This paper presents a technique of synthesis of the boom system with a predetermined path of the cargo on the ropes at changing span distance. A mathematical model has been developed that allows performing geometric, kinematic and force analysis of the boom device. In the part of force analysis, a system of loads is designed, fully taking into account all their directions and combinations. This model is fully parameterized and is suitable for a wide range of cranes. Output data of such a model are sufficient for designing a hoisting machine as a whole and its elements. The law of motion of the control element of the mechanism for departure change is obtained, under which the load moves uniformly. Three variants of the boom device scheme and two variants of the modification of the departure mechanism are considered. The capacities of the two variants of the change in the departure mechanism are determined, which makes it possible to analyze the variants considered.