For cruise ships to float on open seas, they must be able to stand up to the weight of the vessel in addition to luggage, crew, cruise passengers, and supplies. This is done through a combination of buoyancy and density.
Ships can weigh up to 71,550 tons, displacing the same amount of water when in the ocean. They do all this while being pushed up due to buoyancy. So, what does a cruise ship out of water look like?
When examining a cruise ship out of the water, people wonder how such a small percentage of the vessel can be submerged while the rest of the ship towers above and stays afloat. The entire cruise ship looks incredibly top-heavy, making people wonder how it simply doesn’t topple over with the weight.
Taking a ship out of water is known as dry docking; when the ship sails into its shipyard, the water is drained from the dock area allowing its workers to make repairs or inspect it in a dry area. This maintenance is significantly easier for the crew to accomplish on dry land than when the ship is in the water.
In This Article…
Cruise Ship Out of Water – The Naked Truth
When engineers discuss the weight of a ship, they talk about water displacement rather than the actual weight. To prevent a cruise ship from sinking, it needs to displace its own weight in water before being submerged. It is easier to accomplish if the ship is built so it is less dense than the water below it.
To put it in practical terms, if you submerge a bowling ball into the water, it will sink since it doesn’t displace enough of the water before entering it, causing a sinking effect. However, if you put a beach ball in the water, it will always float.
Buoyancy is accomplished by selecting lightweight materials that disperse weight across the ship’s hull yet are composed of sturdy materials.
The hull, the body of a cruise ship below its main deck, is wide and contains deep baselines. Large vessels like cruise ships usually have displacement hulls that push water out of the ship’s way. This allows it to remain floating.
Adjusting for Center of Gravity
Wide hulls, low centers of gravity, and ballast tanks containing sea water and fuel prevent ships from capsizing. The center of gravity can be manipulated by adjusting a vessel’s weight, commonly in the fuel and ballast tanks. In extreme situations, crew members can drain swimming pools on the upper deck for more stability, allowing the center of gravity to move higher.
Cruise ships have mechanical stabilizing systems that deploy when at sea. This mechanism extends fins that rotate and can exert a righting force when the cruise ship moves. While it won’t prevent rolling, it will considerably reduce it.
Bilge keels also assist with roll. They are metal fins that are long and welded on each side of a cruise ship.
Displacement hulls with a round bottom appear like large rectangles with rounded edges. They work to dissipate any force or drag exerted against the ship. Rounded edges decrease the water’s force against its hull, permitting larger, weightier ships to move smoothly.
If you examine a ship when it isn’t in the water, the hull appears to be in the shape of a large “u,” depending on keel size. Keels run from stern to bow, creating the backbone of any ship.
Displacement hulls with rounded bottoms have both pros and cons. These hulls move through the water easily, making them seaworthy and stable. Passengers tend not to notice any rocking movement while on board.
They move fluidly through the sea; however, the water resistance makes it slower. These ships can only sail at a top speed for so long before the engine power reaches points of diminishing returns. The requirements for smoothness and stability will always override high speeds, making this type of hull the best fit for a cruise ship.
Hulls also protect against icebergs, sandbars, and reefs which can tear through their materials. To prevent extensive damage, builders construct the hull using extra-strength steel. They also insert a double hull to provide additional protection. Double-hull designs look like a hull within another hull.
Regrettably, accidents can happen. To prevent sinking if the first two lines are compromised, ships are equipped with bulkheads, which are watertight dividers in the interior of a ship’s hull.
In an emergency, the bulkheads will keep a damaged cruise ship floating by containing any incoming water and placing it into the compartments. This prevents the ship from flooding or taking on water.
The square shape on the bottom maximizes the space on board a cruise ship and allows the vessel to be stable. Flat bottoms make construction simpler and the dry dock process easier. The bottom, however, is not quite as flat close to the bow or at a raised area located where the propellers lie close to the stern.
What About Power?
Ships move by using reciprocating diesel engines for propulsion. The power goes through transmission into propeller shafts. The transmissions are what determine a propeller’s revolution. Most ships contain diesel-electric, gas turbine, or LNG-powered solutions.
The larger the ship, the higher the demand for electrical power. Some ships only need two different sources of power, one for electrical power and one for propulsion.
Looking at its draft marks, people can see how deep the cruise ship is when sitting in water. These marks are at the stern and bow of a ship.
The load line marks the center of the side of a ship and is known as the Plimsoll line, named after Samuel Plimsoll. Samuel Plimsoll campaigned for safe draft marks, which was enacted in 1875.
A line through a circle indicates the lowest a ship should sit in the water when it is fully loaded. There are different lines for maximum drafts in specific conditions. These are:
- T for tropical
- S for Summer
- W for Winter
An S load line is typically used as it is illegal for a ship to sail with the S line submerged. If it is, the cruise ship is overloaded.
N and V designations are the ship’s classification society. They ensure it is maintained and constructed according to the relevant international standards. NV indicates Bureau Veritas while LR is Lloyds Registrar.
In addition to engines and propellers, most guests will note the towering decks on any cruise ship. The upper decks contain all the cabins and staterooms. The lower decks are where the crew live, sleep, and eat.
There are also rooms used as the morgue and jail or brig on a cruise ship. These are all below deck and set apart from guests, with only the crew having access.
Within this construction, on the inside, are specialty dining, entertainment venues, an assortment of activities, pools, water slides, spas, whirlpools, and a myriad of fun activities available to anyone on the cruise.
Is it Possible for Cruise Ships to Roll Over?
While it may be technically possible, it is unlikely. In the cruise industry, navigational officers and the Master continually monitor a cruise ship’s stability. Weight distribution is adjusted as needed to ensure the safety of all guests on board.
Cruise ships, however, can capsize if buoyancy and weight distribution are compromised, creating negative stability. However, in large cruise ships, tipping is impossible even if you are traveling in the most turbulent of waters.
The design of a cruise ship is remarkable. A cruise ship out of water will contain a flat bottom, hulls in a u-shape, plus bilge keels and stabilizers to prevent rolling. All these things coordinate to ensure the cruise ship is kept in an upright position.
Read Also: How Big is a Cruise Ship?
Deck officers and the Master monitor the ship’s stability continuously by adjusting the ballast and other items to ensure the ship remains upright and preserves its stability within the designated parameters.