SCREW PROPELLER BOSS CAP WITH FINS

摘要

A screw propeller boss cap with fins is provided to increase the propeller characteristics particularly the propeller efficiency. Owing to the fins on the boss cap, the water stream rearward of the boss cap is guided to a direction of reducing the generation of the hub vortex and on that score the propeller efficiency is increased. The fins should satisfy the conditions as follows: (i) they are of the same number for each propeller blade, (ii) they have the inclination "Alpha" from -20.degree. to +30.degree. against the geometric pitch angle "Epsilon" of a propeller blade root, that is, -20.degree. ? "Alpha" "Epsilon" ? 30.degree., and the leading edge located between the adjacent propeller blade roots, and (iii) they have the maximum diameter larger than the diameter of the cap-mounting end of the boss 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.