumped into Dorothy 10 years ago at a "jolly-up" (mixer) at Harvard, where he was scrimping by as a researcher between adventures. She'd come to Radcliffe from Dallas and, after graduating summa cum laude, was studying for her Ph.D. in medieval Spanish. Tim found her "enormously attractive," but Dorothy, who had just emerged from a brief first marriage, only saw "an eccentric Englishman" employing the hackneyed line, "Let's get out of here." She did agree, and 48 hours later he proposed "for the first time to anyone." Dorothy ("Dobby" to her friends) resisted for a month until "he finally overwhelmed me by proposing every day and wearing down my resistance."

They set out on a "mutually supportive" life combining her scholarship with his writing. They went back to Oxford first, then the West Indies, where Dorothy taught while Tim finished The Golden Antilles, a study of the region's colonization. Both Severins then lectured at Vassar for a year. Their base ever since has been Britain, where Dobby is an academic star at the University of London. Already as an undergraduate, she had published a study of a 15th-century Spanish work that scholars still consider the definitive treatment. And she has lately developed the gift of imparting her encylopedic knowledge to first-year students. Notes a senior member of her department: "Her lectures used to be too packed with detail, because she knew so much."

Home is a six-room Regency town-house in Bloomsbury. Dorothy is a strict mum("The discipline is in teaching self-discipline," she believes), and Ida will finish first grade at 4. Tim is the breakfast cook, family shopper and gardener. ("I have a black thumb," Dobby groans. "Everything I touch withers.") When his wanderlust phase is over, they hope to find his-and-her professorships at a university. "Women are not aggressive enough in applying for such posts," finds Dorothy, who is sympathetic but not completely converted to feminism. "It's rubbish to polarize the sexes," she goes on. "To declare war on one another is not what life is all about. People ask me how I manage my professional and home lives, as if there were an inherent conflict. Rather, I would not be able to function as well academically without the base of a happy family."

During the voyage on the good ship Brendan, Tim will reunite with Dobby during occasional landfalls like the Hebrides and Iceland. Though he has his book advance in hand, he observes, "This is an extremely hard and stupid way to make money if that were the purpose." He is not represented by Swifty Lazar, and the Severins have profounder satisfactions in mind beyond perish-or-publish. If all goes according to chart, he will hit Labrador by early September and may reach his final destination, Boston, on what until now has been called Columbus Day.