We have invented a new power-saving device for ship drag reduction using microbubbles in order to reduce CO2 emissions from ships. The new device, which consists of angled hydrofoils with air introducers, has been installed on a coaster and helps achieving ～10% net power saving. This device utilizes a low-pressure region produced above the hydrofoil as the ship moves forward, which drives atmospheric air into the water. Emissions can be reduced by about 87 million CO2 ton/year if international shipping uses this new device, with 10% net-power reduction. We present the principal and optimization of this device on the basis of laboratory experiments on hydrofoils moving close to a free surface. In particular, we discuss free surface deformation and entrainment process using hydrofoils.
