Fixed Pitch Propeller

A fixed pitch propeller has its blades cast or machined as an integral or bolted assembly onto the hub at a fixed angle, so that the thrust and direction of the vessel can only be changed by varying the rotational speed of the main engine or by reversing its direction of rotation. This simplicity gives the FPP high efficiency at the design operating point, long service life, and very low maintenance requirements compared with a controllable pitch design, making it the standard choice for large ocean-going cargo ships where propulsion demands are relatively steady and frequent direction reversal is not required. FPP blades are periodically inspected in drydock for erosion, pitting from cavitation, cracks, and damage from debris strikes. Classification societies require propeller surveys at defined intervals — typically at every special survey — involving underwater inspection or drydock measurement of blade thickness and edge condition. Propeller repairs such as re-pitching a damaged blade or polishing to remove roughness can produce measurable improvements in propulsive efficiency. Engineers note any unusual vibration signatures from the shaft that might indicate blade damage and report these for early investigation rather than waiting for the next scheduled drydock.