Friday, July 24, 2009

The Speed of Ship and Propeller Pitch

by Charles Roring

The speed of a ship is closely related to the resistance and propulsion characteristics of the ship. One of them is the propeller pitch. In my previous article, I explained in detail about the propeller pitch ratio. The pitch ratio of a ship's propeller is usually determined from Bp-delta diagram after the delivered horse power or DHP, the rpm of the main engine at the designed vessel's speed and the speed of advance, as well as the diameter of the propeller have been obtained during the propulsion calculation.


So, increasing the pitch of a propeller will not automatically increase the speed of the designed ship. Pitch ratio is not an independent propulsion parameter. There are other propulsion factors that influence the propeller pitch which have to be taken into account during the design process of a ship.


In cruise ships or passenger ships that require high maneuverability, the number of propellers can be more than one. Also there can be consideration to install bow thrusters to help the ships maneuvering in ports and resticted waters.


The speed of ship in fixed pitch propeller is always controlled by the controlling the rpm or the speed of the main engine. In modern ships, the control of ship's speed can also be done with the application of controllable pitch propeller. So, the speed of the ship can be varied through the adjustment of pitch and the speed or RPM of the main engine. In addition, ships such as cruise, and passenger ones that are installed with CP-Propeller can move backward. Such maneuvering capability is highly needed when the ships are arriving or leaving a port. For more discussion about propeller pitch and its relation to the propulsion characteristic of ships, I suggest that you read my other articles: Pitch diameter ratio of a propeller and engine performance of a ship and Propeller Mean Pitch Calculation