Tell the direction of the tide

Tides... put simply, they're the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun, and the rotation of the Earth. And currents – they are what put the motion in the ocean!

To summarise: tides involve water moving up and down, while currents involve the movement of water back and forth – that motion driven by several factors including the tide, wind, the shape of the land, and even water temperature.

Anyone spending time on or in the water needs accurate tide and current data to aid in navigation, but these measurements also play an important role in keeping people and the environment safe – even if you're just walking along a beach, a change in water level due to tides could leave you stranded. Predicting and measuring tides and currents is important, too, for  getting cargo ships safely into and out of ports, determining the extent of an oil spill, building bridges and piers, choosing the best fishing spots, environmental restoration, and much more.

There are a few simple ways to determine the direction of the tide

• Look at how the water is moving around an object within it – a buoy, for example. If the tide is running quickly, you'll see the buoy being 'pushed' by the tide and there'll be a still patch of water just behind it.

• Look at how a boat tied to a mooring buoy or at anchor is sitting in the water. Generally – and particularly with a yacht – the bow will point into the tide. In other words, the front of the boat will point to the direction from which the tide is coming.

• Look at how anything floating in the water is travelling. Detritus will be carried up- and downriver, or towards and away from a beach, depending on whether the tide is flooding (rising) or ebbing (falling).

Did you know that there are two types of tide?

Spring tides occur around the time of a full moon and new moon, approximately every two weeks. Neap tides occur on the half moons. Spring tides are more extreme, so a 'low spring' will be lower than a 'low neap', while a 'high spring' will be higher than a 'high neap'. The actual heights and intervals of tides vary according to where you are, but basically on spring tides, more water is moving further between the two extremes, and this means that the currents are correspondingly stronger on springs than on neaps.

The rule of twelfths

In the UK, there are usually two high tides and two low tides each day – this is known as a semi-diurnal regime. It takes 24 hours and 50 minutes (a lunar day) for any particular location on Earth to re-align with the moon, and this extra 50 minutes means that the same location will experience high tides every 12 hours 25 minutes – the exact time varies between different locations because local geography has an effect on tidal dynamics.

As a general rule of thumb, more water moves during the middle two hours of an incoming (flood) and outgoing (ebb) tide, and this results in stronger currents. For a fast estimate of what the tide might be doing at any particular time, sailors refer to the 'Rule of Twelfths':

In the first hour after low water, the tide rises one-twelfth of its range; in the second hour after low water, the tide rises two-twelfths of its range; in the third hour after low water, the tide rises three-twelfths of its range; in the third hour before high water, the tide rises three-twelfths of its range; in the second hour before high water; the tide rises two-twelfths of its range; and in the last hour before high water, the tide rises one-twelfth of its range. 

If you can grasp this concept, you can see that slack tide – where the water barely moves – is usually one hour either side of high or low tide.

If you're planning to sail into a marina or harbour that's known to be a tad 'tricky', then it's often wise to time your arrival for slack water. Equally, if you're new to 'wild swimming' or Stand Up Paddleboarding, it’s generally safer to do this on a slack tide too. Do note, however, that the actual time of slack water may vary from official high or low tide times, depending on local geography and weather conditions... it's always advisable to seek good local knowledge.