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Propeller Types

Propellers may be divided into the following two main groups:
  •  Fixed pitch propeller (FP propeller)
  •  Controllable pitch propeller (CP propeller)

Propellers of the FP type are cast in one block and normally made of a copper alloy. The position of the blades, and thereby the propeller pitch, is once and for all fixed, with a given pitch that can not be changed in operation. This means that when operating in, for example, heavy weather conditions, the propeller performance curves, i.e. the combination of power and speed (r/min) points, will change according to the physical laws, and the actual propeller curve cannot be changed by the crew. Most ships that do not need particularly good maneuverability are equipped with an FP propeller. 

Propellers of the CP type have a relatively larger hub compared with the FP propellers because the hub has to have space for a hydraulically activated mechanism for control of the pitch (angle) of the blades. The CP propeller is relatively expensive, maybe up to 3-4 times as expensive as a corresponding FP propeller. Furthermore, because of the relatively larger hub, the propeller
efficiency is slightly lower. 

CP propellers are mostly used for Ro-Ro ships, shuttle tankers and similar ships that require a high degree of manoeuvrability. For ordinary ships like container ships, bulk carriers and crude oil tankers sailing for a long time in normal sea service at a given ship speed, it will, in general, be a waste of money to install an expensive CP propeller instead of an FP propeller. Furthermore, a
CP propeller is more complicated, involving a higher risk of problems in service

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