Abstract
While the old yacht used only the drag of the wind, the recent yacht uses the lift force generated by both the sail (wing in the air) and the keel-bulb (wing in the water). When the ship heels, the keel-bulb makes the restoration moment and stabilize it. However, the trailing vortex generated from around the keel bulb is a problem. To solve this problem, it is necessary to know about the trailing vortex. In the wind tunnel experiment using particle image velocimetry (PIV), the flow around the keel-bulb is visualized. As a result, when given the angle of attack to the keel-bulb, the bulb rear end is confirmed two vortex larger in behind it, not only identified a single vortex.
