An anchor winch. A steering mechanism. The advantage from C to D is 3 to 1. The sprocket wheel to the far left, on the same shaft with D, is called a wildcat. The anchor chain is drawn up over this.
Every second link is caught and held by the protruding teeth of the wildcat.
The overall mechanical advantage of the winch is 4 x 3, or 12 to 1. This pinion causes the internal spur gear to turn. Notice that this arrangement has a large mechanical advantage. When the wheel turns full to the right, one rack moves downward and the other moves upward to the position of the racks. Attached to the bottom of the racks are two hydraulic pistons that control the steering of the ship.