Comparison of efficiency of pushing and pulling thrusters
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- Institutt for marin teknikk 
In this thesis the effect of thruster drive mode (pulling, pushing and pushing with duct) on the propeller design was investigated by the means of systematic calculations in a numerical calculating software (AKPA). It was at first also intended to do experimental tests in the la-boratories at NTNU, but it had to be dropped due to the lack of suitable time slots. The propellers were first designed with a program called PPD before they were further re-fined in another program called AKPD, before the final calculations in AKPA. The efficiency of the propellers was also compared in a typical operating profile for platform supply vessels to try to get an impression of the overall efficiency of each drive mode.It became apparent that AKPD could not properly handle the design of skewed propellers, and so the skewed propellers got worse cavitation performance compared to regular propel-lers, contrary to previously published data (Boswell, 1971).This design problem could also be the reason behind the surprising results that show that skewed propellers have higher efficiency than non-skewed ones for open propellers. For the two other design parameters, chord length distribution had minor effect on both cavitation and efficiency, but the circulation distribution had major impact on the cavitation and also quite large impact on the efficiency, where the distributions that gave medium lev-els of cavitation regularly had the best efficiency.It was also shown that for the operational profile and propeller constrains selected the ducted thruster had a power consumption about 90% of that of an open pulling thruster, but this is of course dependent on many factors such as propeller loading and operational profile. Nevertheless, it shows that ducted propellers can be a feasible alternative as the main propulsion for platform supply vessels.