Into the deep
William Trubridge stops inhaling, rolls gently to his left and begins his plunge to a depth where light, sound and smell do not penetrate. He gives Dylan Cleaver the lowdown on his freediving feats.
Freediver William Trubridge stops inhaling, rolls gently to his left and begins his plunge to a depth where light, sound and smell do not penetrate. Dylan Cleaver explores the insane science of freediving.
W hen William Trubridge descended a world- record 102m into the deathly silence of Dean’s Blue Hole it was the culmination of two years of planning.
Armed only with t wo oxygenthirsty lungs, Trubridge submerged himself, returning to the surface four minutes and 14 seconds later.
The feat, in July, was hailed as a triumph of the human spirit, a win for mind over matter and a cosmic feat of spiritual oneness with the ocean — a place where, as if we needed reminding, humans are not physiologically equipped to survive.
In reality, Trubridge achieved nothing except for adding a metre to his own world record and changing perceptions of what might be possible with the right training and in the right conditions.
Strip it back to its essence and it was a very scientific feat.
It’s okay to feel like it was something more, though. It’s been 63 years since humans went as high as they could go while staying connected to this planet, so in many respects the deep blue yonder is the final frontier and, hey, it’s great that it’s once more a New Zealander pushing those limits further than anybody else.
This is a short story about a deep subject, so let’s take the plunge. Trubridge is on his back, with the aid of flotation devices, above the second- deepest saltwater blue hole in the world, which sits in an otherwise shallow bay off Long Island in the Bahamas. He is tethered to the line where, 102 metres, or 334 feet, six inches below, tags sit upon a metal plate. Returning one to the surface will prove his feat was more than a figment of our imagination.
He is “breathing up”, the process of filling his lungs with the oxygen that will sustain him for the minutes he will be unable to inhale.
The average set of lungs has capacity for about six litres of air. Controversial Cuban freediver Pipin Ferreras was said to have capacity for 8.2 litres, a figure Trubridge believes could be counter- productive for his favoured Constant Weight No Fins ( CNF) category of diving.
“My lungs are average size,” he says. “Okay, they might be a smidgen bigger than yours but bigger lungs are not necessarily an advantage. If you think about it, it’s like carrying t wo balloons with you to the bottom.”
Rather than having extraordinary lung capacity, it is more energy efficient to store the oxygen in your tissue through myoglobin, the oxygencarrying pigment of muscle tissue found in high concentrations in diving mammals. Myoglobin is the magic protein that allows whales and seals to hold their breath under water for long periods of time.
Trubridge is not thinking about ocean mammals. He’s really trying to think of nothing except the fact he will soon stop inhaling, roll gently to his left and begin his plunge to a depth where light, sound and smell do not penetrate, effectively shutting down three senses.
As a final act of oxygen engorgement, he starts “packing”, the art of forcing more air into your trachea with your tongue. To a layman it looks, as Trubridge remains on his back, a little like a fish gasping for water when it is brought on to a boat. “It’s a technique you only teach advanced divers,” the 36- year- old says. “It’s the cherry on top, but it can be dangerous.”
The increase in air can cause the alveoli — tiny sacs in the lungs — to swell and air to escape into the lung cavity. Experienced freedivers can usually cope with this, but in extreme cases it can cause a collapsed lung.
Trubridge’s final breath, from the beginning of the inhalation to the completion of “packing”, can take more than half a minute. As Trubridge descends, the principles of Boyle’s law start to apply. The law says the pressure exerted by a given mass of an ideal gas i s inversely proportional to the volume it occupies if the temperature and volume remain the same within a closed system. The simplest way to grasp this concept i s to put your finger over the end of a bike pump but still depress the pump. There’s now less volume in the canister, but the external forces exerted mean a whole lot more pressure trying to get out to “equalise”.
As Trubridge descends, the pressure around him grows and the volume of his lungs decreases in proportion to the increase in pressure. On the surface, the normal atmospheric pressure is 100 kilopascals ( kPa). “At 10m the pressure i s To this point, Trubridge has been making long strokes with a frog- like two- footed kick. It’s a slower, more graceful version of Patrick Duffy’s Man From Atlantis. This technique has been honed over hundreds of dives to the point where it is second nature.
On deep descents, Trubridge cannot be thinking about technique, worrying about whether he is doing it right. It has to be a “form of autopilot”.
At these depths buoyancy is still your enemy, something to cut through without expending too much energy or raising the heart rate, which in turn burns oxygen.
The pressure i s now trebled, meaning the volume of air in his lungs has been squeezed to 33 per cent of the size it was on the surface.
At 23m, Trubridge takes his last stroke on the downward leg as negative buoyancy kicks in. An extremely simple law will guide Trubridge the rest of the way to 102m: gravity.
“Crossing over to freefall is the most enjoyable phase of the dive, but We should probably talk more about equalising here. Most of us have had that uncomfortable feeling that our ears are about to burst while sitting in pressurised aeroplane cabins while ascending to, or descending from, an altitude of about 10km.
Considering the external pressure exerted on Trubridge’s body is now at 400kPa, reducing the volume of air in his body to 25 per cent of what it was on the surface, he must be equalised.
There are a variety of different methods: The basic Valsalva manoeuvre — close your lips and pinch your nose while trying to force an exhale — which works only at relatively shallow depths; the popular Frenzel technique, which effectively uses the tongue as a paddle to force air into the cavities; or the tricky, French Navy- inspired beance tubaire volontaire or BTV manoeuvre. The best freedivers tend to individualise their techniques.
“I shift air by using my tongue like a piston,” Trubridge says.
The importance of equalising cannot be downplayed. Any diver who fails to equalise before the pain hits is almost forced to abort his or her descent.
Crossing over to freefall is the most enjoyable phase of the dive.