Arashigami In order to further reduce the Reynolds number correction, the model propeller in open water is run at as high an axial propulsionn and revolution rate as possible for the required range of advance coefficient, so that the difference shjp the Reynolds numbers of the model propeller and the ship propeller is minimised. Delivery and Returns see our delivery rates and policies thinking of returning an item? These sections are called radial sections or cylindrical sections. Subsequent chapters deal with conventional screw propellers that are used in most ships today. The result is that increased power is required to aUain a given speed, and yhose cases of severe cavitation the ship may not achieve the specified speed.
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Low speed diesel engines can be directly connected to ship propellers and can be reversed to allow the ship to move astern. Another type of engine used for ship propulsion is the gas turbine. Like the steam turbine, the gas turbine runs at a very high speed and cannot be reversed. Gas turbines are mostly used in high speed ships where their low weight and volume for a given power give them a great advantage over"other types of engines. Nuclear energy has been tried for ship propulsion.
The heat generated by a nuclear reaction is used to produce steam to drive propulsion turbines. However, the dangers of nuclear radiation in case of an accident have pre vented nuclear ship propulsion from being used in non-combatant vessels for a few experimental ships such as the American- ship "Savannah", the German freighter "Otto Hahn"and the Russian icebreaker "V.
Nuclear propulsion has been used in large submarines with great success because nuclear fuel contains a large amount of energy in a very small mass, and because no oxygen is required for heat. This enables a nu clear submarine to travel long distances under water, unlike a conventional submarine which has to come to the surface frequently to replenish fuel and air for combustion.
In addition to the conventional types of ship propulsion plant discussed in the foregoing, attempts are being made to harness renewable and non polluting energy sources such as solar energy, wind energy and wave energy for ship propulsion and to develop advanced technologies such as supercon ductivity and magneto-hydrodynamics. However, these attempts are still in a preliminary experimental stage.
Until the advent of the steam engine, ships were largely propelled by oars imparting momentum to the surrounding water or by sails capturing the energy of the wind. The first mechanical propulsion device to be widely used in ships was the paddle wheel, consisting of a wheel rotating about a transverse axis with radial plates or paddles to impart an astern momentum to the water around the ship giving it a forward thrust.
The early steam ers of the 19 Century were all propelled by paddle wheels. Paddle wheels 4 Basic Ship Propulsion are quite efficient when compared with other propulsion devices but have several drawbacks including difficulties caused by the variable immersion of the paddle wheel in the different loading conditions of the ship, the increase in the overall breadth of the ship fitted with side paddle wheels, the inabil ity of the ship to maintain a steady course when rolling and the need for slow running heavy machinery for driving the paddle wheels.
Paddle wheels were therefore gradually superseded by screw propellers for the propulsion of oceangoing ships during the latter half of the 19 th The Archimedean screw. The first actual use of a screw to propel a ship appears to have made in by the American, Colonel Stevens.
In , Josef Ressel of Trieste successfully used a screw propeller in an 18 m long experimental steamship.
The first practical applications of screw propellers were made in by Ericsson in America and Petit Smith in England. During trials, an accident caused a part of the propeller to break off and this surprisingly led to an in the speed of the ship.
Petit Smith then improved the design of his propeller by decreasing the width of the blades and increasing the number of threads, producing a screw very similar to modern marine propellers. The screw propeller has since then become the predominant propulsion device used in shipl3. Certain variants of the screw propeller are used for special applications. One such variant is to enclose the propeller in a shroud or nozzle. This improves the performance of heavily loaded propellers, such as those used in tugs.
A controllable pitch propeller allows the propeller loading to be varied over a wide range without changing the speed of revolution of the propeller. It is also possible to reverse the direction of propeller thrust without chang ing the direction of revolution. This allows one to use non-reversing engines such as gas turbines.
When propeller diameters are restricted and the pro pellers are required to produce large thrusts, as is the case in certain very high speed vessels, the propellers are likely to experience a phenomenon called "cavitation", which is discussed in Chapter 6.
In cjrcumstances where extensive cavitation is unavoidable, t. Such propellers are popularly known as "supercavitating propellers". Problems due to conditions of high propeller thrust and restricted diame ter, which might lead to harmful cavitation and reduced efficiency, may be avoided by dividing the load between two propellers on the same shaft. Mul tiple propellers mounted on a single shaft and turning in the same direction are called "tandem propellers".
Some improvement in efficiency can be 0 b tained by having the two propellers rotate in opposite directions on coaxial shafts; Such "contra-rotating propellers"are widely used in torpedoes.
I Two other ship propulsion devices may be IIl;entioned here. One is the vertical axis cycloidal propeller, which consists 6f a horizontal disc carrying a number of vertical blades projecting below W.
As the disc rotates about a vertical axis, each blade is constrained to t. This direction can be controlled by a mechanism for setting the positions of the vertical blades.
The second propulsion device that may be mentioned is the waterjet. Historically, this is said to be the oldest mechanical ship propulsion device, an English patent for it having been granted to Toogood and Hayes in In waterjet as used today in high speed vessels, an impeller draws water from below the ship and discharges it astern in a high velocity jet just above the surface of water.
A device is provided by which the direction of the waterjet can be controlled and even reversed to give good manoeunability. Because of their overwhelming importance in ship propulsion today, this book deals mainly with screw propellers.
Other propulsion devices, including variants of the screw propeller, are discussed.
Basic Ship Propulsion
Low speed diesel engines can be directly connected to ship propellers and can be reversed to allow the ship to move astern. Another type of engine used for ship propulsion is the gas turbine. Like the steam turbine, the gas turbine runs at a very high speed and cannot be reversed. Gas turbines are mostly used in high speed ships where their low weight and volume for a given power give them a great advantage over"other types of engines. Nuclear energy has been tried for ship propulsion. The heat generated by a nuclear reaction is used to produce steam to drive propulsion turbines.
BASIC SHIP PROPULSION GHOSH PDF
Design Principles of Ships and Marine Structures details every facet of ship design and design integration, and highlights the design aspects that must be put together to create an integrated whole product. This book discusses naval architecture and marine engineering applications and principles relevant to the design of various systems, examines advanced numerical techniques that can be applied to maritime design procedure at the concept design stage, and offers a comprehensive approach to the subject of ship design. Covers the Entire Sphere of Marine Design The book begins with an introduction to marine design and the marine environment, describing many of the marine products that are used for transportation, defense and the exploitation of marine resources. It also discusses stability issues relevant to ship design, as well as hydrodynamic aspects of resistance, propulsion, sea keeping and maneuvering, and their effects on design. In addition to covering the various systems and sub-systems that go into making a complex product to be used in maritime environment, the author explains engineering economics and its application in ship design, and provides examples wherever necessary.
BASIC SHIP PROPULSION GHOSE GOKARN PDF
The propulsion machinery inside the ship is however considered only very briefly. The first chapter describes the development of ships and ship machinery and then introduces various ship propulsion devices. Subsequent chapters deal with conventional screw propellers that are used in most ships today. Among the subjects covered are screw propeller geometry, the theory of propellers, propeller characteristics, hull-propeller interaction, propeller cavitation, strength of propellers and model experiments involving propellers. The design of propellers for ships as well as for tugs and trawlers is given in a separate chapter, which also discusses the application of propeller theory to design. Ship trials and service performance analysis are then described. Some miscellaneous topics including propeller unsteady forces, propeller induced vibration and noise, propulsion in a seaway, engine-propeller matching, and propeller manufacture and repair are discussed next.