VIDEO: Contrapel

By: Chris Lorigan, Photography by: Matthew Jones

This unique technology could potentially change the face of marine propulsion. The guys from Contrapel are excited and justifiably confident. What they’ve built works so well it more than validates the time and money they’ve invested. And the US Navy’s keen to get its hands on it…

If the United States Navy is interested in your technology, you must be doing something right. When your propulsion system works better than anything else they've got, it might be about time to open the champagne and start celebrating, especially after you've invested over ten years and two-million dollars in the design and development of your invention.

When the US Navy's Riverine Squadrons, part of the Navy Expeditionary Combat Command, were operating in Iraq's Tigris and Euphrates rivers between 2003 and 2011, they found their jet engines were blowing out well before their use-by date. They needed their boats to work effectively in shallow silt- and sand-laden water but the jet units were only lasting about three weeks, with maximum speed dropping from 42 knots down to just 17 in that time — not a good proposition with angry insurgents around. They needed something better, and Christchurch-based Contrapel has a solution — a solution with wide-ranging applications across the entire marine industry. As Contrapel inventor Barry Davies summarises, "The unit can operate in sand, weeds and even withstand exposure to gravel with no drop in performance or longevity."

But let's go back a step. Put simply, what we're looking at here is a new form of boat propulsion. It's a hybrid — a clever blend of jet and propeller technology with the advantages of both and none of the disadvantages of either. Big claim, sure, but we've seen how it works and Contrapel Ltd is clearly onto something. The unit has been integrated into the design of a purpose-built Stabicraft 10.2 Supercab, weighing in at eight tonnes and is easily pushed along by two gutsy Volvo Penta D6 engines, both producing 435hp and 1047Nm of torque at 2500rpm. The boat was designed by naval architect Scott Robinson and built to survey standard under the watchful gaze of boatbuilder and Stabicraft boss, Paul Adams. It's worth around a million dollars — these guys aren't mucking around and are very confident about their technology.

Hammer down

The 10.2 Supercab is an impressive, search and rescue-style boat made even more impressive by the Contrapel system that gets the big vessel up and moving more quickly and smoothly than you'd expect. We were lucky enough to hop on board with the guys after the Hutchwilco New Zealand Boat Show, and after we'd passed Auckland Harbour's limited speed zone just beyond North Head, Davies made sure everyone on board was holding on before he put the hammer down. With a huge volume of white water erupting from the stern, the boat almost effortlessly muscled its way from 12 to 32 knots in next to no time. There was no loud lurch of power delivery as the Contrapel system and the big Volvos got into their work — the system is so quiet, in fact, it can run with electric power for silent operation. The foaming white water surged out of the twin Contrapel units before the boat began producing what looked like a more traditional stern drive wash. Top speed is a comfortable 37 knots at 3500rpm, and you get the feeling you could ski behind this boat if you were so inclined. The guys are also testing the technology in a five-metre tinny and a 7.2-metre McLay, and Davies and his team believe it can be adapted to anything from runabouts to ships. In the big yellow Stabicraft, fuel burn is 110 litres an hour at 26 knots. Over the past decade they've got through a bit of diesel during extensive and successful testing in all conditions, heading out into the treacherous Foveaux Strait as well as Fiordland, the southern lakes, Southland's Waiau River and the Marlborough Sounds.

The tech

The Contrapel hybrid propeller drive is a high volume, low pressure system that works above the water line (or below if the application requires it). As Davies explains, "We get a high-mass, low-plume velocity for smooth power delivery. This combined with the triple-vane steering system situated in the wash means we don't need complex or expensive controls. It's a propeller system with the advantages of a water jet, meaning high propulsive thrust at all speeds. At 37 knots (WOT), the internal propellers are doing 1750rpm. If we took this boat trolling on one engine, we'd use 2.5-litres of fuel an hour at six knots."

The drive uses a pair of contra-rotating, fully-enclosed propellers. An alloy intake duct (one for each unit if two are fitted) in the bottom of the hull picks up water to prime the unit, the propellers then accelerate the water through the outlet. This means the system only requires downstream back-pressure to function, and no high pressure needs to be generated to provide thrust. Davies uses a simple analogy to explain the high volume operation of the unit: "If you stand on ice in a pair of skates and throw a tennis ball very hard, you won't move. But if you instead throw a big, heavy medicine ball, you'll move backwards." In this sense, it's based on simple physics, and it's only when you get Davies talking about propeller theory and the like that you wish you'd listened in high school science class just to comprehend the technology at its most basic level. Clever and effective it might be; basic it is not.

The end result

What they've found, among other things, is that the next advance, which is an oscillating Contrapel system (the current system is non-oscillating), halves acceleration time, lifts top speed and halves fuel consumption, giving, in Davies' words, "unbelievable performance" — they can replace a 350hp Chevy V8 with a 180hp two-litre Subaru engine and outperform the US big block. The technology gives smooth, quiet, predictable thrust at all speeds, can operate in shallow or deep water without limitation, produces a low velocity wash (eliminating the problem some fast ferry operators have with damaging coastlines as they pass, as was the case with the catamarans in the Marlborough Sounds in the 1990s) and offers exceptional low speed control and manoeuvrability. To demonstrate this latter feature, Davies put both engines on forward thrust and lightly turned the wheel to full lock — the boat spun 360 degrees within its body length, rotating several times on its own axis as if bolted to the sea floor. It was a striking display of the technology's broad abilities. Another clever feature is the big stainless steel trim plate at the stern, which, even with only slight adjustment, instantly raises and lowers the bow as required.

The Contrapel drive works well at any speed, so slowing down for rough conditions isn't an issue. The weather and sea state when we were on board were calm, and the guys were hoping for conditions to deteriorate to demonstrate the technology's heavy weather capability. "The system really comes into its own in the rough," says Davies, looking out at the windless Hauraki Gulf as if wishing for a mean low to miraculously appear to prove his point. "We've tested it in Foveaux, and it thrives on a big swell and high chop, with no cavitation ever."

In reverse (which holds one of the company's three patents), anti-ventilation plates drop down to prevent air being sucked through the system along with the water. Backing down on game fish or manoeuvring in tight spots for rescues or docking is easy.

The unit is fully enclosed and protected, with no propeller strike possible. It can operate in weeds, mud, sand and ice with no reduction in performance. This is all good news for commercial and military operators, and Davies has in mind the likes of tourist ventures and ferries, particularly those working in places like the Abel Tasman National Park where beach landing in shallow water is commonplace. And Iraq, of course.

Quality control

A week or so before they went to Auckland's Hutchwilco New Zealand Boat Show, the Contrapel guys were testing in shallow waters when Davies accidentally pulled gravel through the system during operation. We could see the tell-tale scrapes in the unit's paintwork, but the system itself shrugged it off like a rhino with a sandfly bite and kept on doing its thing.

Davies and his team have sourced top manufacturing and engineering partners, and won't skimp on quality. They're in no rush and just want to get the technology absolutely right. The unit is made of the highest grade stainless steel to maximise durability. Davies has a goal of servicing intervals reaching 10,000 hours, which is another aspect that will no doubt appeal to commercial and military users.

Gearing is from Auckland's AH Gears, an industrial gear specialist, while Christchurch-based Mace Engineering built all the Contrapel components to Navy specification. Support from Volpower and Stabicraft has been of huge benefit to the overall development project. And Davies also points out he couldn't have brought the project to fruition if it wasn't for the unwavering support of his wife, Stephanie, and co-founders Paul Paterson, Basil Paterson and Gary Lindberg.

A while back they built a manufacturing prototype but lost all performance once they started addressing a small engineering fault. In attempting to fix the problem, they deliberately built another faulty one to see what was happening. After careful observation, they found the seals and bearings needed work, so they've since designed, produced and rigorously tested unique parts that have eliminated the problems they were seeing in their oscillating unit, which is currently being designed by Mace Engineering in collaboration with Davies.

The power and the passion

Davies started working on this idea about 20 years ago, and the result is testament to innovation, lateral thinking and belief. He has engineering experience earned over many years, having first restored a Jeep while still at school. He later spent time restoring Rolls Royce cars while living in London, has built jet boats and figured out how to design sprint hulls that stick to the water through the creation of pressure. The idea for the Contrapel system came to him while he was installing an aeroplane engine into a speed boat. Being a former high school teacher (science, maths, design and technology), he has a staggering knowledge of physics, including the complex science of propellers, slippage, lift, pressure, hydrodynamics and a whole host of other things you almost need a degree to understand. He explains it pretty well, and if you need more detailed scientific information, check out or email

The company owns three patents across 15 countries, and people across the industry are starting to sit up and take notice. The sort of interest they're getting is a tribute both to the innovation inherent in the invention and the hard work Davies and the team have put in over the years. As Davies says: "This is not in any way speculative or purely theoretical. The performance gains can be demonstrated, are quantifiable and backed up by [ten] years of research."

The company is in no way seeking further investment, and is not looking to restrict production of the technology — Davies is more interested in getting the product out to manufacturers and distributors than keeping it all to himself. I got the feeling he's passionate about the development for its own sake, the thrill of achieving something new, something pioneering in science and engineering rather than focusing on potential profit. Having interest from the US military was a big part of that thrill, bringing with it validation and confirmation that what they've been working on for so long is about to find its way into the world.

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