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Hybrid-sail developers envision savings windfall for ocean shipping

May 31, 2017 01:57 PM
Artist’s conceptions for the Wind Challenger Project show an 180,000-dwt Capesize bulk carrier with its hybrid sails raised and lowered.

Courtesy University of Tokyo

Artist’s conceptions for the Wind Challenger Project show an 180,000-dwt Capesize bulk carrier with its hybrid sails raised and lowered.

“It isn’t only about the cost and fuel savings,” explained Professor Yasuo Yoshimura, describing the work he is doing on alternative power systems for deep-sea ships. “We need to reduce the carbon emissions as well.”

Recent years have seen a lot of proposals for ship sails and other projects to reduce the massive fuel burn of deep-sea vessels. Few of the proposals have made it even to the initial testing stage and most are very limited in their practicality. However, when one sees shipping lines like NYK and MOL, the classification society ClassNK and Oshima Shipbuilding getting behind an idea, it deserves some attention.

While Yoshimura is also working on an air-bubble system for ship hulls to reduce friction and fuel consumption, the rigid-wing Wind Challenger Project is further along. A research team at the University of Tokyo began work in 2009 and, with support from Tadano Cranes, they developed a 164-foot hydraulic telescoping mast. The researchers envision four of the masts mounted between the hatches on a 950-by-106-foot, 52,500-dwt Panamax bulk carrier. Designs also have been developed for nine of these sails on a 984-by-164-foot, 180,000-dwt Capesize bulker.

Researchers estimate the hybrid sails could help reduce fuel consumption by 30 percent.

Courtesy University of Tokyo

Each mast supports an aerofoil-shaped sail that can be rotated to take advantage of the wind direction. The sails, built of fiberglass-reinforced carbon fiber cloth, have very specific curves on the forward and aft sides. Each sail has five 32-foot segments — 13 feet thick at the mast — that are designed to be nested, or reefed, into each other when lowered. They can be extended the length of the mast depending on wind conditions, with a maximum sail area of 10,764 square feet. The individual sails will weigh about 40 tons and the sliding mast about 60 tons. Initial cost estimates for the experimental stage are about $2 million per sail. While the hull depth and beam may not have to vary much to accommodate the sail power, it will be necessary to move the bridge and pilothouse to the bow to maintain full visibility forward.

The aerodynamic shape of the sails — they provide forward motion even when wind is striking the ship broadside — has been carefully designed and tested. A half-size model has been built and mounted on a hilltop where wind variables can be tested against varying angles of the sails. The best winds are not “fair winds” on the stern but winds coming on the beam or stern quarter that set up a powerful “push-pull” between thrust forces on the aft side and lift created by lower air pressure on the forward side. The propulsion effects can be enhanced by the influence of the multiple sails on the wind flow between them.

Professor Yasuo Yoshimura’s research at the University of Tokyo includes the Wind Challenger Project and an air-bubble system to improve the glide of ship’s hulls. The hybrid-sail initiative began at the university in 2009.

Alan Haig-Brown

Extensive meteorological study has been undertaken to identify sea routes that are best suited to the hybrid-sail and oil-powered Panamax vessel. One such route is Yokohama, Japan, to Seattle. By using satellite wind tracking, separate routes can be mapped for the passage each way. This is not unlike the wind tracking and routing used by trans-Pacific airlines where the shortest route may not be the most advantageous. Like modern airliners, the Wind Challenger ships will employ computer technology to integrate the oil-based and wind propulsion as well as to track the most favorable wind angles. With projected speeds in the 14-knot range, the ship’s hybrid propulsion system will automatically select the most effective balance of oil and wind to achieve the desired velocity. Projected savings are conservatively placed in the 30 percent range with the help of a smaller engine operated at lower speeds.

Yoshimura worked for 20 years in one of Japan’s major shipyards after graduating college as a naval architect. He then began teaching and researching at Hokkaido University, where he spent 16 years working on ideas that included developing safer designs and wind power for fishing boats. Rather than retire, he joined the team working on the Wind Challenger Project. While a fully operational ship with computer-controlled high-tech sails is still some years away, there is interest in the project in both the private and public sectors.

In the meantime, Yoshimura is moving ahead on the early stages of a system to reduce fuel consumption and emissions on a 262-by-39-foot, 2,000-dwt coastal ship. Working with a 1:36 scale model in the University of Tokyo flume tank, he is testing a design that forces bubbles under the flat-bottomed hull to reduce friction and fuel burn by about 20 percent.

Studies have shown that the most favorable winds for the sails are those that buffer the ship on the beam or stern quarter, as shown in this diagram of apparent wind and thrust.

University of Tokyo/Pat Rossi illustration

On the scale model, he has built a nearly round opening in the hull where a bulbous bow normally might be. Water from the bow flows into a precisely designed funnel-shaped passage and out under the ship some distance aft. The funnel is designed so that it will suck air through a second flume leading from an intake mounted on deck. While other bubble technologies reduce drag and fuel consumption, the energy used to pump the bubbles under the hull negates some of the advantage.

In February, Yoshimura was running a series of tests on his model while still contributing to the Wind Challenger Project. As the hybrid transition continues to evolve in shipping, it seems that Japan has a significant head start.

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