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A pump-jet, hydrojet, or water jet is a marine system that produces a jet of water for propulsion. The mechanical arrangement may be a ducted propeller (axial-flow pump), a centrifugal pump, or a mixed flow pump which is a combination of both centrifugal and axial designs. The design also incorporates an intake to provide water to the pump and a nozzle to direct the flow of water out of the pump. [1]
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 pump can be of a centrifugal design for high speeds, or an axial flow pump for low to medium speeds. 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. This feature is the main reason pump jets are so maneuverable.
The nozzle also provides the steering of the pump-jets. Plates, similar to rudders, can be attached to the nozzle in order to redirect the water flow port and starboard. In a way, this is similar to the principles of air thrust vectoring , a technique which has long been used in launch vehicles (rockets and missiles) then later in military jet-powered aircraft. This provides pumpjet-powered ships with superior agility at sea. Another advantage is that when faring backwards by using the reversing bucket, steering is not inverted, as opposed to propeller-powered ships.
An axial-flow waterjet's pressure is increased by diffusing the flow as it passes through the impeller blades and stator vanes. The pump nozzle then converts this pressure energy into velocity, thus producing thrust. [1]
Axial-flow waterjets produce high volumes at lower velocity, making them well suited to larger low to medium speed craft, the exception being personal water craft, where the high water volumes create tremendous thrust and acceleration as well as high top speeds. But these craft also have high power-to-weight ratios compared to most marine craft. Axial-flow waterjets are by far the most common type of pump.
Mixed-flow waterjet designs incorporate aspects of both axial flow and centrifugal flow pumps. Pressure is developed by both diffusion and radial outflow. Mixed flow designs produce lower volumes of water at high velocity making them suited for small to moderate craft sizes and higher speeds. Common uses include high speed pleasure craft and waterjets for shallow water river racing (see River Marathon).
Centrifugal-flow waterjet designs make use of radial flow to create water pressure.
Examples für centrifugal designs are the Schottel Pump-Jet and outboard sterndrives. [2]
Pump jets have some advantages over bare propellers for certain applications, usually related to requirements for high-speed or shallow-draft operations. These include:
The water jet principle in shipping industry can be traced back to 1661 [4] when Toogood and Hayes produced a description of a ship having a central water channel in which either a plunger or centrifugal pump was installed to provide the motive power. [5]
On December 3, 1787, inventor James Rumsey demonstrated a water-jet propelled boat using a steam-powered pump to drive a stream of water from the stern. [6] [ circular reference ] This occurred on the Potomac River at Shepherdstown, Virginia (now West Virginia) before a crowd of witnesses including General Horatio Gates. The 50-foot long boat traveled about one-half mile upriver before returning to the dock. The boat was reported to reach a speed of four mph moving upstream. [7] [8] [9]
In April 1932, Italian engineer Secondo Campini demonstrated a pump-jet propelled boat in Venice, Italy. The boat achieved a top speed of 28 knots (32 mph; 52 km/h), a speed comparable to a boat with a conventional engine of similar output. The Italian Navy, who had funded the development of the boat, placed no orders but did veto the sale of the design outside of Italy. [10] [11] The first modern jetboat was developed by New Zealand engineer Sir William Hamilton in the mid 1950s. [12]
Pump-jets were once limited to high-speed pleasure craft (such as jet skis and jetboats) and other small vessels, but since 2000 the desire for high-speed vessels has increased [ citation needed ] and thus the pump-jet is gaining popularity on larger craft, military vessels and ferries. On these larger craft, they can be powered by diesel engines or gas turbines. Speeds of up to 40 knots (45 mph; 75 km/h) can be achieved with this configuration, even with a displacement hull. [13]
Pump-jet powered ships are very maneuverable. Examples of ships using pumpjets are the Car Nicobar-class patrol vessels, the Hamina-class missile boats, Valour-class frigates, the Stena high-speed sea service ferries, the United States Seawolf-class and Virginia-class, as well as the Russian Borei-class submarines and the United States littoral combat ships.
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A jet engine is a type of reaction engine, discharging a fast-moving jet of heated gas that generates thrust by jet propulsion. While this broad definition may include rocket, water jet, and hybrid propulsion, the term jet engine typically refers to an internal combustion air-breathing jet engine such as a turbojet, turbofan, ramjet, pulse jet, or scramjet. In general, jet engines are internal combustion engines.
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The Caproni Campini N.1, also known as the C.C.2, is an experimental jet aircraft built in the 1930s by Italian aircraft manufacturer Caproni. The N.1 first flew in 1940 and was briefly regarded as the first successful jet-powered aircraft in history, before news emerged of the German Heinkel He 178's first flight a year earlier.
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A propulsor is a mechanical device that gives propulsion. The word is commonly used in the marine vernacular, and implies a mechanical assembly that is more complicated than a propeller. The Kort nozzle, pump-jet and rim-driven thruster are examples.
The Voith Schneider Propeller (VSP) is a specialized marine propulsion system (MPS) manufactured by the Voith Group based on a cyclorotor design. It is highly maneuverable, being able to change the direction of its thrust almost instantaneously. It is widely used on tugs and ferries.
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A water jet cutter, also known as a water jet or waterjet, is an industrial tool capable of cutting a wide variety of materials using an extremely high-pressure jet of water, or a mixture of water and an abrasive substance. The term abrasive jet refers specifically to the use of a mixture of water and an abrasive to cut hard materials such as metal, stone or glass, while the terms pure waterjet and water-only cutting refer to waterjet cutting without the use of added abrasives, often used for softer materials such as wood or rubber.
A compressor map is a chart which shows the performance of a turbomachinery compressor. This type of compressor is used in gas turbine engines, for supercharging reciprocating engines and for industrial processes, where it is known as a dynamic compressor. A map is created from compressor rig test results or predicted by a special computer program. Alternatively the map of a similar compressor can be suitably scaled. This article is an overview of compressor maps and their different applications and also has detailed explanations of maps for a fan and intermediate and high-pressure compressors from a three-shaft aero-engine as specific examples.
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The Kitchen rudder is the familiar name for "Kitchen's Patent Reversing Rudders", a combination rudder and directional propulsion delivery system for relatively slow speed displacement boats which was invented in the early 20th century by John G. A. Kitchen of Lancashire, England. It turns the rudder into a directional thruster, and allows the engine to maintain constant revolutions and direction of drive shaft rotation while altering thrust by use of a control which directs thrust forward or aft. Only the rudder pivots; the propeller itself is on a fixed shaft and does not.
Marine propulsion is the mechanism or system used to generate thrust to move a watercraft through water. While paddles and sails are still used on some smaller boats, most modern ships are propelled by mechanical systems consisting of an electric motor or internal combustion engine driving a propeller, or less frequently, in pump-jets, an impeller. Marine engineering is the discipline concerned with the engineering design process of marine propulsion systems.
Internal drive propulsion or water-jet propulsion is a form of marine propulsion used in recreational boating. Like other forms of motorized boating, internal drive propulsion employs a motor that turns a propeller to move the boat forward. The primary difference between internal drive boats and external drive boats is that the propeller is enclosed inside the hull of an internal drive boat whereas the propeller is exposed outside the hull of a stern drive, V-drive or straight shaft drive boat.
A ducted propeller, also known as a Kort nozzle, is a marine propeller fitted with a non-rotating nozzle. It is used to improve the efficiency of the propeller and is especially used on heavily loaded propellers or propellers with limited diameter. It was developed first by Luigi Stipa (1931) and later by Ludwig Kort (1934). The Kort nozzle is a shrouded propeller assembly for marine propulsion. The cross-section of the shroud has the form of a foil, and the shroud can offer hydrodynamic advantages over bare propellers, under certain conditions.
