Tidal stream

The rise and fall of the water level in the great oceans naturally causes a flow out of or into narrower seas, such as the English channel, though some (like the Mediterranean) are so narrow and shallow at their entrances that the effect is very limited. The flow of a rising tide is called the Flood, and that of a falling tide is called the Ebb. If the tide starts to come in, one may say that it is ‘Making’, though the same term is used for the period of days between Neaps and Springs when tidal heights are growing greater. During the reverse process, after springs, tides are said to be ‘Taking off’. Tidal streams are important to small craft because they commonly attain speeds of two or three knots, and in a four or five¬knot boat there is a world of difference between two knots against you and two knots with you. Apart from its influence on one’s speed of progress, the direction of the tidal stream is important in relation to the wind: ‘wind against tide’ tends to kick up a rough sea. (See also: Tidal atlas, and Height of tide.)