The hub is bolted to the flanged end of the tailshaft. Without ice class, the hub diameter/propeller diameter ratio varies between 0.20 and 0.25. A typical hub ratio for ice class or very high-loaded propellers may vary from 0.25 to 0.38 or higher. The propeller blades are bolted to the propeller crank disk which is connected to the pitch setting mechanism inside the hub. The hub is filled with pressurised oil from the gravity tank located above the water line. The pressure inside the hub is larger than outside, which prevents water leakage into the hub. Small controllable pitch propellers have a push-pull rod from the mechanism in the hub and forward to the gearbox or in the shaftline. Such a solution is recommended because of its simplicity and well-proven functionality. Larger propellers have the servo cylinder incorporated into the hub.
