Rip currents are offshore surface currents that re-circulate water out to the back of the surf breaks during high surf. They increase in strength as the surf increases and do not occur in calm seas.Rips tend to form in natural channels: between sand bars; in a river mouth or estuary; or along a pier, jetty, groyne or rock stack. In coves, rips tend to form along the edges. Look for a calmer, possibly rippled, channel between the incoming surf breaks. Sometimes the channel is deep green in colour, or may be carrying foam or debris, or stirring up sediment. The waterline at the shore will also be a little lower where the rip begins. Surfers often use rips to take them out beyond the breaks, so ask them for advice.

Tides are created by the moon. The sea floods as the tide comes in and levels rise. It ebbs as the tide goes out and levels drop. The power of the tide varies from day to day and affects the tidal range (height) and the flow rate (current). Tides are predictable but are highly variable and localised. Determinants of the tide’s strength include whether the water is slack, or in full flow (see rule of twelfths, left), and how close it is to a spring or neap tide.

Spring and neap tides are respectively, strong and weak. At full or new moons the sun and moon are, astronomically speaking, in line. This creates the strongest gravitational pull on the sea and therefore strong tides, known as ‘spring’ tides occur, roughly every fortnight. At half-moons, sun and moon oppose each other, resulting in weak gravitational pull on the sea and creating weak tides, known as ‘neap’ tides. Spring tides might typically have a range of 5–6m, and 3–4 knots peak current. Neap tides are about a half to a third of that range. ‘Springs’ and ‘neaps’ always occur at the same time of day for a particular part of the coast. For Atlantic-facing coasts such as Cornwall, Devon and west Scotland, the peak spring high tides are always around 6am and 6pm – very handy for enjoying really low-tide beaches in the heat of the day!

The direction of flow is of vital importance for swimmers. Britain’s south and west shores fill from the Atlantic up into the English Channel and Irish Sea, so tidal currents flow east in the flood and are progressively later as you go east to Dover or north to Liverpool. Britain’s east and north coasts fill from the North Sea, with waters moving south in the flood and becoming progressively later as you go south down the east coast. The east Dorset coast has very small tides where the two flows cancel each other out.

Coves and bays are protected from tidal flows (though of course the sea levels will still change) but open coast is exposed to tidal currents. Currents strengthen around restrictions, such as headlands or islands (Portland Bill or Ramsay Sound) or at estuary or harbour mouths (Chichester Harbour or Blackwater Estuary). Remember that at an estuary or river mouth the current will be carrying you inshore as the tide comes in (relatively safe) but offshore when the tide goes out (potentially very dangerous).

Rule of twelfths
If in doubt avoid the fastest flow in the middle hours of the tide. In the first hour of the tide, approximately one-twelfth of the water moves; in the second hour two-twelfths moves, during the third hour three-twelfths moves, and so on as the flow-rate decreases again.

What time is the tide? Tide cycles repeat every 12 hours, occurring half an hour later each time. They occur about an hour later each day.

Spring tides
Contrary to popular belief spring(strong) tides occur every fortnight at new and full moons and are only partly affected by the season.
Find tides for the whole country at the BBC tide website