Skip to main content

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


Popular posts from this blog

Difference Between A, B & C-Class Divisions?

IMO Symbol A Class Division  IMO Symbol B Class Division  SOLAS has tables for structural fire protection requirement of bulkheads and decks. The requirements depend on the spaces in question and are different for passenger ships and cargo ships. The Administration has required a test of a prototype bulkhead or deck in accordance with the Fire Test Procedures Code to ensure that it meets the above requirements for integrity and temperature rise. Types of Divisions: "A" Class "B" Class "C" Class "A" Class: "A" class divisions are those divisions formed by bulkheads and decks which comply with the following criteria: They are constructed of steel or equivalent material They are suitably stiffened They are constructed as to be capable of preventing the passage of smoke and flame to the end of the one-hour standard fire test. they are insulated with approved non-combustible materials such that the average tempera

Load Line & Why it is Important

Merchant ships have a marking on their hull know as the Plimsoll line or the Plimsoll mark, which indicates the limit until which ships can be loaded with enough cargo, internationally, the Plimsoll line on a ship is officially referred to as the international load line. Every type of ship has a different level of floating and the Plimsoll line on a ship generally varies from one vessel to another.  All vessels of 24 meters and more are required to have this Load line marking at the centre position of the length of summer load water line. There are two types of Load line markings:- Standard Load Line marking – This is applicable to all types of vessels. Timber Load Line Markings – This is applicable to vessels carrying timber cargo. These marks shall be punched on the surface of the hull making it visible even if the ship side paint fades out. The marks shall again be painted with white or yellow colour on a dark background/black on a light background.  The comp

Pump Shaft Alignment Procedure

Types of shaft alignment methods: Visual Line-Up Straightedge/Feeler Gauge Rim and Face Cross Dial Reverse Dial Laser Visual Line-Up The visual line-up method is the most common method of alignment. Used in initial installations, visual line-up allows technicians to analyze the working conditions and feasibility of installation. Straightedge/Feeler Gauge Straightedges are used to determine the offset between coupling halves. Corrections are made under all four of the machines feet. Feeler gauges or taper gauges measure the gap between coupling halves at the bottom and top of the coupling. Rim and Face This method is similar in principle to using a straightedge and feeler gauge, but more accurate since dial indicators are used. The rim reading measures the offset between the coupling halves. The face reading measures the angular difference between the faces of the coupling. Changes are calculated with the same formula as the straightedge/feeler gauge met