A person might comprehend the idea of swimming 500 metres: 10 laps of an Olympic pool; a long swim along the beach or across a lake. A kilometre is comprehensible too, or 1500 metres: that's an Olympic event after all. It's 30 laps. Five kilometres: well that's a bit harder to imagine. It's essentially swimming around the perimeter of Ballarat's Lake Wendouree.
Now - do it seven times, non-stop. That's the equivalent of swimming the English Channel. Minus the giant jellyfish, seaweed, shipping lanes full of attendant superfreighters and ferries with right-of-way, wild variations in water temperature, dangers of being pulled off-course by currents (one swimmer ended up doing 105km instead of the usual 34) , the exhaustion, hunger, water-chafing and the mental challenges
That is one way, from England to France. If you really want to test your comprehension, imagine swimming all that way, getting out of the water near Calais and walking up the beach, turning around, plunging back into the cold waters of the Channel.
And swimming back to England.
That's exactly what Craigie's Rick Seirer plans to do this August. At the age of 59, he will be the oldest person to swim the Channel and then swim back. If he can do it.
He's already swum the Channel, in 2016, and the past three years have been planning the success of this attempt.
Success, says Seirer, is more than physical training, although he does a huge amount of that. Cold-water swims in Port Phillip Bay, long-distance sessions in Jervis Bay, countless hours in local pools racking up kilometres and building endurance. He's mentally planning his crossing continuously, visualising the journey and its end. What propels someone to undertake a 68km (at the best outcome) swim in cold water?
"It was never really a thought so much," says Seirer. "It wasn't a bucket list. I have been doing the Summer Swim Series down the East Coast for a number of years We were down at Queenscliff and saw a group of people standing around talking.
"There was a blonde girl in the middle talking away. It happened to be (distance and marathon swimmer) Chloe McArdel, who's been a channel swimmer for a number of years. And a friend turned around and said 'you want to have a crack at that,' because I enjoyed distance swimming. That's how it started."
Seirer says swimming has been his favoured sport all his life. His Austrian-born father was a mountain climber and cross-country skier; there wasn't a lot of room for swimming in the land-locked country.
"Dad was not a swimmer," Seirer says. "Mum can't swim. But being born in Australia, I started swimming at a very young age. At four-and-a-half years of age I got my Herald (learn-to-swim certificate)."
Seirer lives in Craigie, a former gold-mining village on McCallums Creek 10km from Maryborough. While the area is one of the drier parts of the state, it has a long sporting history and a strong swimming community. Seirer will swim where he can get distance - local reservoirs, when they have enough water and are not tainted by blue-green algae, are popular.
But the training is never much more than 10km at a time. Because the Channel swim is such a shock to the body, a swimmer needs to be able to confront it at peak fitness, with no tiredness, to endure the levels of physical and mental pain it causes.
Seirer's first crossing three years ago was on a Spring tide. He swam 50km. So how does he face potentially doing that distance again, then getting out of the water, turning around and going back?
"I'd just done the single crossing and finished it in good time and felt very good and we were having a celebratory dinner later and (Chloe McArdel's partner) Paul said, 'I reckon he got a double in you,' and that set the seed; it progressed from there."
His first Channel swim took 12 months' training. McArdel has coached Seirer all the way through.
"Every single day I followed a program of sets she would send me. The average distance was 4 to 4.2km sessions, building up to about 25km per week with two open-water swims as well," he says.
The open training was around Brighton, Mentone and Black Rock; Seirer says you'd see the occasional shark or stingray, but they have never concerned him. It was simply the constant work.
"You're looking at about a 12-hour swim across the Channel; the argument is you can't do that in training because the recovery time is too long, you lose too much training time and swimming. So we'd do two 6km sessions on consecutive days.
"It's the exhaustion. It takes you a few weeks to get over the effort that you put into it."
Hour after hour, stroke after stroke, pushing himself against the water. How does someone achieve that sort of endurance mentally?
"I do a lot of visualisation," says Seirer. "Visualising success, visualising the finish. If things start to get a bit tough I start focussing on different things. If you start to get some bad thoughts, think of something better. I practice that all the way through, so when we do get to the stage - because there is going to be pain one way or the other - there are techniques we use to get out of it and stop thinking about it."
Overcoming fear - be it the fear of drowning (10 people have died swimming the Channel), of giant jellyfish swarms, or rain, or a cold current sweeping in - is just part of the challenge.
Seirer says having confidence in the crew which must accompany each swimmer is a tremendous asset. No person can swim the channel without being accompanied by an approved pilot. The window for each year's attempts is limited to about six weeks, and the numbers have to be managed, due to safety and the Channel being one of Europe's major commercial ocean lanes.
"The crew is a major part what happens," Rick Seirer says.
"You're never more than four or five metres from the boat. Everything's prepared to the point where I have to think about absolutely nothing except swimming. I don't have to worry what direction I'm going; I don't have to look anywhere; I don't have to worry about feeding.
"Everything's there for me. Basically I get in there and think about nothing; I just swim. I can sit there for hours and hours and just concentrate on my arms: are my arms going in the right spot, am I pulling in the right way; am I being efficient, are there too many bubbles?
"It's at least as much a mental challenge, and I think it might be even more mental. I've always tended to endurance events, I don't know why. Running, swimming, triathlons. Maybe it's a personality trait. My wife thinks I'm obsessive; when I do focus on something I have the ability to block everything else out."
Triumphing over pain is just part of the mental battle. A human can take a lot of pain, he says; it's a matter of how you approach it inside your mind that can make the difference.
"I remember the first swim, about the seven or eight-hour mark, it started to hurt and it just got worse and it got worse and I got to the point where I felt like I couldn't pull. Both shoulders were just in pain, screaming at me. I thought to myself, 'What's the deal here?'
"I said to Chloe at one of the feeds, 'my shoulders are getting a bit angry,' and I thought, 'Well if my arms give out I'm going to have to kick my way to France.'"
Seirer pushed through the pain.
"The pain will go away. Chloe says all pain is transient; it's not pain from an injury. About an hour out from France I stopped for a feed and Chloe said, 'Now you have to go hard for half an hour,' and I thought, 'Oh righto, let's give it a go.'
"So I started, and for an hour I just went flat out: my breathing was beautiful, I was kicking well - and the pain disappeared. And when I hit France, I felt awesome. It was like two weeks of adrenaline."
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