Paragliding Sea Thermals
Paragliding sea thermal tutorial
Thermal tracking & horizontal speed
Here are some tracklogs of get-aways from inland thermal sites (Greg Hamerton and Hugh Miller). Note the angle at which they climb (which of course will be in part a function of wind strength as well as thermal strength).
Compare with these sea thermal take-offs (Graham Phipps and Richard Osbourne). The climb angle is typically much shallower and the circles are elongated in comparison – skimming back with the fast drifting thermal. The inland thermals have ‘loops’ in the GPS tracks, while the sea thermals do not.
I calculated the angle from horizontal and the speed of some typical inland thermal vs sea thermal flights, and the figures I got were:
Inland thermals (e.g. from Forest Farms): 15 deg angle, and 8.5 – 9 mph (14 kph)
Sea thermals (from West Cornwall coast): 7 deg angle and 15.5 mph (25 kph)
So sea thermals are double the speed and twice as shallow!
Because the wind is typically stronger at coastal sites than inland sites when you fly them, and because sea thermals are weaker than inland thermals, with sea thermals there tends to be a much faster ground speed – skimming along lower, with a weaker climb.
Rich Osbourne has noted the shape of the circles over land (not with reference to the airmass
I went back to basics and studied the local maestros, seagulls. I found a place where I could watch the gulls from side-on as they left the hill. Bingo! They revealed their secret. What I saw was that they flew long, flat, ovalised 360s as they tracked back with the thermal. When they faced into wind, they turned quickly, but critically, only when they had found the upwind edge of the thermal and not a second later.
Next they drifted back to the downwind edge, travelling what looked too far, before facing up again and repeating the process. That’s when the penny dropped as to the shape of the thermal as it tracked back. Because of the fresh breeze, the weak thermal was laid over at a shallow angle and that’s why I was flying out of the upwind edge so frustratingly. I realised too, that once you lose this thermal, you’re likely to descend at the same sort of angle as the thermal, thus explaining why I rarely found them again.
I couldn’t wait to try again, but though I got immediate results, I still lost the lift far too easily. I worked out that our wings are slow to respond to input, and this fact was causing me to whizz past the edges of the thermal. The solution was to learn to anticipate where the edges were and turn within them. I was getting it now. I could reliably stay in the lift, but still something else was needed. The lift is so delicate that often just the physical action of turning was enough to critically unsettle the wing. So I practised turning the wing even flatter, even slower and with massive amounts of weightshift to increase efficiency.
The results were stunning.”
Rules about sea thermalling
1. Thermals at small hills are often small and difficult to track, and will be leaning at a steep angle due to their lack of mass.
2. Blank out the ground. Sea thermals are disorientating. They are faster and more shallow than you would expect if you use the ground for reference. So it’s best to blank out what’s below you completely (while skimming over the terrain super quickly and lower down!)
3. The strongest lift is on the windward side with billowing trailing edge where lift is weaker. Focus on tracking this leading edge of a leaning thermal.
4. If you lost the thermal with a feeling of dropping sharply out of the lift, it’s probably downwind of you as you’ve fallen out of the front.
5. If you lost it because it became scrappy and gradually weaker, it’s likely to be upwind of you – because you got drifted out the back.
6. If your ground speed increases while going upwind, there’s probably a thermal ahead of you. All thermals block the wind to some degree.
7. If you lose the thermal out the back it may be impossible to glide back into it due to the steep angle of the thermal compared to your glide angle. Always make sure you use the best speed-to-fly to get the best glide angle! You’ll need to be on bar if you are flying into wind and/or there is sink.
8. You are always sinking in the parcel of air you are in at around 1 m/sec (min) and more if turns have high bank. So if you are thermalling for 1 minute, you will have sunk through 60m of the thermal; if you are thermalling for 5 minutes, you will have sunk through 300m of the thermal. In this example below even though you may be climbing at 4 m/sec, you will still be sinking the whole time in that parcel of air, and will drop out of the thermal in 30-40 seconds.
9. But this model above doesn’t apply for sea thermals since they are leaning steeply (see diagram). In this case if you have to do non-adjusted circles you will quickly drop out of the bottom of the thermal due to it’s cross-sectional area.
10. You must keep adjusting your circles to push further upwind. Essentially you must continually fly forward while thermalling – i.e. you do not want perfect circles, but elongated circles. A useful tactic is to focus on strongest lift on leading edge. Feel out the upwind edge, use brakes for min sink there, turning the instant you feel the lift weakening. If you keep turning upwind in each circle and keep track of the leading edge where there should be a surge in lift, you can keep tracking the thermal and not fall through it.
11. Use heavy weightshift. Sea thermals are often weaker and weightshift reduces sink rate.
12. Use ‘zig-zagging’ to enable you to push out to see further to connect with stronger sea thermals. The strongest sea thermals often break away from the sea surface further out to sea due to their higher heat energy. The weaker thermals are more likely to come off the sea cliffs in the venturi. (see above) The sea cliffs here act as triggers for thermic air that has skimmed off the sea surface. These drift back fast and are weaker. But they can be like stepping stones to get you higher so you can THEN push out on glide and connect with the bubbles further out to sea – which you often wouldn’t be able to find if you pushed out to sea directly from ridge lift.
Here is an example from one of my own sea-thermal flights at Morvah, West Cornwall – first gaining height with a weaker, fast-drifting thermal, and then pushing back and connecting with a stronger one at 400m that takes me inland.
Extra thermic input & triggers
Rich Osbourne talks about how important additional ground sources and triggers are for the early part of sea-thermal flights. What are possible sources and triggers to add thermic energy to or help trigger sea thermals?
- Dark rocks/sand (e.g. at low tide)
- Cliffs warmed by the sun
- Towns / tree-lines / buildings, etc
From experience in West Cornwall, having a hill within 1 km or so behind the sea-thermal site helps you get away. This could be because the thermic air allways flows ‘uphill’ and a prominent hill collects thermic air travelling over the landmass resulting in hill-based thermic cycles that can add energy to the thermal you are drifting back in.
Down here in Penwith there are a number of such sea thermic sites – shown here (the numbers indicate the distance in km to the trigger).
Sea breeze convection
When there is sun inland, not only is there an opportunity for inland thermals to connect to but also the chance for sea-breeze convection setting up, adding inland drift to the thermals as they come in from the sea.
When to try sea thermal flights?
Conditions should be unstable OVER THE SEA as well as over land on RASP! This is best if the air temperature is several degrees colder than the sea temperature, while inland is also booming. This will typically be in cold late-Winter or Spring conditions.
For conditions here in Cornwall, a useful rule of thumb is that if you’ve gained 250 m (>800 ft) above take-off and are going up in a thermal in anything consistently over a 0.5 up – then try going over the back towards your hill or other thermic trigger. With more skill you could do this at 200m ATO no doubt.
About the Author
Mark Ashton Smith What’s national standard for paragliding in Cornwall - among the best you can find in the country? (1) the coastline 🧗🏼♀️ - the most beautiful in the country. We can enjoy it, explore it, and get good at coastal soaring 🏆 (2) the views 👀from up high - all coastlines of the peninsula that everyone comes to visit all in one panorama - absolutely stunning 🏆 (3) technical tor & small hill, inverted, broken-up, and low base flying 💥- really sharpens XC skills - none of this lobbing into house thermals and climbing to 6-7 grand off the bat. If you lose concentration you’re on the ground. If you can learn to fly XC well in gnarly Cornwall you can fly well anywhere in the UK. 🏆(4) the convergence 🌥🌥🌥 - it’s the best in the UK and if we can fly it, it opens up 150km plus flights and even learning to soar sea breezes gets us in league with that lot around Brighton. 🏆 (5) We got instant access to lots of ace coastal sites/beaches to train at within a short drive which gives us more air time, ground handling skills, and wagga skills (call out to Dunc)🏆,and (6) our sites aren’t busy!! You’ll be lucky to find more than 2 people flying at Carn Brea on a perfect day. In Bodmin moor you’ll be with your mate and that’s it. No crowds. 🏆👌Happy to be in one of the best flying areas in the country - just important not to get pulled into the league numbers games which suits other areas but not ours. Gavin McClurg made the same point. Distance is great but there’s loads of other ways to have top flights. Focus on what’s the very best in your home turf! 🏴☠️
Related Posts
Climbing Out and Going XC from Small Hills on a Paraglider →
Learning To Core Thermals : A Scientific Angle →
