While hybrid fossil fuel-electric technologies are only just getting established in the automotive world, they’ve been around for more than a century in the submarine industry with internal combustion engines being used for surface running, as well as charging batteries for underwater operation.
This system, familiar to most hybrid vehicle owners, is known as a parallel hybrid, in which either (or both) internal combustion engine and electric motor act on the propeller shaft.
Later submarine designs used a series hybrid arrangement, with a separate generator powering an electric motor that turns the propeller, in a similar manner to a BMW i3’s range-extending engine, just predating it by a good 90 years.
The plus side of the latter system is that it eliminates the need for clutches and gearboxes, plus the generators can be acoustically disconnected from the hull, making operation quieter. And the generators can be run at optimal speeds, further improving efficiency.
So what is the pleasure craft industry waiting for?
Surprisingly, hybrid systems are available for smaller pleasure craft, and have been for some time.
Austrian builder Frauscher Bootswerft launched what it claimed was the world’s first hybrid recreational motor boat in 2008, running a parallel hybrid drive system by Steyr Motors.
Given the relative thirst of such pleasure boats, a hybrid instinctively makes sense for those wishing to reduce their footprint. But that assumes hybrid drive equates with efficiency. And while that may apply in a road car where a hybrid system recovers energy under braking, in the nautical world that’s a moot point – one hopes pleasure boating doesn’t involve stop-start traffic in the first place, and because braking isn’t exactly something you do with a motorboat either.
The advantage, however, is in specifying a smaller engine, and using the extra torque of the hybrid system for acceleration, while enjoying better efficiency. Plus there’s the option of silent running at marina speeds.
Frauscher goes a step further and offers fully electric speedboats – the beautiful 750 St Tropez (pictured), being their flagship electric model.
The 750 St Tropez is available with a choice between two drives, starting with a 10kW unit, and going up to a Torqeedo i80, 80-horsepower equivalent. Range at top speed – 15km/h and 30km/h respectively – is only 23.8km for the former and 27.6km for the latter, though if you motor along at 10km/h that improves to 111km, and 70km respectively.
Clearly electric drives won’t be a choice for hardcore offshore boaters, but for a weekend at the Southern Islands, it’s more than enough. And if you could convince your yard to install solar panels to charge you up during the week you may well go boating with no power bills whatsoever.
On larger yachts hybrids make a lot more sense, particularly when you take all the consumption of the house systems into account.
The Mochi Craft Long Range 23 (pictured above) was the first yacht in the world to attain RINA Green Star Clean Energy and Clean Propulsion certification. The 75-foot yacht featured twin 70kW synchronous electric motors attached to the diesel engines, and a lithium-ion battery bank. All this hybrid technology, allied to the FER.WAY (Ferretti Wave Efficient Yacht) trans-planing hull, was supposed to reduce the yacht’s overall environmental impact.
Unfortunately the launch coincided with the global financial crisis, so the Long Range 23 was a victim, though five hulls were launched. And the Engineering Department of the Ferretti Group continues its research into efficiency – particularly hull efficiency – citing Custom Line’s Navetta range as an example of innovation in terms of performance and consumption in response to owner needs.
But every time you visit the marina you’ll see hybrid yachts: Anything with a sail and an engine is, by definition, a hybrid, though the 190-foot Royal Huisman yacht Ethereal – available for charter through Y.CO – does take it to extremes.
Nearly three years ahead of the launch of Ethereal (pictured above), recognised experts in all the yacht’s systems were gathered to conceptualise the most efficient yacht of this type. Interestingly, it was the house systems – those dedicated to the comfort of the guests – that were the first to attract attention.
Captain Andrew Barry says “reduction in demand is what drove the design.” Efficiencies were sought everywhere, from the design itself, with a lot of natural light; to something as simple as white painted external surfaces and effective insulation; to a ducted heating/ventilation system without the usual fan-coil units; to energy recovery systems on the watermaker discharge (which saves an astonishing 4kW); to induction stoves in the galley; to heat recovery from the gensets for water heating; to dimmable LED globes that were designed and manufactured for this yacht.
Ethereal is equipped with parallel hybrid drives too – twin 715hp Caterpillar diesels attached to 300kW Combimatic electric motor-generators. Intriguingly, the 1,500mm controllable-pitch propellers were designed to be used as ‘windmills’ under sail, thus producing power at the expense of speed, but it is a system yet to be commissioned, because it considers that getting to a destination faster may actually be more efficient. But even those large propellers spell efficiency, requiring lower revs to drive.
Captain Barry is highly enthusiastic about the system, particularly where it relates to passenger comfort. “If you aimed to just save fuel with it, you could well do that,” he says. “Our range could be as little as 3,000 miles if we were full revs on both engines the whole way, or it could be 8,000 miles if you did it at seven or eight knots,” he says, “or 50,000 miles if you were going to wait for the wind!”
“From a guest perspective, we see the benefit of the batteries with no emissions coming out of the hull,” he says. It may seem a small thing, but on a still evening those sundowners are going to be that much more pleasant if you’re not choking on generator emissions. Plus there’s the silent running and fine control under electric power, which allows for virtually any propeller speed. “We can leave a dock with silence. The main engines are quiet anyway, but when we do leave the dock in that low velocity mode, guests are able to sleep through.”
“I can vouch for the fact that it has huge benefits, particularly for long distance cruising,” says Captain Barry.
If saving fuel is your goal, then a hybrid may help, and on a large yacht it can equate with passenger comfort. But the common theme seems to be that if you really want efficiency, you can easily do that in any yacht simply by throttling back.
This story was first published in Davison Vol. 31.