Plan Incliné de Saint-Louis-Arzviller
This is going to be a rather long post as there is a lot to say about this thing! But the short version is: this is a boat lift.
Built in the 1960s, this "inclined plane" was designed to carry barges as part of the fluvial coal transportation industry. However, that trade declined pretty much during the edifice's construction, and today, it almost exclusively serves leisure boats. But if you're going to do a canal cruise, this thing gives it quite the difference!
Its function is that of a lock, taking boats from the lower water level to the higher level, or vice-versa, but it does this by technically being a lift or elevator. A caisson carries the boats and the water up and down, using counterweights to ease the travel.
In fact, the caisson will take on more or less water in order to be heavier or lighter than the counterweights. Though the total mass of the caisson and counterweights is enormous, the difference in mass between them isn't, so very little power is needed to get the system moving, and gravity does most of the work. Two relatively modest electric motors (centre of photo below, steps to the right for scale) start the movement and control the speed.
As such, the system uses comparatively little power, for impressive results. The boat lift was built to bypass a "ladder" of 17 locks which required a whole day to go through, while the travel time of the lift is just 4 minutes. The ride is seamless and very comfortable, effortless even, for reasons mentioned above but also because the effort is distributed across 5 times as many cables as physically required to hold everything together!
Water-tightness is also extremely important, not just for the caisson obviously, but also for the other doors, particularly the top door, which is holding back a whole length of canal. A serious incident in 2013 has led to further reinforcement of redundancies and the construction of an emergency dam closer to the lift in the event of major leaks.
With a lot of freight traffic in mind, the structure was actually designed for two caissons, side-by-side, as evidenced by a second gate hole visible at the top of the ramp (4th picture), and extra space at the bottom, visible in the final picture below. Doubling the caissons would have meant doubling the counterweights, and a second set of rails were laid for that scenario and are visible in the 4th picture. As mentioned earlier, demand dwindled as the lift was being built, so it never operated with two caissons.
For a long time, this place was a childhood memory, visited during a school trip. In my hiking spree after the 2020 and 2021 lockdowns, I sought this place out again and was glad to see it was still working. And just this week, I returned with my parents and rode the lift! It's without doubt one of my favourite pieces of engineering.
