Oasis of the Seas Hanging Stern Structure

In the official website of Royal Caribbean International, it is said that there are 2,700 spacious staterooms in the Oasis of the Seas cruise ship. How naval architects who designed the ship arranged the rooms in the superstructure is really amazing. They created a superstructure with a dug out or hollow space in the middle of the superstructure to allow the sun to provide natural lighting to the rooms of the cruise ship optimally - really a smart way of utilizing solar energy without the need of photovoltaic panels.   This efficient natural lighting arrangement makes the rooms of the cruise ship looks brighter without consuming a lot of fossil fuel to run electrical generator. At the stern area of the cruise ship, there is a hanging structure. I take the liberty to call it "stern bridge" because it is located at the stern of the Oasis of the Seas cruise ship. We may think that this hanging structure is a bridge that connects the port and starboard superstructures so that people can cross through it. This might be a good guess. I think yes, one of the functions of the hanging stern structure is to allow people walk through it to the other side of the superstructure. 

source: avidcruiser.com

As a matter of fact, in my opinion, from the ship's strength point of view, the addition of the stern bridge is to give more rigidity to the port and starboard superstructures so that they will be more stable. Stable superstructures will not vibrate easily. Vibration is mostly created by the vibrating forces of reciprocal engines inside a ship especially the main engine. Bad designed propellers may also cause vibrations. With the stern bridge constructed behind the ship, the Oasis of the Seas rooms in the superstructure will be more comfortable to the passengers. by Charles Roring

Oasis of the Seas Bulbous Bow

Oasis of the Seas is currently the largest cruise ship in the world. With a cruising speed of 22.6 knots, this ship needs large propulsion power. In this short article, I want to discuss a little bit about her bulbous bow.

Bulbous bow of the Oasis of the Seas is a bulb located at the front of the cruise ship just below the waterline. This bulbous bow is an integral part of the ship's hull. People cannot easily see it from above the surface of the water. If the cruise ship is at a harbor or being repaired at a dry dock, we can walk to the front area of the ship and then see the bulbous bow. The material of the bulb is the same as the material for the ship's hull which is steel. Its form is not like a soccer ball but streamlined oval. This kind of form helps the sea water to flow around the hull without creating big waves that are part of the sea water resistance of the ship. When I was still in junior high school, I thought that the bulb was made to break ice. After studying Naval Architecture at Pattimura University in the Moluccan islands of Indonesia, I finally know that the bulbous bow is made not to break ice layers in the polar seas but to minimize the wave resistance of a ship. Today most large displacement ships have bulbous bow installed at their front part of their hulls.

Source: http://photos.cruisecritic.com

Theoretically the effective power that is needed to propel a ship at certain speed is determined by the total resistance that it has to overcome. For the simplicity of explanation, the total resistance of a ship consists of frictional resistance and wave making resistance. In the form of formula, we can write it as Rt = Rf + Rw. If the size and form of bulbous bow has been carefully calculated and tested before it is constructed at the bow (or front) part of the ship, it will significantly reduce the component of wave making resistance of the ship.

Source: http://photos.cruisecritic.com

Bulbous bow at the cruise ship Oasis of the Seas is not a new invention. Most of large merchant vessels have bulbous bows installed at the front area of their hulls including the Thomson Celebration Cruise Ship from the Bahamas. With bulbous bow installation, the naval architects and marine engineers who design the ship can improve the ship's overall propulsive efficiency meaning that she can have better fuel efficiency. The purpose of this writing is to help customers of cruise ships understand the technical aspects of the ships without having to understand complicated formulas that are usually studied by students of naval architecture before they do more complicated tasks which are designing and constructing their dreamed ships.

I write this article to make introduce the study of naval architecture to anybody who is interested in cruise ships and other marine vehicles in general. If you come to this blog to find information related to Oasis of the Seas cruise deals and tickets, you have arrived on a wrong place. Please go to the official website of the Royal Caribbean International to get the required info. by Charles Roring

 Source: http://photos.cruisecritic.com

From the aerial view of this cruise ship, we cannot see the bulbous bow structure that is located at the front area of the cruise ship below the waterline

Also read:

Oasis of the Seas engine room

Oasis of the Seas propeller

Oasis of the Seas Damaged Stability Test

On the following Youtube video, we can see how a model of the Oasis of the Seas was being tested in a towing tank. This cruise ship would be expected to carry 6,296 guests (source: Oasis of the Seas Fast Facts). This is a huge number of passengers that has ever been carried by a man-made floating structure. To ensure that the ship is safe at sea, naval architects had to perform a number of model tests that are related to her resistance and propulsion as well as her stability particularly when one or more of her compartments are flooded with water.



In the Youtube video, we can see how a damage stability was conducted to assess how the cruise ship would react if one of her compartments was filled with sea water. The inclination of the hull would not endanger the safety of the cruise ship and her passengers on board. Although cruise ships with wider hulls have better stability performance, their damaged stability performance has to be calculated and tested to avoid catastrophic accident at sea.

Naval architects always have to prepare theoretical stability calculations to assess the metacentric height relative to the positions of the center of gravity and the center of buoyancy of the ship. The ship has to be able to restore herself to upright position when it is hit by big waves from the port or starboard side.

I believe that before she was launched, naval architects who designed the ship had fulfilled the stability requirements stipulated by SOLAS and the classification society which the ship is classed. Theoretically, the hull of a ship is divided into several compartments using transverse and longitudinal watertight bulkheads. When one of the compartments was damaged due to collision, ship crews have to close the effected compartment to prevent water from entering the other compartments. So, it is understandable to see hydraulic powered doors installed in certain rooms of Oasis of the Seas or other ships below their main decks. Usually when a hydraulic door is operated, it will close slowly and most often with an alarming sound and lamp to warn passengers or crews that it is closing. Because the hydraulic powered doors are made of steel and are driven by machines, they cannot easily be penetrated with sea water.

source: http://oasisoftheseas.com

In very rare cases, when a compartment has been filled with water and the degree of inclination is too big thus endangering the ship, another compartment has to be flooded to balance or to make the ship returns to her upright position again. As long as the minimum freeboard, to ensure that she will not sink, can be maintained the flooding of the undamaged compartment is allowed given that the decision to fill the compartment (with full consent from the captain) has been carefully studied based on the available hydrostatic tables particularly the flooding table of the ship. by Charles Roring