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Monday, May 11, 2009

Propeller design methods

There are two methods available for the design of marine screw propeller (both ship propeller and boat propeller) at this time. They are hydrodynamics and aerodynamics theories; and the test results of systematic propeller models carried out by towing tanks and cavitation tunnels.

The hydrodynamics and aerodynamics theories - The propulsion phenomenon of ship's or boat's propeller is still difficult to be explained. The existing theories are divided into two main theories, i.e.:
  • Theory of momentum - this is based on the assumption that the propeller acts as the accelerator of water that passes through it. The resulting reaction creates thrust force which propels a ship.
  • Propeller blade element theory - this is based on the assumption that each propeller blade consists of a large number of concentric strips relative to the boss of the propeller. Every strip acts as a small aerofoil which has resultant velocity as the result of the combination of axial and rotational speeds. These speeds react against the aerofoil and generate elementary lifting forces and drag forces on the blade surface. If they are integrated throughout the whole area of propeller blade, they will provide thrust force that propels the ship, and also torque to the propeller.
In practice, most naval architects and propeller designers use the second design method, i.e. the test results of systematic propeller models. To enable ship and propeller designers do their jobs, a number of research institutions have made propeller model standards whose characteristics are presented in a journal under the title "A New Usable Propeller Series," on page 174, vol. 26 No. 3, July 1989 of Marine Technology tabulated by S.B. Denny et al.
The propeller models which I usually use are Troost/ Wageningen B-Series. Before using the models, a naval architect or a propeller designer must understand the theories of resistance and propulsion of ships. This subject is extensively explained in such books as Resistance and Propulsion of Ships - Sv. Aa Harvald, Resistance; Propulsion and Steering of Ships - Prof. W.P.A. van Lammeren, Troost L, Koning J.G.; The Design of Marine Screw Propellers - T.P.O'Brien.
When designing the propellers of ships, I usually use or read the latter two books as my main references in deciding the parameters of ship resistance and propulsion. The books may not be available on the market. If you are serious about learning this subject, I suggest that you read similar books published by Elsevier publisher. By Charles Roring in Manokwari of West Papua - Indonesia. Also read: Propeller Strength Calculation and Cavitation of Marine Propeller

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