Meet the jetset

Massive power, light weight, insane acceleration – and no brakes. That’s the high-octane stratospheric performance world of jetsprint Superboat racing – a sport in which Kiwis lead the world.

Zero to 130kph in under two seconds, 140kph on a 120-metre straight, into a 180-degree bend. Hitting 6g, with no brakes, in a 500kg boat carving water that’s just knee deep. Superboat racing is extreme, and the men and women who race these boats are extraordinary.

Peter Caughey is New Zealand’s only professional jetsprint racer and the current world champion. He has nine New Zealand titles, of which five are in Superboats, and seven world titles of which seven are in Superboats.

He also builds these craft, delivering his Sprintec boats to clients around New Zealand and overseas.

At first, Superboats seem simple: a compact hull, with a driver and navigator, an eight-cylinder engine, a roll cage and a jet. But at the Superboat level of racing, every boat is more powerful and lighter than an F1 car. It gets complicated.

THE HULL

Built from 5083 marine-grade aluminium, Superboat hulls are typically 5mm thick below the waterline, and a wafer-thin 2mm for everything above the waterline, the minimum thickness allowed under the rules. The aluminium sheets are designed on computer, cut by CNC router and pressed.

“We use the most comprehensive jig in the industry to get consistency,” Caughey says. “Just about anyone can build a boat out of three-mill or four-mill aluminium; two-mill is a whole other world, as we’ve discovered, and only the best of the best can do that.”

The type, thickness, design and configuration of the hull are aimed at a boat sitting higher in the water than its competitors, and cutting through the water with less drag – for traction through the corners the boat depends more heavily than most on the thin fins at the back.

At the outer edge of the delta; ie, the flat, rear section, there are two fins about 25mm deep and up to 40mm long, plus a 60 to 100mm keel about 25mm deep. The race team can tune these between sprints.

“We change their length in one-millimetre increments and fine-tune the boat by redirecting the thrust line of the water by zero-point-one millimetre increments using little shims,” Caughey says. “We design boats to be very sensitive and responsive to those changes, which any racer can do between a quarter final and a final. Dirty water gives more buoyancy; clean water doesn’t need as much fin or keel to achieve corner speed.”

THE JET

The jet is akin to a race car’s suspension and tyres.

“You’re faced with thirty-plus corners in around fifty seconds,” Caughey says. “A race car would want a large tyre in a really sticky compound and wouldn’t be worried about longevity. We have sixty seconds to get the job done, so lean toward a drag-racing

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mentality as we need lots of traction, acceleration and speed.”

Superboats must also hold high cornering speed while remaining stable – and the steering is all done by redirecting the jet stream.

The Sprintec crew completely re-engineer every standard $12,000 Scott jet housing. By the time they’ve finished, it could cost $30,000. The result uses a mostly-inboard jet intake drawing water through an intake grille in the bottom of the boat: “To stop fish and small children getting in,” Caughey says. The water passes through two impellers with a water-straightening stator section between them, using a series of curved vanes to straighten the flow.

“When water leaves the first impeller it’s spinning, but that’s not the fastest way to go. It’s like water swirling down a plughole; if you put a guide in to resist swirl at the plug, the bath will drain much quicker. If you throw 895kw or more at an impeller there’s a hell of a lot of water thrust at that jet unit and water swirl is quite an issue. The force those stator vanes must resist is immense.”

The second impeller accelerates the water, which converges into a tailpipe that’s half the diameter – like putting your finger over the end of the hose, except this hose pumps more than 300 litres per second.

The outlet nozzle size can be adjusted via inserts, anywhere from 110mm internal diameter upward, with Superboats topping out at around 116mm. The impeller diameters vary from 216mm to 228mm.

A water deflecter steers the boat. “Which is also how we stop,” says Caughey. “It’s a bit of a technique that comes naturally when there’s a bank in front of you. Basically you throw the boat sideways and decelerate at the same time.”

A reverse bucket above the nozzle is used for manoeuvring, for example on and off the trailer.

POWERPLANT

Superboat rules allow almost anything – naturally aspirated, turbo or supercharged – but helicopter-style jet turbines and nitromethane are banned.

Methanol fuel allows high compression ratios of up to 16:1, and because it’s an alcohol it absorbs around seven times more heat than petrol or avgas. Injecting cold fuel into the inlet manifold cools the induction charge; cold air is denser, so there are more air molecules, which makes each charge more effective, especially as methanol has a high percentage of liquid oxygen.

Superboats focus more on torque than power. Caughey favours naturally aspirated, as it’s lightweight, responsive and his motor delivers around 1355Nm of torque. A twin turbo may lack a little throttle response and weigh 50-70kg more, but delivers 1600-1900Nm.

As for supercharged, they’re a crowd-pleaser, but often produce huge torque at too low a speed to deliver enough water into the jet intake.

“And the supercharger unit traditionally sits atop the motor, raising the centre of gravity. You start cornering at 4 or 5g on a typical corner and that 40kg effectively exerts 200kg of mass. Even in a straight line you have to accelerate. A top Superboat will exert 2.3g of force, and 40kg becomes 92kg to thrust out of the water.”

The unit’s base in Caughey’s boat is a V8 block, machined from solid billet aluminium. “They’re Chevrolet and Fords, Nissan V8s – pretty much purpose-built racing motors, normally built by racing specialists.”

PERFORMANCE

Top speed is limited by the tight tracks – the longest straight is 120m, and Superboats will briefly hit 130 to 140kph, often through a couple of minor corrections past shallow peninsulas.

“If you don’t stabilise it before the next corner you’ll be a crowd pleaser,” says Caughey, “and if you try to straight-line them, in water waist deep at centre channel and ankle deep on the fast line near the edge, it could get colourful. Yet shallow water gives the boat more lift, so it’s more efficient. Tempting…”

The drivers and navigators are subjected to a maximum of 6g to 8g of force. It used to be higher.

“About 15 years ago, when hull and jet technology wasn’t as good, the boats would resist a turn, bite in and peak g-force would climb. Now we achieve 4g to 6g, but for three or four times as long

– we try to carry the boat like a roller coaster through the corner, maintaining momentum and forward thrust. The trick is to do that in a controllable and easily-driven manner.”

To put that into perspective, a Formula 1 car will reach 5g to 6g in lateral turns, and the Apollo 16 hit 7.19g when re-entering the atmosphere.

WHEN IT ALL GOES WRONG

Caughey says the typical grief in jetsprinting is at least 50 per cent driver-initiated, by clipping a bank. “Or you might hit a wake or disturbed water, and crash.” Hulls can be repaired, if the repairer knows their onions.

The other half is mechanical failure. “Running the motor too lean, or having too much ignition advance and damaging pistons and bearings, or building parts too light – if a crank or cam fails it’s a very expensive rebuild.”

And if the engine stops, the driver has no steering, no reverse, no control. “If the motor stops, the driveshaft breaks or the pump stops and you have some speed on board, you are in for a wild ride.”

If the boat runs wide on a corner and sucks up dirt, or gravel along the edge, it can damage the jet unit. “At 300 litres per second, if 10 per cent of that is gravel, that’s 30 litres of gravel per second and it’s a sad day.”

With racing these days on permanent tracks, that’s less common than it used to be.

TRACKING IT

MOTEC dataloggers are used in most Superboats. “It’s not uncommon to collect info via 30 to 50 different sensors at 10 to 20 times per second, and for short periods at up to 1000 times per second.”

That info is checked in detail later; the ability to assess and interpret it is vital to successful racing. “We may do only one or two testing runs, the rest of the time is spent on the laptop so you don’t have to cause wear and tear on an expensive motor.”

Most engines will do a full season per rebuild, which could cost $15,000 or $20,000 for a Superboat, much less for the entry-level classes. “A crank for a motor like ours costs $7000 to $10,000, a set of conrods anywhere from $5000 to $9000, but often the most expensive parts are your best insurance. They are the most reliable relative to the performance you get from them.”

Generally the team runs the motor rich at the start of the day, then watches temperature, barometric pressure and relative humidity. As the barometer climbs and temperature drops, the motor needs more fuel and will make more power with the right amount. “On a good day in Taupo a motor like ours could be down 105kw compared to sea level. If you’re good at tuning you can recover about five per cent of that.” Forced-induction motors don’t suffer as much, as effectively they make their own air pressure.

COMING UP

The biggest changes Caughey has seen in more than 25 years of racing are hull development, build quality, technology – he’s used the wind tunnel and impeller dyno at Canterbury University to assess and quantify numerous aspects of the boat in the search for optimum performance.

Other significant developments are in motor development and power. Fifteen years ago the top Superboat motors were 7.8-litre small-block Chevs; Caughey’s is now 9.4 litres and they go up to 11.5, fielding as much as 1043kw.

What next? He’s excited by the challenge of developing a turbo single-seater boat for a new, relatively affordable jetsprint class called Turboxtreme and, of course, of going even faster. After all, there’s a world title to win. B