In the middle of the twentieth century, steam power began to give way to diesel power. Diesel engines are smaller, cleaner, far more efficient, and need fewer crew to operate them. Steam had almost completely disappeared by the 1980s. As air travel became convenient and cheap in the 1960s, passengers stopped travelling by sea and the age of the liner came to an end. But as cruise holidays became popular in the 1980s, construction of new, giant cruise liners began.

Propulsion

Most ships have a diesel engine housed low in the hull, which drives a screw propeller under the stern via a shaft. The propeller blades are large and curved. As they turn, the water around them is sucked in and pushed backwards. This drives the boat forwards. A rudder at the stern steers the ship. Large ships also have small, electrically-powered propellers called thrusters for manoeuvring accurately in port.

Electric propulsion

An electric boat is driven by electric motors powered by either on-board battery packs or solar panels. Ships and boats using hybrid power (combining internal combustion engines with an electric propulsion system) were adopted in the 21st century, for example, by some cruise ships and bulk carriers (see below). The Kochi Water Metro in Kerala, India, which opened in 2023, operates a fleet of hybrid electric ferries.
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Some modern ferries now run on fully electric power. The extra weight of the batteries increases the power needed to move the vessel through the water. Use a hydrofoil design solves this problem. The underwater “wings” lift the hull above the surface of the water as the boat picks up speed, significantly reducing drag. The greater efficiency allows the boats to carry smaller battery packs, reducing both weight and cost.

Wind propulsion

On some cargo ships, sails are being re-introduced in order to harness the power of the wind—just as with sailing ships of past centuries. "Wind-assist technologies" aim to reduce fuel consumption and reduce carbon emissions. Launched in 2022, the French freighter ship Canopée became the first sail-assisted container ship. Manufacturers are also experimenting with giant rigid sails made of the same material as wind turbine blades.

Ships are controlled from a room high up near the bow, called a bridge. From here, the crew navigate from place to place, using engine and steering controls, and keeping track of their position using nautical charts, satellite navigation systems, lighthouses and buoys. Radar helps to avoid collisions at night or in fog, and sonar warns of shallow water under the ship.

Modern ships and boats can be categorized by the the jobs they do. Merchant ships include cruise liners, ferries, cargo ships and utility ships, such as dredgers and tugs. Military ships include warships and support ships, called auxiliaries. There are also numerous different types of fishing boat and leisure craft, from luxury yachts to sailing dinghies. Small cargoes are carried in standard-sized metal boxes called containers on container ships. Cargoes such as ores, coal and grain are carried by bulk carriers. Oil and other liquids are carried by tankers.

Container ships, or “box ships”, are cargo ships that carry their load in lorry-size containers, reusable steel boxes can be moved from ship to lorry without unloading or reloading their contents. To avoid wasted space, the containers are packed on the ship as tightly together as possible. Loading and unloading of container ships can be done only at ports, called container terminals, where there are special cranes. Most manufactured goods are transported from port to port by container ships.
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The Norwegian container ship Yara Birkeland, the first autonomous (driverless) ship in the world. entered service in April 2022. Instead of being driven by diesel engines, the usual form of propulsion for other container ships, it will be propelled by electric motors powered by batteries. This will help reduce nitrogen oxides and carbon dioxide emissions that contribute to pollution and global warming.

At 248,663 gross tonnage (GT), Icon of the Seas, built for Royal Caribbean International, is the largest cruise ship in the world. She entered service on 27th January 2024, making her maiden voyage out of the port of Miami, Florida. Longer than the Eiffel Tower is tall, the ship has a crew of 2350 and can host 7600 passengers at maximum capacity. It has 20 decks with seven swimming pools and six water slides. The company claims the ship has the tallest waterfall (17 metres or 55 feet high), the tallest waterslide and the largest waterpark (called "Thrill Island") of any cruise ship.

Oil tanker

Oil tankers are the largest forms of transport in the world. They are specially designed to be very strong so they do not break on waves. But they can still break up if blown ashore. A tanker captain must navigate carefully since he cannot bring the ship to a stop in less than 6 kilometres (4 miles).

Aircraft carrier

Aircraft carriers have a flat main deck, called a flight deck, that forms a runway where aircraft take off and land. Aircraft hangars are on a lower deck. The nuclear-powered Nimitz-class aircraft carriers are the world’s largest carriers. They have a flight deck more than 300 metres (1000 feet) long and provide an operations base for nearly 100 attack aircraft. Carriers have a ship's crew of up to 3000 people.