Yesterday, I had the chance, for the second time, to fly Beachy Head. The conditions were perfect to experience sea thermals and the wind optimal to fly them!
UPDATE: Pilot Martin Long, who was flying at the same time as I, shares his flight log. Note how smooth and linear is his big thermic climb around the middle!
It felt like everywhere was super buoyant! In particular, finding a lift line between two airmasses converging meant that without any effort (keeping my wing straight into wind – a nice strong 20km/h or so), I gained about 500ft in no time. Some more experienced pilots where way higher! What’s more, flying over the sea was producing heaps of lift too. Happy time!
This got me thinking about sea thermals, what they are and how they differ from land thermals, so a quick look around the internet brought up two articles that I urge you to read as they are -super- insightful!
FlyBubble explains the sea thermals as follows:
“The sea temperature at about ± 8.5°C is much warmer than the air temperature (± 3°C yesterday), which creates a layer of warm air above the sea water. Sea surface temperature is an average: as the water swirls, pockets of warmer water appear at the surface between cooler areas, so we might see 10°C in some places, significantly more than the inland trigger temperature of 5°C. Slowly, patches of air begin to warm, becoming thermals. The air only needs to be a few degrees warmer than the surrounding air for it to become buoyant and start to rise. Behold, the sea thermal.”
While Mark A. Smith on his blog provides the following rules to make the most of them:
1. 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. You may try to ‘compensate’ by pushing more into wind – losing it as a consequence. So it’s best to blank out what’s below you completely (while skimming over the terrain super quickly and lower down!)
2. Fly constant circles – not adjusted circles. In land thermals the wind is likely to blow you out of the back of the thermal but not with sea thermals. Inland the thermals travel slower than the wind (the wind rushes around them) but with sea thermals they travel at the same speed as the wind. So in this case there’s no need to make centering corrections by pushing up-wind. Better to fly constant bank/speed circles. On the GPS track over the ground the circles LOOK elongated (without a loop as you turn into wind), but this is only because of the speed of the airmass you are circling in.
3. Bubbles – not columns. Sea thermals cycle like land thermals, but land thermal sources typically create leaning columns so you can join the same thermal even 1000 ft below someone else. Sea thermals work like bubbles or fat cigars, and if you don’t stay in it as it breaks from the source you won’t be able to connect lower down a leaning column. You have to keep up!
4. Use heavy weightshift. Sea thermals are often weaker (and very shallow) and so easier to fall out of the bottom of if your own sink rate is high e.g. with heavy break circles. Also the very shallow angle (6-7 degrees) is a 1:9 glide ratio which means (unlike land thermals) you will not connect with it again pushing upwind. So use weightshift much more while circling and don’t fall out the bottom!
5. Use ‘zig-zagging’. 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 compression. 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.
To be honest, yesterday, it was dead easy to get sea thermal lift, everything was pumping! But now that I have read both articles, I can’t wait to go back to Beachy Head when the conditions are right to put these insights in practice!