Yamaha
propellers are designed with a sophisticated CAD/CAM computer system and
extensively tested to match the Yamaha engine's power characteristics. Although
aluminium is the lowest cost option for most engines Yamaha aluminium
propellers provide better performance than other aluminium propellers because
of their precise matching to Yamaha engines. The light weight and lower cost
also makes aluminium propellers an excellent choice as a spare propeller in
case striking an underwater object accidentally damages the primary propeller.
(Unsure? - just email or call quoting the horsepower, model / serial
number for your engine)