How to calculate crane capacity

I'm guessing that you have a homework problem in statics or physics where they give you a diagram detailing things like the angle of the cables, and the mass of the crane and it's track width - right? Well, in general the lifting capacity will be limited either by the breaking strength of the cables or the turning moment on the crane causing it to topple over. Consider the moments acting around the crane support that is closest to the weight - this support might be the track. The turning moment caused by the weight is the weight times the horizontal distance from the support to the weight. This must be countered by the moment due to the mass of the crane - the crane mass times the horizontal distace from the track to the center of gravity (probably half the width of the crane). If these two moments are equal, then the crane is just about to topple over, so that's the maximum weight.

On the other jhand, if this is a real engineering question, and you're inerested in undrstanding how crane manufacturer's establish design criteria for real cranes, that's a ompletely different problem than just the idealized analysis I outlined above.

In the First Class Boatswain Manual there is a formula for figuring the lifting capacity for booms. I would like to get it.

In the first class boatswain mate manual there is a formula for the lifting capacity of booms. What is it?