Why Don’t Ships Sink? Here’s Why!

Why Ships Don’t Sink – Sinaumed’s, have you ever seen a ship at sea? This transportation is currently often used to transport passengers and goods. When you see a ship sailing, maybe some of us will wonder, “Why doesn’t this ship that weighs tons sink and float in the sea? Pebbles that weigh only a few grams will immediately sink when we throw them on the same surface.

This article will provide a review of the factors that cause why the ship does not sink, even though it has a very large load. However, before that we need to know the etymology and types of ships that exist today.


The word “ship” in Indonesian and Malay comes from the Dravidian language family “kappal”. This word started appearing in Tamil literature after the 17th century, namely கப்பல். Before the 17th century, the word “ship” in Indonesian literature always referred to foreign-made vessels (in this case India), while the word “boat” referred to large vessels (see: K’un-lun po), until eventually actually replaced by the word “ship” to refer to large water vehicles.

According to the Big Indonesian Dictionary (KBBI), a ship is a vehicle for transporting passengers and goods at sea, rivers, swamps, and so on, made of wood or iron, has one or more masts, has a deck, and is driven by engines or sails.

Ship Types

Ships are actually very difficult to categorize, mainly due to the many criteria on which the classification is based. However, the ships that exist today can generally be categorized into three types, namely based on propulsion, type of voyage, and function.

1. Driving Force

Based on the propulsion, ships are divided into five types, namely:

  • human-powered boats (rowers);
  • Diesel or motor boats;
  • Sailing boat;
  • nuclear ship;
  • Steamship or fireboat.

2. Type of Sailing

Based on the type of voyage, ships are divided into four types, namely:

  • hovercraft or hovercraft;
  • floating ships;
  • surface ships;
  • Submarine.

3. Functions

Based on its function, ships are divided into types, namely:

  • Freight ships or cargo ships;
  • Ferries or ferryboats;
  • Passenger ship;
  • Warship;
  • tankers;
  • Icebreaker;
  • tugboats;
  • pilot boat;
  • barges or pontoons;
  • tenders;
  • Ro-Ro Ship;
  • refrigerated cargo ships;
  • Dredger;
  • Container ships or container ships;
  • Tiger trawler.

The Origins of the Working Principles of Marine Ships

Archimedes of Syracuse.

Actually, there are differences of opinion regarding the theory that underlies the working principle of marine vessels. However, the main basis for the creation of ships in the world that is recognized is the law of the mathematician of the third century BC from Greece, namely Archimedes of Syracuse.

Archimedes of Syracuse was a mathematician, physicist, engineer, astronomer, and inventor who lived around 287 BC–212 BC. He studied in the city of Alexandria, Egypt. Some historians view him as one of the greatest mathematicians in history, along with Sir Isaac Newton and Johann Carl Friedrich Gaus.

At that time, Hieron II, a friend of Archimedes, became king of Syracuse. Archimedes became known to people after he received an order from Hieron II to prove the purity of his gold crown.

He then went home and took a bath in his tub. He noticed that there was water spilling out when he went inside. At that moment, he realized that the water that came out weighed equal to the weight of his body that went into the water. He remembered that pure gold would sink and some water would come out, so he could find the density by calculating the weight of gold divided by its volume.

From this event, Archimedes was able to find out the density by calculating the weight of gold divided by its volume. He then compared it to the density of a king’s crown. If the density of the king’s crown is lighter, the crown is said not to be made of pure gold, but a mixture of other metals. This eventually became the formula for buoyancy used in the ship system.

Archimedes’ Law

With Archimedes’ law, we can classify objects into three types. These objects include sinking, floating, and floating objects. Objects can sink if the lifting force of the water is less than the weight of the object, while objects will float if the lifting force of the water and the object’s weight are the same. For objects that can float occurs when the lifting force of water is greater than the weight of the object.

Archimedes’ law reads as follows:

An object that is partially or completely immersed in a liquid will experience an upward force equal to the weight of the liquid it displaces.”

So, this law explains that there is a relationship between gravity and upward force in an object when it is placed in water. As a result of the upward lift (buoyancy), of course, objects that are in the liquid will experience a reduction in weight. As a result, objects lifted in water will feel lighter than when lifted on land.

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1. Drown

This situation occurs when the density of the liquid is less than the density of the object. For example, iron or steel will sink if put in water because the density of iron is greater than the density of water. When submerged, the weight of the object in the liquid is greater than the upward force exerted by the liquid.

The force of water pressure < the weight of the object

2. Drift

This situation occurs when the density of the liquid is the same as the density of the object. The floating object is between the bottom of the vessel and the surface of the liquid. For example, an egg placed in water with a little salt added will float because the density of the two is the same. The same thing happened to fish. The fish can equalize its weight with the weight of the water it displaces so it can float.

The force of water pressure = weight of the object

3. Floating

This situation occurs when the density of the liquid is greater than the density of the object. For example, styrofoam or plastic will float if placed in water.

The force of water pressure > the weight of the object.

Relationship between Buoyancy and Density

If a one cubic centimeter block of wood is placed in a container of water, the amount of water displaced will be equal to the weight of the block of wood. In the case of wood, the weight of the water displaced is small, so the buoyant force is greater than the force of gravity and makes the wood float.

Then, what if the blocks of the same size are made of tin? Tin has a higher density, so it will displace more water than wood. The gravitational force in the lead exceeds the buoyant force and causes it to sink.

Archimedes’ principle states that the force exerted on an object in a fluid is equal to the weight of the fluid displaced (moved out) by the object. The buoyant force pushes it upwards against the object. Gravity exerts a downward force on the object, which is determined by the object’s mass. If the force exerted by an object with gravity is less than the buoyant force, the object will float or float.

Reasons Ships Don’t Sink

Ships can have a mass of hundreds of thousands of tons, let alone those that use steel. Steel is much denser than water. However, the steel ship remained afloat. This is because a large ship displaces a very large amount of water too.

Unlike the case with a stone that we throw into the water will sink. This is because the rock only displaces a small amount of water. The rock sinks because it is heavier than the amount of water it displaces.

An object will float, float, and sink in a liquid because the density of the object is compared to the density of the liquid in which the object is immersed. So, an object will float if the density of the object is less than the density of the liquid. An object will float if the density of the object and the liquid are the same. Objects will sink if the density of the object is greater than the density of the liquid.

So what affects density? As explained above, density is the ratio between an object’s mass and its volume. That is, the smaller the mass of the object (the lighter), and the greater the volume of the object, the smaller the density.

Say, a needle and a vessel are placed in the same liquid (which must have the same density). The needle will sink because the density of the needle is greater than the density of water, and it is still greater than the density of the ship.

Why is the density of the ship smaller than the density of the needle? The reason is that ships have such a large “room” along with cavities filled with air, which makes the “volume” of ships so large and causes their density to become smaller.

Confused? You see, density is mass divided by volume. If the volume increases while the mass remains the same, the result of division will certainly be more. Just try the number 8 divided by 2 = 4, while 8 divided by 4 = 2. So it’s smaller right?

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Density also depends on the type of material. A solid cube of the same size made of wood will of course have a lower density than a cube made of metal.

When a ship sinks, water enters the ship and forces the air inside out, so the average density of the ship is greater than that of the water.

Titanic at Southampton dock before departure.

One of the famous ship tragedies is the sinking of the Titanic. The ship was built from 1909 to 1911 by the Harland and Wolff shipyard in Belfast. There were 1,317 passengers on the Titanic at that time: 324 in first class, 284 in second class, and 709 in third class. 869 (66%) of them were men and 447 (34%) women.

There were 107 children on board, most of them in third class. Titanic was deemed not to have reached capacity on her maiden voyage, as she could accommodate 2,566 passengers – 1,034 in first class, 510 in second class and 1,022 in third class.

After leaving Southampton on 10 April 1912, Titanic stopped at Cherbourg, France and Queenstown (now Cobh), Ireland before sailing west to New York. On April 14, 1912, four days after sailing, exactly 375 miles south of Newfoundland, the ship struck an iceberg at 23:40 (ship time; UTC-3).

This collision and friction caused Titanic’s hull plate to buckle inward in several places on the starboard side and ripped five of sixteen watertight compartments. Over the next two and a half hours, the boat slowly filled with water and sank.

The number of passengers and crew were evacuated into lifeboats, most have been released in a state of half-full. Many men in disproportionate numbers – nearly 90% in second class – left because officers were loading the lifeboats comply with the protocol “women and children first”.

Just before 2:20 a.m., the Titanic broke and its bow sank with a thousand people on board. The people in the ocean died within minutes from hypothermia caused by contact with the freezing ocean. 710 passengers safely removed from the boat by the RMS Carpathia a few hours later.

The wreck of the Titanic was rediscovered in 1985 and is still on the seabed today, but slowly disintegrating at a depth of 12,415 feet (3,784 meters). The Titanic has become one of the most famous ships in history. His existence continues to be remembered in a number of books, films, exhibitions, and memorials.

One of the most important legacies of this disaster is the establishment of the International Convention for the Safety of Life at Sea (SOLAS), which governs maritime safety until now.

Experiments at Home

Even though it sounds simple, some of Sinaumed’s’ friends may be confused about understanding the working principles of marine vessels. So, to make it easy to understand, we will provide an overview using the objects available at home. You only need to prepare a bowl or other container that is similar in shape.

When done, place the bowl above the surface of the water. The object will definitely float and swing to the rhythm of the crashing water.

Then, when you gently press the bowl inward, the water will react in the form of an upward push, so that the bowl can still float. That’s more or less what happens in ships.

So, Sinaumed’s is a brief explanation of the working principle of the ship that keeps it from sinking in the ocean. Archimedes’ law is actually a simple physics principle, that is, any object that is submerged in water, either in whole or in part, will receive an upward force pushing it to make it float. This principle is also often referred to as the principle of buoyancy.

However, it should also be understood that in such cases the density of the ocean liner must be less than that of water in order to float. That is what makes the sea vehicle have a section filled with air cavities. This part of the hull makes the ship balanced and floats in the ocean. Apart from air cavities, one other thing that allows ships to float on the surface of the water is the depressions at the bottom.


“While at sea, the ship exerts pressure on the water. The weight of the ship pushes the water downward, then with the same force, the water exerts pressure on the ship in the opposite direction, namely upward.

(Jalaluddin Rumi).