Abstract
A model system for estimating the shaft torque, blade bending moment and blade turning moment experienced by a propulsion system in ice has been developed. It produces results comparable with limited full scale observations. The primary variables which influence the level of ice forces, torques and moments on propellers are: (1) Angle of attack; (2) Maximum depth of cut; (3) Conpressive strength of ice; and (4) Pitch angle. Blade bending moment at a given angle of attack varies linearly with ice compressive strength, immersed areas and moment arm. Blade bending moment and blade turning torque are relatively low in the regions where the propeller is rotating to produce thrust in the direction motion at low ship speeds. At other off-design conditions, the values of these moments increase markedly. It is clear from these results, that most damage to ship's propulsion systems occur in these off-design conditions. It appears feasible using this modelling system, to examine the effect of variation in blade number, blade area ratio, design pitch on propulsion system vulnerability. The physical model produces results for regions of propeller operation not heretofore covered by the mathematical model.
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