Why do boats sail faster downstream

GPS-controlled mowing under water

In his master's thesis, a student at FernUniversität developed an automatic control system for a mowing boat that can be used efficiently against the rapidly growing water pest.


Mowing underwater with the "GPS-Navi" Elodea: In his master's thesis at the FernUniversität in Hagen, Stephan Werbeck developed a highly accurate autopilot to control a boat, which is used for a "safe cut" against waterweed. The rapidly growing plant makes life difficult for those who do water sports in more and more bodies of water, in the Ruhr between Dortmund, Hagen, Herdecke and Wetter for 20 years. Only frequent mowing helps, but has so far been inefficient. Therefore, the FernUniversität student built and programmed an automatic control system for a mowing boat. Werbeck worked together with the Ruhr Association and the Harkortsee Yacht Club. He was supervised in his master's thesis by apl. Prof. Christian Icking. The innovation supports the boat operator as an assistance system; autonomous operation is not intended, primarily for safety reasons. According to the unanimous opinion of various experts, the system has probably not existed in this form before.

The Harkort and Hengstey lakes are dammed up Ruhr areas between Dortmund, Hagen, Herdecke and Wetter. Stephan Werbeck from nearby Witten also likes to launch his sailing boat on the Harkortsee. In the yacht club he is one of the members who mow the annoying plants. For this purpose, the Ruhrverband - which is responsible for water management in the Ruhr - has provided the local associations with a mowing boat since 2016.

Regular mowing is currently the only way to combat waterweed. Again and again, sailors who were stuck in the Harkortsee had to be dragged free. Often the boats can no longer even leave the small harbors on the lake. Athletes with kayaks and row boats also have major problems.

Elodea forms matted islands

The plants can only be seen from the mowing boat when they have grown to just below the surface of the water. However, it is best to cut off their shoots much earlier: the more light they get, the faster they grow. On the surface, they develop side shoots that spread rapidly and mix with algae. "Ducks and even geese can walk on these matted islands," explains yacht club member Bernhard Vogeler. A late cut results in much more biomass, and the approximately two-meter-long plant remains on the weir downstream can lead to problems.

So it makes sense to mow early for several reasons. "But in contrast to lawnmowers, you can't see where you've been in the water," says Thomas Brinkmann, head of the Ruhr Association's Eastern Reservoir Group. In addition, when mowing, the boat pushes shoots to the side that rise up again a short time later.

Werbeck felt like many other water sports enthusiasts: “Although we cleared our mooring areas with the mowing boat, the lake was still green. Then you want more, there are desires. ”The mechatronics technician with a technical college diploma, who enrolled in 2014 at the FernUniversität for the master's degree in practical computer science, spoke to Bernhard Vogeler about the problem. Vogeler coordinates the mowing operations for the club: "So far we have always mowed for good luck." In addition, the short boat is extremely manoeuvrable, but the straight-line stability is unstable - partly due to currents: "Like a car on black ice" , explains Werbeck. "The boat is moving forward, it is turning quickly and changing speed."

So how should mowing be carried out "track by track"?

"FernUniversität team"

The solution for Werbeck and Vogeler was a GPS-based driver assistance system that supports the boat operator with navigation. For this they brought Christian Icking “on board”. He is an adjunct professor in the cooperative systems department at the FernUniversität. “We discussed until late at night,” Werbeck looks back. Vogeler is a mathematician and until his retirement worked, among other things, in the FernUni data center and its successor in the Center for Media and IT (ZMI). Like Icking, Vogeler was an “intellectual sparring partner” for Werbeck, and he was also used as a “test driver”.

The development makes it possible to define mowing areas in the lake and to drive them systematically, even when Elodea cannot be seen. The development began with the programming of a log function that recorded the lake areas already traveled and the current route and displayed it live on a computer monitor. A big step forward, but too imprecise because only data from a single GPS device was used. In addition, the manual control based on live data on the monitor was exhausting and error-prone. In 2019 Werbeck improved the development. Thomas Brinkmann from the Ruhrverband and his team supported him, among other things, with modifications to the boat controls.

Fully automatic control

The current expansion stage of the driver assistant uses two GPS devices on board and another differential GPS that is permanently installed on land. The location is now accurate to within two and a half centimeters.

With the help of this data, a mathematical model was developed in cooperation with Prof. Icking and linked to the software system of the boat control. The software can now even control the boat fully automatically while its crew observes the traffic on the lake and intervenes if necessary. But the boat remains manned for safety reasons: An autonomous system would have to meet extremely expensive requirements. Thanks to the automated control and the high accuracy of the GPS data, mowing can be carried out largely without gaps and without any gaps.

Graduate with many skills

“Stephan Werbeck brought a lot of skills with him, it was about more than just IT,” Icking praised the graduate. As a mechatronics technician, among other things, he was also very familiar with control and regulation technology. The professor continues: “Actually, what he has done is a project for a whole team.” It took a total of around two years, with preparations such as data collection taking up most of the time. At the end of the day there was a brilliant master’s degree, acquired in parallel to the job.

The Ruhrverband is also very satisfied with the development. When Werbeck and Vogeler approached him, Thomas Brinkmann was initially opposed to the idea. However, he quickly realized that professionals were at work here and that the planned development could greatly relieve the operator of the boat - on whom many demands are made - and significantly improve the efficiency of mowing.

When the system was presented to the public, it became clear that there is also great interest in Essen in using the system to make a good cut against Elodea on Lake Baldeney in the future.