Wednesday, December 1, 2010

Oasis of the Seas Propeller

The propulsion system of Oasis of the Seas really attracts my attention. Please, look at the photograph of the stern area of this cruise ship below when she is still on the dry dock. If we look closer to the propellers, we can tell that they can be rotated 360 degrees to propel the ship to any directions. This kind of propellers is usually called azimuth propeller or azimuth thruster. The blades are installed into a boss that is connected to a pod that can be rotated in any horizontal direction. Because of the characteristics of this azimuth propeller, the vessel does not require ship rudder.
From the technical specifications which I read from ship technology website, it says that Oasis of the Seas is powered with three 20 MW azimuthing Asea Brown Boveri Azipods. These propellers can thrust the ship to a cruising speed of 20.2 knots.
Azimuth propellers are usually installed in vessels that require high maneuverability such as tug boats. Ship designers do not choose such propellers for ships that do not require high maneuverability such as tanker and cargo vessel. These ships might be installed with controllable pitch propellers to help them moving around restricted waters or harbor area. Although azimuth thruster is very good for ship maneuvers, its propulsion efficiency is usually lower than the conventional marine screw propeller whose horizontal shaft is fixed and runs from the stern area to the main engine. The additional mechanisms that are installed inside the hub and boss of propeller cause the efficiency of the azimuth thrusters to be lower than the conventional fixed pitch propeller. Also read: Controllable Pitch and Fixed Pitch Propeller
The earliest propulsion in mankind
I remember rowing canoes with two Dutch girls in Numfor island last week. The canoes were not equipped with outboard engines. Instead, we had to propel the boats manually using oars. This is the earliest form of propeller that is still being used by the indigenous people of Papua of the island. We went by the outrigger canoes to enjoy snorkeling over the beautiful coral reef near Numpuri island. It is interesting to see that in this modern age, we can still see that even the latest technology in propulsion system such as azimuth thruster cannot totally replaced the earliest form of propulsion of a simple canoe which is oar or paddle.
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