A ship will drift regardless of whether she is stopped or underway due to the action of the wind and sea. A knowledge of this movement is necessary in order to correct the course, to deduce the estimated position, for manœuvring at slow speeds and for search and rescue work. The causes of drift are the force of the wind on the upperworks, drift current whose strength depends on the wind, rolling which is caused by the action of sea and swell and, finally, ocean currents and tidal stream currents. To study the effect of wind on drift an experiment was carried out in which this effect was isolated from the other causes mentioned above.

A salmon drifter was used in which a gill-net was observed by radar from the time of the net being shot until it was hauled in. The net was then allowed to drift with the ship with the ocean current, the tidal stream current, the drift current and the wind and sea. The ship itself, however, was also subject to drift from the wind whereas the corner reflector on the net (which was several miles long) was not subject to this effect, the net acting as a sea anchor. It was thus possible to isolate the effect of wind drift.