Dynamic Positioning
With the use of a dynamic positioning system a vessel is kept at a location with the use of thrusters. These thrusters provide a certain amount of thrust in a specific direction. This can be done with multiple types of thrusters. Commonly used are azimuthing thrusters, pods, tunnel thrusters, fixed thrusters or cycloidal thrusters.
Check out our brand new
DP Failure Simulation Tool
Azimuthing thruster
The azimuthing thruster is a propeller which can rotate in 360 degrees to provide thrust is the needed direction. It has a mechanical transmission with a motor inside the ship. This motor is usually a diesel engine or a diesel-electric.
There are two commonly used arrangements. The first is the L-drive, this means that the input shaft is in a vertical position and the motor is tilted as well. The drive shaft makes one 90 degrees turn and looks like the letter L. The second is the Z-Drive, in this configuration the drive shaft makes two 90 degrees turns. So the engine can be in a horizontal position.
POD thruster
The pod thruster is an azimuthing thruster with an electrical transmission, with the electromotor placed in the pod hanging below the vessel. This way there are no losses in gears are minimized. The electricity is produced onboard with usually a gas turbine or a diesel engine.
Tunnel thruster
Bow thruster, also known as a tunnel thruster is mounted in the hull at the bow or at the stern of the vessel to provide sideways thrust. An impellor inside a tunnel can provide thrust in either transversal direction. Usually driven by an electric motor, but sometimes they are hydraulically powered.Bow thrusters make it easy to maneuver a vessel and make it possible to dock a vessel without the help of tugboats.
Some other examples of bow thrusters are, externally mounted thrusters, these can be mounted in case it is not possible to integrate one in the hull. Another bow thrusters is a waterjet thruster. This uses a pumping device to blow out water instead of a conventional propeller. Waterjets generally have the advantage of smaller hull penetrations for an equivalent size thruster. Additionally, the higher exit velocity of the discharged water increases the relative efficiency as speeds of advance, or currents, increase, as compared to standard tunnel thrusters. Some waterjet bow thrusters can be configured to provide forward and aft auxiliary propulsion, or even full 360 degree thrust.
Fixed thruster
The fixed propellers are mounted at the stern of the vessel and usually provide the thrust for cruising speeds, but can also be used for dynamic positioning.
Cycloidal thruster
A cycloidal thruster, also known as a Voith Schneider propeller consists out of multiple wing shaped blades which can rotate around its own axis and are mounted on a large rotating ring. This thruster can easily change its direction an magnitude of thrust by adjusting the angle of the blades. The acoustic signature of this thruster is very low, since the rotation speed does not have to be very high to provide sufficient thrust.
