Macfa1,
When buying any crane, the first thing you should prepare is a hook map. That is, determine how much weight you will lift at what radius from the center of boom rotation, and how often each weight will be lifted. What you will probably find is that 80% of your lifts will be at 10 Tons...
It sounds like you have what the crane guys call a pillar jib crane. That is, a vertical support capped with a rotating horizontal beam that supports a load. The overturning moment is, conservatively, the total of horizontal beam weight, the weight of any load supporting hoist or harware, and...