Skip to main content

Measures for improving the Propulsion Efficiency


These consist of hydro-dynamically based thrust augmentation devices also called as energy saving devices. These devices can be considered to be operating in three basic zones of the hull as follows

i.   Located before the propeller.
ii.  Located at the propeller.
iii. Located after the propeller.

Before the propeller

1. Pre-swirl Stator (PSS)

It consists of a set of blades right in front of the propeller. The aim is to reduce the rotational losses in the propeller slipstream by introducing a rotation in the inflow to the propeller.
PSS increases the hull efficiency and hence the total propulsive efficiency. DNV classification society has reported a 6% power saving in design draught but just about 1% in ballast in a Kamsarmax bulk carrier that gives indication of the potential of PSS for the full form vessels.


2. Becker Mewis Duct

It is a Pre-swirl Stator with Accelerating Duct. The role of the
duct is to homogenize the axial wake component. It increases the efficiency of the pre-swirl fins by providing a more important water inflow to the stator. Also the duct contributes to the total thrust by virtue of the lift created by the accelerating flow over its walls.

3. Schneekluth Wake Equalising Duct (WED)

It aims to improve the overall propulsive efficiency by reducing
the amount of separation over the afterbody of the vessel by helping to establish more uniform inflow into the propeller by accelerating the flow in the upper part of the propeller disc and minimizing the tangential velocity components in the wakefield.
It also helps in the selection of largest possible propeller diameter. 

At the propeller

1. Propeller Boss Cone Fins(PBCF)

The idea of fitting fins to the cone of the propeller, is to enhance the
efficiency of the screw propeller by reducing the energy loss associated with the propeller hub vertex. Principally fins of flat plate form and having span of the order of 10% of the propeller blade span are fitted at a given pitch angle to the cone of the propeller. The number of fins correspond to the number of

propeller blades.

2. Unconventional Propellers

Kappel propeller has been developed by Prof. J.J. Kappel. The pressure on the suction and discharge side of the propeller at the tip equalises due to the tip vortex and hence the efficiency of the tip region is low. Kappel propeller minimises the flow over the tip and the outer region of the propeller therefore retains high efficiency. The efficiency of Kappel propeller is appreciably more than
the efficiency of the conventional propellers.

Behind the propeller

1. Rudder Bulb

It comprises of a large bulb having a diameter of about 30-40% of the propeller diameter which is placed on the rudder close behind the propeller boss. This has been in application as Costa Bulb since 1950s. It is aimed to prevent flow separation and excessive vorticity behind the hub by effectively extending the propeller boss. Additionally in some cases there are fins fitted to the bulb and these fins then produce a lift force. A component of this lift force then acts in the forward direction to produce thrust augmentation.

Comments

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

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 through the

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