Marine gear drives are the transmissions carrying power to the
propeller on a marine drive. They generally provide single forward and
reverse speeds and use friction-type shifting clutches. In the beginning of 1990, Percy Day in America designed and built the world's first commercial scale hobbers for herringbone gears. The Power Plant Company was soon selling speed reducers to industrialists, hoist gears to South African gold mines and gear drives to ship builders. In those days electric motors were becoming the prime movers in manufacturing. With the motors, steam driven turbines were replacing steam engines in ocean-going ships. The higher turbine speeds made reduction gears a necessity, and in about 1909 Percy Day built the first marine gear drive ever installed, a 1000 horsepower unit. Universal marine gear drive has adapters that accept any prop shaft that has an outside stern tube diameter of 6mm, 8mm, or 10mm. The drive accepts 1/8" output shaft motors. Gear reductions are 2.5:1 or 2:1. The output gear accepts 4mm prop shafts.