Wind Drift

Abstract

A STRONG wind at sea has long been known to cause a drift of the upper layers of water superimposed upon the regular and periodic tidal currents. Sailing coastwise in clear weather, the navigator can determine the position of his vessel by bearings on landmarks, but in thick weather he can no longer do this, and it then becomes a matter of importance to know the velocity and direction of the currents, both tidal and wind-blown, to which his vessel may be subject. In sailing and slow-moving ships, seamen have need to make a rough allowance for this wind drift, in addition to the leeway made by the vessel, when calculating their position by dead reckoning in bad weather. The necessary allowance has never been more than a guess, usually on the assumption that the wind-blown current runs in the direction of the wind, simply augmenting or decreasing the normal speed of the tidal currents.