Tides for Sea Kayakers

Tides are as important as the weather to sea kayakers. Channels may be impassable, launch sites may involve long walks over sand or mud at low tide, whilst dumping surf, rocky landings or heavy traffic may occur at high tide. But the water doesn't just rise and fall as if by magic - to fill several square kilometres of a bay or sea loch with a three or four metre rise in water means moving tens of millions of cubic metres of water horizontally, creating significant flows which the paddler would prefer were helping him on hos way, not opposing him. The tide is basically just a big wave with a period a little over 12 hours. Off the North east coast that wave is travelling southwards, so the flood tide pushes water south and the ebb pulls it back north. In bays and estuaries the tidal streams turn at about the same time as high and low tide (although ebb may be stronger and flow for longer if there is a lot of river flowing out). But along the coast, the flood tide continues south for some time past high tide, and the ebb similarly continues after low. By how much depends on the location.

The tides are generated by the gravitational effects of the sun and the moon. There's a useful description of the basic theory on this Land Information New Zealand web page. When the sun and moon are on the same or directly opposite sides of the earth (at new moon and full moon) the effects combine and we have spring tides, whilst in between we have neap tides, with a lesser rise and fall and weaker tidal streams. The earth orbits the sun and the moon orbits the earth such that the moon is back in the same place relative to where we see the sun about once every 29 days. Spring tides lag the full and new moon by one or two days because the gravitational pull is a pumping effect and the tides build higher whilst the effect is big and dies off slowly with friction as the pumping weakens. The day after full moon, the pumping effect still puts more energy in than is lost to friction so the tide gets bigger for a day or two. Similarly, neaps lag first and last quarter by a day or two. The lag is less nearer the open ocean, so is typically one day in the West of Scotland, but two days on England's East coast.

Simple theory makes it easy to see why we have spring and neap tides and why the tide times change from day to day, but simple theory only describes a planet uniformly covered in sea. In practice, continents get in the way, and there are other complications to do with the tilt of the earth's axis, the inertia of the water and the effects of rotation. Each major ocean basin has a natural "sloshing period", which, for the North Atlantic, is about 12½ hours, which is close to the tide interval predicted by the simple theory, so western europe mostly has twice-daily tides. The natural period of the Pacific is nearer 25 hours, so much of the Pacific rim has once-daily tides. Tides in the English channel are also a product of a natural period along the length of the channel, which is of great significance if you are paddling near the Isle of Wight where you may find four high tides a day.

The "tidal bulge" travels at a speed that depends on the depth of water, and is considerably slowed over continental shelves. In the open sea, the rise and fall of the tide is relatively weak and streams not that significant either. The tide travels faster up a deeper channel, so, for example, high tide arrives earlier on the west side of Jura than in the shallower Sound of Jura to the east. The slowing of the tide also makes it steeper, so the shallower channel has a bigger tidal range. This can produce a height difference of 2m across a short distance at the Gulf of Corrievreckan, creating fierce tide races and the world's second biggest whirlpool. The biggest, caused exactly the same way, is in The Lofoten Islands where SOC paddled in 2005.

As the sea becomes shallower towards the coast, not only do tidal ranges become higher, but flows are constricted around headlands and islands and where the water is shallower, so the strength of the current is faster. Narrow entrance channels to sea lochs, gaps between islands or where the tide flows over shallow reefs can have very fast tides indeed - considerably faster than a paddler can paddle against. Where the tide is opposed by the wind, waves steepen and slow down, so the wind blows over the same wave for longer, making it get bigger too. Wind against tide can produce some spectacular sea conditions, which may not be what you had in mind if you planned a peaceful day out around the islands. On the other hand, if you are seeking out tide races for excitement, it pays to know when overfalls form, where the tide will take you if things go awry, and when you will be able to get back to a safe landing.

To avoid rough conditions, and to have the tide flowing in your favour to make paddling easier, it is important to plan trips taking tides into account. You can get various tidal prediction programs which will give you the heights and times of tides at a number of standard ports. Information in guidebooks or Pilots (and indeed, in our Favourite Sea trips pages) is usually given relative to one of these standard ports, in a form such as "N-going stream sets at HW North Shields +01:30 and runs at 4 kt springs, S-going sets at HW North Shields -04:40 and runs at 3.5 kt springs". This tells you when the tidal stream changes direction, but doesn't tell you when the peak flow occurs. Usually the peak occurs about halfway through the tide (so about three hours after the stream sets) but this is not always the case, as local factors may change this. For instance, as the flood starts when the tide is still low, a channel may not be able to carry a large flow, but as the tide rises the channel cross section increases and the flow can "catch up", so peak flow may be well after mid tide. There are plenty of places where tide flows through channels between islands where the peak flow often occurs very quickly after the stream sets, so read up very carefully to avoid being caught out.

Like flowing water in a river, tides may also create eddies, especially when the tidal streams are fast. This may be to your advantage as you can eddy-hop to make progress against a tide, but equally it can catch you out in a big bay where the tide may seem to be flowing the wrong way unless you paddle far out to sea. Some eddies only work with the tide in one direction, whilst water goes with the main flow in the other half of the tide. This produces a few places where the tide always flows the same way - there's a couple in Skye, for example, which make a clockwise circumnavigation easier than the other way. Wherever tides are constricted into narrow channels or around headlands, or where a stream flowing one way meets another stream, such as from an eddy, you can get sharp eddy lines, turbulent water, and big steep waves in tide races. These are usually referred to as "overfalls" in pilots, and marked by wavy lines on charts. They can provide you with a perfect playspot if that is what you are after, or a perfect nightmare if you hadn't planned accurately. By the time you see an overfall coming it may already be too late to paddle back or out to sea to avoid it. There's a video clip of such a situation in the North Stack Tide race article.

Along the NE coast, tidal planning is mostly a matter of working out the best direction in which to do one-way trips or round trips in order to avoid paddling against the tide. In a few areas, such as the Farnes or Holy Island, tidal planning is more intricate and the wind direction may become a critical factor too.

For a typical out-and-back beginners' trip on the North Sea coast, we aim to be on the water by 11 or soon after, and want to be off by 3 or 4. Ideally therefore, you want to pick a day when the tide stream turns about 1 or 2. If it is a high tide in the middle of the day, you'll want to put on at the northern end of the trip, paddle south with the flood, have lunch and paddle back with the ebb. With a typical summer wind from the south or southwest, this will make for calmer seas on the return leg, so if conditions were OK on the outward journey you can be fairly confident of your ability to make it home. A week later, the tides will be almost exactly reversed, with low tide in the middle of the day. A trip now would be easier starting at the south and paddling north for lunch before returning with the flood. In this situation, if winds are southerly, conditions may be rougher on the return leg. Fortunately, in this area, low tide in the middle of the day happens at neaps, so the flows are less and wind-against-tide less likely to be an issue.

The 29-day periodicity means that spring tides get about a day later every month, so if it was springs on a Sunday at the start of the season in May, springs will have slipped back to Thursday by the end of the season in September. On the east coast, tide streams turn earlier further north (St. Abbs about two hours earlier than Whitby, for example), so you can usually plan an out-and-back trip somewhere along the coast that will work on any given Sunday. Similarly, if you want to do a one-way trip you want to pick a day and location when the tide turns between 10 and 11 in the morning (and thus between 4 and 5 in the afternoon) so it goes the same way as you all day. This all matters somewhat less at neaps when the tides are weakest. You also have a bit of leeway because most tide streams take time to build up. If the stream will be 3 knots at its peak, it will only be 1.5 knots an hour after the stream sets or an hour before it turns. If you must paddle against the tide at some point in your trip, it is probably better to do so on the outward journey (or early in the day). Your worst scenario is to be paddling against a tide that has just turned and is building strength against you as you struggle to reach home at the end of a trip. If caught out, remember that eddy-hopping can save the day, but surf or swell may be an issue if paddling close inshore.

For the Farnes you are essentially spending the entire day paddling across the tides, and there are some fast streams to consider, and several races that can rapidly build into very rough conditions. If you choose a day when the streams turn in the middle of your trip, you will have the weakest tides when furthest from home, which has advantages, but if the wind was with the tide on the outward trip, it will be against it on the way home, which can make the crossing from Inner Farne back to the mainland rough. Conversely, if you pick a day when the tide flows in the same direction all the trip, you can go when the wind is with the tide all the time, but you will encounter peak flows in the channels crossing to Longstone, which can make for some hard work ferry glides. With springs, you will be paddling the flood (south-going) flow all day and Staple Sound can be very exciting, as well as the last crossing to Longstone. With neaps, you will have ebb (north-going) all day, and lesser flows. A southerly wind will tend to produce a glassy calm in Staple Sound on the ebb, but a swell can make all this reasoning go to pot. On a typical Farnes trip in less-than-perfect conditions you can be surrounded by confused and breaking waves whose size and direction seems to change every couple of minutes as swell windows open and close, tide speeds vary with the water depth and even the wind may change direction around the islands.

Scotland has the additional complication of tides that move up either side of chains of islands at different speeds. Big height differences across short gaps like the Grey Dog, Cuan Sound, the Gulf of Corrievreckan and others make for spectacular tide races ! Trips here are best organised by someone who has been before and who is good at tidal planning. Your  timing be good (which may involve getting on the water very early in the morning), and delays en route must be avoided if you are to hit crucial "tidal windows" at the right time. But planning must allow for the fickle weather (which can change tide times, as well as make for rough seas) and include escape routes which work with the tides. It is all good stuff, but beyond the scope of this article.

A Few Tidal Constants for Our Area

Tidal streams at the Farnes - north west stream (ebb) starts +01:30 Tynemouth, south east stream (flood) starts -4:30 Tynemouth.

Tides at Amble roughly 1 hour 35 before North Shields - the put-in/take-out at Amble marina picnic area is very muddy within an hour or two of low tide, and swell can produce big breaking waves in Amble harbour entrance (over the sand bar) in the bottom half of the tide, or when there is a strong ebb (a lot of water flowing down the river). This means trips to Coquet Island are best with a high tide a little before mid-trip. That tends to be on the build up from neap to spring tides, a couple of days before new or full moon. Of course, there are other launch spots that avoid the river or harbour entrance ...

The UK Hydrography Office provides tidal predictions for a lot of ports, but only for a week ahead. Proudman Oceanic Laboratory provides fewer ports (a particular omission which affects a lot of club trips is Oban), but will give you 28 days ahead. Anglesey is another fine paddling destination, tides usually given relative to Liverpool, and predictions are available several years ahead from the University of Bangor Department of Applied Oceanography, but the URL for that information keeps changing (the easy-to-find pages were out of date last time I looked), so it's best to Google into their site.

If you read our Previous Sea Trips articles, you will often find a link to an Additional notes page which gives lots of information on the tides for that area, including the tide times on the day(s) of the trip. For trips in areas we visit often, there are a few Favourite sea trips pages, which give more detail, and aren't tied to a particular previous visit. Some of these also link to map pages showing the route of the paddle, tidal information, location of overfalls and lights that you may need to know about if paddling in low light.

Read 4732 times