I like the idea of a crane which would be necessary to load ships with vehicles.

A crane wouldn't make much sense for a bike or skateboard though and I also suspect that it could complicate proramming.

At least RL skateboard or bike, but somehow I don't see those having locks that'd prevent people who don't have a key from sitting/standing on them.

It's all Cantr. We can make the crane neccessary if we want to

And if we want to, we could make it not necessary. I don't quite see your point.

Vehicle locks could by the way be removed from (new) skateboards if that's desired by the players.

If there would be a code for loading vehicles on board, all we need to add is a check if the crane is in the location. If not - loading impossible. Sounds simple that way.

Another way crane could work - if we use dragging for loading - crane would add his strength to every vehicle dragging action.

It doesn't need to be called crane, it could also be a ramp. Or ramp would work for small vehicles like bikes and skateboards, and crane for cars etc.