Fancy a ride in my shark? It looks like a great white, soars 12ft into the air then dives under waves

As we scud over the surface of the water, the theme music from Jaws is the last thing I want to hear. But inventor Rob Innes begs to differ. He's playing the tune at top volume over the sound system.

Which perhaps isn't that surprising. I am, after all, the nervous and not entirely willing passenger in an extremely fast, fibreglass shark.

The Seabreacher X  -  co-created and now driven by Rob  -  is the ultimate millionaire's boy-toy: a James Bond-style craft that can dive under water, roll from side to side and jump 12ft into the air.

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It looks like a great white shark, complete with dorsal fin, gaping jaws and rows of dagger-sharp teeth. At 16.5ft in length, it is even the same size as one.

Unlike the real thing, it also has a 260hp engine, which powers it to 50mph above water, and 20mph below it.

Rob, 37, is a watersports fanatic. And along with friend Dan Piazza, 52, he has turned his hobby into a thriving business.

The pair built their first submersible 12 years ago and today their company, Innespace, has a year-long waiting list of rich adrenaline-junkies eager to buy one of their custom-built playthings.

Toys they may be, but each one costs about £60,000.

'The seabreacher is really for people with a large disposable income who want to have fun,' explains Rob.

'It's pretty popular in the Middle East, but we've also sold them to clients in Korea and the Caribbean.'

he seabreacher is unlike anything I've seen on the water before.

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'This isn't a submarine  -  you're not going to visit the Titanic in it,' Rob warns. 'It's more of a cross between a plane and a boat, and we've been improving the models constantly so they can do more and more tricks.'

Just how many tricks, I am about to discover. For Rob, Dan and myself are on Whiskeytown Lake, just outside Redding, California, on the Seabreacher X's maiden passenger voyage.

Seabreacher X is a snug two-seater. So Rob and I squeeze in and leave Dan on the shore, clutching a contact radio.

Then we're off  -  skimming at high speed across the water. We roll 90 degrees to the right, then the left.

I wouldn't recommend it to those with sea sickness, but it is exhilarating  -  I'm just glad that a 360-degree roll is out of the question. For now.

'The next one we're building should allow us to roll a lot quicker,' says Rob cheerfully. 'we're also trying to get those barrel [360-degree] rolls sorted.'

Operating the submersible is, says Rob, fairly easy, 'although you do need to have good spatial awareness. Unlike a boat where you have left and right, fast and slow, this is more like an aircraft. You have to think about pitch, roll and yaw.'

I am gripping the back of Rob's seat after a couple of minutes. But just when I think the worst is over, Rob yells: 'Now for the fun part  -  jumps!'

He pushes forward on the boat's joystick, we plunge a couple of feet under the water  -  the craft can remain submerged for 20 seconds  -  and for a moment we are enveloped by a watery blanket of silence; mercifully, Rob has turned off the Jaws soundtrack.

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But we don't stay under water for long. After gaining a bit of speed, Rob pulls back on the controls and we burst out of the water into the open air. I experience a rush (even if it is partly with fear) as we shoot out of the water like a cork popping out of a champagne bottle.

The downside comes when we hit the surface with a jarring thud.

There is, says Rob, 'a little timing involved' in perfecting the manoeuvre, which he performs a number of times. Each time he promises we won't go too high, only for us to fly more than 10ft into the air.

Rob and Dan are even working on a model which will be able to perform turns in mid-air and back flips.

The sight of the seabreacher emerging from the waves, foam crashing around its fins, is truly impressive. Whenever it or one of its submersible siblings  -  there is also a Seabreacher J, shaped like a dolphin  -  makes a public appearance, it always attracts a crowd of gawpers.

Each machine takes a team of seven people three months to build. And when you consider that this is just the ninth Seabreacher to be built by Innespace  -  and they have a further 31 on order  -  you realise how much time and energy they are devoting to their rather eccentric enterprise.

'We're not interested in making a mass-market product,' says Rob, 'just one-off pieces that we customise for each buyer.'

They recently custom-made one for a client in Dubai, for example, who wanted it with air conditioning.

As well as a stereo system, the Seabreacher Rob takes me out in is also fitted with a camera and  -  should the passenger get bored  -  a screen that allows them to play videogames.

So just how long does it take to master the controls of an artificial shark? While it is more difficult to drive than a conventional pleasure cruiser, Rob insists he can teach someone the basics in just three to four hours.

'One guy ended up doing a barrel roll when he wasn't supposed to,' says Rob, 'but no one's ever crashed one. They're pretty safe.'

A U.S. Navy research officer has even visited Innespace's California base to inspect their designs. 

But Rob insists that the main reason they love their invention is that it is 'so impractical'.

'We'd eventually love to race them as a sport  -  but with the boats costing around £60,000, they're not something people can really afford to destroy. Basically we're just big on the silly factor,' grins Rob. 

Rob is even hoping to drive the Seabreacher alongside some real sharks later this year, off the coast of South Africa or San Diego.

'It would be amazing to do the jump side-by-side with a real great white,' he says.

'But to be honest, I don't know if the sharks would come alongside the boat. It makes a real growly noise and isn't what you'd call stealthy. Sharks can be pretty shy.'

And the boys' next project? well, it's still shark-shaped. A hammerhead, to be precise.

So next time you think it's safe to go back in the water . . .

 For more information, visit www.seabreacher.com