This is an accessory to the "EMMA - a Maersk ship" by vandragon_de. https://www.thingiverse.com/thing:3142367
The crane has two functions, one for raising and lowering the container gripper, the other for sliding the trolly along the crane arm. If you mount the wires correct, these functions work independently.
There are two versions of the gripper, one that fits the original containers and one with 4 holes in it. The one with the holes can be used if you want a very compact version, use it as a template and drill coresponding holes in the containers. Then put 4pcs M2 screws in the gripper that extends a couple of mm below the gripper. This way the gripper with the screws can be pushed on-top of the containers without the need for anything to reach the sides.
Note: In order for the cable line not to slip on the wheels, you need to have many turns around the wheels. You can also increase the friction by making small cuts to the surface in the grooves with something sharp, just to make the surface less even. Maybe a very rough sand paper would work as well.