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Occasionally, the current drags a line of debris along its edge and, in clear shallow waters, marine plants will be deflected along its course. There may also be changes in the colour of the water caused by the disturbance of mud, silt, sand or gravel from the sea bed. On a rising tide, sea birds hovering and diving for fish, or an increase in the sea breeze, may provide further evi dence of surface movement. Becalmed a nd adrift on the current, a high sided craft is slowed by air resistance, whereas floating debris has little or no windage and a gradual separation of the two usually indicates the set (direction) of the current.

The Two Seconds Log

As a rough guide to the drift (speed) of the current, an item drifting past an anchored object at one knot will cover about one metre in 2 seconds. So, two metres in two seconds would represent two knots and so on.

Wind and waves

On a windy day in an estuary or a river, when the tide is ebbing or flowing, the current will be seen working with or against the wind through the behaviour of the waves. If the wind is against the current, the wave faces become short and steep and the sea is choppy. When the wind is with the current, the waves are much smoother and longer. In light winds and a calm sea, a related effect may be observed. With the wind and current working together, long smooth patches on the surface will often indicate where the current is flowing faster and offer ing less resistance to the wind. In the photo below, the yacht

Osmosis