.A sleek British sportsboat - a Hunton 43 Gazelle - is screaming down a Moroccan river, chased by two black gunboats manned by vicious looking bad guys. The Hunton swerves, trying to elude its pursuers, but they're not budging and the chase gains pace. Suddenly, there is a huge explosion and the Gazelle is no more. Standing on the riverbank and wincing is Geoff Hunton the boat's Hampshire-based designer.

As the remains of his carefully crafted hull float to the surface, there is a yell of "Cut!" and Geoff manages a smale. It's all in a day's work for the cast and crew of Paramount's latest adventure epic Sahara, but for the Hunton team - movie novices - watching their boat being blown to smithereens must have been more than a little bewildering.

It's not often that a small British boatbuilder enters the glamorous world of Hollywood. But when Hunton were approached in the summer of 2003 to build the good guy's boat for Sahara, the were quickly swept up by the lightening-paced movie industry. "The production team came to us in August and needed three boats - two full-spec and an empty hull - by the following January," explains Martin Payne at Hunton. "They had to be absolutely identical, two with jet propulsion, and all with specifically chosen upholstery amd exterior colouring. It was the biggest challenge we've encountered time-wise, and I'd be wrong to say there wasn't a little concern, nay panic, in the yard, but we were all excited to take it up."

"A bit different form providing camera boats for Howard's Way!" Geoff laughs, remembering his last dalliance with the showbiz set.

Sahara might not seem an obvious title for a film that features boats so heavily. The story ends up in the heat of the African desert, but starts in Morocco where adventurer Dirk Pitt is searching for a sunken Civil War Confederate ship and its fabled haul of gold coins. Played by chisel-jawed Hollywood actor Matthew McConaughey, Pitt is assisted by his faithful sidekick Giordino, and the beautiful UN scientist Dr Eva Rojas, played by Penelope Cruz.

The story takes a turn when Dirk joins Dr Rojas in her crusade to find out who is behind a strange pollution incident that is causing an epidemic of madness, cannibalism and death among thousands of North Africans. Racing to save the world from environmental catastrophe, the team, equipped with a state-of-the-art powerboat, run the gauntlet between a billionaire industrialist and a bloodthirsty West African tyrant.

Based on a Clive Cussler best-seller, it’s your classic Indiana Jones-type adventure – treasure maps, exotic locations, sweaty heroes, wisecracking baddies, and lots and lots of explosions. And the Hunton 43 Gazelle really is up there with the film’s top-billing stars.

“The boat features heavily in the first 40 minutes of the film,” says Geoff. “We made three boats, but they feature in the movie as Matthew McConaughey’s only boat. Sahara was shot in several locations and often required hours of stuntwork, so there was no way they could have got by with just the one. And, of course, one of them came to a rather sticky end!”

Calliope, the boat that features most prominently in the filming, is not your average Hunton. For a start, the sterndrives that usually propel the speedy Gazelle range have been replaced by jet-drives, which were vital for the kind of shallow-water locations where the boat was going to be used.

“Before we started the project we were visited by a huge entourage from the movie’s production team, including the director Breck Eisner, and Lance Julian, the marine co-ordinator,” explains Martin. “It was very surreal having them here – you don’t get many blacked-out limousines in Romsey!

“They had already been scouting locations for the film and had decided on the river Azemmour and several reservoirs in Morocco for the major part of the shoot. Water depths were not great, and the production team had to ask the King of Morocco’s permission to raise the levels in one reservoir in the Atlas mountains. And with the kind of on-water stunts the director had in mind, jet power was the only feasible option. And it worked really well.”

After several more meetings with the movie’s executives, the Hunton team began to realise just what goes into making an epic Hollywood picture. And just what it costs. The production team paid out over £750,000 for the three Huntons they used, but that is just small change when you look at the estimated $130 million (approx £68 million) it took to finish the film.

“There were hundreds of people working behind the scenes on Sahara and we only encountered a few,” says Geoff. “But the professionalism and focus was outstanding – and no wonder with the sums of money we’re talking about to produce it!”

After some successful sea trials in a bitterly cold Solent in January, the boats were shipped out to Africa and Spain. Geoff, Martin and Steve Colley, Hunton’s general manager, were invited to Marrakesh in March to watch a couple of days’ shooting and keep on eye on how the boats were coping with the rigours of film stardom. Martin was impressed. “The whole set-up was such a well-oiled machine, with an amazing infrastructure, even for such a relatively undeveloped area. The atmosphere had a real buzz, but everyone was working really hard to get as much done in as little time as possible,” he says.

The boatwork was being supervised by Lance Julian, the head of Marine Team, a group of marine co-ordinators from New Zealand. Lance had found Hunton at the beginning, so already knew the boats well. The stunt sequences also involved several Halmatic gunboats, which were the preferred mode of transport for the film’s bad guys, and with so much on-water action Marine Team really had their work cut out.

Each boat had its own skipper throughout filming, and engineers were on standby to carry out regular maintenance checks on the Sahara fleet. The film’s heroes spend most of the first half of the film on the Hunton, so the boat had to be specially adapted for cameras doing close-up work, but the exciting stunt action took place in the capable hands of Marine Team’s drivers. “I was really proud to see the boat going through its paces in Morocco,” says Geoff, whose invaluable knowledge of the Hunton’s workings and skill in handling the boat proved indispensable to Lance and his team. “I did wish that I could drive Calliope on film though!”

The climax of the Gazelle’s stunt sequence in Sahara is that explosion, which puts paid to the gunboats in pursuit after the heroes have jumped overboard, of course. “I have to admit I felt funny watching one of our boats go up like that,” Geoff laughs. “There were actually four small explosions, caused by detonators in different parts of the boat, that built up to one enormous wall of fire. But I suppose we should be relieved that the stunt co-ordinator’s meticulous planning paid off and we didn’t have to start blowing up any more Huntons!”

Sahara comes out on UK release on April 8, and Geoff and his team are eagerly awaiting their first glimpse of the finished film. Nearly every PC at their Romsey offices has a behind-the-scenes, on-the-film-set screensaver and everyone is full of tales of their brush with Hollywood. But until that first screening, they will have to make do with the trailer, showing their Gazelle exploding in glorious technicolour. “It still makes my heart jump every time I see it,” says Geoff.

New Zealander, Captain Lance Julian, is head of Marine Team, Sahara’s on-water co-ordinators, and one of the most respected names in the film-making business. He has worked on numerous sea-strewn classics, such as Titanic, Pirates of the Caribbean and Waterworld, and was the reason that the producers of Sahara got in touch with Hunton in the first place. He tells us how a small British boat company became part of the Hollywood circus:

“I’d been given a photo of the type of boat Breck, the director, had in his head. We’d already been scouting for possible film locations for months, so I knew the kind of terrain that we were dealing with and had already decided that jet-drives were our only option – working in depths of 3ft and less, we couldn’t have worked it any other way. Then it was just a case of scouring magazines – Motor Boat & Yachting was a revelation – and the internet to find that perfect model. We did focus on the UK boat industry, mainly because many of the production team were based in England, but also because we knew that you make some of the best powerboats in the world.

“Eventually, we found an article singing the praises of the Hunton 43 and knew we had found the boat we needed. I knew that the timescale was extremely tight, so we were just completely honest with Geoff, telling him exactly what the film required and trusting that he wouldn’t slip the information out – the film world is ridiculously secretive sometimes. He had to be very adaptable and rose to the challenge admirably.

“Sahara’s art director had decided on the colour scheme – a shiny black hull with coffee-coloured upholstery and a teak deck fore and aft – so Hunton had to adapt their boats to fit. Then the jet propulsion was fitted, the boats were tested and the end result was a fantastic powerboat that met our demands exactly. There are two sides to every film – the creative types and the money men. Keeping them both happy can be a thankless task, but we managed it.

“The boats were shipped out for the start of shooting, but we had five weeks of training on them first. Our stunt co-ordinators had to get used to handling the jet system – us New Zealanders have been using them for donkey’s years and once you’ve mastered driving a jet-boat you can do some amazing things. But it does take practice to convert your mindset from conventional engine power. We had to train up a big group of North Africans to handle the gunboats as well, as Sahara’s baddies are all from that part of the world, so we had to really focus on getting as much done in as relatively short a time as possible.

“Marine and stunt co-ordinators get hold of a copy of the film’s script really early on in the process, so we can see what the director has in mind and tell them if anything is completely unachievable. You can’t just say yes to everything and then cross your fingers and hope for the best! But you do have to be brave – after all, you’re using boats in deeply unusual circumstances and a lot of the time you need to be doing things in them that they’re not really built for.

“By the time it came to the actual shoot, the boats were romping along at a huge rate of knots, which is quite scary for

an old sea-dog directing from below decks! The stars, Matthew McConaughey and Penelope Cruz, were great at handling the Hunton. I’ve worked with Matt three times now and he’s always very hands-on with his boat driving. He mastered Calliope in a couple of days, whereas Penelope was much more relaxed and took it all in her stride.

“The Huntons operated exceptionally well in all the location shoots. There were some mechanical failures – there always are – but they were fixed easily and having Geoff in Morocco for a couple of days to do some tweaking was invaluable. Of course, a highlight was the big explosion. That was a hell of a lot of fun!

UK boatbuilders VT Halmatic were chosen by Sahara’s production team to produce the baddies’ fleet of menacing-looking gunboats. And with a respected track record of building specialist military craft, rising to the challenge was all in a day’s work for the Halmatic boys.

“The boats we settled on were 9m logistic support boats that are often used by the Royal Engineers,” says Seb Freeman at Halmatic. “We obviously had to make a few alterations – we turned the boats into bow-riders, made room for the baddies’ guns and connected Hamilton waterjets to the boats’ twin Yanmar 300hp engines. The two models they used to film could reach speeds of over 40 knots and were able to go from 40 to standstill in a boat’s length.

“We also supplied several other Halmatic craft for Sahara’s crew to use as camera boats, as well as two 5.2m Mark 1 Rigid Raiders. These were commandeered by the baddies too.