Electric propulsion solves triple keel conundrum

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Unlike the usual two-keel design common to most yachts, it is uncommon to see a boat with a triple keel. In fact, the concept is unique to the Triakel, a vessel conceived by Netherlands-based designer Bart Pothoven. The vessel has completed a circumnavigation of the globe with Pothoven at the helm and in doing so, has proved the worth of its electric propulsion system, deployed when there is insufficient wind for sailing.

Pothoven believed he could improve on the twin-keel design by adding an extra keel. His idea was to add lift to the righting moment. By placing a keel on each side of the boat, facing inwards underneath, 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 sailing direction.

Transferring this conceptual design to reality was not easy. Typically, a sailing ship has one rudder with a propeller positioned in front. Pothoven’s design, however, utilized two rudders. Such layout on a small boat made it difficult to install two propellers and the solution was a pair of electric motors, supplied by WEG and an inverter system linked to a diesel generator.

The layout sees the diesel generator in the middle of the boat, providing a 400V, AC power supply, which is then split between two variable frequency inverters and then to the motors and propellers. The use of one inverter per motor gave the option of individual control of each propeller, enhancing maneuverability.

For example, Pothoven said as example that when he arrived at a harbor in Cuba he to needed to pass two ferries that were blocking his path. By controlling each motor individually, he was able run one motor forward and the other in reverse, turning the boat sideways to navigate past the larger ships.

Though Pothoven said the electric drive performed faultlessly, the use of twin motors also provided a useful degree of redundancy. Even if one failed, drive could still be maintained with the other.

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