Tides are one of the most important natural forces any boater needs to get their head around. Yet they’re often misunderstood or ignored entirely. Whether you’re planning a short motor cruise along the coast or preparing for an extended trip, understanding how tides work can make all the difference between a smooth passage and a frustrating or even dangerous experience.
What Makes Tides Happen
Tides are caused by the gravitational pull of the moon and the sun, along with the rotation of the Earth. Twice a day, seawater rises and falls in a pattern known as the tidal cycle. This rise and fall affects both tidal height and tidal flow, which are related but distinct phenomena.
Tidal height is the depth of water at a specific point at a given time. It matters when you’re thinking about whether you’ve got enough depth to float your boat safely over sandbanks, through harbour entrances or alongside a pontoon.
Tidal streams, on the other hand, are the horizontal movement of water caused by the tide. These can run at anything from a gentle drift to several knots, especially around headlands, through narrow channels or in estuaries.
Spring Tides and Neap Tides Explained
There’s nothing to do with the seasons here. Spring tides happen roughly every two weeks when the sun, moon and Earth are in line. This causes a bigger gravitational pull, leading to higher high tides and lower low tides. Tidal streams are usually stronger at these times as well.
Neap tides occur during the first and third quarters of the moon when the gravitational forces are more balanced out. That means the range between high and low water is smaller, and streams tend to be weaker.
If you’re new to tidal planning, neap tides are generally more forgiving, especially in tricky areas where a strong current could catch you out.
How to Read a Tide Table
A tide table gives you the predicted times and heights of high and low water for a given location. Most UK tide tables are based on a local standard port and often provide the time in either GMT or BST, depending on the season.
Here’s what to look for:
- The time of high water (HW) and low water (LW)
- The height in metres above chart datum
- Whether it’s a spring or neap tide (usually based on the tidal range)
For planning purposes, remember that tidal changes are not instant. The tide turns gradually, and the flow can continue even after the tide has technically ‘turned’. It’s worth knowing the rule of twelfths to estimate tidal height during the hours between high and low water, though modern tools can help you do this automatically.
The Difference Between Flow and Height
This is where some confusion creeps in. You might have high water at midday, but that doesn’t mean the tidal stream stops at that moment. In many places, slack water (when the stream pauses or turns) happens before or after high tide, depending on local geography. So, when you’re checking a tide table, don’t assume that slack water and high water are the same thing.
That’s why it’s always worth checking a tidal stream atlas or using a reliable forecasting tool that gives specific information about flow direction and strength.
Handy Tools for UK Tidal Forecasts
There are some brilliant apps and online tools to help you make sense of the tides:
- Admiralty EasyTide is a popular choice and gives detailed info for many UK ports
- Tides Planner (from Imray) offers tide times, height predictions and even tidal curves
- Local harbour websites and marina offices often publish tide tables and notes on tidal flows in their area
Paper-based tide tables are still a great backup, and many local chandlers or yacht clubs give them away free at the start of the season.
Learning to work with the tide rather than fight against it is a key boating skill that will save you time, fuel and stress. Once you get to grips with the difference between height and flow, how to read a tide table and what spring and neap tides mean for your plans, it all starts to feel much simpler.
It might seem like a bit of a mystery at first, but with a little practice, tidal planning becomes second nature. And when you’ve got the tide with you, there’s nothing better than the feeling of making smooth, easy progress through the water.