Plunged into frigid water, it takes just a few minutes for a human being, robbed of strength and co-ordination, to start slipping away.
Serious kayakers know the drill inside out, but dealing with a real capsize situation is never like practising. When adventure sportsmen Patrick Winterton, Olly Hicks and Mick Berwick turned back part way into a planned crossing from Shetland to Norway, it was the exhaustion after 30 hours without sleep that caused one of them, Winterton, to tip into the sea. What turned a frustrating setback into a dangerous situation was the fact that Winterton was at the rear of the three kayaks and his two companions were 200m ahead, hidden by the 10ft swell and with a sharp wind blowing in their ears.
"My first thought was not 'the water is so cold' but 'God, I hope they've seen I've gone over'," recalls Winterton.
Hicks remembers it well. "It was grey, windy and quite cold," he says. "I heard this shout - I caught it very faintly because of the wind - and turned round and saw the boat upside down. I couldn't see Patrick, who was on the other side. So I shouted at Mick and we had to paddle back against the wind."
It took less than five minutes for them to reach Winterton, manhandle him back into the boat and turn him upright, but he was already losing dexterity in his hands. He sat in the boat, cold and wet, while they gave him chemical heat packs to warm him up and wrapped him in heat-conserving reflective material before they all set off again. Even with good conditions it took them seven hours to arrive back in Shetland safe and sound. The journey was a reminder of how unpredictable sea journeys can be, and never more so than when your mode of transport is a fibreglass boat barely big enough to lie in.
It made a particular impression on Hicks: "It was hugely eye-opening to me, how rough and exposed it can be on a kayak."
That was two years ago. This summer, Winterton and Hicks attempted the crossing a second time, in a two-man kayak, and this time they succeeded. They became the first people to kayak from Shetland to Norway, their achievement commemorating the wartime Shetland Bus operations, in which fishing boats covertly carried agents out of occupied Norway back to Shetland (they also raised money for the RNLI and Make A Wish Foundation). The 240-mile journey took 62 hours in a boat called The Larsen, named in honour of Shetland Bus hero Leif Larsen, who made the journey from Shetland to Norway and back 52 times during the war.
It was undertaken without back-up teams or sponsorship deals, but in the spirit of plucky seafarers from times gone by. Their success was not only a tribute to their skill and determination, but highlighted the daring of the sailors who navigated the North Sea without the aid of modern technology.
It helped that the pair had total trust in one another. Winterton, 51, from Oban, is a married father of a one-year-old girl and works as a winter sports commentator. A former Royal Marine and one-time Olympic skier, he has kayaked between Lewis and the Faroes. Hicks, 31, from Suffolk, who works for a renewable energy company, is relatively new to sea kayaking, but holds the distinction of being the youngest person to row any ocean solo, and the only person to row solo eastbound across the North Atlantic, which he did aged 23 in 2005.
The system they had for keeping out of the water first time round on the voyage hadn't worked, so this time they built up the sides of the fibreglass boat by three inches and redesigned their "canopy" - the cover they could pull over the cockpit - so they could enclose themselves in a watertight environment to get some sleep.
The pair set off from Out Skerries at 4am on Wednesday, July 17, in strong winds. Hicks remembers it as "intimidating". "You left the shelter of the island into this foggy grey sea like a scene out of a film," he says.
For both, committing to the journey was a scary moment, particularly when they found themselves riding "huge" waves. For the first 48 hours, the waves were walls of water 10-17ft high (3-5m), but the wind helped the pair cover a massive distance. On day one they covered 71 nautical miles (each nautical mile is roughly 1.15 land miles) and their progress was aided by the use of small sails. Staying upright, avoiding being swamped by the towering waves and keeping on the right course required relentless concentration. On the second and third days, the waves came from behind, making it harder to spot the big ones. "The sky darkens a bit just before the wave hits you," says Winterton. "There is no sound until it breaks."
They had a close shave when a particularly formidable wave picked up the kayak and suddenly propelled them from three knots to 20 knots (roughly 23mph). Hicks screamed to warn Winterton but he had no time to brace. It was all they could do to surf along the face of the wave until it spat them out 100m along.
"You realise then that if something is going to go wrong, it will happen very quickly," Hicks reflects.
For both, the thought of capsizing was always at the back of their minds; had they both gone in the water, their lives would have been at risk "without a doubt", says Winterton, not just because of the cold, but because they would have lost vital equipment and, once full of water, the kayak would have weighed two tonnes.
While kayaking is usually a safe sport, paddlers have been lost on long-distance expeditions. In 2007, seasoned Australian kayaker Andrew McAuley died while attempting to kayak from Australia to New Zealand after capsizing within sight of land.
"You always think about incidents like that," says Winterton. "It's good because it makes you concentrate, but it also makes you realise what you're trying to do."
At least Winterton had something to distract him: chronic sea sickness. He managed 12 hours before it hit him. "It was grey seas, grey skies, no horizon, just the perfect conditions for it.
"The thing that gets you is when you have to look straight down to undo a knot or something. After 12 hours that was it, I was a goner for the next 48 hours."
Sometimes the vomiting was so bad he had to lie down and let Hicks paddle solo.
Winterton managed only a tin of rice pudding and a jaffa cake in the first 55 hours, right up until he could see land and stopped being sick. He kept going taking tiny sips of water.
Sleeping, thankfully, was less problematic. They threw out a drogue (stabilising device) at the front, and some buoyancy bags, and tucked in beneath the canopy where they managed to lie down, at an angle. It was smelly, but marginally warmer than outside and allowed them to rest.
A bigger challenge was responding to calls of nature. It meant kneeling in the boat (not over the side, that would unbalance it) and stripping their body suits down to the knees. Winterton had learned a valuable lesson from his Faroes trip with Mick Berwick, as he explains matter-of-factly: "We'd had these little silicon trays which we both missed so that was pretty messy. This time we both took something the size of a dustbin lid."
They finally landed on the Norwegian archipelago of Sotra at 7.30pm on July 19. After nearly three days sitting down, they could not walk and had to crawl ashore. There was no welcoming committee although their families - Winterton's wife Cathy and Hicks's parents - had flown out, and met them shortly afterwards.
"There was an intense sense of relief and satisfaction that we achieved the crossing in conditions which would have persuaded most to stay at home," says Winterton. Later, in Bergen, the locals celebrated their achievement with a feast of barbecued elk, boar and venison.
Winterton describes Cathy as amazingly supportive of what he does. A more conventional sport would be less risky, of course, but to Winterton adventure kayaking is "far more gratifying". "You're trying stuff no-one's done before. There's no book to tell you how to do it."
The next plan is to re-enact the route of a Greenland Inuit found on Aberdeen beach in his canoe in the early 18th century. If the pair can raise enough money, they will depart next summer, going from East Greenland to Iceland, the Faroes, Orkney and Aberdeen, taking at least six weeks.
Stories of epic historical voyages inspire Winterton. "I think they just make you a bit tougher," he says. "You think: if they could do it, we can do it." n
Patrick Winterton and Olly Hicks made their crossing to raise funds for Make A Wish and the RNLI. Visit kayaksonshetlandbus.org.