84 bit rough from the extrusion as we don’t presently grind or polish it, as we don’t need to streamline it for any high speeds,” van den Heuvel says. Additionally, a conventional boat would make use of anti-fouling and anticorrosion treatments, such as specialised coatings, particularly if made from steel, but for the printed composite, this was unnecessary. “If we travel about 100 m of the Seine, we consume less than 1 kW/h, meaning a return trip across and back over its breadth takes less than a kilowatt per hour. It’s always good to save energy, of course, but in this application, and with our powertrain, we didn’t have to fight for every last watt/hour,” van den Heuvel adds. Electric powertrain “Basing the ferry’s thruster arrangement on the Roboat USV reduced risk in our development. The timeline for this project was very tight, with a hard deadline to make it in time for the Paris Olympics,” Jordan says. “Since we had a powertrain that we knew worked for autonomous water transport, it made sense to just scale it up. We’re now doing water tests in Amsterdam with the full-sized ferry, and it behaves much as our Roboat USV does.” Tony integrates two 11 kW pod thrusters for main propulsion at the ferry’s port and starboard mid-sections, and two 7 kW bow thrusters (a nautical term for laterally disposed manoeuvring thrusters) at its bow and stern centres. They are powered by a 28.8 kW/h battery pack, which can be charged at a rate of up to 12 kW via a conductive charging port. Additionally, HSG designed a proprietary automatic mooring system, by which the conductive charging connector at the vessel’s port side is slid into a funnel at the pontoon side to ensure its correct positioning for a secure connection and power feed. Getting the charging port to enter and exit the funnel requires high precision in the vessel’s movements, made possible by Roboat’s autonomous localisation and control. Once securely in the funnel, automatic charging continues, stable and safe under variable water levels, with up to 1 kW/h replenished every five minutes. So, if the ferry waits for five minutes while off- and onloading passengers, it could sail 24/7 without running out of energy. “We had to do some calculations as the minimum speed required by the transport agency is 12 kph, and there aren’t many manufacturers of electric boat powertrains, particularly in this size and application, but we found and worked together with Kräutler in Austria for the thrusters and Top Systems here in the Netherlands for the batteries,” van den Heuvel says. The reasons for choosing Kräutler included its thrusters’ high-power outputs, and its use of nickel, aluminium and bronze in its propellers, per industry standards on high-end and professionally made vessel propellers (some electric thruster suppliers still make their propellers from plastic, which HSG and Roboat deemed mechanically unsuitable). A key benefit of Top Systems’ battery packs is that they can be configured for a 48 V battery bus, efficiently matching the 48 V of the Kräutler thrusters. They are built from lithium iron phosphate (LFP) cells, which come with a reduced risk of fire, compared with other cell cathode chemistries such as NMC, and have electrical efficiency advantages such as their output voltages not lowering with their state of charge. Separate from the powertrain bus is a module with a DC/DC converter for stepping down to 30 V buses for the cabin, enabling passengers to plug in and recharge their personal devices during transit. The cabin has an open-air design for working in the Parisian summer, so there are no environmental systems requiring power. Multi-layer navigation To perceive its environment for localisation, navigation, and obstacle detection and avoidance, the ferry is equipped with a suite of sensors encompassing Lidars, cameras, inertial measurement units (IMUs), GNSS receivers, and a doppler velocity log (DVL). The vessel will carry human passengers, so it was deemed imperative to have multiple overlapping and redundant sensors. “We have two sensor hubs on the ferry, set at opposite corners of the outer hull; one at the bow-starboard end and one at the stern-port corner, which gives us an effective, 360° view of our complete surroundings,” Jordan explains. April/May 2024 | Uncrewed Systems Technology The thrusters are 48 V systems, 11 kW for main propulsion and 7 kW for bow thrust, with propellers of nickel, aluminium and bronze (Image courtesy of Holland Shipyards Group)
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