How Are Cargo Ships Powered?

Thousands of cargo ships traverse the seas, bringing with them goods, materials and much more. These behemoth vessels handle the bulk of international trade, often powered by bunker fuel which gets them from one destination to another. Read more to find out how…

SA Oil explains how cargo ships are powered

What is a Cargo Ship?

Cargo ships are the massive sea vehicles seen at ports and in harbours across the world, often laden with large, colourful containers carrying a variety of goods being imported or exported. Designed specifically to traffic goods, these ships are huge, flat and broad, spanning a length of up to 400m (the length of an Olympic running track!) and can be up to 55m wide. Mechanical beasts of burden, their powerful engines can weigh up to 2,300 tonnes, enabling a total load of up to 11,000 20-foot containers at a time. Cargo ships are often equipped with advanced computer software which limits the amount of human supervision and involvement needed, allowing for precise planning for and loading and offloading of cargo.

How Diesel Changed Propulsion Systems Used on Cargo Ships

Apart from their advanced technological systems, cargo ships can make use of a variety of propulsions systems to get from one port to another. Several factors determine the type of propulsion system used on a cargo ship, including safety standards, cost, cost effectiveness, and environmental impact, although the marine propulsion systems available today are a stark contrast to the limitations faced when cargo ships first started operating.

Prior to the invention of Rudolf Diesel’s diesel engine, steam power and the internal combustion engine, which burned petrol, gas and even gunpowder, were the most advanced modes of mechanical power at the time, used mostly in cars, locomotives and ships and boats. The diesel engine changed this, being considerably more efficient than other engines available at the time. The progression of the diesel engine continued long after Diesel’s mysterious disappearance in 1913, and today his engine model is considered one of the most efficient in the world. His invention also had a massive bearing on the course of the trading industry, including cargo ships, even though it was almost a century after the invention of the diesel engine before cargo ships began operating commercially. The first commercially successful cargo ship was the Ideal X, a converted World War II oil tanker that could carry 58 metal containers. Arguably, it was this ship that revolutionised trading and started the modern shipping industry as we know it today. 

Types of Marine Propulsion Systems Used on Cargo Ships

Far advanced from (but because of) inventions like Diesel’s, the shipping industry now makes use of many different types of propulsion systems. The most commonly used marine propulsion systems for large vessels like cargo ships are the diesel and slow speed engine variants, the latter of which makes use of bunker fuel, or heavy fuel oil.  LNG (liquified natural gas ) tankers use steam turbines, powered by massive high-pressure boilers which produce the steam to turn the turbines and power the propeller. These boilers usually make use of dual fuels; either diesel or heavy fuel oil (bunker fuel). 

What is Bunker Fuel?

Bunker fuel, also known as residual fuel oil or heavy fuel oil, is a residual fuel produced during fractional distillation of crude oil, and is commonly used in the marine industry, in boilers and furnaces, and in other combustion equipment. Heavy fuel oil (bunker fuel) is also used in many other industries, such as in mining, and even in power stations.

Alternative Energy Solutions for Cargo Ships

There are several alternative energy solutions on the market for use on cargo ships, including nuclear propulsion, LNG fuelled engines and dual engines. Nuclear power is mostly used on naval ships, although it is gaining popularity in merchant ships. This propulsion system is incredibly complex, involving a power plant, turbines, technical gearboxes and generators. Nuclear power offers energy-intensive industries numerous benefits, including a reduced usage of hydrocarbon fuels which in turn reduces carbon emissions; however, risk factors involved with this energy option make it less viable than alternatives. The use of LNG in the marine industry is also gaining popularity due to the resource’s relatively stable prices and the fact that it is currently the cleanest burning hydrocarbon fuel on the planet. However, out of these alternatives, the use of dual engines on ships, and therefore the ability to make use of dual fuels, is favoured. This is because, although a reduction in carbon emissions and environmental impact is important, using fuels like diesel or heavy fuel oil is by far the most cost-effective means of powering a ship.

Bunker Fuel and SA Oil…

The marine industry in Africa is reliant on hydrocarbon fuels like heavy foil oil (bunker fuel) to power their trade, and bring the goods people around the world need and want. Prompted by the IMO’s 2020 Low Sulphur Fuel Directive, though, and as technology advances, cargo ship engines will be adopting cleaner fuels like low sulphur fuel oil. Get in touch with us for more info on which fuel can power your operation…