Royal Caribbean operates the biggest cruise ships in the world, and a ship (if stood upright) the is double as high together the Washington Monument can leave girlfriend wondering exactly how it doesn"t sink.

You are watching: How does a cruise ship stay afloat


Symphony the the Seas has actually water slides, an ice skating rink, and an entire park. She have the right to accommodate increase to 6,680 guests and weighs 228,081 gross tons (GT).

Whether you have actually been on a cruise ship, or just seen a photograph of one, you might have wondered just how such a huge ship deserve to float in the water.

How does a cruise delivery float? and why doesn"t it fall over when the wind blows?


Royal Caribbean"s cruise pearls are impressive pieces that technology, naval tradition, and innovation, yet they space not magic. That is all about physics.

The concept of buoyancy is what keeps a cruise ship favor Symphony the the Seas upright and also floating.

The scientific research of buoyancy was found by Archimedes in 246 BC, once he developed Archimedes" principle.


"Any object, totally or partially immersed in a fluid or liquid, is buoyed up by a force equal to the weight of the fluid displaced through the object."

Essentially, cruise ships have the right to stay above the water as long as they room displacing an same amount of water to their mass.

A cruise delivery displaces an amount of water indistinguishable to its very own mass. The push of the sea pushes up versus the vessel’s hull to respond to the downward force of the ship’s mass. Unlike air, water can not be compressed, for this reason the merged forces produce buoyancy.

As the cruise delivery moves forward, water is moved away and also that water do the efforts its finest to go back to fill the displaced room and that energy forces the ship upward.

While the delivery is undoubtedly quite heavy, there is a many open room onboard and also that north volume method the delivery is not prefer a huge rock in the water.

When a cruise delivery is designed, designers pay careful attention to store the average thickness of the ship (considering both the physical weight of the vessel as well as all the air) less than the average thickness of the water. 

The s is large and incredibly dense. So if the cruise ship have the right to have much less of a thickness than the ocean, that it floats ~ above the surface.

If you ever meet one engineer, castle will regularly talk around a ship"s displacement, fairly than its weight. Ships to rise because they weigh less than the weight of the water they displace.

One other thing you might notification about a ship prefer Symphony that the Seas is her wide hull. That design an option is no accident.


When Oasis course ships were designed,the engineers chose a vast hull to disperse the weight throughout it.

Think of the hull as the human body of the ship, and also the component that is below the main deck is usually quite vast and has a deep bottom (known as a basic line). Cruise pearls (and other big vessels) commonly have displacement hulls, or hulls that press water out of the way, to continue to be afloat.

Another major difference between a cruise ship and a watercraft is the style of the hull.


Boats have a "v-hull", which method if you took it out of the water and looked underneath, the bottom resembles the letter "v". Cruise ships have a hull that looks prefer the letter "u".

Round-bottom hulls move through the water and make them much an ext stable and also seaworthy than a v-shaped watercraft hull. This is generally why cruise delivery passengers feeling much much less rocking or motion contrasted to a boat.

However, that security comes at a price: speed. Boats move v the water much much faster than cruise ships.


So with every one of that said, I have not yet tackled how a cruise ship is going to float. Why is there just 30 feet listed below the water and also over 200 feet above the water, and also how carry out they keep the upside up?

It is a matter of weight distribution. The engines and other machinery, fuel tanks, water tanks, and also ballast tanks space all low in the ship, if lighter, less thick spaces room up higher.

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The more comprehensive hull help a lot with stability. Symphony is practically as vast as she is tall. It is why a strong wind hitting the next of the delivery doesn’t reminder it over. This is calculated together a wind heel moment and is a large part the the stability calculations for any kind of vessel.


If Yoda had actually been an engineer, he could have said, "Size matters not. Referee me by my buoyancy carry out you."