Rising fuel prices mean the Clyde paddle steamer the Waverley may never again sail 'doon the watter' on a Fair Friday

They have been making an annual trip on the world's last seagoing paddle steamer for the past four years, and have chosen, on this occasion, to take their cruise on the first day of Glasgow's traditional holiday fortnight.

"We try to keep it the old Scottish way - doon the watter for the Fair," says Rena.

She sips her drink. "And this is another great Scottish custom - Irn-Bru with vodka."

The Waverley launched in the winter of 1946. At the time, she would have been just one ship among many on the Clyde, but as the decades have passed, and shipping has declined, she has become an icon, symbolic of all the great vessels built and sailed on these waters, and of the glory days when Glaswegians would travel by steamer in their tens of thousands for the villages and towns of the coast. Those ships have gone now - the Jupiter, the Jeanie Deans, the Caledonia and King Edward, all scrapped - but the Waverley has survived, a great beauty for her age.

Sadly, her own future is now uncertain. Thanks to a string of rainy summers which have kept passengers away, and rocketing fuel costs - 60% more this year than last - the charity that owns the vessel has used up all its cash reserves. It is seeking to negotiate a six-figure funding deal with the Scottish Government, but for the moment has set a fundraising target of 350,000. So far, over 130,000 has been raised. If the balance is not met, 2011 will be the ship's final season. This, in other words, could be the last Fair Friday on which the Waverley ever sails. Doon the watter and into the past.

"The Clyde without the Waverley?" says Billy Bennett, the one-man-band, shaking his head. For him, it does not compute. Many of the 300 passengers on board today share his mystification and horror at the very thought, and have come on board today as an act of solidarity with the ship. But they are determined to have a good time while they can. And how. "Here's one for the linedancers and the sloshers. Well, for the get sloshed-ers, anyway," says Billy, launching into Amarillo. Straight away, folk are up dancing in the middle of the bar, fortified by Smirnoff Ice and mint humbugs. It is 10.45am. "You can't interrupt the line-dancing," I'm advised. "That's sacrosanct."

One of the less welcome Fair Friday traditions is that it always rains. Today, however, the sun is splitting the sky. "We've been due a wee turn with the weather, eh?" says Ross McCulley, 44, invoking Scottish karma. He is making his maiden voyage on the Waverley in case this should turn out to be its final season, and is accompanied by his three children. The youngest, two year old Ryan, is a bit tired and out of sorts, but Ross offers words of comfort: "Don't worry, son. You'll get a fish supper at Rothesay."

The Waverley, it has to be said, is a smart looking ship. Neat riveting on the two red, white and black funnels recalls the buttoned spats worn by Highland regiments. From keel to wheel, every piece of wood, brass and steel has been polished and gleams. This is a ship which commands respect. Welders wave to her from the decks of the Type 45 Destroyers being constructed at the BAE shipyard in Scotstoun, and construction workers sound the horns of their diggers and bulldozers as we pass the site of the old John Brown's yard in Clydebank.

We pass, too, the site of the A&J Inglis yard where the Waverley was built, now occupied by the new Riverside museum. There is talk of the Waverley berthing beside the Riverside, rather than at the side of the Science Centre as she does now, in the hope of attracting more passengers. It would be a sort of homecoming.

For many of today's passengers, the Waverley herself is a home from home. They travel on the ship, for the sheer pleasure of it, no matter where she goes - Lochranza, Loch Long, Loch Goil, the lot.

Archie McDougall, 69, is wearing a Waverley T-shirt and cap and carrying a Waverley bag in the same striped livery as the funnels. He is a season-ticket holder who sails every day of the week during the summer, having first travelled on the ship as an 11 year old living in Tarbert. His father and twin brother were fishermen, and Archie longed to join them in the trade, but paralysis of his right side prevented him from doing so. The Waverley allows him to experience something of life on the waves. "My heart's in the sea," he says. "I would sail on this boat till the end of time."

Another regular passenger is 17 year old Iain Goodall, who can be found on board three or four times a week, up on deck with his MP3-player. He likes to listening to the Kings Of Leon as the Kyles Of Bute slip by. He first travelled on the Waverley, with his grandpa, eleven years ago. He is about to start nautical college. "I'd love to be captain of this ship one day," he says.

The Waverley leaves a milky wake on the brown water, froth on beer, as she sails down the Clyde. We pass the sites of former shipyards, scrapyard ziggurats of rusting metal, and rotten, slimy, splintered old wharves. A boatyard to starboard is the last resting place of the two Renfrew ferries which were scrapped last year, their names, the Rose and Swan, just visible through a patch of foxgloves. In trees overhanging the water, two herons perch mournful and pale like funeral mutes.

Up on the top deck, Amelie Falconer is wearing a pink badge announcing that she is nine today. "This is fun," she grins. "I like the funnels and the engines." She would get no argument from another passenger celebrating his birthday - 90 year old George Boyter, who has popped down below to inspect the engine. He was once a chief engineer himself, sailing on oil tankers during the 1940s and 50s, and it's clear from the look on his face that the deafening rumble and whoosh of the Waverley is, to him, a comforting heartbeat. "Just magnificent," he says. "Engineering gets into your blood."

Even for those of us for whom the workings of an engine are a mystery, the engine of the Waverley is a marvel. The public can get very close to it. Close enough to feel the rising heat and smell the incense-like oil. The pistons, conrods and crank shaft move with a great, driving, mesmeric rhythm. The gauges and levers are brass and steel, the piping copper, the entablatures painted green, red and gold. The engine dates from an era when things that were useful were also beautiful. "Awesome, I think, is the word," says Iain McCorkindale, Corky, the second engineer.

We pull into Kilcreggan at noon. A piper plays Scotland The Brave. The pierman's two terriers - Stella and Bella, according to the names on their lifejackets - are excited to greet the Waverley. They know to expect titbits of beef from Janosz Luhski who, like the rest of the deck crew, is Polish.

Kenny Morrison, 61, gets on at Kilcreggan. He lives on Arran but travels on the Waverley four days a week, which can mean a very circuitous journey, depending on where the sailing begins. Today, he took the ferry from Brodick to Ardrossan, then a train to Paisley, another to Gourock, and finally the Seabus to Kilcreggan. He will stay on the Waverley back to Glasgow then take the train back to Ardrossan and the ferry to Arran. He can't explain why he does it.

"It's just a compulsion," offers his friend Tim Geaney, a 65 year old church organist in socks and sandals. "It's something you have to do."

The afternoon wears on. Stormclouds shroud the Cowal Hills. Everyone piles off at Rothesay and returns an hour later with bellies full of beer and ice cream and fish suppers. On the top deck, a man stoats over to one of the benches and lies down with no apparent hope or intention of ever rising again.

Down in the bar, the dancefloor is heaving. Rena Hewitt and her pals are giving their all to Ob-La-Di, Ob-La-Da, having been sustained by an all-day breakfast in Dunoon. Amelie Falconer, the nine year old birthday girl, dances with her Aunty Linda, while, just a few feet away, a 70 year old woman slides up and down a pillar in a very frank and surprisingly accomplished manner. Everyone sings along with the song: "La, la, how the life goes on."

As we arrive back into Glasgow, it finally starts raining. The party is over. But what a party. If this does turn out to have been the Waverley's last Fair Friday, she will have finished on a high. If not, it will have been one more grand day out in decades of them, with hopefully many more to come.

"This is the best time I've had in 20 years," says Rena. "If this ship's still here next year, I'll be back, I guarantee you that."