Gweduck: The experimental dream machine

If you are not from the Pacific Northwest the term Geoduck — pronounced “Gooey duck” — probably conjures up an image of a mallard in molasses. Actually, it’s a form of shellfish native to Washington state. Recently, the term became synonymous with an experimental aircraft.

The Mahon-Ellision Gweduck — note the phonetic spelling — is a composite boat-hulled twin engine airplane. It was designed and built at Renton Municipal Airport (RNT) south of Seattle.

At first glance the Gweduck looks like a Grumman Widgeon. The designers, Marty and Ben Ellison and Ross Mahon, seem to be expecting that, because when the airplane made its debut at AirVenture last year they had a placard on the nose reading “NO THIS IS NOT A GRUMMAN.”


Marty and Ben Ellison

“The name Gweduck is a working name, what we are calling it for now,” Marty Ellison explained. “Geoduck is a Native American name that roughly translated is ‘clam that digs deep.’”

They opted for the unusual name because, as Marty noted, the Grumman company always named its aircraft after amphibious birds. “They have mallards, the albatross, the widgeon,” he said. “All the amphibious bird names have been used up, so my brother Ben decided why not name the airplane after a clam?”

The design was about 20 years in development, according to Ben Ellison. It began to take shape when he was considering getting a Widgeon aircraft. The corrosion factor weighed heavily in his mind, so the concept of using composites was explored.

“It is all composite, so it loooooves saltwater,” he said. “You could anchor it in saltwater for a week and it is not going to corrode, rust or dissolve.”

If you compare them by size, the Gweduck amphibian is halfway between a Grumman Goose and a Grumman Widgeon. It has two 300-hp, normally aspirated Lycoming engines. The airplane will cruise at about 138 to 140 knots at 75% power. “Typically, we cruise at about 120 knots,” he said. “It only burns 10 gallons per hour per engine for a total of 20 gallons per hour.”

IMG_2421 The airplane has three fuel tanks in each wing. If all the tanks are full, the Ellisons say the airplane has the range to go from San Francisco to Hilo, Hawaii.

I first caught up with the Gweduck in Lakeland, Fla., during Sun ‘n Fun. Marty Ellison noted that the Gweduck made the trip across the country in three days. “It was a comfortable trip with four and five hour legs,” he said. “It is a very comfortable airplane. It is big enough that you can get up and walk around in it. There is a enough room between two seats to push a beverage cart through if you wanted.”

IMG_2411 He is not exaggerating. The cabin of the Gweduck is tall enough and wide enough to allow for stretching during a long flight.

The roominess of the aircraft was important, but not the most important criteria, he said. “Our first priority was that it had to be good handling on the water,” he said. “The first flight it was off and on the water. We didn’t land it on land until we had five or six hours of flight time.”

The design is still being fine-tuned. One of the things they are tinkering with is the landing gear position indicator and gear placement warning. Right now there is a little window to visually check position of the gear.

IMG_2424 The Ellisons note that even if there was a gear up landing on a hard surface, the aircraft would be able to manage it, because the fuselage is fiberglass with a foam core body and has a couple of layers of Kevlar and carbon fiber hybrid.

When the Gweduck appeared at the Arlington Airshow and Sport Aircraft Convention in July, people gathered around it and fantasized about what they would do with such versatile machine. Round the world flights and fishing on lakes where the salmon normally die of old age were suggested. One man wanted to live on it as sort of a flying yacht.

It will be awhile before the Gweduck is available to the masses. The model is a one-off right now.

“I’m not interested in going into the kit manufacturing business,” said Ben Ellison. “We’re hoping that someone who wants to manufacture the aircraft in kit form will partner with us. It is a proven design with a complete set of tooling and engineering drawings.”

For more information:



Specifications are preliminary and subject to change.

  • Length: 32.5 ft
  • Height: 10.8 ft
  • Seats: 2 pilot, 4 passenger
  • Cabin width: 54 in
  • Airfoil: GA35U-A315
  • Engines (2): Lycoming, IO-540 & LIO-540
  • Propeller: MT Propeller, 3 Blade, constant speed, feathering, reversing
  • Design Gross Weight: 6,000 lbs
  • Useful load (Typical): 1,800 lbs
  • Fuel capacity (each side): Inboard tanks 40 gals/Outboard tanks 60 gals
  • Performance (Estimated): Estimated Cruise Speed 135 knots at 65% power, at 3,000 ft MSL


  1. Stevenwightman says

    The Geoduck is a terrific accomplishment. this kind of airplane is needed to bring back the romantic travel days of the Yankee Clipper. My PT6-20 powered Seawind is not quite as spacious however it too is all composite and it flies up to FL 240 and well over 1,000 NM with IFR reserve. With 200 Kts TAS and an auto pilot coupled to a G 900X, the G1000 equivalent, I can make a long trip and still be unfatigued. To lighten the workload were I crazy enough to take on another decade-long airplane build project, I’d certainly add AP and IFR capabilities. Bahamas and Mexico, here I come!

  2. says

    Beautiful machine. If you can get it going it will be a plus to aviation. We need new aircraft that pilots can enjoy and have fun with them. Also, It could very well be an exeutive aircraft both in far away places or in the Caribbean . Here this would be an asset to aviation. this could get us out of landing on wheels all the time. things are getting stagmant , the same feelling all the time.
    Good luck to you , may it work out for the best.

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