NAVIGATING BY OCEAN SWELL:
Prevailing winds or storestormsms generate swells which pulse across the ocean for thousands of miles. Under overcast skies navigators could maintain their heading by keeping a constant ration between the amount of pitching or rolling induced by a dominant swell, holding direction until guiding stars became visible again.

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NAVIGATING BY ISLAND GROUPS:
Signs of unseen land expand low or obscured island targets by 25 or 30 miles. In island groups these extensions often overlap, forming broad targets. To fins an island within a group, voyagers could aim for the approximate center of the group, then change course to specific destination after sighting a familiar island. Sailing from Ra'iatea to Rarotonga, navigators sighting any known landfall in the Cook Islands chain could then sail to a position for an accurate course to Rarotonga.