During the summer of 2016 a couple of older articles will be republished. This article was first published in 2014.

Ship transport is energy efficient, but it is also a significant source of emissions because of the globalized world huge transportation needs. In large measure, these vessels are powered with high-sulphur fossil fuels. New technologies have made sail propulsion possibly competitive – at least as a component of a highly automated hybrid system.

Ship transport of containers is the backbone of world trade; 90% of all goods moved by any of the many thousands of freight and container ships are constantly at sea. Almost exclusively, they are powered by fossil fuels, and carbon dioxide emissions are equivalent to those from a larger country.

Trade routes in the global shipping industry ( T.Hengl, http://www.nceas.ucsb.edu/globalmarine/impacts)

Trade routes in the global shipping industry ( T.Hengl, http://www.nceas.ucsb.edu/globalmarine/impacts)

A quarter of the world’s energy consumption comes from transportation. Although maritime transport is relatively very energy efficient, efficiency could be improved which would have a major impact on emissions. The fact that the oil used is normally the cheap bunker fuel – viscous distillation residue with high sulphur content – means that shipping traffic and fuel combustion causes significant sulphur and nitrogen oxide emissions.

Lower speeds saves fuel and emissions

In 2008, oil prices reached record highs. Shipping companies, with the Danish Maersk Group in the lead, responded by letting their ships go at reduced speeds – below 18 knots instead of around 25. The concept is called “slow steaming,” with the intention to reduce fuel consumption and greenhouse gas emissions.

When the speed is reduced 10%, emissions can be reduced by 30%. Parallel to this, there is a trend towards larger container ships: a hundred vessels in the global fleet have a capacity of over 10,000 containers, and the largest, Maersk’s newly launched Triple- E, takes 18,000 in the same load. This is a factor that reduces fuel consumption and emissions per container.

Maersk Triple- E

Maersk Triple- E

Same speed with sails

Slow steaming has led to transport speeds are now comparable with fast sailing vessels. During the sailing ships golden age, before coal-fired steamships and later oil-driven motor vessels took over the oceans, they could fully-rigged do speeds of 16 knots. Should we not revert to sail operation and eliminate emissions?

Too true. That sailing ships were abandoned had to due to more factors than just speed. They were at the mercy of, and dependent on the wind. They had limited cargo space, and deck space could not be used to load the volumes of modern cargo ships, which standardized and streamlined port procedures and made world trade to explode. The handling of the rigging and sails were too laborious and sailing ships needed a much larger crew – the modern container ship Emma Maersk can get by with half the crew as the classic clipper Cutty Sark, but takes nearly a hundred times as much cargo.

But there is something, however, in the idea. On the horizon a glimpse promising new sail designs, more efficient than yesterday’s, which in the future may come to play an increasingly important role. Maybe not as the only method of propulsion, but definitely as an energy saving support operation – hybrid solutions that have both motor and sail will of course not be at the mercy of the wind’s discretion.

Technical solutions make sails manageable

A foretaste of what the future sails may look like, we can go to companies like Kite Ships and SkySails, each of which develops various forms of large, free-flying sails without masts, which are anchored at the bow of the ship with long, adjustable ropes.

They are hoisted and reefed automatically and are controlled and positioned by wind situation by means of an electronic control system. The automation does not require additional crew and the lack of a fixed rig does not disturb the ship in port. The sail is deployed several hundred meters high, and draws advantage of winds that are smoother and stronger than at sea level.

SkySails smaller sails have already been installed on a number of vessels, where it has reduced fuel consumption by 10-35 %. In the future, 1,600 sqm sails are envisioned to halve fuel consumption.

There may also be a niche in the future of sailing ships with a more traditional look but with a higher degree of automation.British B9 develops a three-masted cargo ship with square sails but without rigging. The high carbon masts rotate freely to adjust to the wind direction, the sail folds automatically into the masts when reefed, and all controls are done by keystrokes from the bridge. Another possible support control system utilizing wind is known as Flettner rotors – tall, vertical, rotating cylinders. The rotation, combined with the wind creates a pressure difference that drives the ship forward.

Norska Vindskip has another vision, appealing in its simplicity. The designers intend to remove the sails and rigging altogether, but believe they can achieve 80 percent emission reductions by an aerodynamic vessel design where the hull itself acts as a sail.The vessel is designed as a hybrid, which first accelerates on gas and then balances between wind and supportive gas to maintain a constant speed. When the ship comes up to speed it encounters a backwind. Although this apparent wind gives effect on the hull’s symmetrical aerodynamic profile, and generates traction even when there is no wind – there is a contributing factor to large emissions reductions. The concept includes a computerized navigation system using GPS and weather data to adjust the route continuously, to constantly give the ship the most optimal angle to the wind as possible. It is thought then to hold 18 knots in average and large portions of the time is powered exclusively by wind.

When sailors with the mission of transporting grain to ancient Rome refused to go to sea in a storm, they were admonished by the statesman Pompey with the words: “Navigare necesse est, vivere non est necesse,” (to sail is necessary, to live is not necessary). The harsh wording reflects a state of affairs that prevailed in ancient times and still prevails in today ‘s globalized world. Transport by sea is essential to the world economy, as we know it works. So it will almost certainly look like in the future – but the individual cargo vessels will look different. The ancient idea of sails carried by the wind still pops up in many minds, with one thing in common: they are less labour intensive, more automated and easier to control, thanks to technological advances. Future sails and similar structures can utilize wind as a clean and cheap source of energy as a complement to other methods of operation, and contribute to reducing the vessel’s fossil fuel consumption and emissions.

This article was published in February 2014