⚓ Ships and navigation

For thousands of years, sailors used the position of the sun, stars, and a compass to figure out roughly which direction they were heading, carefully calculating their position using speed and time travelled. Today, most ships use satellite navigation systems, the same basic idea as the GPS in a phone, which can pinpoint a ship's exact location anywhere on the entire ocean within just a few metres. Ships also use radar, which bounces radio waves off nearby objects, to detect other ships, coastlines, or storms, even in thick fog or complete darkness when nothing can be seen by eye.

A container ship carries goods packed inside thousands of identical metal boxes, called containers, which can be lifted directly onto trucks or trains without ever having to unpack and repack the goods inside. Using the exact same size and shape of container everywhere in the world means cranes, ships, trucks, and trains can all be built to handle them identically, making loading and unloading remarkably fast and efficient. A single large container ship can carry an enormous number of these containers stacked many layers high, both above and below deck, carrying goods for thousands of different businesses at once.

A canal lock is a section of waterway with gates at both ends, built to raise or lower ships between two stretches of water that sit at different heights. A ship enters the lock, the gates close behind it, and water is either let in or drained out until the water level inside matches the water level on the other side. Once the water levels match exactly, the far gate opens safely, and the ship simply floats out at its new, adjusted height, having climbed or descended without ever needing to be lifted mechanically.

Sonar works by sending out a burst of sound underwater, then carefully listening for the echo that bounces back after hitting something solid, like the seafloor, a rock, or another submerged object. By measuring exactly how long that echo takes to return, a computer can calculate precisely how far away the object is, since sound always travels at a known, steady speed through water. This lets ships and submarines effectively "see" underwater using sound instead of light, which is essential since light does not travel far at all in deep, dark ocean water.