Technology
The boat lift overcomes a normal water level difference of 16 metres, however, changing water levels on the Elbe causes this to vary between 11 and 18 metres. The trough moves between levels in 3 minutes. A boat can pass through the lift in 20 minutes. Approximately 70 ships with a maximum displacement of 1,000 tonnes pass through the lift daily. The dimensions of the caisson are 85 x 12.2 x 2.5 meters.
The Rothensee boat lift utilizes floats in float chambers in a similar manner to that at Henrichenburg. In this case only two float chambers were needed. The lift follows the patented plans of Rudolf Mussaeus. The trough is 85 metres long and 12.2 metres wide and is supported on two 36 metre long 10 metre in diameter cylindrical floats submerged in two 60 metre deep float chambers. The floats are internally sub-divided into three separate chambers. Each of these chambers is filled with air compressed to a pressure appropriate to its depth in the float chamber in order to prevent implosion. The floats provide buoyant lift equivalent to 5,400 tonnes, enough to balance the weight of the trough and its load of water and ship. The trough is set in motion using four worm geared shafts, 27.3 metres long and 42 centimetres in diameter moved by eight 44 kW electric motors. Because the trough and its load are in equilibrium with the floats only the friction opposing the troughs movement needs to be overcome by the motors. A complete lift can be achieved using less than 500 kW of power.
This method of construction was selected because a standard lock was not technically possible over this height difference at the time. This method also saved the cost of back pumping lost water. Today 110 million m³ of water are back pumped for the parallel ship lock each year.
The overall height of the lift measured from the base of the underground float chambers to the upper cross beams is 97.21 metres. The water depth in the trough is usually 2.5 metres.
Read more about this topic: Rothensee Boat Lift
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