Video: Behind the scenes of Alex Thomson's death-defying 'skywalk' stunt

The daredevil sailor admits, "If something was to go wrong, I could be seriously injured." See the footage.

What does an adrenaline junkie yacht racer do when he’s not chasing solo round-the-world speed records? Puts on a suit and puts his life on the line in a heart-stopping kiteboarding stunt.

As part of a series of extreme sailing exploits for his Hugo Boss racing team, Alex Thomson, 41, can be seen in the video above soaring nearly 300 feet in the air while attached by a rope to the one of the world’s fastest monohull racing yachts.

“We are going to combine my two greatest loves: kitesurfing and sailing,” Thomson says at the start of the video. “If we get the timing right, we’re going to pull off something spectacular.”

The British sailor begins the stunt he called the “skywalk” by kitesurfing upwind behind his 60-foot IMOCA open 60 Hugo Boss yacht in Alvor, Portugal, a world-class kitesurfing spot.

While the yacht cruises along at 12 knots, a member of Thomson’s team throws him a rope that’s attached to the top of the yacht’s mast.

Thomson expertly retrieves the line, attaches it to his kiteboard harness and suddenly leaps off the water, within seconds reaching the height of a 25 story building using the speed of the huge yacht to catapult him.

A series of still images chronicling the skywalk stunt show Thomson as he sails to more than twice the height of the Hugo Boss’s 30m mast, equivalent to a 25-storey building.

The most dangerous moment in the stunt comes next, as Thomson releases the line and guides the kite back to the surface of the water.

In his own words: “There were lots of things that could have gone wrong. Perhaps most concerning for the team was the prospect of an uncontrolled descent causing me to come back down too fast. Water can be as hard as concrete if hit with enough velocity, so this was one of the most dangerous aspects of the stunt. But I had a brilliant team around me, and, with their help, we managed to pull it off.”

Thomson was keen to complete the stunt both because of his love of kiteboarding and from a desire to finish a trilogy of high-profile and extremely risky stunts. Two earlier feats saw the sailor running up and diving off the 30m Hugo Boss mast and walking down the yacht’s keel whilst it was heeled over and sailing at high speed.

“The previous two stunts that we carried out — The Mastwalk and The Keelwalk — were so successful that, as a team, we just knew we couldn’t stop there. We were all in agreement; we wanted to do something even bigger and better.

“I’ve always had a love for all things wind-powered so naturally a stunt which involved kite surfing was the next step. The idea of combining two of my favourite sports and executing something which, to our knowledge, had never been done before was really exciting.”

In November, Thomson hopes to best his 2013 third-place finish in the Vendée Globe race. A highlight of the Ocean Masters race calendar, the non-stop, solo, unassisted, round the world race takes approximately 80 days to complete.

Apart from that, he’s left the door open for future stunts.

“What’s next?” he says. “Who knows.”

For a behind-the-scenes look at the planning and preparation that went into the stunt, watch the video below to see how Thomson kept himself safe in a stunt he called, “incredibly dangerous.”

“At 100 metres, that’s your limit for opening a parachute. So if I was to drop out of the sky, if something was to go wrong, I could be seriously injured,” Thomson chillingly explained.