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New Electric Lake Tender

Hits all the Right Buttons

By Polly Saltonstall

The electric motor is hidden under the curved transom, giving the boat a clean profile. A section of the transom lifts up to provide access to the motor when needed. Rendering courtesy Stephens Waring

Electric boat propulsion has been a hot topic for boat owners in recent years as the price of fuel and environmental concerns have risen. A challenge has been marrying elegant design with efficiency and the ability to go far on one charge, since the constant friction of a vessel in the water requires more energy than automobiles rolling down the road.

Bob Stephens at Stephens Waring Yacht Design in Belfast, has been intrigued with marine electric propulsion for some time—his firm designed one of the industry’s earliest hybrid electric boats in 2008 ( /online/tradition/history-of-maine-boatbuilding). So when a long-time customer came to him looking for help in finding a commuter lake boat, he jumped at the chance to go electric. 

The result is Isobel, a sleek new launch under construction at Belmont Boatworks, featuring a classic design with a sophisticated and innovative electric power train and battery that will allow both speed and relatively long-distance cruising. 

Under construction at Belmont Boatworks, Isobel is scheduled for a summer launch. Photo courtesy Belmont Boatworks

The customer had just bought land on an island in Searsmont’s Quantabacook Lake, where she planned to build an off-the-grid vacation home. She knew she would need a boat, but it couldn’t be just any boat. A sailor, whose husband was on his second project with Stephens Waring when they met, she experienced the custom process on two subsequent boats. She had always admired the curvy lines of Italian-built Rivas from the 1950s, and wanted something that looked like a Riva, but that also was quiet and efficient. 

“Coming from sailboats I wanted to preserve the soundscape not only for my own experience, but for the natural wildlife and others living on the lake,” the client explained. “An electric motor decreases noise pollution and allows a stronger connection with nature which is more in keeping with the off-grid island project goals.”

The boat’s primary use is for the mile-long commute between the mainland shore and island, and leisurely lake cruises on the 693-acre lake, but the client also wanted to be able to go fast for waterskiing and tubing. After going for a test drive in a production fiberglass runabout, the client and Stephens went for lunch and revisited a previous conversation about Rivas. She asked if he could design a boat with that sweep and grace in a 28-foot model. He drew a quick sketch. And so the project began. 

She wanted a good-looking boat that also functioned well.

It took time to find the right motor, Stephens said, which turned out to be a 40kW (54-hp) motor from RAD Propulsion, a UK-based company founded in 2018 that has developed cutting-edge electric propulsion for the marine industry. Isobel’s motor is one of the first 100 production versions off RAD’s assembly line, he said. Because the motor is electric and does not need ventilation, it can be concealed under a lifting cowl at Isobel’s stern. With only the lower unit swiveling for steering, the boat’s sleek profile echoes the quiet elegance of its operation. 

Energy storage is provided by Fellten, a British battery manufacturer whose specialty is electrical repowers of classic automobiles. The 55-kWh battery power pack outputs a nominal 350 volts and peak output of 330 kW. At 26 inches long by 21 inches wide and just under 2 feet high, the battery nestles under a cover in the center of the rear cockpit, creating a convenient spot for seating or a table top for picnics.

Added benefits of the electric propulsion include far less maintenance and greater reliability than a conventional engine, points out Stephens, as well as ease of refueling on a remote lake, far from gasoline stations. 

The Fellten (which means “lightning” in Welsh) battery system supports fast charging via a CCS standard system, but Maine doesn’t have any fast chargers for boats, Stephens said. Instead, Isobel’s battery can be charged in about four hours from solar-powered batteries on the client’s island dock or from a 220-volt hookup on the land side. 

“This is a boat where you can get the power you need at the place where you need it,” Stephens said. 

At full power, the system provides a range of 25 miles or approximately one hour of top performance operation. This equates to half a dozen round-trips to the mainland at top speed. At a cruising speed of 12 to 15 knots, the range is doubled. 

At 27 feet, 10 inches long and 8 feet wide with a draft of 11 inches, Isobel has a low sheer allowing comfortable stepping aboard amidships. The simple dash behind a curved windscreen features faux leather and metal-lined panels. Her stern platform allows for water access and facilitates swimming and waterskiing. Her shallow draft makes trailer-launching viable even on a basic ramp. For any planing watercraft, weight is the enemy of speed and range. The wood-composite construction—cedar-strips sheathed in fiberglass for the hull and a plywood/foam/plywood sandwich for the deck and cockpit sole deliver a light displacement of around 2,866 pounds (with two persons aboard), as well as a cost-effective custom build, Stephens explained.

The client wanted a powerboat with the sleek looks of a Riva, but not the noisy and smelly engine. Rendering courtesy Stephens Waring

The client is thrilled with the design and the collaboration with her team.

“This is a great team that is excited and invested in the project. It’s satisfying to be able to tailor the build,” she said. “Building a custom boat has an increased financial commitment, but the gain in building a team with the experience, integrity, and expertise that Bob and Belmont Boatworks bring to the project is hard to put a price on.”

Construction of Isobel is under way at Belmont Boatworks in Belmont, with an expected launch this summer.

Polly Saltonstall is MBH&H’s editor at large.



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