January 2021

30 n VARIABLE-SPEED DRIVES January 2021 www.drivesncontrols.com Inverter-fed motors help to make three- keel yacht a reality A ound 25 years ago, a Dutch boat designer Bart Pothoven had the revolutionary idea of designing a sail ship with three keels and to sail this vessel around the world. Most yachts have one or two keels – structural members that run from the stem to the stern and help to keep the vessel upright. Pothoven believed he could improve on this design by adding an extra keel to help prevent heeling – the side-to-side tipping of a boat. As a boat heels, it ventures towards the direction that the wind is blowing, and develops a righting moment to restore back to its original orientation. Pothoven’s idea was to add lift to the righting moment. By placing an inwards- facing keel on each side of the boat, the ship could gain height to maintain stability and increase speed. For example, if the wind pushes the boat to the left, the keel on the right side would lift and cut through the water to increase force and correct the sailing direction. Making this concept a reality was not easy. Typically, a yacht has one rudder with a propeller positioned in front, allowing it achieve speed without relying on the wind behind the sail. Pothoven’s design needed two rudders. Such layout makes it difficult to install two propellers and generate speed without wind. He therefore decided to use electric motors and frequency inverters to propel the ship. Pothoven’s shore captain Henk Mezger approachedWEG, the Brazilian-headquartered manufacturer of motors and drive technology. He asked the company to supply two electric motors and two of its CFW700 frequency inverters. A 400V, 50Hz diesel generator located in the middle of the boat powers the two motors, each of which is connected to two side propellers. Each motor also connected to one of the frequency inverters, allowing Pothoven to control each motor independently to change the speed of the boat and make steering easier. If one of the motors fails, the other can power the ship. During periods of low wind, the diesel generator can be turned on to propel the boat via the motors. While the equipment must be flexible for to manoeuvring around harbours, it must also withstand the rigours of the ocean. If both motors failed when there was no wind behind the sail, the vessel would simply not move. To minimise the risk of the motors failing at sea, they were put through a series of rigorous tests before Pothoven embarked on his trip. After almost 25 years of development and construction, Pothoven set sail from the Netherlands on his vessel, called the Triakel, in May 2017. In 2019, he returned after visiting 25 countries and demonstrating that his three-keel design worked well in practice. The propulsion system proved its worth when Pothoven arrived at a harbour in Cuba and needed to pass two ferries that were blocking his path. By controlling each motor individually, one motor provided forward propulsion, while the other was operating in reverse. This allowed the boat to turn sideways and squeeze past the ferries. Pothoven did not experience any issues with the vessel’s motors and drives during his two-year voyage.“Although this is a new market for us, we can provide motors and drives to sail ships,”says Harry Swennenhuis, WEG’s general manager in the Netherlands, . “We already provide much bigger drives, generators and motors to the marine industry, so sail ships are a possible new avenue for WEG.” n A Dutch marine designer has built a yacht with an unusual three-keel construction, designed to help prevent the vessel from heeling over. A key element of making the idea work was the inclusion of two inverter-controlled motors. Bart Pothoven’s three-keel yacht, the Triakel, under full sail and the interior of the yacht, showing the diesel generator and the two electric motors on either side of the vessel.