Wind Ships Coming
The physical principle is the same one humans have used on sailing boats since eons ago: the wind hits the leading edge of the sail and splits into two flows which are redirected and travel at different speeds towards the trailing edge, causing a pressure difference that simultaneously pulls and pushes the sail and the craft forward. What has changed is the efficiency. Advanced science has doubled the amount of propulsion power per square meter of sail surface, says Marc Van Peteghem, naval architect and co-founder of VPLP Design. Together with the French engineering firm CNIM, VPLP has developed a new wing sail concept they call OceanWings, based on an existing VPLP idea.
From plane to ship
In recent years a number of attempts have been made to combine the propulsion principle of traditional sailing boats with the aerodynamic efficiency of an airplane wing with the trailing edge flap extended for starting or landing. “There is a slot between the two elements of the wing, and the air going through the slot accelerates the flow and pushes the turbulence towards the trailing edge”, explains Van Peteghem. While in the case of an airplane, the thrust created by the engine moves the craft against the air, causing the airflow to divide at the wings and generate the uplift force, the principle is reversed in the case of a sailing boat: the wind hits the sail rather than the sail being pushed against the wind. The physics is the same, however. Transferring the two-part concept of the plane wing and flap to a sailing boat results in a wing sail, which consists of two vertical, more or less symmetric, parallel “blades” or “wings” with a narrow gap between them. The gap splits and redirects the airflow again, reinforcing the aerodynamic effect and producing an additional thrust.
The concept has been the subject of various experimental designs for some time, including inflatable as well as rigid or segmented hard-shell prototypes. While significant efficiency improvements have been achieved, controlling and reefing the sail has been complicated, requiring exceptional skill and experience.
OceanWings wing sails are reliable and can be fully furled, apart from being controlled automatically. Image: VPLP Design
The OceanWings design takes a slightly different approach: each of the two straight blades has a mast of its own and consists of several horizontal segments, the “body” of each segment formed by a flexible fabric. Raising or lowering these segments along the mast allows the surface of the sail to be increased or reduced, or “reefed”, and lowering all segments to the lowermost position “furls” the sail entirely. The angle between the two parts of the sail can be adjusted as desired; each blade can rotate 360 degrees around its mast.
To avoid the complexities of wind measurement and sail handling, the designers of the Oceanwings® system have developed a fully automated, digital control concept. There is no need for a crew with special sailing knowledge. Image: VPLP Design
The second key element of the OceanWings concept is that the complications associated with finding the proper position for the given wind condition and desired direction of travel is eliminated because the entire wing sail is fully computer-controlled. All the operator needs to do is choose the heading, and the computer will position the two parts of the sail to achieve optimum thrust, adjusting the camber and twist as required. The sail has been tested successfully on VPLP yachts, including the hydrogen fuel-cell co-powered catamaran Energy Observer launched in 2017, and is commercially available. According to Marc Van Peteghem, OceanWings sails can reduce fuel consumption by 18 to 42 percent, depending on ship type, route and sail arrangement.
"It is time to transfer the technology we have developed in the yachting industry to the shipping industry. A wing sail could be installed on any ship where it is freely exposed to the wind." - Marc Van Peteghem Naval architect and co-founder of VPLP Design