Wednesday, January 5, 2011

Oasis of the Seas Engine Room

I have just found a video in Youtube which shows the engine room of the Oasis of the Seas. As we have known before that this largest cruise ship in the world is not propelled by a conventional marine diesel engine - shaft - propeller arrangement. If we see the propellers at the stern area of the ship, we will not see shaft coming out of the back part of the hull. What we see is that the ship is propelled by 3 Azipod propellers that are able to be rotated 360 degrees eliminating the need for controllable pitch propeller. These are actually electric propellers which are able to give high maneuver capability to the cruise ship. CPP or Controllable Pitch Propellers are usually installed on ships that need higher maneuvering capability without jeopardizing much of her propulsion efficiency. Fixed pitch propeller has long been considered to have high propulsion efficiency. From the picture of this ship's stern and her hanging propellers, we can easily conclude that there are not shaft tunnels in the Oasis of the Seas' engine room.
From the video the engine room is quite noisy. I think the video was taken when the ship is moving. From wikipedia, I read that Oasis of the Seas propellers are powered by 3 x 20 MW ABB Azipod, all azimuthing and 4 x 5.5 MW Wartsila CT 3500 bow thrusters. These diesel engines must be very noisy.
In the past, ship designers were reluctant to choose diesel engine as the prime mover of passenger or cruise ships. They knew that diesel engines create noisy sounds that would be bad for the passengers and also the fumes they release had bad smell. In addition, diesel engines create vibrations that were harmful to the whole steel construction of the ship and also to the passengers. The prime mover of old cruise ships was steam turbine. It did not create noisy sound. And it did not create significant vibration. The problem is that steam turbine is not efficient because it needs a number of reduction gears to reduce the revolution of the turbine to a level where marine propellers will be able to work without structural failure or cavitation.

The passenger rooms of Oasis of the Seas have to be free from the negative diesel engines characteristics. Marine engineers who were working on the design and construction of this ship must have worked hard isolating the vibration and sound from these marine diesel engines. I think they would not put passenger cabins near the engine room. Instead, the area close to the engine room might have been given to other purposes where passengers will not sleep there. Or they might allocate the rooms near the area only for ship crews. The Oasis of the Seas Interior in the area near the engine room has also been covered with certain anti-vibration material that can significantly reduce the sounds and vibration created by the diesel engines. I believe that the naval architects and marine engineers had dampened the vibration from these diesel engines perhaps by installing certain rubber between the bolts and nuts; and the engine foundation. by Charles Roring