Abstract: A gear-based airboat transmission is provided for driving a pair of coaxial, counter-rotating propellers. The transmission includes a fore output gear rotatably affixable within a housing and affixable to the inner shaft for rotating the outer propeller. An aft output gear is rotatably affixable within the housing and is affixable to the outer shaft coaxial with the inner shaft for rotating the inner propeller opposite the outer. The aft output gear is generally coaxial with the fore output gear. An intermediate gear shaft has a fore end and an aft end, and both ends are opposedly and rotatably affixable within the housing. This bracing confers additional stability to the transmission, conferring longer life and decreased vibration. An intermediate gear is mounted thereon, and is positioned in driving relation to the fore output gear. A drive gear is rotatably affixable within the housing and is affixed for corotation with a drive shaft.