A marine transmission with a 1.5 to 1 ratio is often called a reduction gear, because that's what it does - it REDUCES the speed of the prop by 50% and increases torque by same amount, allowing you to turn a larger diameter prop. Big slow turning props are generally more efficient and produce more thrust, except for light, very high speed (over 50 mph) boats. The Suzuki 4-stroke O/B's put an extra gear between crank and driveshaft to get more gear reduction and turn a bigger prop without increasing size of the bullet in lower unit.
Years ago British Seagull made a 5 hp outboard for use on sailboats. It spun a 5-bladed prop that looked like a windmill, about 10" diameter with a hub that must have been about 5" in diameter; must have had about 5:1 reduction gear in it. My neighbor used one on the dinghy for his 42' Wheeler sedan cruiser, which displaced about 20 tons. He could TOW that big Wheeler with that old Seagull!!
