When skies are too overcast for navigators to use the sun, the moon, planets or stars, ocean swells can fill in as a rough guide to direction. An experienced navigator can sense the direction swells are coming from as they pass under the waka. If you note the direction from which the swells are coming at a time when the stars are visible, those same swells can guide you when the stars disappear.
In the Pacific, prevailing north and south-easterly trade winds push up swells that remain constant for long periods. Navigators keep their waka at the same angle to these swells. Sudden changes in waka motion indicates that it has changed course.
But swell patterns can and do shift, so a navigator can't rely on them all the time. When all else fails, and there's no way to keep a correct bearing, a good navigator 'heaves to'; that is, takes down the sail and waits until he or she can set the course again.
In the Pacific, prevailing north and south-easterly trade winds push up swells that remain constant for long periods. Navigators keep their waka at the same angle to these swells. Sudden changes in waka motion indicates that it has changed course.
But swell patterns can and do shift, so a navigator can't rely on them all the time. When all else fails, and there's no way to keep a correct bearing, a good navigator 'heaves to'; that is, takes down the sail and waits until he or she can set the course again.