The century-old ship sail technology finally catching on

It must have been a strange sight when a cargo ship equipped with two large rotating turrets passed under the Forth Bridge a hundred years ago.

Experimental sail technology on the rotary ship Buckau was first demonstrated in 1925 while transporting timber from Danzig (now Gdansk, Poland) to the Scottish port of Grangemouth.

Rotating towers were designed to use wind as a way to save fuel, but it didn't catch on for about 90 years.

Flettner's innovative rotors are now used on at least 35 commercial cargo ships to improve fuel efficiency and reduce their climate impact.

The original ship was modified to include tall rotating turrets driven by engines to save money on fuel.

Experts say the relatively low cost of fossil fuels such as diesel meant the shipping lines of the 1920s were unlikely to recoup the investment required to install them.

The Great Depression of 1929 was the final nail in the coffin of this project: shipowners canceled orders.

But modern decarbonization targets mean that technologies that can improve fuel efficiency, such as this, are increasingly valued in the maritime sector.

The technology, known as Flettner rotors, was developed by aeronautical engineers led by German inventor Anton Flettner.

The towers are driven by engines that effectively redirect the wind to create forward thrust.

It's called the Magnus effect, and it's the same principle that causes a spinning soccer ball to curve in the air, especially when kicked by David Beckham.

Operators say this can cut fuel costs by up to 20%, as well as reduce planet-warming greenhouse gas emissions from burning diesel.

Modern rotors are even more efficient than the rotors on Bukau in 1925 because they are made from lighter composite materials such as carbon fiber.

Professor Mehmet Atlar, a fluid dynamics expert at the University of Strathclyde, said there was a lot of initial interest in the project and the order book began to grow.

A larger ship called the Barbara was launched and six more were awaiting construction.

But by the end of the 1920s, these orders were canceled and the project concept was shelved.

He said: “In my opinion, this is nothing new.

“Need is the most important thing. There is a need now, so the Flettner rotor is back.”

He said lighter materials combined with more efficient motors to drive the rotors meant it was much more efficient than it was a century ago.

Finnish company Norsepower revived the design when it began studying fuel efficiency systems for ships more than a decade ago.

Since then, the company has built 35 sails, mostly upgrades, and has an order for 48 more.

The company said some ships are even being built “rotor-ready.”

CEO Heikki Pontynen said: “I would say this will become very commonplace.

“We see the market growing and developing rapidly.”

He added that lighter materials are important.

But Mr Pontynen said using artificial intelligence to control the placement of the “sails” against the direction of the wind made it most effective.

He also said the Flettner rotor is a “truly sustainable solution” for decarbonising shipping.

This technology can be installed on any ship as long as there is enough space on deck.

This makes it ideal for cargo carriers and tankers.

However, Mr Pöntynen added that it would be difficult to install rotors on container ships that use all the available space.