Looking like a set of bridge supports that were accidentally installed on a cargo ship, a new wind-driven system by startup CoFlow Jet promises to reduce ship fuel costs by up to 90% using stationary cylinders with no moving parts.
Between rising fuel costs and increasing government mandates requiring shipping companies to go carbon neutral by 2050, there's a strong push to increase the efficiency of cargo ships while reducing their emissions. One way of doing this is to take a page from the history books and readopt sails to harness the wind.
On the surface, that makes sense. Sails have been propelling ships all over the world for millennia and were still used for commercial transport until after the Second World War. However, there are two problems with sails that have pushed them out of the cargo market for all except the most local of niches.
First, traditional sails require huge crews. Something the size of the 921-tonne tea clipper Cutty Sark needed a crew of about 30 to handle the sails and the complex sheets and lines that controlled them. Compare that to a modern 196,000-tonne container ship that needs only 13 officers and sailors – and most of them are pushing buttons instead of hauling lines.
The second problem is that sails are completely dependent on the wind. If the wind is blowing hard enough and in the right direction, great. If it's blowing too little or too hard, or if it's blowing from the wrong quarter, that's not so great. If it's not blowing at all, you're not going anywhere.
As a result, once steam and diesel power became practical with their lower labor costs and energy on demand, sails were soon shifted to recreation and explorers.
Today, the idea of using sail is undergoing a similar renaissance as the one during the energy crisis of the 1970s, as shipping companies look at updated versions of the old technology to reduce fuel costs. However, instead of acres of canvas strung from a forest of timber masts, the new systems use kites, wind vanes made of composites or are inflatable, while some even use the hull of the ship itself as a sail.
GeCheng Zha, a professor of aerospace engineering and director of the Aerodynamics and Computational Fluid Dynamics Lab at the University of Miami College of Engineering is using an approach that is a variant of the Flettner rotors developed in the 1920s, but with a fundamental twist.
Flettner rotors are large rotating cylinders that produce aerodynamic thrust at right angles of the air passing over them. The CoFlow Jet cylinders developed by Zha don't rotate. They draw in a bit of the air from the wind blowing across and through them and then expends it at another part of the cylinder. By drawing in a small amount of air from the intake, pressurizing it using an impeller, and squirting it through the outlet, this generates a pressure imbalance and a considerable amount of thrust, which extends the full length of the cylinders.
According to Zha, this makes for a very effective wind propulsion system that can provide 100% of the needed thrust to move the ship due to the system's very high lift coefficient and drag reduction. Unlike the Flettner system, there are no rotating parts and it can deliver a fuel reduction of up to 50% in large cargo ships and 90% for small ones.
That may seem sensational, but bear in mind that any sailing ship can get a 100% reduction by setting the sails and turning off the engines entirely. Of course, this all depends on the force and direction of the wind. However, one other advantage is that the system can be retrofitted to existing vessels and the cylinders can be retracted for getting in and out of harbor.
"What’s old is new again," said Zha. "With the technological advancements of today, wind-assisted propulsion is an efficient alternative to diesel engines. And the major advantage is that it’s environmentally friendly – an effective way to decarbonize the shipping industry that’s responsible for about 3% of global greenhouse gas emissions. The shipping industry has had a tendency to resist change because diesel engines are so powerful but now, with pressure mounting, either willingly or unwillingly, it will have to change."
Source: University of Miami
