HMS Upholder

How does a diesel submarine work?

​A diesel submarine, also known as a conventional submarine, operates using a combination of diesel engines and electric motors for propulsion, along with various systems for control. 

Surface Operation

When the submarine is on the surface, it relies on diesel engines for propulsion. These diesel engines are similar to those found in many surface ships and submarines.

The diesel engines burn diesel fuel to generate mechanical power. This power is used to drive the submarine’s propellers, which move the submarine forward through the water.

Submerged Operation

When the submarine needs to submerge, it shuts off the diesel engines. Diesel engines require air for combustion, which is not available, unless the submarine is running at periscope depth and has raised its snort mast.

underwater, unless it is using its snort mast, shutting off the diesel engines is necessary to prevent them from using up the limited oxygen supply inside the submarine.

Instead of the diesel engines, the submarine switches to electric motors for propulsion when submerged. These electric motors are connected to the same propellers.

The electricity required to power these electric motors comes from onboard batteries.

Battery Systems

Diesel submarines are equipped with large battery banks that store electricity generated either by the diesel engines when the submarine is on the surface or by dedicated generators.

These batteries serve multiple purposes. Firstly, they provide power to the electric motors for propulsion while the submarine is submerged. Secondly, they are used to supply electricity to various onboard systems and equipment.

The batteries are rechargeable and are continuously replenished when the diesel engines are running on the surface.

Depth Control Systems

To control its depth when submerged, the submarine uses a combination of ballast tanks and variable buoyancy systems.

Ballast tanks can be flooded with seawater or pumped dry of seawater to adjust the submarine’s overall density. Filling the tanks with water makes the submarine heavier and causes it to descend, while emptying the tanks makes it lighter and causes it to rise.

The submarine’s crew uses these systems, along with the hydroplanes (small wing-like surfaces on the hull), to maintain the desired depth.

Directional Control Systems

To control the direction in which the submarine is traveling, it uses control surfaces such as rudders and diving planes. These surfaces can be adjusted to change the direction of the water flow around the submarine, allowing it to turn and maneuver.
The crew can adjust these surfaces as needed to steer the submarine on its desired course.

In summary, a diesel submarine relies on a combination of diesel engines for surface operation, electric motors for submerged operation, and a sophisticated system of batteries, ballast tanks, and control surfaces to provide propulsion, depth control, and directional control.

This combination of technologies allows the submarine to operate effectively both on the surface and beneath the water, making it a versatile and capable vessel.