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

Labels:

Comments

Post a Comment

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...
14 comments
Read more

Bilge Injection Valve

Bilge Injection is a valve that enables the engine room bilges to be pumped out directly overboard in the event of an emergency such as flooding. The valve is normally fitted to the end of a branch connection with the main sea water suction line. This enables large main seawater cooling pumps to be used as a bilge pump in an emergency. Emergencies like fire and flooding involve the use of seawater. If there is a fire, seawater is the biggest resource of water available in the sea. Similarly, if it involves flooding of the engine room, cargo spaces or any other place on the ship for that matter; you would again require pumping the sea water out of the ship. In both these cases, you require pumps.  There are two valves in close proximity namely main injection valve and bilge injection valve. Both of them have their own independent controls. The diameter of the bilge injection valve is kept nearly 66% of the main valve diameter which draws water directly from the sea th...
Post a Comment
Read more

Why do we blow through engine before starting ?

The engine is blown through on air before starting it : a) To Blow out through indicator cock any residual exhaust gas or     other products of combustion trapped inside the cylinder after     shutting the engine. b) To check if any jacket cooling water from cylinder head or     turbocharger or any other source, has leaked while the engine          was shut and collected on top of piston. If while blowing                  through, water comes out of indicator cock or relief valve, we          need to investigate and rectify the fault before starting the                engine. It is imperative that the engine is blown through before        starting. There have been cases where the generator engine has        been started from control room without bothering to blow     th...
13 comments
Read more