In the previous paper 1), authors presented the results of propeller open test, self-propulsion test and cavitation test (cavity extent and thickness) which were performed by using MAU type conventional propeller (MPNO. 80-3), conventional 90° Highly Skewed Propeller (HSP) (MPNO. 80-4) and theoretically designed 72° HSP (MPNO. 80-5).
They also described the outlines of simplified method to calculate Wake Adapted Skew Distribution (WASD) and non-linear lifting surface method to estimate propeller open characteristics which were applied to MPNO. 80-5 propeller design. The result of propeller open test reveals utility of non-linear lifting surface method for high efficiency HSP design.
In this report, the test results of fluctuating pressure induced by the above-mentioned three propellers and measured in cavitation tunnel are presented. Comparing with fluctuating pressure amplitude (1 st blade frequency component) of MPNO. 80-3, that of MPNO. 80-4 is reduced to about 57% and that of MPNO. 80-5 is reduced to about 12%, which reveals that skew distribution as well as skew angle significantly effects on fluctuating pressure and simplified method to calculate WASD is useful for HSP design.
Then, authors propose a practical method for calculating necessary skew angle to reduce propeller-induced fluctuating pressure amplitude to allowable level. The method is based on Holtrop's statistical method for predicting vibratory hull forces and Holden's criterion for fluctuating pressure amplitude. Recommendable skew angles indicated by examples of numerical calculation for eight ships are as follows ;
0°30° skew angle for bulk carrier
40°60° skew angle for pcc
50°70° skew angle for container