How do large ships survive being tossed and heaved by waves on a rough open sea without breaking apart?
In: Engineering
These ships survive because of their design and different systems on the ship that can work together to keep the ship stabilized.
The most common system onboard to stabilize the ships are their ballast tanks. These tanks generally hold seawater to create weight.
Because of this weight, the ship has a lower point of gravity thus giving it more stability.
Imagine a Formula 1 car. It is designed for high speed. One of the reasons it can go that fast is because it is build as low to the ground as possible. Because the F1 car is lower to the ground, it has a lot more stability to handle these high speeds. The stability comes from a lower point of gravity.
The placement and dimensions of these tanks are calculated before the ship is build. They come in many different shapes and sizes but generally have a squarish or rectangular shape.
The seawater is pumped into, or out of, the tank via pumps. These pumps are either operated by crew onboard (most common) with the use of Alarm and control systems, or by manual control on a switchboard. Depending on the design of the piping system that is installed they generally come with one or two valves on smaller ships but can have more depending on the use case of the ship and the tank.
The amount of seawater in the tank is managed by trained crew on board with the piping system. There is more to it than just filling the tanks. You have to take into account your current cargo on the ship as well as different types of liquids in different tanks located throughout the ship. For example: The more weight on the left side of the ship facing forward means you will have a bias towards the portside of the ship. The more weight on the right side facing forwards means you will have a bias towards the starboard side of the ship.
Other than the ballast system there will be electrical systems that will help stabilizing the ship. These systems can help with planning the route of the ship so they don’t catch bad weather or heavy winds. They can also take over steering to stabilize the ship. The captain will be in charge of this and will judge whether or not it’s safe to go through storms and what route to take.
All of the systems are driven by an onboard power plant which will generate power for the ship. If these power plants fail then the aforementioned systems don’t work.
The captain also has to go to manual steering when there’s no power. You can imagine on a large ship that the rudders will be driven by large electrical motors. In the case these don’t have power, you won’t be able to rotate the rudder. With all of these systems having failed, the chance of capsizing or splitting will increase tremendously.
Of course there is backup power after the power plant fails. This is only for a certain amount of time. The minimum amount of time you’ll have is based on regulation for different components on your ship.
I am a project engineer for a company that is specialized in Alarm and Control systems on different sized ships. For us the general minimum norm is 30 minutes after the power plant fails. This can differ for electrical motors on a rudder or pumps on a ship.
If you have any other questions about a ship or about it’s control and logic. Please reply or send me a DM!
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