Mapping Ocean Swells with Marshall Islands Stick Charts
Until World War II, Marshallese islanders mainly used stick charts to navigate canoes between the islands of Oceania. Lacking astrolabes, sextants or even a compass, they instead constructed maps from the midbribs of coconut fronds. Lashed together to form an open framework with islands represented by shells, the maps encoded complex information about ocean swells, the prevailing ocean surface wave-crests, and the directions they followed to approach an island. In this way, the stick charts captured data not traditionally included in navigation maps, but integral to safely navigating the seas. Furthermore, each map was unique, interpretable only by the navigator who made it. The maps were not taken along during navigation, but studied and memorized prior to a trip. Once on board, the navigator would would crouch down or lie prone in the canoe to feel how the hull was being pitched and rolled by underlying swells.