Abstract
Various attentions have been paid to improvement of propeller efficiency. Among these devices, the free rotating propeller (vane wheel) to be fitted additionally behind conventional main propeller is the most attractive one. However the design method, blade strength, etc. of the free rotating propeller are not specified.The authors designed the free rotating propeller for the ship by applying the momentum theory and the blade element theory that are used for designing the hydraulic machineries. In this report, the design accuracy is compared with full-scale measurements and as the results, the following conclusions are obtained.(1) The calculated revolutions and energy saving rate of the free rotating propeller show a similarity to those of measurements.(2) Measured energy saving rate is 6-8.5% at same speed condition.(3) The mean blade stress is 2.6kgf/mm2 {25 MPa} and the fluctuation of blade stress for a rotation is 8.8kgf/mm2 {86 MPa} in peak-to-peak value.(4) The pressure fluctuation caused by main propeller is reduced by 20% at the blade frequency components.
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