Vehicles of the wheeled variety aren’t the only ones going green. U.S. companies International Battery and Electric Marine Propulsion (EMP) are partnering up to build a hybrid power train for the world’s largest plug-in, hybrid electric boats and yachts. The partnership has resulted in one of the world’s largest plug-in hybrid sailboats, a Tag 60 catamaran christened Tang, hitting the water on September 21. It is a 60 ft (18m) carbon-fiber speedster that can be powered by the wind, even when the wind isn’t blowing.

Tang is powered by twin EMP E motion 18 kW permanent-magnet electric motors and International Battery lithium battery cells configured into a 144-volt battery pack providing a total energy capacity of 46 kWh. The boat’s main renewable energy input to the large-format battery pack is electricity regenerated by wind power as the boat’s propellers spin in the boat's wake when it is under sail. The propellers turn the 18-kW motors, which automatically become generators and send electricity back to the batteries. The companies say solar panels can also be set up to feed into the battery pack, but Tang is not equipped with them.

Tang is the first boat to have the new motors installed but assuming the system performs as expected, they’ll also be installed on the next Tag 60, which is already more than half built.

When there’s not enough wind, twin 22-kW diesel generators kick in, either together or individually as needed, to recharge the batteries. The generators are 144-volt dc units that recharge the batteries directly without the normal energy loss incurred through a charger.

The batteries can also be charged with a 144-volt charger that plugs into shore power and is designed to handle a wide range of voltages and frequencies – handy for those out-of-the-way ports with erratic electricity supplies.

“The initial thrust and response when engaging forward is vastly better than anything experienced with standard diesel propulsion,” said Tim van der Steene, managing director of Tag Yachts. “It’s quiet, and the power is there instantly. It goes hand-in-hand with sailing, which is about moving in harmony with nature, quietly, without polluting the environment.”

While the main power output from the battery pack goes to power the twin propulsion motors, it also sends power to a DC-AC inverter that makes 110/220-volt, 50/60 Hz alternating current for powering AC appliances, a DC-DC converter that steps down the voltage for 24-volt and 12-volt house power and a pair of 144 vdc hydraulic pumps. These pumps power a hydraulic system that operates the rotating wing mast, centerboards, sheet winches, anchor windlass, dinghy platform, controllable-pitch feathering propellers and other moving parts on the boat.

The battery pack’s 46 kWh capacity is more than twice the usable capacity of an 8D battery pack – the largest conventional size carried with the E motion system – yet weighs roughly 40 percent less.

International Battery CEO, Ake Almgren, says, “Using our large-format lithium prismatic cells as the building blocks, we can provide battery systems with high energy density, which means smaller footprints and lower weight. In addition, because we use a unique, environmentally friendly, water-based manufacturing process, our batteries will feel right at home storing clean, renewable energy for this hybrid vessel and others to follow.”

The extra energy capacity allows the yacht to include a variety of creature comforts, including a 37-inch TV, Bose entertainment system, LED lighting, café-size espresso machine, two refrigerator-freezers, microwave, conventional oven, gas or electrical burner top, washer-dryer, air-conditioning and a water maker.

The Tag 60 line was designed by New Zealand naval architect Greg Young and Tang is currently undergoing tests at Tag facilities in St. Francis Bay, South Africa. She’s due to set sail across the Atlantic to her owner in Florida later this year and will appear at the Miami Sailboat Show in February.