I'm looking for some input on the design of a lifting device. The design is required to accurately lower lower a load of 400 metric tonnes through a height of 50m, return to the top of it's travel and lower the next load and so on. I'm currently thinking along the lines of a two-pronged tower arrangement with guide rails located inside of the tower. The power is supplied by heavy duty anchor chain on each inside side and a windlass-type pulley system at top and bottom. Does anyone have any suggestions as to next steps to take?