Hybrid superyachts are no longer novelties, yet they are still scarce enough that their technological features are highly specialized and unique.
According to the First Export Association of Dutch Shipbuilders (Feadship), Savannah is the first hybrid superyacht, and the first to feature an eco-friendly blend of single diesel engine, three gensets, batteries, propeller, azimuthing thruster, and a streamlined hull shape.
Awards and Competition
The 83.5 m yacht has been garlanded with a host of awards since her launch in 2015.
But there are arguably two other contenders for first hybrid/diesel-electric superyacht, Lürssen Werft’s 2005-built Air (now renamed Ice) and Royal Huisman’s Ethereal, built between 2005 and the second half of 2008.
In describing Savannah, Feadship claims that “fuel economies of 30%, the pioneering electro-mechanical propulsion platform marries our past experience and forward-thinking approach.”
Her main engine is a Wärtsilä 9L20 4-stroke, producing 1,800 kW at 1,000 rpm, with the generators from Caterpillar, one C32 and two C18s. The combination gives her a maximum speed of 17 knots and a range of 6,500 nm from her 170,000 fuel tanks.
The Pros and Cons of Hybrid Propulsion
Hybrid/diesel-electric propulsion has been refined over the years, but why has it taken so long for superyacht builders and owners to catch on?
NauticExpo e-Magazine asked Lürssen Werft about this as well as the pros and cons.
“Sustainability is the new buzzword—every company wants to be seen as sustainable,” a spokeswoman said. “Yachts also need to be sustainable, and research into sustainable, environment-friendly propulsion systems is in full swing.
“We first installed a diesel-electric hybrid propulsion system on a yacht back in 1997. Then in 2005 came Air, the first diesel-electric yacht with two Azipod propulsion units.
“Air was fitted with eight Deutz TBD 616 v16, 842 kW diesel generators, mounted in pairs on elastically mounted rafts in four separate rooms, which could supply the required power for both the hotel load as well as for propulsion. The power generated was fed through the power management system to two electric motors housed in two Azipods from [manufacturer] ABB, which hung under the stern.
Reducing Emissions and Noise
“Diesel-electric propulsion is the most widely used technology in our large yachts, those upwards of 90 m,” she continued. “The generator engines run at optimal capacity, which greatly reduces both emissions and structural-borne noise by avoiding a conventional gearbox arrangement.
“Azipod units also improve a yacht’s maneuverability as the turning capability is much higher than with a conventional propeller and rudder system.
The turning capability is much higher than with a conventional propeller and rudder system.
“But,” she explained, “the clear disadvantage of diesel-electric propulsion is that it takes up more space in the engine room—for example, for the converters—and is therefore more suitable for larger yachts.”
As to the future, Lürssen believes that over the next eight to 10 years, batteries will become more compact and efficient. That means the large amount of space needed today will be cut back, making hybrid/diesel-electric propulsion suitable for smaller yachts.
Stored Electrical Power
In terms of batteries, Royal Huisman took advantage of lithium polymer technology when building Ethereal, which the shipyard claimed was “the world’s first hybrid superyacht.”
A 58m world-cruising ketch, Ethereal has a hybrid electro-mechanical propulsion system that can recharge her lithium polymer battery bank through the drive train under sail, rather than relying on generators. “She is able to raise anchor, motor, hoist sails and run ships’ systems from quiet, stored electrical power,” Huisman states.
The system consists of two drive trains, each comprising a Caterpillar C18 diesel engine producing 533 kW at 2,100 rpm, together with a 300 kW Combimac electric motor/generator running through a ZF MM 2700 NR reduction box. The drive trains turn twin Wärtsilä 1,500 mm-diameter four-blade controllable pitch propellers, and she has a hull speed of 17 knots.
Finally, rising to the challenge and perhaps taking the crown as the most advanced superyacht yet, is the ‘188,’ which is currently under construction by Damen Group superyacht specialist AMELS and scheduled for delivery in early 2018. She boasts hybrid power from three sources—mechanical (auxiliary generators), electrical (battery bank) and engine heat recovery (residual energy).
AMELS promise it will save owners €100,000 annually for yachts sailing about 8,000 nautical miles a year.
“When we started looking at the power systems on board the 57.7 m AMELS 188, we realized we could deliver far greater benefits by finding smart ways to reuse energy already on board,” AMELS design manager Hans Konings told NauticExpo e-Magazine.
“I speak to owner representatives, crews and designers all over the world,” Konings continued, “and any mention of hybrid power is often when people’s alarm bells start ringing. Experienced yacht owners are wary of expensive, rarely used ‘gimmicks’ that occupy valuable luxury space on board. Chief engineers and captains are concerned about operating and maintaining a whole raft of complex equipment. Plus, the environmental benefits are often questionable at best.
“But we’ve successfully factory tested our new, holistic approach to hybrid power. It will not only stop the alarm bells ringing, but also deliver tangible, high value benefits that you won’t find anywhere else.
“We realize that nobody wants to be a guinea pig for technology that is rapidly outdated,” Konings added. “We are building the AMELS 188 with tried-and-tested solutions from advances made in commercial shipbuilding and the automotive industry. Our solution includes the AMELS waste heat recovery system, plus two generators with a father-son configuration for optimal engine output, plus a compact battery bank for peak shaving and managed load shedding.
Hybrid power will make your chief engineer smile.
“And hybrid power will make your chief engineer smile,” Konings grinned. “For the AMELS 188, we’ve developed smart power management that automatically adjusts the balance of engines and battery power for optimal efficiency and lowest fuel consumption. So your chief engineer doesn’t need to worry about power management system alarms going off when the stewardess switches on the clothes dryers.
“The crew has more time to focus on what really counts—the best luxury yachting experience,” Konings concluded.