Shape and size are the basic characteristics of macroscopic, classical systems, and as such represent a special challenge within the fundamental problem of "transition from quantum to classical", but also the problem of quantum measurement. Propeller-shaped molecules are excellent candidates for analyzing the effects of size and shape because of the linear dependence of both the moment of inertia and the damping factor on the number of propeller blades. Also, such research can be useful for their practical application within molecular machines technology. The obtained results indicate a very complex dependence of dynamic stability on the size of the system, as well as some unexpected characteristics of the time evolution of standard deviations in some cases. The new method called "the quantum first passage time" also led to unexpected conclusions, just like the analysis of the role of decoherence in the transition from quantum to classical behavior.