Abstract
Today, optimal propellers are designed by using advanced numerical methods. Major revolutionary improvements cannot be expected. More essential are the design conditions and the optimal adaptation of the propulsion system according to the operational requirements. The selection and optimisation of the propulsion system based on a systematic analysis of the ship’s requirements and the operation profile are the prerequisites for reliable and energy-efficient propulsion. Solutions are presented, which accommodate these issues with a focus on steerable rudderpropellers. Considerations include the efficiency potential of the propulsor itself, optimisation of the engine propeller interaction, and optimisation of a demandresponsive energy supply. The propeller-thruster interaction is complex, but offers some potential for optimisation. Results of examinations show this. The power distribution between multiple propellers at high loads of limited propeller diameters increases the efficiency. This can be done by double-propeller systems like the SCHOTTEL TwinPropeller or by distributing the power on several thrusters. This distributed propulsion offers economic operation and an increased lifetime by means of the demandresponsive use of energy. An efficiency-optimized electric motor instead of the upper gear box reduces the mechanical losses in the case of diesel-electric propulsion. An example: the SCHOTTEL CombiDrive.
Highlights
Ideal propeller efficiency is derived from the ratio of thrust-to-propeller power, which gives the following relationship as a function of the thrust load coefficient CTH.Three approaches are indicated below: 1. Improvement of efficiency by means of doublepropeller systems, e.g. STP. 2
With an angle of attack of 0° and +/10°, the housing is absolutely free from cavitation (Fig. 15)
With the exception of a slight tip vortex, the intensity of which depends on the angle of attack, the propellers are free from cavitation
Summary
Ideal propeller efficiency is derived from the ratio of thrust-to-propeller power, which gives the following relationship as a function of the thrust load coefficient CTH. 3. Dosed, load-dependent power distribution, e.g. double-ended ferries. These equations clearly show that increasing thrust load coefficient correlates with decreasing potential efficiency of the propeller. This is the case if the thrust requirement is high and/or the propeller diameter is small and/or the inflow velocity is low. This is basic information and nothing new.
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