Swim Planning - West Cornwall

We’re focusing on the highlighted area of west Cornwall…from roughly Penzance

Harbour to Mullion. I’ll take you through the conditions you want to look for and

avoid, in terms of swimming. Below, represents the area we’re looking at.

Now obviously the whole stretch is exposed to a southerly wind….especially a SW

wind! If you look at the second image (below), it demonstrates how many 100s of km of open

sea this coastline is exposed to, if a strong southwest wind is blowing. It has a

fantastic opportunity to create chop and swell, so even a moderate wind strength can

produce unfavourable swimming conditions. Fairly similar with a straight south wind

and a westerly wind, to an extent…as wind, swell and chop will wrap around the

headland that offers a little bit of protection.

Best wind direction along this stretch is a NE or straight north wind. It’s nearly

directly off-shore and as the wind hits the water on the waters edge…has very little

opportunity to create any chop/swell or influence the conditions. Some people worry

about an off-shore wind, which would be fully justified if you were on an inflatable or

something like a SUP but when you’re swimming, there’s very little surface area

above the water, so doesn’t do a great deal to swimmers.

Wind strength : depends which direction it blows from but… 0-10 kmph creates very

little chop and is ideal in any direction, 10-20 kmph tends to create ripples and small

chop (in most directions), 20-30 kmph can create decent sized chop (if it’s onshore

or cross-shore), 30kmph+ you start to experience big chop and potentially swell

(unless of course, you find the shelter of cliffs etc and it’s in an offshore direction).

Wind can bring swell…particularly strong wind but this isn’t always the case.

You’ll occasionally get swell from one direction and wind from another…particularly

in the colder months. So it’s always worth checking the swell direction and size. In this

example, a big south or SW swell (2m+) isn’t great and will produce surf and

swell….as will a large SE swell. Swell has the ability to wrap around headland and

come back on itself. On the map, typically the Mounts Bay Area (around St Michael’s

Mount), will get good protection from the shape of the land/headland. Once you get a km or so

to the east, this swell has far more of an influence. It’s also worth noting the wind direction and strength for the 24 hours before you swim. If the wind direction and strength was ideal for your swim BUT it was howling in from the south the day before, you may still get chop and swell coming from yesterdays conditions. So, as good as forecasts are, it’s always worth checking the conditions again, when you get to your swim destination.