Purpose of Gearbox in Ships

The function of gearbox in the ship:

- convert high speed, low torque rotation of prime mover (gas turbine, steam engine, diesel engine...)
into
low speed, high torque rotation for use by the shaft and propeller

Why lower speed has higher torque?

- torque is the twisting force that causes rotation

TORQUE = FORCE x DISTANCE

- the greater the distance, the greater the torque
- the greater the diameter of the gear, the greater the torque
- the greater the torque, the more power for lifting, moving or towing heavy loads of the ship

SPEED IS INVERSELY PROPORTIONAL TO DIAMETER OF GEAR

- the smaller the gear, the faster it turns
- the bigger the diameter of the gear, the slower it rotates

but from the torque equation:

- the bigger the diameter of the gear, the larger is the torque

therefore:

LOW SPEED HAS HIGH TORQUE