Tidal Streams
As opposed to tide which is the vertical movement of water, tidal streams are the horizontal movement of the water that accompanies tides. They are
not to be confused with ocean currents which are also horizontal movements but are not caused by the gravitational forces of celestial bodies. Another
major difference which is of particular importance to us is that while currents are more or less steady throughout the year, the strength (drift) and
direction (set) of tidal streams vary hourly and depend upon the celestial configuration of the sun and moon (spring/neap)

Tidal streams may be rectilinear (i.e. they have only two directions - flood and ebb) as found in port and river approaches, or they may be rotary 1.e
their direction changes continually right through a 360° circle in open waters. Tidal streams may also have diurnal and semi-diurnal components.

It is important for the mariner to know the direction and strength of the stream be ita current or tidal and to allow/counteract for it so that the course
made good is as laid out in the passage plan.

In earlier sections we have learnt how to counteract/allow for set and drift, but in those cases the set and drift was given to us in the exercise. In
actual practice it is essential for the mariner to know from where he is to obtain the set and drift of currents/tides.

Ocean currents information can be found in routing charts, sailing directions and on the navigation chart itself.
On routing charts the streams are shown with current roses and consistency information.

Set and drift Information is obtained from these sources and then used to calculate course to steer/ make good/ made good.

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