The Last Navigator <i> by Stephen D. Thomas (Holt: $19.95; 299 pp., illustrated) </i>

Explorations of the unknown become ever more difficult--ever more seductive--in a world shrunk by jet speeds, electronic images and computer communication.

Stephen D. Thomas is a dual explorer, simultaneously trying to rediscover an ancient system of sailing, using only nature’s navigational signals, and trying to find himself in the myth-made culture of Micronesia. Boat-maker, photographer, author Thomas has already turned his travels into a PBS documentary, “The Navigators,” and here in book form offers an expanded log, introspective and instructive, with illustrations and diagrams tracking his search.

A man in quest may need a mentor. Thomas’ mentor is a native of Satawal, a remote island among the Carolines, two weeks away from Yap by slow freighter. Navigator Mau Piailug is a proud, sometimes angry descendant of a people who sailed into the unknown about 6,000 years ago: “Long before Columbus and Magellan, before Europeans had even dared to venture beyond the sight of land, a nation of seafarers had already discovered and colonized the vast expanse of Pacific islands.” Translating Piailug’s lore for becoming a respected palu , or navigator, often becomes hard going. Pookof is a system of charting based on the sea creatures living around each island. Pukulaw is a way of analyzing ocean swells to determine course in daytime. Etak is a mental construct of a voyage, not-so-unlike dead reckoning but with far fewer reference points.

Easier going is Thomas’ explanation of his two long excursions in Caroline culture, where itang is “the talk of wisdom” and where the aging navigators sometimes battle with the tribal chiefs for resident respect. Piailug frequently complains about seeing his people--his own children--ignore the ancient ways and desert the traditional values as they explore a less familial society based on an American model. His children went to high school but did not sit at his knee for lessons in boat-building or fishing: “They never came to learn from me.”

Thomas came instead, looking for a father figure, for a kind of cosmic navigator who could plot a way across life as well as a way across oceans. Both mentor and student were bound to be disappointed. The palu sometimes seemed remote, sometimes drank too much, sometimes was too easily offended when Thomas searched out other authorities. The palu once even made a navigational error. The author always seemed to expect too much, to want to become at one with Satawal, although his looks and language and lore were so obviously alien.

To Thomas’ credit, what he learns by the end of the book is the vainglorious nature of his quest: “My original dream to apprentice myself to a master of forgotten knowledge still seemed worthy, albeit naive.” He poured gin into a coffee cup and “snorted at the puerility of it all. If I stripped away all the romanticism of the Pacific-island setting, the outrigger canoes, the leathery, tattooed men and bare-breasted girls, all I really had was a dozen notebooks full of notes. . . . Piailug could have been a house-builder in Milwaukee who had learned his craft from his father.”

Certainly. And the father complaining about the kids who wouldn’t listen to him could also be in Milwaukee or other parts of the Western World. Ralph Waldo Emerson discovered the impossibility of finding a new self through travel in the 19th Century, reminding any outgoing voyager that the old self is always part of his luggage.

But Thomas came home from school on Satawal with some valuable lessons and larger luggage. Several appendixes describe the old navigation in sufficient detail for moderns who may want to venture from San Pedro by bird and cloud cover. Navigation itself, in island terms, is a course in “fierceness, strength and wisdom”--a metaphor for being able to chart a life and follow it. And sailing backward in time along the itang may be a necessary method of plotting the future, recognizing the astonishing accomplishments of human continuity. A travel book with a dream, even one unrealized, teaches more than travel with a mere destination.