ballast tank

shipbuilding

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Last updated

June 18, 2026

Quick Summary

Ballast tanks are compartments within a ship that can be filled with water or other heavy material to improve stability and control buoyancy. When a ship is light, it can be unstable in rough seas. Filling ballast tanks adds weight, lowering the hull deeper into the water and increasing the ship's inertia to better navigate waves.12

For submarines, ballast tanks are crucial for submerging and surfacing. When flooded with seawater, they increase the submarine's density, allowing it to dive. Compressed air is then used to expel the water, enabling the submarine to surface. Variable ballast tanks help maintain a precise balance between the submarine's weight and the displaced water, adjusting for changes in water density.1

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naval architecture
Ballast tanks
When a ship is running rather light with its hull relatively high out of water, it is at a disadvantage in winds and waves. It needs added inertia to help it drive through waves, added weight to put the hull farther down in…
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When a ship is running rather light with its hull relatively high out of water, it is at a disadvantage in winds and waves. It needs added inertia to help it drive through waves, added weight to put the hull farther down in…
Read More

harbours and sea works
Floating dry docks
…that involves filling the water ballast tanks along one side to induce a list that lifts those on the other side part of the way out of the water. On completion, the process can be reversed for the other side.
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…that involves filling the water ballast tanks along one side to induce a list that lifts those on the other side part of the way out of the water. On completion, the process can be reversed for the other side.
Read More