Why is the output shaft on gear reduction motor larger than the shaft of a standard motor?

Question

Why is the output shaft on gear reduction motor larger than the shaft of a standard motor?

Answer 1

For increased redundant reliability. The shaft must handle the resistance of the marine gear box without twisting or snapping. Because of it's ratios, an automotive tranny doesn't offer the same resistance to input.

Answer 2

a simple explanation is: when you reduce the final drive ratio, you multiply the torque by the same ratio. So if you have a engine that has 700 ft lbs of torque at the crank/flywheel and run it threw a 3 to 1 gear reduction you now have  2100 ft lbs on the output side  (give or take a few because of internal friction) So you now have to use a shaft that can handle that torque load.

           It works the same way in the automotive industry---most people snap u-joints  and twist axles in their lowest gear. Why, on modern diesels industrial trucks the computer for the engine can be set-up to limit torque in relation to what the final gear ratio is verses the max torque the drive train can handle. known at "torque limiting"