We're willing to bet you don't know much about diesel-electric hybrid drive systems, but you should, because they're gaining popularity.
A few years ago, I attended the Electric & Hybrid Marine World Expo in Ft. Lauderdale, Fla., to research hybrid propulsion systems on yachts for another story. To my dismay, I found mostly applications from vendors that suited commercial vessels or the larger and smaller recreational product stream. I was more interested in the “silver bullet” of hybrid systems for the mid-range market, about 35-footers up to approximately 100-foot yachts.
Vendors I spoke to back then were a bit shy, telling me there really wasn’t a strong desire
from the mid-range U.S. recreational market and that builders, and certainly owners, didn’t want to be the first one to incorporate it into a yacht. Between the price for such systems, the perceived long return on investment and the brand impact if it didn’t succeed, there wasn’t an open forum to support the opportunity to satisfy a potential need.
Well, something must have been going on behind the curtain, because a few short years later, we are seeing yacht brands selling in America that tout the virtues of such systems, along with their benefits to the recreational boater. Let’s see what the hubbub is all about regarding diesel-electric hybrid systems on boats, and who is doing what.
The Big Kids
Large-yacht applications of hybrid systems have made a splash, including Oceanco’s massive Project Bravo, a 357-footer that features a hybrid propulsion system. M/Y Savannah, a 274-foot Feadship, is touted as the first hybrid motoryacht. With a single Wartsila diesel engine and central prop shaft, Savannah also has three gensets to generate electricity and an azimuthing stern thruster.
Heesen Yachts is also in the hybrid business. One of its recent launches, the 163-foot M/Y Home, can be operated on diesel mechanical or diesel electrical mode using its twin MTU 12V diesels and electric shaft motors.
So the transition of hybrid power from the commercial sector — freighters, offshore supply vessels and others — to superyachts is proven. But are the systems and benefits scalable to the mid-range market?
What Is It?
The word “hybrid” can have a number of dictionary-defined applications, but for our purposes, let’s keep it simple and go with this: a hybrid vessel is one that is able to operate using either two fuels or power sources. And for the context of this story, we’ll limit those two sources to diesel and electric.
Just like in a hybrid automobile, there are two power sources for propulsion: a combustion engine and an electric motor. This differs from an electric car or boat, which has only an electric motor spinning the driveshaft(s) — no combustion engine component.
In a hybrid boat, the propeller shaft is driven by a combustion engine, an electric motor or, at times, both. Powering the electric motor is a series of batteries, charged either by the diesel engine when it’s running, a generator or, in some systems, solar chargers.
Is there a need for hybrid propulsion systems? Just because they can, does that mean they should? There are many compelling reasons to go hybrid, which can include the following:
• Quieter operation
• Improved efficiency
• Increased range
• Reduced emissions
• Allowed in zero-emission zones
• Decreased running costs
• Reduced vibrations
A look at the benefits to the recreational boating sector reveals one big advantage: a reduced carbon footprint. Reduced, or even eliminated, exhaust gases is a significant reason some buyers and builders go hybrid. Reduced exhaust odors is another. A quieter boating experience is created by reduced noise and vibrations, as electric motors run smoother than combustion engines.
Another benefit of electric motor propulsion is the fact full torque is created instantly, which improves the response from the throttles when the system is in electric drive mode.
Even though there may be multiple propulsion systems, what stays the same is the number of drive shafts. On a single-screw boat, there is still one shaft and prop. Same rule for a twin screw: two shafts and props.
What is different is the drive connection to spin the drive shaft and prop. With a true diesel-electric hybrid propulsion system, the shaft from the diesel engine runs to the gearbox and the propeller shaft runs from the gearbox through the hull to the strut.
Power is provided from the diesel engine to the shaft. There can be an electric motor that is either geared to the gearbox that takes over the drive job or that is in-line with the shaft.
Who Has What?
Several builders are now in the hybrid game. One is Adler Yacht, with its 76-foot Suprema, which is built of carbon-fiber. It’s a semi-custom yacht with Adler’s first hybrid propulsion system, created by a team of specialists from the aviation, automotive and marine industries.
Adler’s development, a Hybrid Marine System, consists of twin 1,150 hp Caterpillar diesel engines and twin ATE high-efficiency 100 kw motors/generators. This configuration allows for three cruising mode options:
3 Direct diesel
The ATE units are mounted on the shaft between the engine and the gearbox and can either drive the shaft or declutch and act as a generator. This configuration allows one engine to run in diesel mode and one in electric mode. In electric or ECO mode, the Adler Suprema can run up to 11 knots; in diesel mode it can run wide open at 30 knots. Adler touts an ultra-long range of 3,500 n.m. at 8 knots.
Greenline Yachts is also a player, with a series of hybrid yachts. Launched in 2009, the Greenline 33 was the builder’s first yacht with the hybrid, or H-Drive, system, which has expanded to some of its other models. Coupled with Volvo or Cummins powerplants, the H-Drive can run in diesel or electric mode, and it can operate in charging mode. Greenline goes a step further with solar panel options that assist in charging the batteries, for extended power without running the generators.
Volvo has tossed its hat in the ring, too. Last year it introduced a hybrid system for IPS pod drives that will be available in 2021. Promoting better low-end torque than a combustion engine offers, Volvo expects better maneuvering at low speeds with the hybrid system coupled to an already proven pod-drive system. Here’s a synopsis from the manufacturer:
“A clutch and electric motor are added between the engine and the IPS pod. The electric motor is supported by scalable (depending on application needs) Li-ion battery packs that can be charged externally using AC or DC chargers; or recharged using the primary diesel engine. Opening of the clutch allows the boat to run in electric- only mode, and with the clutch closed both diesel and electric power can be used in parallel. In terms of operation, the captain will use the familiar control interfaces of the IPS system, with the addition of new drive modes to choose from.”
How it Works
Greenline In full electric drive mode (above), the diesel engine on a Greenline yacht is bypassed in favor of the electro-motor/generator, which is fed by the batteries and solar power. When the batteries need a recharge or more sustained speed is required, diesel mode is available, but the diesel engine doesn’t just drive the shaft and prop. It feeds the generator, which in turn supplies juice to the battery bank.
ELCO A combustion engine, an electric motor and batteries comprise Elco’s Hybrid Electric Parallel system. For quiet cruising, electric mode is the choice. To move along much more quickly and charge the system’s batteries, the traditional engine is the correct option. Elco offers a purely electric system and a hybrid system that uses a DC generator instead of a combustion engine, too.
Understand that when a hybrid propulsion system is in hybrid or electric mode, the boat’s speed is typically on the lower end of the range, usually not more than 15 knots. Above this speed, the diesel configuration typically powers the vessel. At lower speeds, combustion engines are not at their peak performance, but electric motors can be, and with maximum torque, tight-quarters maneuvering is not an issue. At planing speeds, diesel engines perform better and are more efficient.
Additionally, all that power to run the electric motors requires a bank of batteries and power distributors or switchboards to manage the juice. This equates to needed space and maintenance items, in addition to the engines.
Hybrid propulsion systems are here to stay. From commercial vessels to cars to boats, hybrid propulsion is a new alternative that is going mainstream quickly.