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A jet pump is a step-up compressor that allows a boat to travel across shallow water. The jet unit is streamlined and does not sit below the bottom of the boat. The jet stream can be pointed in one direction to force the stern of the boat in the opposite direction, turning the boat. The jet unit pumps water out through a nozzle, with the water pressure inside the inlet increased by the pump.
| Characteristics | Values |
|---|---|
| How it works | Water enters the pump through an intake at the bottom of the hull. The water pressure inside the inlet is increased by the pump and forced backwards through a nozzle. |
| How it differs from a normal motorboat | A jet unit is streamlined and does not sit below the bottom of the boat, meaning it can travel across much shallower water. |
| How to make the boat reverse | An astern deflector is lowered into the jet stream after the water leaves the nozzle. This reverses the direction of the force generated by the jet stream forward and down, keeping the boat stationary or propelling it in the opposite direction. |
| How to steer | Change the direction of the jet of water as it leaves the jet unit. |
| How to increase speed | Achieve high intake pressures without loader grates and the sq footage of the intake. This will start lifting the back of the boat out of the water and, when the boat is set up correctly, a great increase in speed is seen. |
What You'll Learn
Jet boats can travel across shallow water
The jet pump is a step-up compressor, and the higher the inlet pressure, the higher the outlet pressure. When high intake pressures are achieved, the back of the boat is lifted out of the water, increasing speed. The jet stream can be pointed in one direction, forcing the stern of the boat in the opposite direction and putting the boat into a turn. Steering is achieved by changing the direction of the jet of water as it leaves the jet unit.
The jet pump can be of a centrifugal design for high speeds or an axial flow pump for low to medium speeds. Water enters the pump through an intake, usually at the bottom of the hull, and the water pressure inside the inlet is increased by the pump and forced backwards through a nozzle. Reverse thrust can be achieved by using a reversing bucket or an astern deflector, which is lowered into the jet stream after the water leaves the nozzle. This reverses the direction of the force generated by the jet stream, keeping the boat stationary or propelling it in the opposite direction.
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Jet boats can reach high speeds
The design of the jet pump also contributes to the high speeds achievable by jet boats. The pump can be of a centrifugal design, which is optimised for high speeds, or an axial flow pump for low to medium speeds. The true jet pump boat is well-balanced, and when the perfect balance is met, speeds with marginal hp are amazing. Over 100mph can be achieved with around 500 hp.
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Jet boats can be steered by changing the direction of the jet of water
To make the boat reverse or stand still, an astern deflector is lowered into the jet stream after the water leaves the nozzle. This reverses the direction of the force generated by the jet stream, keeping the boat stationary or propelling it in the opposite direction. The jet stream can also be used to slow the boat down when braking.
The jet unit pumps at 4000 R.P.M, enabling jet boats to reach speeds of up to 95kph in water that is less than 5cm deep.
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Jet boats can reverse or stand still
A pump-jet works by having an intake (usually at the bottom of the hull) that allows water to pass underneath the vessel into the engines. Water enters the pump through this inlet. The water pressure inside the inlet is increased by the pump and forced backwards through a nozzle. With the use of a reversing bucket, reverse thrust can also be achieved for faring backwards, quickly and without the need to change gear or adjust engine thrust. The reversing bucket can also be used to help slow the ship down when braking.
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Jet boats can slow down quickly
To make the boat reverse or stand still, an astern deflector is lowered into the jet stream after the water leaves the nozzle. This reverses the direction of the force generated by the jet stream forward and down, keeping the boat stationary or propelling it in the opposite direction. Steering is achieved by changing the direction of the jet of water as it leaves the jet unit.
The jet stream can be pointed in one direction to force the stern of the boat in the opposite direction, putting the boat into a turn. Jet boats can also use a reversing bucket to help slow the ship down when braking. This can be achieved without the need to change gear or adjust engine thrust.
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Frequently asked questions
A jet pump boat works by using a jet stream to force the stern of the boat in the opposite direction, turning the boat. The jet unit is streamlined and does not sit below the bottom of the boat, meaning it can travel across shallow water.
To make the boat reverse or stand still, an astern deflector is lowered into the jet stream after the water leaves the nozzle. This reverses the direction of the force generated by the jet stream, keeping the boat stationary or propelling it in the opposite direction.
A reversing bucket can be used to slow the boat down when braking.
Steering is achieved by changing the direction of the jet of water as it leaves the jet unit.
