How to simulate the crane grab the bulk cargo?

I am puzzled about one problem that how to simulate the crane grab the bulk cargo. In this progress, the bulk cargo can be simulated in the ship hold and can be grabed by the crane. Furthermore, the bulk cargo in the hold can subside. In the grab of the crane, there is some bulk cargo. I have to consider the realtime characteristic of this entire progress. The crane and grab now can operate flexiblely. But the grabbing progress is killing me and I am longing for your help. Thanks a lot.