From The British Museum:
The Marshall Islands in eastern Micronesia consist of thirty-four coral atolls spread out across an area of several hundred miles. In order to maintain links between the islands, the Marshall Islanders built seafaring canoes. These vessels were both quick and manoeuvrable. The islanders developed a reputation for navigation between the islands - not a simple matter, since they are all so low that none can be seen from more than a few miles away.
In order to determine a system of piloting and navigation the islanders devised charts that marked not only the locations of the islands, but their knowledge of the swell and wave patterns as well. The charts were composed of wooden sticks; the horizontal and vertical sticks act as supports, while diagonal and curved ones represent wave swells. Cowrie or other small shells represent the position of the islands.*
From "Traditional Marshallese Stickchart Navigation:"
While modern charts are universal and can be used to navigate from any location on the chart to any other location on or even off the chart, the Marshallese stick charts are predominantly uni-directional. They explain how to get from a given starting point to one or more target points. As the wave patterns for the return voyage are different from the patterns of the initial voyage, the charts of little use to navigate back, let alone to navigate between other islands marked on the stick chart. In the light of this, then, it is not surprising that the charts were not taken along on the voyage. The necessary knowledge would have been memorized anyway, and the chart would have been useless at any location other than the starting point.*
As a graduate student in 2005, Genz traveled to the Marshall Islands with a team of anthropologists and oceanographers for what he calls a “revival project.” Traditional navigational knowledge, he says, was dying out with the islands’ oldest generation, and the team from the University of Hawaii agreed to help the elders document and resurrect the Marshallese understanding of the seas.
Using a combination of satellite imagery, computer modelling and a buoy to measure wave frequency, size and direction, they were able to “validate and confirm some of the local explanations with the scientific explanations,” Genz says—but out on the water, away from their equipment, the researchers still found themselves at a loss to explain some of the things the Marshallese seemed to know instinctively. “A lot of times the navigator would say, ‘There’s the wave, can you feel it?’ and I’d say, ‘No, I can’t,’” he recalls. “Part of it was trying to feel what he was feeling, but not being able to see it.”Cari Romm, "How Sticks and Shell Charts Became a Sophisticated System for Navigation." Smithsonian.com, January 2015.
Mattang, 19th–early 20th century. Republic of the Marshall Islands. The British Museum.
Rebbilib, 19th–early 20th century. Republic of the Marshall Islands. The Metropolitan Museum of Art.
Rebbilib, 19th-early 20th century. Republic of the Marshall Islands. The British Museum.
More images of stickcharts at the nonist.