Yamahas Dual Thrust propeller is the answer for heavy loads such as sailboats and pontoons.
They are standard on the High Thrust T9.9, and optional on other mid-range engines using the K series (4.25 inch) gearcase. They are excellent for use on Yamaha High Thrust models (T50 and T60), as well as the F70, particularly on pontoon applications.
Dual Thrust propellers feature a large diameter and blade surface area, a low pitch and rake angle, and a patented oversized center tube which re-directs the exhaust away from the blades when in reverse. This helps the prop bite clean water, resulting in awesome thrust and control regardless of direction.