The design of highly skewed propellers requires that special attention is given to the stress analysis of the blade. In this paper a number of Finite Element computer programs are applied to different element layouts on a highly skewed reference blade with uniform load. The calculated stresses are compared with measurements, the result of which shows that a certain care must be exercised for the choice of elements as well as node-pattern if the resulting accuracy is to be acceptable.
In order to simplify indata preparation a suite of existing programs giving propeller geometry, profile loading conditions and pressure distribution have been linked together and supplemented with a program that converts the output from these programs into a complete in data deck for a Finite Element Program. The program package produces plots and print-outs at a number of control stations during the process. The thus developed method for calculation of load and resulting stress distribution is applied to the SSPA skew propeller series. Stress distribution for forward and backing cases are studied as a function of skew angle, all other factors being kept constant. The results indicate an increase in stress with skew, which is of particular importance during backing.
Hydroelastic effects become potentially dangerous during backing of extreme skew-back propellers. When gradually increasing speed during backing a critical speed is approached at which the hydrodynamic forces and moments increase faster with angle of attack than the restoring elastic forces and moments do. This is a point of instability. Also well below the critical speed the hydrodynamic effects cause an increase in stress levels that cannot be neglected. One approximative and one more rigorous method to determine these effects are presented.
