A screw propeller boss cap with fins.

摘要

A screw propeller boss cap (5) with fins (6) is provided to increase the propeller characteristics, particularly the propeller efficiency. Owing to the fins (6) on the boss cap (5), the water stream rearward of the boss cap (5) is guided to a direction of reducing the generation of the hub vortex and on that score the propeller efficiency is increased. The fins (6) should satisfy the conditions as follows: (i) they are of the same number of the propeller blades (3), (ii) they have an inclination alpha from -20 DEG to +30 DEG against the geometric pitch angle epsilon of a propeller blade root, that is, -20 DEG </= alpha - epsilon </= 30 DEG , and the leading edge located between the adjacent propeller blade roots, and (iii) they have a maximum diameter larger than the diameter of the cap-mounting end of the boss (2) and not larger than 33% of the propeller diameter. Thus the propeller characteristics can be greatly improved by a rather simple and economically practicable means.