Feature 3 | PROPELLERS AND THRUSTERS It’s in the RANS New research delivers greater propulsive efficiency, writes Patrik Wheater.
coming September, in Tokyo, Sing-Kwan Lee, principal engineer, ABS Corporate Research and Development, will provide naval architects and marine engineers with invaluable direction as to just what innovations are required to optimise a ship’s propulsive efficiency. In his paper – a synopsis of which Te Naval
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Architect has seen – Mr Lee will argue that, despite the multitude of currently available technologies to reduce fuel consumption and emissions, the most cost effective way by far is to figure in energy efficiency at the basic design stage and, specifically, to optimise propeller design. With the focus on efficiency never having
been so acute, Mr Lee’s paper reviews a real case study in which an integrated propeller design for an 8200TEU containership might be implemented to maximise its energy-saving potential. Te classification society’s investigation found that due to the restriction of propeller aperture, propeller diameter enlargement cannot be adopted while a reduced blade area ratio and skew are applicable to the optimal design for propeller efficiency. Te study, far-reaching in scope, went on
to investigate the manufacturing process and, according to Mr Lee, it was found that in order to minimise propeller fabrication costs, the propeller blade should be as thin as possible to reduce the amount of expensive alloys used. While a series of propeller stress analyses should be performed to determine the minimum allowable thickness distribution on the blade, in order to achieve this design intention, Mr Lee says the resulting data would provide the necessary information to ensure that the propeller is fatigue-failure- safe for normal ahead operation and failure safe under emergency stop operation. In an integrated design, propeller-induced
vibration should also be considered. Mr Lee says that propeller cavitation cannot be avoided in a practical design. Due to the large ship size, the ship structure becomes more flexible and more prone to the vibration
The Naval Architect July/August 2009
n a paper to be presented at the International Symposium on Ship Design and Construction (ISSDC) this
MARIN new pod set-up on a ship model.
problem from the cavitating propeller excitation. Thus, to control the vibration, so that it will be within an acceptable level during operations, propeller induced hull vibration analysis would be performed before the necessary modifications can be made at the propeller design. Optimising propeller design has also been
the basis of research carried out by Lloyd’s Register. In a paper on ship hydrodynamic propulsion presented in London earlier
this year, LR’s John Carlton suggested that, where a vessel operates prolonged services and during different operational conditions, a propeller redesign could indeed optimise energy efficiency. “By developing conventional propeller
design techniques in which a redesigned slow-running propeller is permitted to have the same margins against cavitation as an existing higher speed design it is possible to optimise the benefits in terms of enhanced
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