How Do Large Ships Float?

Large ships command the seas, are built to withstand extremely challenging weather conditions in stormy waters, and can carry thousands of tonnes at a time. However, the concept of a gigantic ship floating on water can only be explained by science.

As a leading supplier of marine products in the UK, we are interested in how these magnificent vessels work. From how big ships are made to how they float, we need to know this to supply their operators with only the best materials to help them carry out their work. So, today we explore the principles of science and learn about how these almighty ships can float on the water

What Contributes to a Ship Floating?

No one factor helps a ship float, but a combination of elements all work together to ensure that the ship stays level. For example, a large cargo ship alone measures, on average, 1400ft long and can weigh an almighty 220,000 tonnes, varying on what the vessel is transporting. Yet, with all this weight, it still successfully crosses the oceans with ease.

The Principle of Buoyancy

The principle of buoyancy was discovered by Ancient Greek mathematician Archimedes, who found that an object’s ability to float relies on a gravitational force being lower than the buoyancy force.

Essentially, the weight and distribution of the weight contribute to the overall downward force the object produces. There are a few key aspects to understand.

Density is the weight and distribution of weight. For example, a golf ball is much smaller than a tennis ball. However, the inside of a tennis ball is hollow, which allows the ball to be much lighter. On the other hand, a golf ball is solid, which means it is much denser than a tennis ball. However, a football, on average, weighs much more than a golf ball but will still float, much like a tennis ball. This is because the weight is spread over a more extensive surface area, which means a football is less dense than a golf ball.

Using the density of an item and the density of the liquid it is submerged in, you will be able to calculate if it will have the ability to float. So keeping with the idea of the football, if it were to land in a small puddle, it would still touch the ground because the density of the water is not enough to push against the football’s weight and the gravitational pull. However, if it landed in a pond, the football would most likely float as there is a greater mass and density below the ball to overpower the weight and gravitational pull. This is the basic idea of Archimedes’ principle: to float, the object’s density and gravitational force must be equal to or less than the density of the liquid.

Designs of a Ship

The design of a ship is an essential factor in its ability to float. As mentioned above, the density of the vessel is critical for its success in sailing on the water. A ship designer will spend months with a team of expert engineers using calculations and measurements and assessing suitable materials, allowing the ship to become as buoyant as possible. This will include calculating the weight distribution, and in the case of cargo ships addressing additional weight it will carry. Over the years, many cargo ships have sunk due to a miscalculation in addressing the weight and distribution. Minor errors in these calculations can have devastating effects, putting lives at risk.

A ship’s hull is possibly the most significant aspect that must be considered. The hull will consist of hollow shells of air which will help reduce the density of the ship and satisfy the laws of buoyancy to allow it to float successfully. Although many ships are made from steel, more vessels choose aluminium for their design. Aluminium is a very lightweight metal that offers the best solution to ships at sea with its anti-rust properties whilst still offering strength.

Controlling the Onboard Cargo

As weight distribution contributes to the ability to float successfully, it must be monitored. Although the ship may be designed to carry significant weight, too much will cause the ship to have a greater downward force than the buoyancy force and will cause the ship to flood. But how do you weigh a ship in the water to ensure it’s not overloaded?

This is where Archimedes’ theory of displacement comes into force. Displacement is the volume of an object replacing the liquid it’s submerged into. The more displacement of water due to a ship’s weight, the further it will dip into the water, reducing the buoyancy force against the vessel to keep it afloat. Keeping control of the weight of a ship means limiting what is onboard, including the crew, equipment and any cargo.

Markings measure this on the ship’s side, known as the Plimsoll Line. Every ship will have lines on the hull, which signifies its displacement within the water. They offer various safety levels where the vessel can still sail before becoming dangerously unstable. As the weight increases, the ship will submerge more into the water. By checking the markings, you can tell how much room is left on the ship for more cargo. These markings are determined in the design and will have been tested through many days of trials and calculations.

Keeping Ships Maintained

The most important element of keeping a ship sailing is ensuring it remains watertight. A poorly maintained ship will subject it to the risk of flooding at sea, and any excess water onboard will alter the ship’s weight and cause it to sink. In addition, the build-up of contamination within the engines can cause them to cease, leaving even the most impressive vessel stranded.

At Offshore Supply, we provide a range of solutions to help maintain the entire vessel in perfect condition. We offer Unitor marine chemicals to help keep engines running well and Nalfleet marine chemicals, which can offer protection against seawater scale deposition to prevent engine equipment deterioration. All our products can be viewed online for easy ordering before your next maritime adventure.