What characterizes a frame derrick?

A frame derrick is characterized by the boom being hinged from a cross member that connects two vertical uprights. This design allows for the boom to have a range of motion to facilitate lifting and lowering loads, providing a versatile and stable structure. The hinging mechanism at the cross member helps distribute the stresses effectively and allows the crane to handle various lifting tasks.

The other characteristics mentioned do not accurately define a frame derrick. For instance, if the boom is fixed at the base without any movement, it would not function as a derrick; instead, it would be a stationary structure, limiting its operational capabilities. Similarly, a boom without support from side members suggests a lack of stability and would not conform to the design principles of a frame derrick, which relies on structural integrity provided by the uprights. Lastly, limiting the derrick's design to be suitable only for heavy-duty lifts does not reflect the operational flexibility that frame derricks typically offer. They can be utilized for a variety of lifting tasks, making them useful in many situations beyond just heavy loads.