Navigating without instruments is not a precise science. Poor weather and reliance on one person’s memory affect its accuracy. Therefore, if wayfinders are navigating to an island group, they can aim for a ‘screen’ of islands rather than a particular destination. Islands in the Pacific are often found in clusters, giving wayfinders a target screen of up to 600–800 km sometimes. Once an island is reached, the navigator can reorient the waka after identifying that island and sail to the desired destination.
Once the waka is in the vicinity of its destination (according to the wayfinder’s dead reckoning and latitude measurements), wayfinders can start looking for land. They look for signs of land that might suggest the proximity and direction of land even when it is not visible.
Using behaviour patterns of diurnal birds
Seabirds that feed on fish during the day and return to land at night to rest are the best sign of land for navigators. As the birds leave land in the morning (to feed from the ocean), wayfinders can sail in the direction they are coming from to find land. In the evening, wayfinders follow the birds as they head back to land from the ocean. In the Pacific, the two birds that are the most reliable indicators of land are the white tern, which can travel nearly 200 km out to sea, and the noddy tern, which can travel about 65 km out to sea.
During the nesting season, the behaviour patterns of the birds change. The birds fly out to sea before sunrise and then fly back mid-morning to feed their young. Seeing a bird flying with a fish in its mouth in the morning is a strong clue the bird is nesting. Without this knowledge, wayfinders could be fooled by these nesting activities and direct their vessel in the opposite direction.
Generally, sighting a large group of birds is more reliable than sighting one or two stray birds.
Signs of land
Besides looking for seabirds, wayfinders depend on a number of techniques to avoid sailing through a screen area without seeing any land. Signs of land include drifting land vegetation, clouds piled up over islands, the loom above an island created by sunlight or moonlight reflecting up from white sand and smooth lagoon water and distinctive patterns of swells created as they refract around or reflect off islands
Wayfinders also look for deep phosphorescence, which can appear like underwater lightning, flashing out when nearing land. Scientists think this flashing could be the defence response of dinoflagellates against predators, such as fish larvae and small crustaceans. The flashing signals the predators’ presence to their predators such as fish. These flashes can be spotted 130–160 km from land and can be used to steer by on dark nights.
In the same way that people use landmarks to get their bearings, wayfinders use seamarks. For example, the famous navigator Mau Piailug once told his crew on a voyaging expedition to look for a school of porpoises to indicate they had reached around 9°N latitude en route to Tahiti. The porpoises were duly sighted at this latitude.
Seamarks are sightings of certain phenomena within a particular region that indicate to the sailors where they are in that region. Hundreds of traditional seamarks are stored up in the memory of navigators as a result of the cumulative experience of generations of sailors within a region. For example, extraordinary numbers of sharks or jellyfish or terns in a particular region may indicate that the vessel is a day’s sail downwind of land or is approaching the entrance into a particular lagoon.
Micronesian sailors have described seamarks such as a tan shark making lazy movements, a ray with a red spot behind the eyes, a lone noisy bird, a row of whales and so on. Each of these phenomena is associated with particular islands and is a strong clue as to the sailors’ whereabouts and distance from land (for example, the row of whales indicated that a day’s sail south would reach land).
Calculating the distance to visible land
Islands that have high mountains can be spotted from over 100 km away. However, if the land is low lying with trees the highest points, wayfinders must be within about 10–16 km to see them.
A formula for calculating an approximate distance to land is: D = 3.57(√H + √h)
If the highest point of distant land is H metres and we are standing h metres above water, then we will see the first tip of land on the horizon (in clear weather and calm sea) when we are approximately D km from the peak.
For example, say the highest point of a mountain on an island (H) is known to be 1500 m. The square root of 1500 is 38.73. On the deck of the waka, a navigator stands about 2.7 m above the water (h). The square root of 2.7 is 1.64. Adding those together (38.73 + 1.64) and multiplying by 3.57 gives the number 144. Therefore, the navigator will see the tip of the mountain from a distance of about 144 km.
More accurate formulae for calculating distances to land and horizon.
This Hawaiian site shares more about navigational signs.
This Hawaiian site describes making landfall.