swim safer — England / UK open water swimming & wild swimming blog

There is an art to reading the conditions and planning a swim. It really isn’t a difficult art to pick up though. The longer you look at the conditions and get used to planning, the better you tend to get at predicting the conditions.

Below, we’ll look at a specific swim and then how you’d go about checking the conditions and planning a route or possibly finding an alternative swim.

So we’re looking at Penzance sea front / Penzance Promenade. As you can see, by my dodgy scribbles - with a south, southwest or southeast wind, the wind (and chop) will be blowing straight in there. A wind strength of 0-10 kmph won’t produce a great deal of chop. 10-20 kmph will produce a little. 20km+ will start producing enough ‘chop’ to make the swim far more challenging and far less pleasurable. You also need to consider the state of the tide. At high tide the water level is half way up the sea wall. If chop and swell hits the wall it’ll bounce off and send that chop back out to sea. So…if you were swimming at high tide you’d be hit by chop from a few different directions.

START PLANNING when looking at where to swim you should always start the plan at home on the internet. There are a number of different resources that you can use. We like ‘Tides4fishing’, there is also Swimfinder, Windfinder, Magic Seaweed (soon to have a name change), Windy App, Nautide, local to Cornwall is the free My Coast App (I think they’re starting to roll this out nationwide). When looking at these resources you should be checking the wind direction and strength, tide times, swell, you can also look at the weather forecast (avoiding any storms/predicted lightning/drastic wind changes…). Below, we’ll use the Tides4Fishing website. A great starting point would be Swimfinder, which you’ll find towards the bottom of the page.

In our example at Penzance sea front, we’re looking at a 10am swim. The wind will be Northerly, at 31 kmph. So, whilst that is a little strong, it’s off-shore for a south facing swim. That means that the wind has no opportunity to influence the conditions, in terms of chop, as the wind only hits the water on the shoreline. You may think that this wind would push you out to sea…if you swim front crawl, there’s a tiny surface area exposed to the wind. This will have minimal impact on the swimmer. If you swam head-up breaststroke and you weren’t such a strong swimmer, you have more surface area exposed to the wind. This may make it trickier to swim back to shore. In this instance, you could plan a high tide swim…so that the harbour wall offers protection from the wind and the off-shore wind blows straight over your head. Next we’ll look at swell. Swell isn’t so much a factor in Penzance (sometimes local knowledge is crucial).

Again, in our example the swell for 10am is around 1.8m. You don’t really get breaking waves in our Penzance example. So whilst this is a decent size swell, breaking waves aren’t a factor. If we go back to the wind direction, we know that it’s 31 kmph from the north. So that wind will be pushing against any swell and flattening it right out. If it were 31 kmph from the south, with a 1.8m swell it’d be a very different story. Anyway, with a strong offshore wind and 1.8m swell there isn’t going to be too much to worry about. The only slight issue you might have is getting in off the slipway at hight tide. There may be a little bit of water sloshing around. *At this stage I will point out that the swell section of the website is my least favourite and least accurate. I’ll always double check the swell with Surfline.com. I’ll pick a nearby beach, that faces the same direction…like Praa Sands or Perranuthnoe and check the surf prediction. This will give you a good indication of the swell size.

Lastly, we’re looking at the tide. At 10am, it’s around a 1.9m tide. Bear in mind that tidal ranges can have massive differences from area-to-area, around the country. You need to specifically look at the area where you’re planning to swim, for accurate tide times and an idea of the tidal range. The ‘tidal coefficient’ is a great feature and gives you a visual representation of exactly how much water is moving around. In our example, it’s 75/120. So it’s not a huge tide but it’s not a small one either. A 120/120 is the biggest possible tide you could experience and a 0/120 would be the smallest. Above, it also gives you a text description of the tidal movement…’a high value and therefore the range of tides and currents will also be high’.

Back to the example swim, a 1.8m tide would make it tricky to get in along Penzance promenade, as it’s quite rocky. You’d have to head for the beach towards Newlyn or swim off the Battery Rocks area, at the back of the Jubilee Pool. If you were the head-up breaststroker we spoke about earlier and were worried about the wind you might wait for the afternoon high tide and get protection from the sea wall along the promenade.

OTHER FACTORS :

land mass. You often get large tidal movements through narrow land masses. You can get this with long narrow beaches or area like Dover. You have water funnelling through narrow gaps or land masses and can get strong currents on an outgoing tide or almost constant lateral currents, as the tide goes in and out.
tides. You have the most water movement in the middle two hours between a high and low tide. These are hours you can avoid. Particularly if you’re experiencing spring tides. If unsure of an area normally best to ‘test’ on an incoming tide, avoiding those middle two hours.
headland. You can experience currents moving around headland and islands, particularly when there’s deep water in these areas. Remember that most people would struggle to make any forward movement against a current as small as 2 knots!

BE FLEXIBLE WITH SWIM LOCATION

Our example location was Penzance sea front. If we look at Carbis Bay (10-15 minute drive away) on the same day. The wind would blow straight in here. It’d really be whipping up some chop and wouldn’t be the most pleasant location to swim in. The swell is coming from the south so you wouldn’t have surf but you would have constant lumpy chop and plenty of it.

ADDITIONAL CHECKS

You can always make additional checks if your swim location has a webcam. Just remember that most webcams are wide angle and aren’t always that close to the water. So any chop or swell may look a little smaller than it actually is.

FINALLY

You can do all the checks in the world at home…but it’s really important to re-check the conditions when you arrive. Ensure that the conditions are behaving in the way you’d expect. Be prepared not to enter the water and possibly have a plan B…just in case.

COURSES

Sea Swim Cornwall have set up an affordable course to teach the fundamentals of planning your swim and understanding the conditions and rip currents. Our ‘First aid for swimmers’ course is available in a number of locations throughout the summer. CLICK HERE for more info.

ADDITIONAL WEBSITES :

SURFLINE, FORMERLY MAGIC SEAWEED

ABOVE : We’ve started by highlighting the search bar at the very top of the page.Put in the location of your swim. Bear in mind that this website is primarily for surfing and if you live in an area that never gets surf/waves, they may not cover your area. I was quite surprised there were search results when I put in ‘Penzance’.

At the bottom of the page I’ve circled a little summary of the conditions. So today we’re looking at 5-7ft of swell, next to the 5-7ft prediction it says ‘9s’ in small text. There’s a 9 second gap between each significant swell. This means there’s a decent swell, with some power. If the gap was really small ie. 2-3 seconds, we’re now really talking about waves with far less power ie. chop or choppy conditions.

We then go onto wind strength and they supply a handy little map that shows you how and where the wind will hit that particular stretch of coast. In this example 37 mph is a significant strength of wind! Below in smaller text you also have the ‘gust’ strength. This can have a real influence in whipping up chop, so is also important. There’s then a small visual representation of what the tide is doing at the time you’re checking and a guide to the water temp.

IF YOU SCROLL BELOW THIS INITIAL INFO THEY GO INTO FURTHER DETAIL: (see below)…

Figure A - takes you through the changing swell size and wave period through the day. Next to figure A are little arrows. They show you the swell direction.

Figure B - Wind strength through the day and a visual of the direction (arrows).

Figure C - summary of the weather.

Figure D - very handy…goes over the probability that this forecast is accurate. Todays forecast is around 90%. If you look at ‘tomorrows’ it’s only around 65%.

WINDFINDER

When using Windfinder always use the exact area you’re in or intend to swim in. For me, in this example I’ve typed in ‘Windfinder Penzance’. This website primarily focuses on the wind direction and strength. Great if you don’t ever get much swell in your local area but not so good if you do. I like using Windfinder as a secondary check, after using another website that’s better with swell.

So…they give you an exact location ie. Penzance Heliport, which is a nice central location. They then give you a quick summary of the wind direction and strength….and a summary of the weather.

Circled below this is another summary of the wind through the day and it strength. If you look at the Friday (today), it’s strong wind all day, building through the morning, peaking in the afternoon and dropping off in the evening.

Above red circle gives you a visual representation of the wind direction.

Blue circle is wind strength in knots (roughly the same as mph) and then gust strength below.

Green circle really summarises the days weather.

Black circle, goes over swell. This includes a visual of the direction, height in metres and the wave period. So…today it’s 10-12 seconds, which suggests a good strength swell.

Yellow circle at the bottom is the tidal info. This is the bit I don’t really like, as they don’t go into specifics. It’s difficult to figure out the exact tide times etc.

SWIMMER SPECIFIC WEBSITES :

SWIMFINDER

A website aimed at swimmers that supplies you with all the info you’ll need. I feel that this website dumbs it down enough to be really easy to understand, whilst still making you engage your brain a little and forcing you to think about what’s going on with the conditions and how this’ll impact your swim and the conditions. They strike a good balance.

Firstly, select your swim by the exact location or town in the search bar and then select the location on the map. The map is handy as you may be on holiday / not know the local area and it gives you an idea of your options. Once you’ve selected the swim…

I’ll point out that this is a big website, with lots of info. However, after spending 5-10 mins on here I started to get to grips with it and after that time period I found it far easier to navigate. So if you struggle a little initial, persist! There’s a lot of useful info on here and it’s presented in a way that makes it easy to digest, even if you’re new to look at this sort of info.

ABOVE - We’ll start by looking at the forecast. You get a summary at the top of the page, which I’ve circled in red. It goes over wind speed, direction (telling you whether it’s onshore, offshore, cross-shore…), wave height, weather forecast… It then details the rest of the week and the likely swimming conditions.

As already stated, you have a summary of the swimming conditions (circled red). Today ‘challenging conditions’. Circled blue is then more info on those conditions : including wind strength, direction (visual arrows), wave height, direction and wave ‘periods’. In addition, there’s a lot of info regarding the weather conditions.

They have this great little feature (above), highlighting the water quality.

You have a visual representation of the tide for the day.

Another great feature is the above. It highlights local swimming groups and businesses…as well as handy info on how to get to swims.

If you find the idea of reading the conditions and planning swims a little intimidating, Swimfinder is a great place to start. The summaries are really helpful, as is the initial info on the local area, parking, facilities etc.

If you liked this article it might be worth reading our Safe Swimming Guides to various areas… CLICK HERE

Sea Swim Cornwall

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The winds influence on swimming conditions

READING THE CONDITIONS / PLANNING A SWIM