How do cruise liners float

A solid bar of steel dropped from a cruise ship balcony will undoubtedly sink until it reaches the bottom of the sea. But a boat actually has a lot of open space.

No matter how many restaurants, bars, swimming pools, and casinos they cram into these floating cities, there's still an awful lot of empty volume. Engineers are careful to keep the average density of a ship considering both the physical weight of the vessel as well as all the air less than the average density of the water. After all, the ocean is massive—and extremely dense. To the seas, a cruise ship is nothing more than a leaf drifting effortlessly along the surface.

So don't spend any time stressing about this one. Your ship is an engineering and entertainment marvel. This must be less than the average density of the water, which thankfully in the open ocean is very dense. So dense is the body of water in fact that a giant cruise ship is light as a feather on its vast surface. There must be ample air to keep the vessel afloat. An analogy to demonstrate this is to think about a bowling ball being dropped into the ocean as compared to a beach ball.

Ships are specially designed with lightweight, stable materials to evenly disperse the weight. How do huge ships manage to stay afloat? It can fit 6, passengers, boasting an ice-skating rink and a movie theatre on board. The surrounding fluid pushes back with a force equal to that of the amount displaced; when the two are equal, the object floats. Here's another way to look at it. When a cruise ship sits in the water, it makes room for itself by displacing water out and down.

The water responds by pushing up and in as it tries to take back the space the cruise ship occupies. The balance of these opposing force are what makes the ship float. In addition to buoyancy and displacement, there are several other factors that help cruise ships remain on the water's surface. To achieve buoyancy, a ship must be made of lightweight, sturdy materials which are denser than water, such as extra-strength steel.

Additionally, those lightweight materials need to be used in a design which allows them to displace their weight in water before they submerge.

Most of that design is implemented in the hull which is the body or shell of the ship which sits below the main deck and pushes the water out of the way and allows the vessel to float. Through years of trial and error, engineers have found making the hull rounded, wide and deep helps disperse the weight of the ship across the body of the ship.

Large cruise ship hulls are shaped like the letter "U. Just staying afloat and cruising smoothly isn't enough; a cruise liner's hull design must also protect the people inside against obstacles like icebergs, reefs and sandbars which could rip apart the ship's outer layers. To prevent a major catastrophe , shipbuilders typically use extra-strength steel and build their ships with double hulls meaning one hull inside the other as an extra precaution.

Cruise ships also have bulkheads which can help them stay afloat in case of major damage. These watertight dividers are installed throughout the interior of a ship and can be closed to seal out water rushing in through a damaged hull. Limiting the water inflow can ultimately keep the ship from flooding and sinking. As of , the biggest cruise ship in the world measures about feet tall, and even the average cruise ships still have impressive height.

So what keeps them from tipping over in the water? The answer is, again, in the hull design.