Modeling Performance Improvement of High-Speed Boats Running on an outboard engine

Abstract

The marine propeller is among the most important components of the outboard engine. It transmits power by converting rotational motion into thrust. Blade cavitation in high-speed boats has been found to reduce the performance of the propeller since it results in blade erosion and corrosion, induced vibration and noise. This leads to an inefficient propeller for an outboard engine which in turn causes fuel wastage, high power consumption, harmful emissions and boat accidents. Research have shown that the affected propeller reduced the performance of the outboard propulsion system in transmitting power to move a boat forward. There is therefore a need to improve the efficiency of the propeller for an outboard engine. The improved outboard marine propeller is one way which can be adapted for use in high-speed boats running on an outboard engine. In this research, an outboard marine propeller model was designed, modeled and its performance analyzed, with the focus of improving the performance of the propeller for a high speed boat running on an outboard engine. This is expected to result to reduced fuel consumption due to improved efficiency. A geometric model oftheoutboardpropellerwiththreebladeswasmodeledinSolidWorks2017software. Numberofthebladesandpitch-to-diameterratiowasdesigned, modeledandtheopen water propeller performance assessment of each parameter has been tested. The flow around rotating outboard propeller model was analyzed as the advance coefficient increased in the steady state using RANS equations solved through simulation. The effect of rotational speed on open water propeller performance was also evaluated. The open water propeller performance was evaluated in terms of marine propeller performance characteristics (thrust coefficient (KT), torque coefficient (KQ), and open water efficiency (η0)) as the advance coefficient (J) increased in the commercial software STAR-CCM+ version9.06. Thecomputationresultsindicatedthattheregionofrecirculation varied on both sides of the blades based on variation in advance coefficient. An evaluation of the propeller performance was carried out by studying the effect of blade number. 3, 4 and 5 blades were tested. The numerical results showed that a decrease in a number of the blades causes an increase in efficiency of more than 6%. This was found for the propeller with three blades which had the best open water propeller performance characteristics. The numerical simulation performed to study the pitch-to-diameter ratio (P/D) on the propeller performance proved that an increased pitch-to-diameter ratio caused an increase in efficiency of approximately 15%. Moreover,thenumericalresultsshowedthatanincreaseinrotationalspeedcauseanegative effect on propeller performance. This was observed in the decreased performance characteristics (KQ and KT) of open water propeller as the rotational speed increased. The propeller performance characteristics of the improved outboard propeller were compared with historical experimental results of a conventional marine propeller. It is projectedthattheresultsofthisstudywillhelpmarineenginemanufacturerstodesign efficient marine propellers. Consequently, this will also help the marine engine and high-speed boat industries to reduce maintenance expenses that occur due to frequent replacement of outboard propellers.