Sailing around a headland in the British Isles will nearly always involve an encounter with tricky tidal races and overfalls, a ‘commotion of the sea’, best visualised as broken or disturbed water.

But before you let the spray scare you, remember it’s not all bad. Sometimes you can use tides and tidal currents to your advantage.

Tidal races: what to look for on the chart

The first thing to do when considering tackling a headland and an associated tidal race is to look for the overfall symbols on a chart. Imray charts mark them with ‘curling waves’. Garmin’s Navionics have grey ‘shark fins’. Admiralty publications have a single peak ‘mountains’. This is similar to the insignia for ‘sand waves’.

There are several of these, for instance, in Mount’s Bay off south-western Cornwall. These denote an underwater feature, not a surface one we are concerned with here.

Small-scale charts can denote overfalls with two parallel wiggly blue lines. Eddies (disturbed water) are identified by a whirlpool symbol. For instance, there are a few chartered ones off St Catherine’s Point on the Isle of Wight. UK Hydrographic Office (UKHO) eddies spiral anticlockwise as they go towards the centre. There are also a variety of digital tools and tidals apps available to help cruising sailors prepare for their passage.

Spotting tidal races on the water

A reef extending underwater from a headland will interfere with the water in all sorts of ways. It’s important to understand how you can interpret wave patterns, so you know what you’re up against.

If it were smooth like a train station platform, there would be arrow-straight lines of breakers on each edge where it dropped into deeper water. The waves on the side to which the tide is going will generally be steeper.

River outflows can also have this effect. They produce lines of breakers on either edge of the fresh water washing out. The water in between could be almost as smooth as a duck pond. A whirlpool can look almost flat, with just a few bubbles from upwellings, while water on either side can be a maelstrom of very confused seas.

I’ve rounded a few headlands, and can speak to the different ways of tackling them, and I’ve learned that a passage plan starts with a good understanding of what the seabed is like.

Tidal race examples

The UK has its fair share of fierce tidal races.

We’ll take Start Point and Dungeness, both of which stick into the Channel, as a comparison.

They’re not very similar. Start Point is more like a high, three-sided promontory. It has a line of rocks and submerged reefs extending diagonally out to sea. Dungeness is much shallower. It’s more like the corner of two sides of a thin napkin laid on a table.

Portland Bill is different again. It’s connected to England by Chesil Beach. The sand is what’s known as a ‘tombolo’. The Bill is a lump of rock almost held back like a slingshot, with Chesil Beach as the stretched elastic. Charts will show you a rock ledge off the south, and the Shambles Bank as a submerged echo of the Bill’s shape. The feared Portland Race is generated by these bathymetric features as well as the south-going eddies of the Channel’s tidal stream. The ‘Shambles’ is an apt way of describing the scatter of submarine masonry which roughens the sea surface above.

A different scenario for a tidal race would be the Fromveur passage inside the Isle of Ushant. The French hydrographic service has produced a three-dimensional image of the seabed. It looks like a rubbish dump down there.

A further example would be the Faroe Islands’ extremely detailed tidal app. Tidal energy firms want to know the speeds of tide at various depths within the water column so they know where best to put their turbines.

This kind of evidence need not put off passage-making boaters. Tidal behaviours in northern Europe are very well-documented. Tidal races are highly predictable, and a real wealth of information is available to small craft navigators to improve their passage-making.

Variables influencing tidal streams and tidal races

Coping with currents is a big part of sailing safely through tidal streams, but the number of variables can be confusing.

One way of appreciating this is by considering the way a river’s surface ruffles as it travels down over shallow stones. Although we tend to see ‘the sea’ and ‘a river’ as separately behaving things, ‘the sea’ is essentially a set of complex tidal rivers.

If you go onto the Windy app for instance, and look at the ‘current’ overlay around large promontories, you can often see how currents reflect off the land. If you look at the ‘swell’ overlays you can see directions and heights of swells generated either by past or distant weather systems.

Tidal water zips along at far greater horizontal velocities at the surface than it does when churned up by friction with the rough seabed.

What the ground consists of will have a bearing on the tidal streams. It might be rock, gravel or sand, or most usually a mix, with one of these elements predominating. Although rocks don’t move, sandbars definitely do, so charted positions can change.

Tidal forecasts

When preparing for passages around headlands or through races, there is the same provision as to weather forecasting.

Computer modelling for tides only generates predictions. The actual wave energy you encounter (the overriding important factor in your passage) is as indeterminate as the precise wind speed at a fixed point.

Particular headlands have their own characteristics. There’s no league table of tidal races as such, but the Alderney Race and Pentland Firth rank among the speediest in UK waters, the Fromveur in French.

Is an inside passage available? Usually, but sometimes not. Is there a back eddy in said inshore passage, allowing you to ride around seemingly against the tide? It is worth saying a back eddy might still have plenty of wave energy to throw the boat around.

Passage planning for tidal races: always have a way out

Pilotage is an art unto itself, and can be what makes or breaks a race or a passage. Planning for tides and strategising for overfalls is a big part of that.

A good navigator will calculate options for alternative ports; alternative routes should also be considered. ‘Points of no return’ require some thought.

Tide is committing. If there is no ‘door’, as it were, through a line of disturbed water, going through the central point might give you the biggest safety margin from land.

The Bitches adjacent to Ramsey Island off St David’s Head in Pembrokeshire, as well as the Merry Men of Mey, across the Pentland Firth, have reputations for producing unbroken walls of overfalls, almost like standing waves between two chunks of land – although not as clean. Even so, nothing is always absolutely certain.

Tidal race timing

Route options in hand, as with almost everything in life, timing is everything.

Land’s End has a detailed rounding plan described in the PBO Reeds Small Craft Almanac. Ingeniously devised, it will take you close inshore, weaving through the reefs and rocks, with a nine-hour favourable tide.

But be cautious. Do you really want to get that close inshore? Reeds Nautical Almanac has the extra warning: only approach in settled conditions, ie smooth to slight sea state, 10 miles of visibility, and daylight.

Understanding slack water

Slack water is something of a misnomer when it comes to headlands and tidal races. It often describes the time when forces are counteracting.

There might be a great interaction of forces. The line of overfalls might be exactly where all available information predicts. They might be regularly shaped waves, but they can belie the power they carry. The time of slack water might only denote when two powerful and opposing forces are briefly matched before the balance quickly tips to one side.

Slack water is a prediction. It might not begin precisely at HW Dover -5, but in the hour containing HW Dover -5 at its halfway point.

Slack water is also not, as some texts might have you believe, when the raging walls of water part so you can, Moses-like, lead your followers to safety. It is, of course, disappointingly in reality, when the waters are ‘least violent’.

Slack water discounts the action of wind on the tidal river. Say you have the wind behind you for the run around the headland, you will have the tide against you, and therefore choppy water, if you’re doing a straight line to hit the headland at slack.

Wind and Waves

Assessing wind speed is a critical part of the ‘on-the-day’ decision.

Waves topple into crests because the top of the wave is moving more quickly than the base. Breakers form when swell waves meet tide, in part because the tide is impeding that base speed. If the wind is contending against tide, the crests are being blown over the sluggish water underneath.

Wind-managed wave sets are driven by fetch and ocean swell. For instance, rounding the Lizard from the Falmouth side, higher waves will be generated from the underlying ocean swell, the prevailing south-westerly wind, and from the airflow ‘trapped’ by higher ground to the west; the wind will also be accelerating as it goes around the headland.

Visibility is the other consideration when choosing your time. With poor or very poor visibility, rounding any headland or tackling any tidal race would be inadvisable indeed in a small craft.

Course adjustments for tidal races

Your course is prepared, and you’ve reached the critical corner at the advised time – what now? Press on regardless? Here, the ‘macro’ navigation of shaping a course at a scale of tens of nautical miles becomes the ‘micro’ navigation of steering to the wave sets found prevailing, and even to the individual waves.

At the South Stack light near Holyhead in Anglesey, a ‘reliable’ race will form. But what if you can’t see the breakers at night? You will feel the boat lolloping around in the swell. There’s no rustling of breaking waves seething towards you, perhaps the luminosity of white water looms from the murk only when it’s a metre away.

The sensation is like being aboard a toy boat in a bath that’s being filled. GPS-based instruments might show you skidding round the corner into Holyhead at 12 knots speed over ground (SOG), but it doesn’t feel half that fast. The motion as your feet are borne along by the tidal current’s kinetic energy does not necessarily tell you what your brain and perhaps the GPS are indicating: that the boat is accelerating.

When you look at a tidal atlas, the neat, straight black arrows indicate a constant speed. The tidal river velocity is changing minute-by-minute, not jumping on the hour. Exploiting this river’s energy is, therefore, a matter of monitoring the SOG as it creeps up.

The sensation of being ‘swept’ up or into a tidal race is, to some extent, the surprise at noticing this acceleration. It is only troublesome if it is accompanied by a loss of control. The first lolloping around as you hit the overfalls will not be the highest SOG you hit. Manage it by steering out of it and away from danger as you accelerate.

As will have been identified at the planning stage, the areas of overfalls switch places between predictable but still not completely distinct zones, according to the flow of the tidal river, directed as it is by flood and ebb.

The Shambles race off Portland can look like an oval pool of overfalls, or a line of ‘washing machines’, depending on conditions.

Rounding the Needles off the western end of the Isle of Wight, the flood can set up a zone of breakers immediately to the west of the Bridge west cardinal. This patch can ‘migrate’ around quite a bit.

To be fair, the Bridge buoy has been set up there for ships to avoid the reefs and Varvassi’s boiler, and not to be a spot-on marker for overfalls for the attention of small craft.

Exercise caution in tidal races and overfalls

Besides wind direction and speed, sea temperature and saltiness all have an influence on wave energy in races. Sometimes the only way to discover these is through experience.

Having your auxiliary motor ticking over or in gear is a good idea. The surety provided by a dial pointing at your desired rpm, for instance, can be set against the somewhat unquantifiable: whether the smooth rocking of your entry to the race will be followed by sharply steepening waves; whether the breakers will intensify as you accelerate further against them.

Trusting local advice: a safe bet?

Local knowledge is often cited in advice. Suppose you don’t have a local expert on board, and you don’t have one available on the phone (assuming you even have reception), then an option is to follow a local. This comes with the assumption that the local knows what they are doing.

It is not unknown for a local fisherman, a crabber, say, with low freeboard, to become overwhelmed after having set off in inappropriate conditions with an abundance of misplaced confidence.

There are examples aplenty in yachting literature of foreign-registered recreational craft travelling in the wake of the local fishing armada, out to pluck the native bounty, steaming through the shortcut through overfalls.

Consider the scenario: you have opted for rounding the furthest rock on the regular planned passage, taking into account the timing for the turn of the tide, and the constraints of your craft (draught, speed).

A fisherman on a small motorboat merrily makes for the most risky path between the rocks, seemingly against the tide, apparently taking advantage of what (to you) is an unseen eddy. The sight of this brave local has emboldened you to imitate their course. This certainty is shored up when you see another locally-registered vessel (say a sailing yacht with an auxiliary engine, more akin to your own craft) also apparently following them.

But then both vessels take slightly different courses. The fishing boat goes through the shallowest, riskiest-looking gap, and the yacht turns before them, and goes through the slightly less dangerous gap.

Adlard Coles was in a similar situation trying an inside route on the Pointe du Raz in 1966. The yachting writer wanted to venture close by a rock called Gorlegreiz, christening the path ‘Millar’s Passage’ in honour of the former special forces soldier George Millar, who himself followed the fishing boat Jean Jaures through the gap.

A clear view of the overfalls

When racing there is a school of thought that in pursuit of another vessel, you match your opponent tack-for-tack and indeed track-for-track. Here though you have information on their draught and relative speeds.

When following an unknown craft, there is more doubt. Sure, you can pick up data from their AIS if you can attain it on the move. But it’s not a list of keel construction and modifications, nor a clear-cut statement of pointing ability.

This all said, following another boat around a headland, into a tidal race, or through overfalls, supplies something like the assurance of a pilot boat.

Their mast flipping back and forth before the white line of breakers will show you indubitably where the swells really begin; the spray shouldered up from the ‘lead boat’ indicates ‘in real time’ the effects of the conditions.

There is a foreshortening of perspective in binoculars, and a mental concentration on a line of white water or standing waves, but a hull swooping up and then disappearing from view, mast switching back and forth pendulum-like, is the best tell-tale you could wish for.

I confess to having spent an hour or two bobbing at a standstill over ground waiting for the tide to turn, about two miles west of Portland Bill; a German man single-handing a slightly larger yacht motored up to shout over that he’d lost his patience and was promptly heading straight back to Germany. The lesson learned was that fatigue and crew capacity dramatically cut into waiting time.

Top tips for helming through overfalls

Key advice for facing these challenging waters.

Slow down

It’s best not to view the overfall entry point as an intimidating ‘wall of water’. You’ll see an often dark-looking line of standing waves, crested with white water. Perhaps you can view these ‘white lines’ across your path as ‘give way’ markings.

In the same way as for a motor vehicle, they show the need to ‘slow down and stop’ if necessary, but you’ll need enough speed to steer through the steepest wave crests.

Going too fast into short seas will drive the bow under the breaker, stop the boat and swamp the cockpit. Taking off the way will allow the boat to rise to meet the wave as much as possible.

Meet each wave

Prime consideration – when steering through a tidal race – is to keep pointing almost directly into the waves. This way you’ll minimise the risk of broaching. Aim to maintain progress under control. I say ‘almost directly’ because switching the helm slightly off-centre as the boat goes over the crest is usually a kinder action for your yacht.

A little ‘twist’ can prevent the bellying-down shock which so often comes when the yacht sails up into the air off a wave and crashes into the trough. An ever-so-slight shouldering into the wave can help. But it shouldn’t be too much, or the wave will barge the whole boat and get it beam-on for the next wave.

That said, there is a whole science of naval architecture behind optimal conditions for steerage in surf.

Concentrate your crew effort

Unpredictable nature is a tiring thing to confront. You can get rogue waves, and be caught off-guard between breakers which come from opposite directions.

It’s not unknown to be rushed towards a wave set by a large roller from astern, only to be sent flying into a somewhat shorter roller breaking towards you.

Steering through overfalls requires a lot of attention. Factor in the time it will take to make the intended passage and consider your crew’s capabilities. The time to do this is well before committing to the route, and not during.

Switching over helms can be very problematic once ‘in amongst it’. This is especially true if both the current person at the wheel, and their relief, have to clip and unclip several times to move around the cockpit safely.

Headlands, tidal races, and overfalls can put even the most experienced skippers to the test. With these tips, hopefully you’ll feel more equipped to plan a successful cruise.

Ben Lowings has worked for the BBC World Service and has sailed yachts from the Norwegian Arctic to New Zealand. He also skippers commercial yacht deliveries around Britain and is a cruising instructor. He has written three sailing biographies: The Chancellor, The Dolphin and The Sun of May.

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