Meddo charts also showed the direction of main deep ocean swells and distance from a canoe at which an island could be detected .
The direction of main deep ocean swells is the way the swells curved around specific islands and intersected with one another .
Meddo charts also showed the direction of main deep ocean swells , the way the swells curved around specific islands and intersected with one another , and distance from a canoe at which an island could be detected .