How Do Jet Boats Work? The Technology Behind Queenstown's River Rides

How waterjet propulsion works, step by step

The principle is simple: push a stream of water backwards and the boat moves forwards. Making that efficient and controllable takes careful engineering.

Step 1: Water enters through an intake beneath the boat

A waterjet starts with an intake opening in the bottom of the hull. When the system runs, water flows in through this opening and into an internal duct.

The shape of the inlet matters. It has to feed a steady, fairly smooth flow of water to the pump across a wide range of speeds and turns. If the flow becomes turbulent or picks up too much air, the boat loses thrust. A grate over the intake keeps larger objects out, although small stones, sand and debris can still cause trouble.

Step 2: The engine drives an impeller

Inside the unit is an impeller, a spinning part that looks like an enclosed, specially shaped propeller. The engine turns it through a drive shaft and, on some installations, a gearbox. As it spins, it adds energy to the water passing through the pump, raising its pressure and speed.

The impeller is why the system can make strong thrust without a propeller exposed under the hull.

Step 3: The stator straightens the flow

Water leaving a spinning impeller swirls. A stator, a ring of fixed vanes inside the unit, straightens that flow and turns some of the swirl back into useful pressure, which makes the pump more efficient. Jet units differ in their internal shapes, but an impeller and stator sit at the heart of most modern marine waterjets.

Step 4: Water accelerates through the outlet nozzle

The water leaves through a nozzle at the stern. The pump and nozzle are designed together to send a fast stream of water backwards.

As the water is pushed back, the boat is pushed forward. This is Newton’s third law of motion: when the boat pushes water one way, the water pushes the boat the other way.

Step 5: The driver redirects the jet stream to steer

A typical jet boat has no rudder behind a propeller. It steers by changing the direction of the jet: a movable steering nozzle points the outgoing stream left or right, and the thrust swings the boat with it. At speed this makes the boat very responsive.

Step 6: A reverse deflector redirects thrust for manoeuvring

Waterjet boats also carry a reverse deflector, sometimes called a reverse bucket. Lowered over the nozzle, it turns the outgoing jet forwards to give reverse thrust.

By adjusting it, the driver can slow the boat, reverse or balance forward and reverse thrust to hold position. The impeller keeps spinning the same way the whole time; only the direction of the jet changes. This is a large part of why modern jet boats handle so precisely.

The propulsion system at a glance

In one sentence: a jet boat uses an engine-driven pump to draw water into the hull, speed it up and push it out backwards, making thrust without a propeller under the water.

Why can jet boats travel through shallow water?

This is the biggest advantage of jet propulsion, and the reason the New Zealand river jet boat was developed in the first place.

New Zealand has many fast rivers with shallow channels, gravel bars and shifting beds. Propeller boats struggle there because the propeller, shaft or lower drive unit sits below the hull, and if it hits submerged stones, the boat can be damaged. Jet propulsion largely removes that problem.

No exposed drive propeller below the hull

The impeller is enclosed inside the jet unit, and the intake can sit almost flush with the bottom of the hull. There is no propeller, shaft or drive leg sticking down below the boat, so a jet boat can work in much shallower water than many propeller-driven designs. HamiltonJet, the company Bill Hamilton founded, lists shallow-water operation and the flush-mounted intake among its waterjets’ main advantages.

The hull rides higher when travelling at speed

Many jet boats have planing hulls. As a planing boat speeds up, lift from the water carries more of its weight and it sits higher, drawing less water than it does at rest. A planing hull and an internal waterjet together let some river boats cross remarkably shallow stretches.

How shallow can a Queenstown jet boat go?

Shotover Jet says its purpose-built canyon boats can manoeuvre in water as shallow as 10 centimetres. That needs context.

It does not mean every jet boat can run safely in 10 cm of water, or that a boat can stop, restart and turn freely at that depth. The real minimum depends on the hull, the load, the speed, the intake and the riverbed. A jet boat still needs enough water to feed the pump and to keep the hull off the bottom.

How do jet boats make 360-degree spins?

The 360-degree spin is the moment everyone remembers from a Queenstown jet boat ride. From the bank, the boat seems to turn almost on the spot, throwing water out in a wide arc. On board, the sudden change of direction feels like being flung round across the river.

What actually happens?

The driver makes a tightly controlled, high-speed turn using the steering, engine power and the way the boat handles. The steering nozzle swings the thrust to one side, and the hull reacts to that thrust, the water and its own momentum by rotating sharply. Done right, the turn carries the boat through a full circle.

The boat looks as if it pivots instantly, but it does not turn around a fixed centre point. The spin is a fast, moving manoeuvre that depends on the hull’s inertia and how it grips and slides on the water.

Does the jet boat stop before spinning?

No, not usually. A typical spin uses the boat’s existing speed and the instant steering response. Exactly how it is done depends on the driver, the boat, the speed and the river.

Why does so much water spray into the air?

In a sharp spin the boat changes direction fast and pushes water sideways. The hull, the wake and the rotation throw up the wall of spray you see in the photographs, and that often lands on the passengers.

Are 360-degree spins possible on ordinary speedboats?

Some powerboats can make tight, aggressive turns, but waterjet steering and a purpose-built hull make the quick spins of a commercial jet boat ride far more practical. Not every jet boat is built or driven to spin like a tourist boat, either. Shotover Jet says its drivers complete at least 120 hours of training. Leave these manoeuvres to professionals.

Jet boat vs conventional speedboat: what’s the difference?

“Speedboat” describes a fast motorboat, not how it is driven. A speedboat can have an outboard, an inboard engine with a propeller, a sterndrive or a waterjet. A jet boat is defined by its waterjet.

Our guide to jet boats vs speedboats compares the ride itself, the prices and the Queenstown options.

Are jet boats faster than propeller boats?

Not necessarily. Top speed depends on engine power, hull design, weight, water conditions and how efficient the drive is. Waterjets work very well at certain high speeds, but there are extremely fast propeller boats too. Queenstown’s operators chose jet boats for the shallow water, the acceleration and the precise handling, not for top speed alone.

Do jet boats use more fuel?

It depends on which boats you compare. Waterjets can be efficient at medium and high planing speeds, especially when hull and drive are well matched, while a propeller may be more efficient at low speeds in some uses. HamiltonJet says its modern waterjets can match a well-designed propeller’s efficiency at suitable planing speeds. The idea that jet boats always burn more fuel is too simple.

Who invented the jet boat? The New Zealand story

The high-speed river jet boat is one of New Zealand’s best-known engineering inventions, and it is tied to Sir William Hamilton, usually known as Bill Hamilton.

Hamilton was born in 1899 in South Canterbury and grew up among the rivers and mountains of the South Island. He was an inventive engineer drawn to practical mechanical problems. One of those was getting a boat up the shallow, fast rivers near his property, Irishman Creek Station in the Mackenzie Country. Propeller boats could not cope, and Hamilton thought that pumping water through the boat might.

The breakthrough in 1954

Hamilton tried several designs before he had a waterjet boat that worked. His early boat used a small plywood hull, a Ford engine and a centrifugal pump. The first working designs came in the early 1950s, and 1954 is usually given as the breakthrough year.

Engineer George Davison joined him and helped make the jet unit more efficient. Later units moved to more advanced axial-flow pumps. The result let powered boats travel up rivers where they had been impractical before.

Did Hamilton invent waterjet propulsion itself?

No. Moving a boat by pushing out water was understood and tried long before Hamilton, and he himself said he did not claim to have invented marine jet propulsion.

His achievement was making it practical and effective for fast boats in shallow rivers. He did not invent the physics or the first water-propelled boat; he turned a known idea into a working technology that sold around the world. The Museum of New Zealand Te Papa Tongarewa holds an early Hamilton jet boat, and Te Ara, the Encyclopedia of New Zealand, records his work.

Jet boat history timeline

How did jet boats become famous in Queenstown?

The Shotover River could hardly suit jet propulsion better. It runs through steep rocky canyons with narrow passages, shallow stretches and conditions that change all the time, the kind of water Hamilton’s technology was built for.

Shotover Jet started commercial trips in 1965, and as Queenstown grew into an adventure capital, jet boating became one of its signature activities. Today the red boats run through the narrow Shotover Canyons on a ride of about 25 minutes.

Shotover Jet has exclusive commercial access to this section of the canyons. It is run by Ngāi Tahu Tourism; Ngāi Tahu’s connection to Kimiākau, the Shotover River, goes back long before European settlement.

Why are the Shotover Canyons particularly impressive?

Steep rock walls make every manoeuvre feel bigger. The thrill comes from 90 km/h with the walls close on both sides, then the sharp turns and the spins. The technology makes the route possible, and the landscape is why you remember it. Our page on how fast Shotover Jet goes puts the speed in context.

Are all Queenstown jet boats built the same way?

No. They all use waterjets, but the hulls, engines, passenger numbers and routes differ a lot.

Shotover Jet’s boats are hand-built in heavy-gauge marine aluminium, with two 350 MerCruiser V8 engines (700 horsepower combined) driving two Hamilton 212 jet units that move 760 litres of water a second, according to the operator.

A boat made for tight canyon turns is not built the same as one carrying passengers along a long braided alpine river. Each operator picks engines, jet units and handling to suit its route, so the tour you choose changes more than the time you spend on the water. Our Shotover Jet vs KJet comparison covers the two best-known rides side by side.

Are jet boats safe?

Jet propulsion has real advantages, but it does not remove the risks of boating.

With no exposed propeller, one hazard of an ordinary motorboat is gone. Jet boats can still hit rocks, run aground, break down or meet dangerous river conditions.

Waterjet steering has one important weakness: it needs thrust. If the engine or jet loses power, the driver loses most of the ability to steer, and a jet boat cannot be steered like a boat with a separate rudder.

Why professional driver training matters

Commercial river jet boating in New Zealand is regulated under Maritime Rules Part 82, which sets requirements for operators, driver competence, equipment and safe operating procedures. Maritime New Zealand also publishes safety advice on jet boating and river hazards.

There have been serious commercial jet boat accidents. In February 2025 a Skippers Canyon Jet boat lost its engine to an electrical fault, lost steering with it and hit a canyon wall. The Transport Accident Investigation Commission (TAIC) published its findings in April 2026 and recommended that Maritime New Zealand work with operators to improve passenger-protection requirements. An earlier TAIC inquiry, into a 2021 KJet incident on the Shotover, found that a failed fuse in the engine control system had stopped the engine.

These cases show why high-speed river trips need competent operators, well-maintained boats, a thorough briefing and close attention to conditions. Our Queenstown jet boat safety guide covers the rules and the record in full.

What should passengers do?

Follow the crew’s instructions, wear the life jacket properly, stay seated and keep your hands and arms inside the boat during manoeuvres. Before you book, tell the operator about any medical or mobility issues and check its restrictions. A good jet unit is only one part of a safe trip.

What happens if a jet boat sucks in rocks or sand?

The shallow rivers that make jet boating exciting are also hard on the machinery. A waterjet has no exposed propeller, but its intake can draw in debris: small stones, gravel, weed or other objects.

That can cause:

• Less water flowing through the pump.
• Damage or wear to the impeller.
• Vibration and lost efficiency.
• A blocked intake or internal passages.
• Cavitation in some conditions.

What is cavitation?

Cavitation happens when the pressure in fast-flowing water drops low enough for vapour bubbles to form. When the bubbles collapse in higher-pressure water, they cause noise and vibration and can damage the pump’s surfaces. Air sucked into the intake causes a related problem, often called ventilation, which also cuts thrust. Designers reduce both through careful shaping of the intake, impeller and hull.

Jet propulsion makes shallow-water boating practical, but it does not make a boat immune to submerged hazards or mechanical damage.

Do jet boats have brakes?

Not like a car’s. A jet boat slows by cutting thrust, through the drag of the water and, when needed, by turning the jet forwards with the reverse deflector. The deflector can produce braking force while the impeller keeps spinning forwards, and some modern waterjets give strong reverse thrust and fine control at low speed.

That is not an instant stop. The boat carries momentum, and how far it takes to stop depends on its speed, load, the river and the design of its jet unit.

Can jet boats travel upstream against strong currents?

Yes, as long as the boat makes enough thrust and speed to beat the current. Getting up rivers was one of the main reasons Bill Hamilton started his work.

A jet boat does not need the current to carry it. The engine drives the pump, which makes the thrust. Going upstream, the boat has to overcome both the drag of the water and the river flowing against it, so its speed over the riverbank is lower than its speed through the water.

Getting up fast, shallow rivers opened remote waterways to recreation, transport and exploration, and it is why jet boats became so closely tied to New Zealand’s braided rivers.

Can jet boats be electric?

Yes. A waterjet does not need a petrol or diesel engine, only something to turn the impeller, and an electric motor can do that. The jet unit stays much the same; the combustion engine is replaced by a battery pack, an electric motor, a battery-management system and power electronics.

Shotover Jet’s electric boat project

Shotover Jet has tried it. Ngāi Tahu Tourism started its electric jet boat project in 2019, paused it during COVID-19 and restarted in September 2021, converting one of its petrol commercial boats, the T3, to fully electric power. It was tested on Lake Wakatipu at Glenorchy and on the Shotover River in May 2022.

The project showed that electric power can work in demanding commercial jet boating. A prototype is not a fleet, though: the operator describes the boat as a prototype in testing and plans to bring the technology into the fleet once that testing is done.

Why aren’t all jet boats electric already?

Power is not the problem; high-performance electric motors produce plenty of torque. The harder questions are energy storage, battery weight, range, charging time and fitting charging into a busy schedule. A high-speed tour boat needs a lot of power for repeated acceleration and turns, and operators have to balance performance, passenger numbers, reliability and emissions. Electric jet boating is a developing technology, and the right answer will differ from boat to boat and river to river.

What does jet boat propulsion feel like for passengers?

The mechanics sound complicated, but the ride feels simple and immediate. You hardly notice the machinery under the hull. What you notice is the boat leaping forward, the river scenery rushing past and the sudden change of direction when the driver turns. The acceleration often makes more of an impression than the top speed.

In a Queenstown canyon, the narrow rock walls make the speed feel even greater. Then comes the spin: the boat swings round, spray flies sideways and suddenly you are facing the other way. Every turn shows how quickly a waterjet responds.

The technology is interesting on paper. On the Shotover River it is a lot more fun.

Where can you experience jet boat technology in Queenstown?

If you want to feel the technology, not just read about it, Queenstown has several different rides.

These rides do not follow the same routes, even where two operators use the same river.

Our recommendation

For the most dramatic show of high-speed handling, choose Shotover Jet. Its short canyon ride shows exactly why a responsive waterjet mattered so much. If shallow-water travel across wide river country interests you more, look at the Dart River. To combine jet boating with the gold-mining history of the Skippers road, take Skippers Canyon Jet. Our guide to the best jet boat tours in Queenstown compares them all.

Frequently asked questions

How does a jet boat move without a propeller?

A jet boat has a spinning impeller inside its jet unit, but no propeller outside the hull. The impeller speeds water through a pump, and the water leaves through a nozzle, making the thrust that moves the boat.

Do jet boats use jet engines like aeroplanes?

No. Most river jet boats, leisure and commercial, use ordinary combustion engines or electric motors to drive a water pump. They do not use aircraft-style gas turbines.

Why are jet boats so fast?

Strong engines, efficient planing hulls and a well-matched jet unit. Waterjets give strong acceleration and good high-speed performance, but that does not make every jet boat faster than every propeller boat.

How does a jet boat steer?

A movable steering nozzle points the high-speed water stream left or right. Changing the direction of the thrust changes the boat’s direction.

Can jet boats operate in shallow rivers?

Yes. The drive sits inside the hull and the intake can be flush with the bottom, so a well-designed jet boat can run in much shallower water than many propeller boats.

Can a jet boat reverse?

Yes. Many waterjets use a reverse deflector to turn the jet forwards and make reverse thrust, without the engine changing direction.

Do jet boats have brakes?

Not mechanical brakes. They slow by cutting thrust, through water resistance and, when needed, by applying reverse thrust.

What makes a jet boat spin 360 degrees?

The driver combines thrust, the quick response of the waterjet steering and the boat’s momentum to turn it hard through a full circle.

Who invented jet boats?

Sir William Hamilton of New Zealand pioneered the practical high-speed river jet boat in the early 1950s. He refined and commercialised existing waterjet ideas; he did not invent the concept from scratch.

Are jet boats safer than propeller boats?

With the impeller enclosed, there is no external propeller to strike anyone or be damaged underwater. Jet boats have their own hazards, including high-speed collisions, loss of propulsion or steering, and blocked intakes. Overall safety depends on design, maintenance, the driver and conditions.

How fast do Queenstown jet boats go?

Shotover Jet advertises up to 90 km/h. Other Queenstown operators use different boats and routes, with different speeds.

Can jet boats operate in salt water?

Yes. Waterjets are used at sea on coastal boats, ferries and commercial vessels. In salt water, the right materials, corrosion protection and maintenance matter.

Final verdict: a New Zealand invention that changed river travel

A simple idea, drawing water into a boat and pushing it out again, became a drive that could take boats up rivers propeller boats could not use, and that matters as much as the speed.

Bill Hamilton’s work changed shallow-water boating and helped build an industry that is now part of New Zealand’s adventure tourism. In Queenstown you can ride that legacy yourself. A 25-minute Shotover Jet ride is a working demonstration of a jet unit, a hull and a skilled driver handling river water most boats could never run. Knowing what is happening under the hull makes the next 360-degree spin even better.

If you want to try it, check dates for the Shotover Jet canyon ride early in your stay, because river conditions can move a departure, and read how long the Shotover Jet ride takes before you plan the rest of the day.