How Does a Submarine Work? I-KIT LAB

Submarines

Students, welcome to the fascinating journey of submarines. Today we are going to discover the remarkable working principle of submarines, so stay tuned with us till the end to explore the mysteries of these underwater marvels and discover how they rebel against gravity and explore the hidden depths.

So, what is a submarine? A submarine is a military machine that is patterned and designed to work underwater. Ohh wait, are we talking about a giant object containing hundreds of people, weapons, and whatnot which sinks, floats, and sails on its own wish? How is it even possible, and how can it challenge gravity? And what about the buoyant force exerted on a body to push it back?

These interesting questions lead us to our next segment, which is: how does a submarine work?

The submarine operates using Archimedes’ principle of buoyancy which states that “the upward buoyant force which is applied on a body that is submerged in a fluid, whether fully or partially, is directly proportional to the weight of the fluid it displaces”. Agh, another scientific definition that goes over the head like a bouncer. Don’t worry, I’ll explain this practically so that you can play this bouncer with a cracking pull shot for a six. Let’s imagine a scenario when you dive into a swimming pool. After a little while, water pushes you out towards the surface, and at that particular moment when you are coming upwards, you feel zero body weight. And that is exactly what Archimedes’ principle is, which says that when an object with a certain mass dips into the water, it feels the upward buoyant force which is equivalent to its body mass, and that is the reason why your body does not feel any weight when it is pushed upwards by the water. Now, it raises a question: according to this principle, a submarine should always float on the surface. Then how is it able to float, sink, and sail at will? Let’s clear this concept with the help of the Mug and Tub experiment. When we observe a bath mug placed on the surface of a tub, we notice that it floats initially. This occurs because the empty mug contains air, which is less dense than water. As a result, the mug’s overall density is lower than that of the surrounding water, allowing it to float. However, when water begins to fill the mug, its density gradually increases. Once the density of the water-filled mug surpasses that of the surrounding water, it promptly sinks down in the tub. So, coming back to submarines, the buoyancy of the submarine is controlled by ballast tanks. For the submarine to float on the surface of the water, these ballast tanks have positive buoyancy by being filled with air and having a lower density than water. Meanwhile, to immerse the submarine, the air in these ballast tanks is vented out, causing negative buoyancy and making its density greater than the surrounding water. And to keep the submarine stationary, the ballast tanks are half-filled with air and water, making the density of the submarine equal to the buoyant force of the water.

Let’s go a little deeper to understand these ballast tanks.

There are two vital parts of the ballast tank: flood ports and air vents. Flood ports are openings at the bottom-most position of the outer hull that allow water to enter and leave the tank. Air vents allow the air in the tank to escape, and seawater floods in from the flood ports. The ballast weight now added helps the submarine to dive in. When it’s needed to empty the ballast tank, air is filled in the tanks through air vents, which creates pressure on the water to exit the tank through the designed outlet. Ok, we have talked a lot about how submarines go up and down. Now, let’s move ahead and talk about the engine of submarines, which helps them to move underwater. Let’s talk about the mechanism of the propulsion system in submarines.

Propulsion System of Submarines

The first step is to choose the type of propulsion that suits the mission and specifications of the submarine. There are different types of propulsion systems, such as diesel-electric, nuclear, air-independent, and hybrid. Each has its own advantages and disadvantages in terms of efficiency, reliability, and stealth.

Diesel-Electric Propulsion: Many conventional submarines (non-nuclear) use a diesel-electric propulsion system. Diesel engines drive generators, which produce electricity to power electric motors connected to the submarine’s propellers. Diesel engines are used when the submarine is on the surface or snorkeling, allowing it to recharge its batteries. While submerged, the submarine runs on battery power.
Nuclear Propulsion: Nuclear-powered submarines use a nuclear reactor to generate heat, which is then used to produce steam to drive a turbine and generate electricity. This electricity powers the submarine’s electric motors or, in some designs, a pump-jet propulsion system. Nuclear propulsion provides virtually unlimited underwater endurance and high speed, making it suitable for long-range and fast-attack submarines.
Pump-Jet Propulsion: Many modern submarines, especially those with nuclear propulsion, use pump-jet propulsion systems. Instead of traditional propellers, pump-jets draw in water and expel it at high pressure, providing both propulsion and a reduced acoustic signature, which is important for stealth. Pump-jets are more efficient and quieter than traditional propellers.