Jet propulsion

The idea of ​​the principle of water discharge, based on the Archimedean screw , is known for two inventions in 1661 in England , but only with Watt's invention of a steam engine in 1765 tangible results were achieved when Rarrisi and Meyen created a steam driven pump for pumping water out of the holds ships with a jet of water emanating through the stern, and for the period from 1830 to 1860 only in England alone were issued at least 35 patents for the implementation of such devices.

The most advanced type of pump was created in London by Henry Bessemer in 1849. It was an axial pump with one suction pipe in the bow of the vessel and with two pipes on the aft side. Bessemer even placed the impellers in front of and behind the water supply screw to straighten the jet and to compensate for the losses caused by the rotation of the water jet. Alexander Hadyard in 1852 proposed another design: there was a rotary nozzle that could be directed forward or backward. This pump sucked water through a hole in the bottom of the vessel and threw it through the stern . The rotation of the jet led to the rotation of the vessel.

By the end of the XIX century , in the era of Queen Victoria , water cannons were tested on a variety of vessels. So, the British Admiralty adopted a project of a water cannon with an impeller, which in the late 1860s. has been replaced by a conventional screw. The Admiralty went so far that it even agreed to conduct full-scale tests of two types of engines. Two absolutely identical gunboats of 4.2 meters in length were built, on one of which a water jet was installed, and on the other an ordinary propeller . "Reactive" gunboat with a centrifugal pump, which ejected water through two holes in the stern, with a motor power of 760 liters. sec., developed a speed of 17 km / h, which was slightly inferior to the performance of a traditional propeller, with which a 696 liter engine. with. has a speed of 18 km / h.

Around the same time, several European countries showed an interest in the water-jet principle of movement of sea vessels. In 1878 , that is, only 12 years after the experiments in England, the Swedish government conducted a series of similar experiments to introduce the water-jet principle of movement on torpedo boats . Propeller vessels (with engines of 90 hp) showed a speed of 18.5 km / h, while water-jet vessels (with engines of 78 hp) developed a speed of 15 km / h.

A year later, in Germany , similar tests were organized for a ship with a water cannon called the “Hydro” motor. Like their predecessors, the Germans quickly became disillusioned with the possibilities of the water-jet principle of movement. In all comparative tests of screw engines against water jets with centrifugal pumps, the former showed better results.

Subsequently, many people did not abandon attempts to find a suitable water-jet for specific tasks. In 1888, the British National Institute for Rescue Vessels placed the world's first order to build a boat with a water cannon. This steam boat was equipped with a water jet pump with a centrifugal pump and was supposed to replace the screw ships during rescue operations in shallow water or in silty ponds.

In 1900, Sydney Barnaby's classic shipbuilding book described in detail the jet propulsion principle.

Although it is officially believed that the New Zealand sheep breeder and inventor Chris William Fileden ("Bill") Hamilton (Bill Hamilton, born in 1899) is the inventor of the modern jet engine, he himself, however, does not agree with this, in 1962 he answered the direct a question on this subject: "I do not claim authorship of the invention of a ship's water jet." ^[one]

The jet propulsion device was widely used since the 1930s, when high-speed aircraft-type engines began to be used on high-speed ships. In this case, the water cannon made it possible to obtain greater efficiency rather than a propeller and less prone to cavitation. The first carriers of water cannons were torpedo and patrol boats, shallow-sitting river vessels. Subsequently, with the development of super-cavitating propellers, the use of water jets on high-speed vessels decreased.

The water jet propulsion unit consists, as a rule, of an impeller (screw) with a shaft, a water conduit (water pipe), a straightening device and a reversing-steering device (RRU).

In the conduit, which is a profiled pipe, the water flow is accelerated either by a blade mechanism ( propeller , impeller of the pump), or by the energy of fuel combustion or by the pressure of a compressed gas , which ensures directed discharge of the jet through the outlet in the feed. The thrown mass of water creates an emphasis on the mover, which sets the vessel in motion.

Water conduits are located inside or outside the hull. The efficiency of the jet propulsion device depends on the shape of the conduits, the location and design of the water intakes, and is usually less than that of the propeller.

If the water flow is accelerated by a blade mechanism:

• in the lower part of the bottom there is a hole through which water enters the watercourse (which is a curved pipe) in which there is an impeller, during the rotation of which there is a vacuum , due to which water moves along the intake (intake pipe). Having received some acceleration, it is ejected through a nozzle , the output diameter of which is less than the diameter of the conduit.
  In the front part, the water conduit has a socket for fastening the propeller shaft support unit; in the opposite part of the conduit there is a flange for fastening the impeller shell, which, with its front end, rests on the bearings of the support unit. Torque to the impeller is transmitted through the pin of the safety clutch . A fairing and an impeller are installed at the rear end of the propeller shaft. The sliding sleeve rotates in the rubber-metal bearing of the rectifier (Goodrich sleeve, such a rubber-metal bearing only works in an aqueous medium), pressed into the bronze bush of the rectifier. Tightness of the bearing cavity is ensured by cuffs and gaskets.

RRU, when turning in the horizontal plane of the flow, provides the rotation of the vessel. When the flow from the nozzle is blocked, the water jet turns back, which allows the vessel to reverse.

A water cannon, like an outboard motor , is prone to clogging with algae , which, wound on a shaft with an impeller, can jam it. In case of jamming of the water jet, a cut-off key is provided on the shaft to prevent damage to the stationary engine. You can clear algae by opening the inspection hatch and removing them. The inspection hatch is located in a kind of "well", the edges of which are raised above the waterline , which allows you to have access to the aqueduct afloat. The grate in the inlet protects the large stones from getting into the water cannon.

Advantages

• Good protection against mechanical damage and the ability to avoid cavitation .
• The possibility of the ship passing through shallow water , overcoming clogged sections of water bodies (littered fairways ) and even individual obstacles protruding from the water ( rifts , shallows , etc.), where the screw, or even the motor itself, can be destroyed on an ordinary screw motor. ^[2]
• Safety - the impeller is located inside and is not dangerous for people nearby in the water.
• At high speeds, the efficiency is higher than that of the propellers (either an increased maximum speed or fuel economy is provided. ^{[2] [3]} )
• Water-jet boats are more stable and controllable - this is because the water-jet is “sucking” the boat to the water, due to which it steadily behaves even in sharp turns at high speed.
• The ship can make a turn practically on the spot and even move with a “lag” - board forward, in contrast to a ship with a classic screw propulsion. ^[2]
• It is not necessary to use a reverse gear, braking from full speed is possible - the ship coasting during emergency braking is the shortest. ^[2]
• Less hydrodynamic noise compared to screw propellers, which is very important for submarines .

disadvantages

• Efficiency lower than that of screws at low speeds (for example, during start / acceleration) due to:
  • The need for transportation, in addition to the payload itself, also water in the pipeline (as a working fluid );
  • Power loss due to friction of water on the walls of the pipeline;
  • Power losses due to turbulent eddies of the water flow in the channels of the jet.
• The difficulty of supplying water through the bottom of the vessel to the pump, the effectiveness of which will be affected by the speed of the vessel relative to the water.
• The water intake works just like a pump and can drag stones, sand, trash from the bottom. This can clog the cooling system or damage the impeller and water conduit.
• The degree of wear of the rotor - stator pair is high, since the vessel is often operated in shallow water.
• Repair is more expensive than screw repair. ^{[ specify ]}
• Also, a jet boat is characterized by a peculiarity of behavior at low speed.

Jet propellers are usually used on ships navigating in shallow water, ranging from light motor boats to high-speed vessels (for example, the Zarya type) and tugboats (for example, the BM type) or serve as a bow thruster to improve the agility of vessels.

Water cannons are used on boats (for example, some modifications of Amur boats with a water-jet propulsion unit were produced in series at the Yuri Gagarin aircraft plant in Komsomolsk-on-Amur ). Many manufacturers of outboard motors ( Suzuki , Yamaha ) produce outboard motors with a jet propeller or attachment modules designed for independent installation: on jet skis , which are used when towing skiers and wakeboarders .

For example, the prototype of the Riddle Marine Maximog Jet water-jet boat (Lewiston, Idaho ) accelerates from 0 to 100 km / h in 4 seconds thanks to a dual marine water-jet gas engine with a capacity of 450 liters. with. ^[four]

Military equipment

The jet propulsion device is actively used on floating armored vehicles of the USSR and Russia, in particular, on the PT-76 amphibious tank (withdrawn from service), BTR-50 , BTR-60 , BTR-70 , BRDM-2 armored personnel carriers (withdrawn from service), BTR- 80 (is in service), BTR-90 "Rostock" (adopted for service).

Project 21631 surface ship . In the submarine fleet: submarines of the Triumph type (France) and project 955 Borey (Russia).

• Impeller
• Comparison of movers

• The history of the "water cannon". How it all began // float.ru