Splashy white water usually means: Alps or foothills of the Alps, a valley cut, sometimes with a wildly romantic gorge, like on the Isar, above Scharnitz in the Karwendel. And it means a lot of effort with safety equipment such as a wetsuit, life jacket and a sturdy kayak when adventuring among the rocks. Thomas Meyer junior, a fifth-generation showman, also offers something similar at the Oktoberfest with his wild water ride: compressed into a four and a half minute ride in the water canal, with wild descents, without a life jacket and neoprene – and even without a paddle.
“We want to be a family facility, not a thrill ride,” says Meyer, who is also vice president of the German Showmen’s Association, and that’s why grandma and grandchildren can also sit in the 24 boats. You just can’t complain about getting the odd splash or even splash on the approximately 500-meter-long track: why else does the wild water ride tap a total of 600,000 liters of water with its own standpipe from the Munich municipal utility? Most of it flows in the train, with a little bit bubbling in fountains and decorative waterfalls. The finest Munich drinking water from the Mangfalltal. That’s right, the Mangfall is very popular among kayakers as a light to medium-heavy whitewater option.
At the same time, the Oktoberfest railway, which weighs a total of 400 tons, is also a kind of “hydraulic fake” in the steep sections, say those who should know in their Neubiberg laboratories: the engineers from the Chair of Hydromechanics and Hydraulic Engineering at the University of the Bundeswehr in Munich. Because unlike outdoor sports, the 350 kilogram fiberglass plastic boats with a tree trunk design do not float continuously.
In the flat areas they swim in the current of the track, they are pulled up with rubber mat elevators, and down they travel on axles with rubber rollers, which are also guided laterally by such rubber rollers in the track. Of course, these non-swimming passages with some steep gradients do not give any reason to be disappointed, quite the opposite: the up to five passengers in their boat accelerate up to 60 km / h – only to then kick up a pretty veritable bow wave at the bottom when they transition into the flat swimming area. to stir up the passage
Ivo Baselt, the scientific laboratory manager of the Chair of Water Engineering in Neubiberg and a doctor of engineering, does not have a water ride in his test hall that goes down from a height of 17 meters, but he does have a lot of interest in the physics of the Oktoberfest wild water ride. It cleverly simulates the two states that exist when water is moving in a channel: the flow state is sometimes “flowing” and sometimes “shooting”. Quite comparable to the speed of jet aircraft, which have subsonic and supersonic speeds.
And just as the famous Mach number marks the boundary between the two states, i.e. the speed at which the sonic boom occurs (Mach 1), there is also a number for flowing states in water: the Froude number, which is used in physics Marked “Fr”. It is reminiscent of the brothers William and Robert Edmund Froude, who researched the laws for stable flow and driving behavior for the British Navy in the 19th century.
It is a “dimensionless ratio”, i.e. a simple number like the Mach number, and is composed of the quotient of the flow velocity and the root of the (multiplication) product of the gravitational acceleration and the water level in the channel. Sounds complicated, but Baselt can illustrate it: In flat parts of the railway, there are quiet sailing zones for the log boats, with high water levels and low flow speeds (the Froude number is less than 1); However, if it becomes steep, the level drops and the water flows much more quickly (with the same flow rate) – the Froude number is then greater than 1.
Of course there is no bang in water if it goes over the Froude number limit of 1, which is relatively unspectacular (and only comparable to a limited extent because water is less compressible than air). But there is a spectacle in the water ride when it transitions from the shooting to the flowing state. The engineers call this “alternative jump”; and if it happens as violently as possible, when the load rushes back into the water from 17 meters below, then Thomas Meyer’s Oktoberfest white water results in a quite sensual experience of what physicists mean by “alternative jump”: a shower that makes people cheer loudly may.
As with canoe paddling, not all passengers are affected equally. Showman Meyer roughly sketches it out like this: “You’re more likely to get wet at the front.” Flow expert Baselt can define this more precisely. First of all, it is important that the transition of the orbit from around 30 degrees to zero degrees of inclination does not occur abruptly, but rather in a so-called vertical clothoid. So in a design with rows of growing or decreasing radii: a gentle outlet.
Because otherwise the boat’s impact on a standing wave would be so hard “that no passenger would come back,” as Baselt says. With Clothoide, on the other hand, “it’s fun”, especially for those in the second row: “You get wet from the front and the side” because the displaced water is then pushed up to the side as a “secondary side surge”. It’s also rather damp at the front because of the “first surge”, but at the back there’s a real chance of getting out of the four and a half minute fun session dry.
The university scientist is impressed by what showman Meyer “does.” Baselt is particularly impressed by the dimensions and the amount of water. 600 cubic meters is “a hammer”. That corresponds to around 4,000 filled bathtubs and is significantly more than the 340 cubic meters that he has available as a reserve in a basin under his laboratory hall in Neubiberg. On the other hand: If you compare the 600,000 liters of water with the Oktoberfest beer consumption in 2017, it’s no longer so wild: compared to 7.7 million liters of beer, that’s one thirteenth. And without foam, because from the Mangfall, not from the brewhouse.
Baselt estimates that whether a boat is occupied by one or five people makes little difference in speed in terms of rolling and air resistance on the steep ramps. Much more important is the British brothers’ insight: “When Fr becomes >1, then the fun comes!”
In the series “The Physics of the Oktoberfest” the SZ analyzes various components of the Oktoberfest according to scientific criteria.
Good Oktoberfest stories stay good. This text was first published on October 4, 2018 published.