What you are trying to think of is a Ratcheting Winch.
A winch itself is very simple, defined as "A stationary motor-driven or hand-powered machine used for hoisting or hauling, having a drum around which is wound a rope or chain attached to the load being moved."
In our case, a Stationary motor-driven machine used for hoisting, having a drum which is wound a rope or chain attached to the load being moved.
A very useful site for information on winches (and a few other things) is:
http://pergatory.mit.edu/2.007/hando...c.html#winches
It also has an excel file for calculating data about the winch using real values from the motor.
A ratcheting winch however is very slightly different. It has something to ratchet along the gears
Note the shape of the ratcheting gear. When turning clockwise, the gear pictured will lock into the two pieces that ratchet along the gear. when turning counter-clockwise, the two pieces will "jump" to the next tooth. This is a means for safety and preventing slipping.
The effect of this can however be replicated without a ratcheting gear. There is more than one way to lock a gear box.