For a vessel drifting or sailing at low speed in the eastward portion of the tropics — which is exactly where the Hazana was — the North Equatorial Current is a significant factor in determining where the vessel ends up. At up to six knots in the strongest parts of the current, it moves a vessel substantially faster than a jury-rigged storm jib under most conditions.
Oldham found the current in the second week of her solo voyage. The specific observation that told her she had reached it was likely the apparent increase in her daily positions: when the chart showed she was covering more ground each day than her sail power alone could explain, the current was the explanation. The 19th parallel — approximately 19 degrees north — was the latitude at which the current was strongest and most reliably directed toward Hawaii.
Her goal, once she identified the current, was to maintain her latitude near the 19th parallel while the current carried her westward. This is an example of intelligent use of environmental resources: rather than fighting to maintain a direct course toward Hawaii at the cost of leaving the current, she used the current’s energy to cover the distance and adjusted her course as needed to stay in it.
The current reduced the number of perfect navigation days she needed. Instead of requiring that every day’s celestial observation be precisely accurate and that every steering decision be exactly correct, the current provided a buffer: as long as she was approximately in the right latitude band, the current would carry her roughly in the right direction. The precision still mattered — missing Hawaii to the north or south was still possible — but the tolerance for small errors was wider than it would have been without the current’s help.