He begins with an outline of the problems he faced investigating indigenous navigation in the 1960s and 70s and the complexity of the evidence: often fragmentary and partial continuing traditions, early European contact records, archaeology, and so forth. And he outlines his own experiences learning from indigenous navigators, and the practical problems he faced, linguistic and logistic. His own experience mostly came from the Carolines, "where a relatively complete navigational discipline is still extant", the Santa Cruz Reef islands, the Gilbert Islands, and Tonga, but he draws on evidence from across the Pacific and island Southeast Asia.
First comes a survey of the key material infrastructure, looking at voyaging canoes and their sails and at their capabilities in terms of speeds and loads. Then he looks at steering by the stars, at keeping course by sun, swells and wind, at dead reckoning and the estimation of time and speed, and at the use in orientation of etak or reference islands. He also considers some skills that were "very possibly limited to highly trained specialists", notably position reckoning using zenith stars and possibly water temperature and salinity.
"Of course, steering by horizon stars is every bit as accurate as by magnetic compass and probably easier than trying to follow the gyrating compass card of an island schooner or a yacht. The snag is that the navigator who is going to use the stars as we would a compass must be so thoroughly familiar with the night sky that he can orient himself when no more than one or two stars are visible, an ability shown repeatedly by both Tevake and Hippour."
Landfinding was assisted by various methods of "expanding the target". Here Lewis looks at island blocks, birds, clouds, swell patterns and phosphorescence, and at some examples of how this works in practice.
"Noddies and white terns, as we know, are consistent land guides to double the sight-range of atolls, or 20 miles offshore, and this applies throughout the Carolines and Gilberts. That it holds good elsewhere is suggested by the observations of Captain Anderson, who was born on Fanning Island and who gives the same figure of 20 miles for noddies, though a much greater one for white terms. Hawaiian data seem to indicate that these ranges apply there also. It seems reasonable to suppose, therefore, that the fishing zone of the noddies is the same in Polynesia as in Micronesia, and that of the white terns at least as big and possibly bigger.
Stepping back a little, Lewis considers the reasons people in the Pacific had and have for voyaging and applies "navigational criteria to certain ancient routes that we know were once traversed either accidentally or with intent". An addition to the 1972 first edition is a chapter describing the high profile 1976 voyage of the "performance equivalent" replica Hokule'a from Hawaii to Tahiti.
"If this necessarily incomplete examination of the motives for voyaging has illuminated the subject at all, it will have shown the plurality of the travelers' aims, the only common factor in their attitudes being self-confidence at sea. Extant Carolinean practice shows that this is the reverse of recklessness, caution and conservatism being stressed."
Lewis provides enough background — with explanation of even basics such as the problem of dead-reckoning in the presence of currents — to make the material accessible to someone like myself with no sailing, let alone navigation, experience. I had expected to skim much of We, the Navigators, but ended up reading almost all of it. (Some details are left to 15 pages of appendices and 30 pages of notes.) It's an engaging treatment of a fascinating subject.