Moving the ship by Oladokun Sulaiman

Reads: 294  | Likes: 0  | Shelves: 0  | Comments: 0

More Details
Status: Finished  |  Genre: Science Fiction  |  House: Booksie Classic
technology of propeller

Submitted: April 26, 2008

A A A | A A A

Submitted: April 26, 2008

A A A

A A A


what it takes to move that ship against water resistance

\"333\"\"magnify\"

Moving that ship is and moving in the vastness of the ocean is work of the most, and of course triumph of human and the quest for a much better life. The ocean was the fist thing that linked human together, human wanted to reach others from other part of land .early people started with log, before Archimedes came up with his brain storming principle that led to the first design of ships. Ships are vehicles made for transportation by sea, according to the type of cargo they can be can be divided into different categories, classes, and types- The three largest categories of ships are:

- Container ships,
-Bulk carriers (for bulk goods such as grain, coal, ores, etc.)

-Tankers, which again can be divided into more precisely, defined classes and types-oil tankers, gas tankers and chemical tankers, but there are also combinations, e.g. oil/chemical tankers. In reality there are many other combinations, such as “Multipurpose bulk container carriers”.

Ship propulsion normally occurs with the help of a propeller, the primary source of propeller power is the diesel engine, the power requirement and rate of revolution very much depend on the ship’s hull form and the propeller design. Due to complexity of the ship itself and the environment it operate Ship is subject to risk of bad weather and other extra resistance like fouling, at sea during their operation.

Ship’s resistance

To move a ship, it is first necessary to overcome resistance, i.e. the force working against its propulsion. The calculation of this resistance R plays a significant role in the selection of the correct propeller and in the subsequent choice of main engine. General a ship’s resistance is particularly influenced by its speed, displacement, and hull form. The total resistance RT, consists of many source resistances R which can be divided into three main groups, viz.:

1) Frictional resistance

2) Residual resistance

3) Air resistance-direct wind force on above water part – from all direction

The influence of frictional and residual re resistances depends on how much of the hull is below the waterline, while the influence of air resistance depends on how much of the ship is above the waterline

Ship Hull factors

The part of the ship which is of significance for its propulsion is the part of the ship’s hull which is under the water line. The following are some of the hull factors that are being considered at the stage:

  • The lines and letters of the Plimsoll Mark, which conform to the freeboard rules laid down by the IMO (International Maritime Organisation) and local authorities, indicate the depth to which the vessel may be safely loaded (the depth varies according to the season and the salinity of the water)and to keep the propeller in submerged position .
  • Displacement and deadweight is when a ship in loaded condition floats at an arbitrary water line, its displacement is equal to the relevant mass of water displaced by the ship.
  • The length overall length (LOA) of the ship is normally of no consequence when calculating the hull’s water resistance. The factors used are the length of the waterline LWL and the length between perpendiculars LPP.
  • Breadth on waterline BWL is another important factor is the hull’s largest breadth on the waterline.
  • Block coefficient CB is the various form coefficients used to express the shape of the hull. It is defined as the ratio between the displacement volume and the volume of a box.

Propeller

Today, the primary source of propeller power is the diesel engine, and the power requirement and rate of revolution very much depend on the ship’s hull form and the propeller design. Therefore, in order to arrive at a solution that is as optimal as possible, some general knowledge is essential as to the principal ship and diesel engine parameters that influence the propulsion system.

At the bottom of the ship, the propeller is fixed on a shaft connected to the engine and it is being control by the rudder at a control surface, while rudder is controlled by the steering gear which is located on the deck.

Propeller remains an intricate complex part of ship that needs diligent and careful consideration at the design stage. efficient design of propeller need to account for gain life cycle of the ship as well as tremendous saving in fuel economy that has a lot of influence inship and its needs. The ship’s resistance and propulsion system will frequently be checked against the results obtained by testing a model of the ship in a towing tank. The experimental tank test measurements are used for optimizing the propeller and hull design. When the ship’s necessary power requirement, including margins, and the propeller’s speed (rate of revolution) have been determined, the correct main engine can be selected based on result deduced fro such test, in this connection the interaction between ship, propeller and main engine is extremely important.

Today I will not discuss the principle behind how propeller works, I will rather talk about historical development, how human strive to reach what we use today.

  • 287-212 BC – Archimedes invented his archmedian screw pump to irrigate the field of Syracuse in Sicily
  • 1452-1519-Leonard Da Vinci sketched screw principle to be used in helicopter rotor
  • 1661-Toogood and Hayes of Britain claimed patent for using helical surfaces (archimedian screws) as a propeller
  • 1680-Hook an English physicist suggested using Archimedean screw for ship propulsion
  • 1802/04-C. Steve an American used a kind of screw propeller similar to today screw to propel a 7.5m twin steamer
  • 1828-R. Wilson a Scottish farmer successfully demonstrated the first principles
  • 1836-P. Smith, an English farmer achieved the first practical application he used single bladed screw of two turns made by wood.
  • 1836-J. Ericson a Swedish engineer developed fore runner of contra-rotating propeller (i.e. two wheels of three helicoidally blades rotating in opposite direction.
  • 1839-Smith equipped 237 ton of ship Archimedes with screw props having a great success and this led from paddle propulsion systems to screw propulsion
  • 1840-50-Development of steam engines contributed to effective use of screw propellers
  • 1845-Great Britain was the first screw propeller across the atlantics
  • 1880-Thornycroft designed propellers similar to today’s propellers
  • 1980-1970-Basic shape of props remained unchanged
  • 1940-1960-Development of propeller theory a direct benefit from the development of hydrofoil theory
  • 1970-1990-Fuel crisis and enviroenmetakl effects (low noise and vibration) had impact on propeller shape and stern configurations as well as the development of unconventional propeller.

Modern propeller include fixed pitch propeller:

  • Ducted propeller
  • Contra rotating propeller
  • Overlapping propeller
  • Controllable pitched propeller
  • Water jet propeller

On a final note most human activities and invention has followed the same trend, we have done many things in past through try and error. We have no choice, and it is significance truce that is always better to learn by practice, and experience. But today is different world, is world when a lot of information is available and knowledge is available. And there is indicating of system failure and records of lesson learnt. much design will be done based on goal and assessing risk—one thing I will like to also point out is the fact that –by working together ….we can always achieve success –eventually it is the unity that work best in everything no matter what .


© Copyright 2017 oladokun sulaiman. All rights reserved.

Add Your Comments:

More Science Fiction Articles