A new crane design, labeled "SpiderCrane", is proposed to handle fast load displacements. Its main particularity is the absence of heavy mobile components. The system beeing underactuated, its control is challenging. Hence, as a step towards easier and more efficient control, this paper proposes a dynamic model and investigates the two control-relevant properties of flatness and observability. SpiderCrane is shown to be flat with respect to certain outputs and observable from the motors positions.