The Future of Marine Power

Emissions-free, green power trains are closer than ever to ubiquity
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An 80-foot concept from Daedalus Yachts utilizes three zero-emission energy sources. 

An 80-foot concept from Daedalus Yachts utilizes three zero-emission energy sources. 

During the next decade, our boats will look, sound and even smell a lot different than they do today.

“The toothpaste has been out of the tube for a long time, and there’s no going back,” says Steve Trkla, president of Torqeedo North America in Crystal Lake, Ill. “Boatbuilders know it, and they’re starting to prepare for the future.”

Tomorrow is likely to deliver emissions-free marine propulsion by way of electric engines and hydrogen fuel cells. And the fossil-free emphasis is expected to go beyond the exhaust vent, as these green power trains would exist completely off the grid, running on solar, wind and regenerated power.

The technologies needed to make this vision possible already exist, and they’re in use in various applications around the world, including trains, buses and cargo ships. In the marine sphere, electric outboards range from trolling motors to 80-hp equivalents, while there are inboards powerful enough to push a wakeboard boat or a cruiser, and big enough to replace massive diesels in superyachts. As this tech becomes more popular, the barriers to entry in the recreational market should drop. Already, Volvo Penta has announced that it will introduce a series of all-electric and hybrid-electric engines in 2021 with an eye toward eventually removing all internal combustion engines from its marine line.

“With the pandemic, we’ve seen what clean water looks like. We’ve seen the fish undisturbed by pollution,” says Andy Rebele, CEO of Pure Watercraft, a Seattle-based maker of electric outboards. “Why would we go back?”

Michael Reardon, the CEO of Daedalus Yachts in Edenton, N.C., is more blunt. Asked what’s preventing fossil-free boating from taking off, he says: “The space between our ears.”

Highfield Boats teamed with Pure Watercraft for a line of electric RIBs.

Highfield Boats teamed with Pure Watercraft for a line of electric RIBs.

Motor Head

Emissions-free boating starts with electric motors. In many cases, they can now match the output of an internal combustion engine. They are highly efficient, converting about 98 percent of stored energy into power, compared to around 35 percent for a fuel-burning engine. And, since they have few moving parts and no oil or transmission fluid, they’re largely maintenance-free.

“Tesla has shown us an electric car that can go 100 mph and have a range of 200 miles,” Rebele says. “People look at that and say, ‘Why can’t I have that for my boat?’”

They can, sort of. High performance is possible — and decent range is possible — but having both at the same time remains a matter of trade-offs.

“A boat has higher resistance than a car, so it’s not quite the same,” says David Czap, founder and managing partner of Soel Yachts in the Netherlands. More range comes through larger battery banks, but because the batteries are heavy, adding more of them decreases performance. For each boat, or each user’s boating plans, it’s a matter of finding the sweet spot of speed and range.

The Deep Blue electric inboard system from Torqeedo is available in power equivalents of 40 and 80 hp.

The Deep Blue electric inboard system from Torqeedo is available in power equivalents of 40 and 80 hp.

“We start by defining what our customer needs and work from there to match the system to those inputs,” Czap says. His company has built a 32-foot speedboat with solar cells embedded in the deck that reportedly tops out at 30 knots, although it can only run at that speed for an hour; it can cruise at 16 to 20 knots for two or three hours. Another model, the SoelCat, has a reported top speed of 14 knots, but at about 8 knots it can run for eight hours. Depending on what sort of boating someone does, he may prefer one application over the other, or something in between.

But that gap is closing. “Most of the success so far has been smaller boats that operate for a long time at slower speeds, like trolling motors, or larger ones that go slow, like ferries or tour boats,” Trkla says. “What’s had a slower success rate is the weekend recreational boat that’s made to go fast for a long time. That’s hard, but we’ve seen breakthroughs.”

Battery technology changes annually, and on average, capacity has increased by 7 percent a year for the past four to five years, which means the same battery bank can supply more power.

“In the next five to seven years, we’ll have another leap in battery technology that will bring them close to the energy density of fuel,” says Michael Köhler, the CEO of Silent Yachts, which is headquartered in Austria. “If the choice is 1 ton of batteries or 1 ton of fuel for similar performance, fuel will go away.”

The Hull Story

Many of the boats built for use with low-emissions power have highly efficient hulls, including catamarans, trimarans and flatter-bottomed monohulls. “An electric boat has to be designed for the purpose of being an electric boat,” Czap says.

Tom Watson, the general manager of Highfield Boats in Canton, Ga., says Pure Watercraft approached his company for that reason: “We’re known for having a lightweight, hydrodynamic hull that pushes easy. That’s why Pure Watercraft came to us when they were looking to develop a tender for their 25 kW motor.”

His company’s collaboration with Pure Watercraft resulted in 12- and 13-foot RIBs that hit 25 mph and that have a range of 17 miles at 16 mph.

“By designing the whole package together, they’ve been able to get very comparable performance to a gas engine, except for the range,” Watson says. (At a harbor-friendly 3 mph, range is boosted to 68 miles.) Pure Watercraft’s Rebele says that at $24,000 and $29,000, the new RIBs are competitive pricewise, too.

The boats also have space carved out to suit electric systems, which are not necessarily bigger than combustion engines but are arranged differently.

“For a long time, we were putting a round peg in a square hole, retrofitting our systems to existing boats,” Trkla says of Torqeedo, which hit the market 15 years ago. “Now, builders are starting to build the boat around the system, rethinking hull design to make it lighter and more conducive to electric power. That leads to better performance all around.”

According to Trkla, in the past six months, Torqeedo has been fielding increased calls from naval architects looking for specs because they, too, are starting to design boats around electric engines.

“Look at the BMW i3,” Trkla says. “They’ve had success because they used carbon fiber and lightweight components made especially for that car. It has to be the same with boats.”

6_Daedalus-Energy-Overview-Graphic

Sunnier Days

An electric engine alone doesn’t make for emissions-free boating. If the batteries are being charged through a grid that doesn’t run on solar or wind power, then that Saturday cruise is still burning fossil fuel. That’s why some boats are incorporating solar power into decks, roofs, canopies, trampolines and even in places that catch light reflected off the water, such as the transom.

“It’s not for people who only want to go fast, but it’s comparable to a worldwide sailing boat,” Köhler says of his solar-equipped cruisers between 55 and 80 feet length overall.

At 10 knots, Silent’s boats can run for about four hours without recharging, he says; at 5 knots, they can recharge as they go. “And unlike a sailboat,” Köhler says, “you don’t need wind, and you can determine the speed and direction at any time.”

For the most part, though, solar hasn’t advanced enough to allow boats to simply recharge as they run, and solar-only recharge times are slower than connecting to shore power. Still, solar panels continue to get more efficient. They now convert about 23 percent of the sunlight they absorb into power, and that number increases every two years or so. There are even companies that manufacture docks with solar panels built in, and Czap says many of Soel’s clients, especially on the commercial side, install land-based solar arrays for off-the-grid charging when boats are at the dock.

Cell Service

The default option for someone who wants to go electric but needs greater speed or range is a backup generator that can recharge the batteries on the fly. Such hybrid setups are more efficient and environmentally friendly than classic engine packages because they usually only require one relatively small generator to feed more powerful electric motors — and those generators often run for limited times.

A cleaner option is to replace the diesel generator with a hydrogen fuel cell, which uses a chemical interaction between hydrogen and oxygen to produce electricity while emitting only water and oxygen. Hydrogen matches the power density of traditional fuels and weighs about the same.

“We can store 2.2 Megawatts of energy in hydrogen, and it weighs 3.5 tons,” Reardon says of his Daedalus project. “To store that much energy in batteries would weigh 26 tons.”

As with electricity, though, it’s important to consider the source. Making hydrogen is power intensive, so if that energy doesn’t come from renewable outlets, the engine isn’t really green. Daedalus got around that problem by setting up a system to manufacture hydrogen on board. Its 88-foot catamaran has solar panels on the trampoline, roof and dinghy cover, along with wind turbines on the transom of each hull. And, when the boat operates under sail, the free-spinning prop turns a turbine that generates power.

At 10 knots, the boat will reportedly run for about four days on the batteries and hydrogen. And once the power runs out, the skipper simply hoists the sail. In about four hours, the solar panels, wind and prop turbines will recharge the batteries. At that point, the renewable energy will run a system that purifies seawater and converts it into hydrogen.

Silent Yachts’ 55-foot, solar-powered catamaran.  The company builds 
vessels to 80 feet. 

Silent Yachts’ 55-foot, solar-powered catamaran. The company builds vessels to 80 feet. 

“You never have to stop,” Reardon says. “Our motto is ‘global range, zero emissions.’” The first Daedalus is about 50 percent built, and the company eventually hopes to sell similar models ranging from 60 to 110 feet length overall.

Hydrogen has its drawbacks, though. Cells are dropping in price, but still expensive; Reardon says the price of a 100 kW unit has gone from $160,000 to $80,000 in the past decade. And for boaters who don’t have the capacity to make their own, the gas is hard to get. For now, hydrogen is finding a home primarily in large, commercial projects that often have some sort of public funding attached.

Netherlands-based commercial shipbuilder Ulstein introduced a vessel last year with a 2.2 Megawatt hydrogen cell that reportedly can run for four or five days in zero-emissions mode before it will need to resort to its diesel generator. And, Ulstein designed the ship to run on cryogenic liquid hydrogen, which the company says will let the vessel store three times more than the compressed liquid hydrogen typically used for fuel cells, thereby extending the range.

Of course, to an even greater degree than with compressed liquid hydrogen, the infrastructure to deliver cryogenic hydrogen doesn’t exist. Still, if builders can find a way to meet the boating world’s power and range needs, the rest of what’s needed will likely fall into place.

“If you give people an actual choice between being clean and not clean,” Reardon says, “they’ll chose to be clean.” 

This article was originally published in the July 2020 issue.

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