Stick chart. "The Marshallese recognized four main ocean swells: the rilib, kaelib, bungdockerik and bundockeing. Navigators ... mainly concentrated on refraction of swells as they came in contact with undersea slopes of islands and the bending of swells around islands as they interacted with swells coming from opposite directions. The four types of ocean swells were represented in many stick charts by curved sticks and threads." From http://en.wikipedia.org/wiki/Marshall_Islands_stick_chart
Polynesian star charts made of sticks for navigating at sea. The charts were made by men from thin strips of coconut frond midribs or pandanus root. They were then bound together with coconut sennit in geometric patterns depicting sea currents around the low lying atolls. Small money cowrie shells or coral pebbles indicated islands and curved sticks represent wave patterns.