Electric Multihulls

Multihulls like this Fountaine Pajot Isla 40 make great candidates for alternative drives

Well, as ever in the world of sailing, the electric revolution is taking a little bit longer to filter down. “We are so far behind Europe in this technology,” says Sally Reuther of Annapolis Hybrid Marine. “But we’ve seen a change in [recent] months. At boat shows, people come up to us with questions, and they’ve already done their research.”

Indeed, there is a growing crop of system suppliers, among whom the best known for leisure sailors are Torqeedo, Oceanvolt, Bell Marine and Elco. Volvo Penta is also making strides with a comprehensive electric range in the work, a project in which it has been working with catamaran builder Fountaine-Pajot.

Among the chief attractions of this kind of technology are its silent operation, instant torque, the absence of exhaust fumes and freedom from the tyranny of having to buy diesel. If it was that simple, though, boats would all have converted to electric long ago. The problem is that there are also two major problems with electric propulsion for marine. The first is cost: you can expect to pay a good deal more for a new boat when you spec electric motors. The second is that even if you go wild in terms of battery capacity there is still the problem range and what to do to keep from running out of power.

There are some savings, of course. There’s the diesel itself, for one. Electric motors are also more reliable than combustion engines, cutting maintenance costs. “Running costs were incomparable,” says Pierre Vanwinsberghe, who installed two 8.6kW Oceanvolt motors on his Aventura 33. “An oil change every year and one $220 seal kit every five years. Nothing else to do!”

Beyond that, it should come as no surprise that Volvo decided to work with a multihull builder, as catamaran and trimaran hulls are more easily driven than traditional monohulls, making them better suited to a hybrid or electrical propulsion system.

Multihulls also offer a good deal more surface area for fitting solar panels, courtesy of their broad beam. “A multihull gives a lot of possibilities in space for energy ‘scavenging’, think here about solar panels, solar collectors, wind generators,” says Bart Meenks of Dutch supplier Bell Marine.

Solar, I hear you snort in disbelief? Absolutely, because solar panels are increasingly seen as a key element in the design of any electric propulsion system for yachts. In fact, if you speak to Michael Köhler of electric catamaran brand Silent Yachts, solar is the only game in town. “When you hear the wind turbine making all that noise, you think it will be producing lots of power, but it’s not. When we did the measurements, solar produced much more.”

Solar panel technology is also improving all the time. Where once, a good panel offered 5 to 8 percent efficiency, they can now manage more than 20 percent. With its 49 square meters of solar panels, the Silent 55 can generate some 10kW when the sun is high in the sky. “The boat’s house load is 5-10kWh per day,” explains Jean-Marc Zanni, who designed the 55’s electrical system. “So you can go for weeks between recharging. The aim is to provide full comfort and silence at anchor or in port.”

François Bouffard, who specced his Slyder 47 with twin Oceanvolt 15kW motors, agrees. “Solar, solar, solar!” he says. His boat carries 880W of solar panels, but he says he would install three or four times this capacity if he were designing the system again. “With 3,000W of solar panels, there would be a slight surplus on the whole domestic load.”

Along these same lines, Jan-Dirk Lohmüller fitted his Fountaine-Pajot Saba 50 with an Oceanvolt system for a world tour and has enlarged his solar array at every opportunity. He began with 880W from the yard, then added three 320W panels in Panama. The boat is now in Tahiti, where it has just had a further four 320W panels fitted on a gantry over the davits. “Since then we enjoy complete energy independence from fossil fuels on medium sunny days,” he says. “Even with intensive induction cooking, a coffee machine for 12 or so coffees and one or two washing machines, we have no problem.”

The schematic of a Gunboat electric drive system

And Solar is only part of the story when it comes to renewables. Nothing but the water turning the propeller under sail can also generate from 100W at 5 knots up to 5kW on a big yacht at speed. Here again, multihulls are far more effective than monohulls, due to the fact there faster cruising speeds deliver much more power from this hydrogeneration. Catamarans, in particular, enjoy a further because they have two motors.

As an example, Bouffard says his Slyder managed a full week of fossil-free sailing during a 2017 Atlantic crossing. “For our water and cooking needs, and everything else, we relied solely on regeneration.” He estimates his two Gori props generated a combined 300W to 500W over the course of the week—equivalent to around 9kWh per day.

That said, he also says he is cautious about the technology’s potential. “On my boat, which is a heavier prototype, I start to produce over 100W at 7 knots. But when the waves come from the back, regeneration is much less. Something to do with the motion of the boat.” Things improved when he removed the mini skegs that protected the saildrives. “They were creating turbulence and reducing the efficiency of the propellers,” he says.

Other installations have also had positive results. Lohmüller says that at 5-8 knots, each motor on his Saba 50 can generate up to 700W, while on fast passages above 10 knots they have seen 1kW from each unit. Similarly, Oceanvolt has now developed a proprietary regenerative system with a variable-pitch propeller with blades that sweep through a full 180 degrees. The electronically controlled ServoProp, as it’s called, can produce 1kW at 6-8 knots of boatspeed. Tests on a 38ft monohull produced 3kW at 12 knots…

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