shift one's tides

Verb

 * 1)  To record the variations of the tide and the positions of the sun and moon using a nautical almanac and sextant to determine the location and phase of the moon and to calculate the relative effect of the tides on the navigation of the ship.

Usage notes
The term appeared (as shift his tides, referring to the male sailor performing the operation) on the certificate of examination for prospective lieutenants in the Royal Navy.