I’m at the helm of a 15-foot rigid inflatable boat (Rib) in terrible weather: there are storm clouds approaching from the south-west and the wind is already gusting at 35 mph. Waves are breaking over the bow, dropping a bucketful of water into my lap each time. As I bear off to port, the boat lurches in the heavy swell, and someone at the starboard bow shouts, “Man overboard!”

I should also probably mention that I’m in a reservoir, between the M3 and Heathrow airport, less than 12 miles from my house. And also: the man that’s gone overboard is a buoy with a face drawn on it in permanent marker. I’m not here to save anybody; I’m here in pursuit of a Level 2 Powerboat Handling certificate.

Like a lot of men my age, I imagined I’d reached a stage in life when I could coast to the end without further qualifications: no more badges, degrees, licences or clearances. I’d got this far without them – why bother to have my competency tested, approved and registered with some governing body?

I can’t speak for everyone aboard – just me and my friend Alex, because we’re here for the same reason: we went on holiday with a bunch of people last year, and neither of us was allowed to drive the boat we hired. I don’t recall being all that outraged at the time, but Alex was outraged on my behalf. The next time we went on holiday, he said, we’d both be qualified, with cards in our wallets to prove it.

When we booked the course back in January, I think we imagined two balmy April days on a big pond. As the weekend in question approached, the forecast seemed to rule out the need for suncream.

On the morning of the first day it’s cloudy and cold, but hardly ominous – there’s a faint breeze. From the car park, the reservoir is just a massive earth bank with a long staircase to the top.

It’s only when we get over the lip that the situation becomes clear: flags are whipping, trees are swaying and the waves are edged with white. From the top of the slipway, spray reaches our faces. In a matter of hours we will learn to describe this as force five according to the Beaufort scale.

“Windy,” says Alex.

“Yeah,” I say, thinking: if I was on holiday, I wouldn’t go out in this.

Fortunately, the lesson starts in an overheated classroom. The only other student in our group, Chris, is also here because he wants to hire boats abroad. It’s the reason most people take the course, since owning a boat in the UK requires no level of competency.

“You could go to Portsmouth tomorrow,” says Mike, our instructor, “and buy a secondhand car ferry.”

By the time we get out on the water, the wind is worse. Zipping across 700 acres of turbulent drinking water in a low-sided Rib is exciting; trying to pick up an upwind mooring in it is less so, especially if you’re being assessed. And I’m poorly dressed for the weather, which is morale-sapping. I think: all this because you wanted to go to a restaurant on an island.

I find it difficult to explain the day I’ve had to my wife.

“Feel my trousers,” I say. “I’m drenched.”

“Was it fun?” she says.

“It was carnage,” I say. “Huge waves, high winds, constant danger.”

“It’s a reservoir,” she says.

“You don’t understand,” I say. “Conditions were adverse.”

“I was out in the garden,” she says.

“It’s different up there,” I say, pulling a 2-foot length rope from my bag.

“What’s that for?” she says.

“To practise my knots,” I say. “I get tested.”

The next morning – having raided the attic for foul-weather gear – I make my wife drive me to the reservoir so she can see for herself. Pleasingly, conditions are even worse – the wind, evident nowhere else, is howling across the water from the west.

“I do see,” my wife says, heading back to the car. “Have fun.”

Under classroom conditions, I prove capable with knots. Out on the water, I manage to reach the man overboard first time when approaching from downwind. But the other kind of approach – where you come around upwind of the buoy and drift on to it – eludes me. Each time I overshoot, and the little smiling face disappears behind white-capped waves.

“Another marine fatality,” I say, thinking: shut up – you need to pass.

Riding home on the train – the only person in the carriage dressed for a sea rescue – I reflect on the irony of possessing a card with my picture on it that attests to my competency in powerboat handling, having spent two full days demonstrating the opposite. Then I think: it’s not ironic; that’s just how qualifications work.