Life

"No kneeling up on the seats. If you go in, you don't come back." Those were the not terribly reassuring words of our captain, Lindsay Johnston, as he cast off the ropes and we sailed out from Ardfern Yacht Centre on the west coast of Scotland, through the Sound of Jura, headed for the Corryvreckan whirlpool.

I gave my four-year-old my sternest be-on-your-best-behaviour look. But Johnston was not being alarmist. The Old Hag, as the Corryvreckan whirlpool is otherwise known, is unquestionably powerful. You don't mess with her.

I was glad of the near-calm day as we left the yacht centre; but, as I was to discover, the weather in the harbour is no indication of the tidal conditions outside. The Royal Navy classes the Gulf of Corryvreckan as impassable at times; at best, it should only be traversed with caution.

Billed as the third largest whirlpool in the world, it sounds impressive and, sitting off the west coast of Scotland, adjacent to the island of Jura, is practically on my doorstep. But though we'd get close, I didn't want to get that close. How near, exactly, would we get? Johnston laughed; he'd been sailing here for 28 years. Relax.

And so I did. The light was clear and the waters smooth. This was, as it turned out, deceptive. We sailed out of Ardfern - a village that is almost all yacht - and into the Sound of Jura, saying hello to basking seals on the shoreline. This place hoaches with wildlife - silhouettes of red deer, in rutting season, spanned the hilltops. The small Garvellach Islands - site of a monastery founded by St Brendan in the 6th century - slipped in and out of view, and at least one eagle skimmed the sky. On the previous day's trip, the whirlpool had been abandoned in preference for pursuing a shoal of dolphins, which were contentedly followed for the afternoon.

As we left the Sound, entering the Gulf of Corryvreckan itself, we were in the middle of a spring tide, and the conditions were setting themselves up nicely. The waters were changing, becoming visibly and palpably agitated. I was deeply appreciative of the engine power - yachts can get near the whirlpool only in slack water - but, even if conditions are OK, there are only about 10 minutes for getting in and out.

We could hear something strange in the marked rush of water; the whirlpool itself, which can be heard up to 10 miles away. The boat began to sway. My four-year-old was delighted - this was, to him, "real" sailing. ("Mummy," he said, grinning. "Do you think we'll sink?")

But once we were full-on down the Gulf, the oddest thing happened. We were travelling on the tide at one side of the channel but, watching, one becomes aware that the tide along the opposite bank is moving in the opposite direction. Slowly it dawns on you that this is not an optical illusion but a division of tides, halfway across the channel. This intersection of tidal pathways - coming from the west and east side of Jura, and then through the deep and narrow Gulf - is part of the reason why the whirlpool exists. As the flood tides - which can flow at up to nine knots - run over the sea bed, the mass of water collides with a steep column of rock (the "Hag" herself), which rises to within 90ft of the surface. The sea bed in this area is hugely erratic - dipping into great holes 300ft deep - and can result in the difference in height of water in the opposite sides of the Gulf of half a metre. With the right westerly wind and timings of opposing tides, spectacular "standing waves" can form around the whirlpool. But predicting whirlpool conditions is high art as well as science.

I had been expecting a grander version of a bath-sized plughole, but what I got was something on a different scale altogether. The opposing tidal systems make the view at first difficult to fathom, even slightly bewitching, then I realised: this was actually very big. The whirlpool is almost subtle in effect until you realise that most of the water in view is moving in circles. This whirlpool is rather enormous.

It was, admittedly, at its most dramatic during a spring tide; raw undiluted fury, churning in the middle of the Gulf. It is also slightly eerie; the boat was skirting the edges and there was a certain thrill feeling its resistance to being drawn towards the centre. Apparently Corryvreckan changes not only in size but in position and effect: drift divers, quite madly in my view, throw dummies down into the whirlpool to see where they emerge, and then get a boat to go and wait at the appointed place while they dive into the whirlpool, to hopefully emerge at the boat - supposedly, this is among the most dangerous dives in the world.

Personally, I thought that it was quite satisfying to see the whirlpool from a safer distance. But the appeal to get closer to nature - possibly too close - is strong. Swimtrek, a specialist adventure holiday company, bills the whirlpool as the main attraction on its Hebridean tour, with swims through the Gulf timed for slack tides.

But there's no need to go quite that far. Believe me, it's a pretty good view from the boat.