Located on the Marne-Rhine Canal in Lorraine, France, the Saint-Louis-Arzviller inclined plane is an engineering masterpiece designed to bypass a steep 44-meter vertical drop. Before its opening in 1969, canal barges had to navigate a laborious four-kilometer stretch containing 17 individual locks, taking an entire day. The inclined plane replaced this grueling process with a single transverse caisson that glides along steel rails at a 41-percent incline.
What makes the mechanism fascinating is its counterweight physics. The caisson—a giant watertight steel box filled with water—weighs approximately 900 metric tons when carrying a vessel. According to Archimedes' principle, a boat entering the caisson displaces an amount of water equal to its own weight.
Consequently, the total mass of the caisson remains virtually constant regardless of whether a boat is inside. To move this massive structure, two huge concrete counterweights weighing 450 tons each are linked to the caisson via steel cables running through overhead sheaves. Because the system is nearly in perfect equilibrium, only two modest 120-horsepower electric motors are required to overcome friction and inertia.
The caisson ascends or descends the 108-meter-long slope in just four minutes, using a fraction of the energy traditional pumping systems require while conserving millions of liters of canal water.