http://www.yamaha-motor.com/outboard/accessories/acscitemdetail/5/250/1113/8468/all/1/4047/0/detail.aspxSpecially designed for sailboats and other displacement craft, Yamaha's patented Dual Thrust propellers are built to handle the job of pushing heavy loads through water. The hub is carefully designed to redirect exhaust flow away from blades, so Dual Thrust models cut through "clean water" for higher efficiency and better acceleration. Thrust is improved up to 70% in reverse and 10% in forward.