Not Your Grandfather's Duck Boat

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Lockheed Martin 8x8 Amphibious Vehicle

Any vehicle that can swim, climb out of the water on its own and then drive on land is considered an amphibian. There have been many attempts at these wheeled amphibious vehicles—from the dainty German Amphicar of the 1960s to the wild Gibbs Aquada or Rinspeed Splash of more contemporary design.

For military use, the most famous wheeled amphibian is World War II-era DUKW or Duck boat, repurposed today for tourists to sightsee along city streets and waterways.   

“In the past, the challenge in designing amphibians has always been an issue of making compromises in the design, which has generally led to vehicles that weren’t very good in either ‘land mode’ or ‘sea mode,’” said David Hunn, senior fellow and technical director working on Lockheed Martin’s Amphibious Combat Vehicle (ACV) program.

The real design challenge, according to Hunn, is how you can make a military vehicle that is good at being both, while also being very survivable on a modern, hostile battlefield.

“I think of it like designing a four-legged stool,” Hunn said. “One leg is vehicle survivability, one leg is water operations, one leg is land operations and the fourth leg is affordability. If you have any shortfall with any of those legs, your stool is not going to work very well.”

The ACV will meet the basic mission of getting Marines safely from the ocean to the land to the fight, especially important today considering that the service’s current amphibious vehicle, the Assault Amphibious Vehicle, is more than 40 years old.

“For military amphibians, you don’t have the benefit of swimming in calm lakes or canal ways and then driving on smooth roads,” Hunn said. “You’re swimming through, oftentimes, big waves, ocean currents, nighttime and storms—and then operating in rough, off-road land conditions.” 

acv-design

THE PHYSICS OF FLOATING

How do you get a vehicle that weighs over twenty tons to float? Thanks to the insights from the ancient Greek philosopher Archimedes, we know that for an object to float, the volume of water displaced by the object must weigh the same or more as the object itself.

That’s where design comes into play.

An efficient swimming amphibian design starts by first understanding the vehicle’s mass, followed by “architectural studies” so designers can get the hydrodynamic shape of the vehicle just right. This shape also has to consider land survivability—certain hull shapes are more blast resistant than other shapes.

A clever intersection of these two, often competing needs, results in an optimum design that swims efficiently and is very survivable, a characteristic the old Duck did not possess.

“Of course, hundreds of other considerations come into play, as well,” Hunn said. “For instance, the design has to be entirely waterproof, without any leaks. The fewer openings you have, the fewer places you have for it to leak.”

There are also no windows except for the driver. Hatches only appear on top of the vehicle to help keep it water-tight, while a large backdoor opens up for everyone to get in and out on land. Plus, a sealing and locking system make sure it’s completely waterproof.

A tricky thing about the engine—like the one in your car—is that it needs air to breathe. How do you get air if you’re underwater, which can happen in certain rough sea states or during vehicle launch?

“You have to design an air system for the engine and the people inside so that they have a continuous air supply,” Hunn said. Pumps inside the bottom of the vehicle will auto turn on if water gets in and then pump the water out.

And finally, there’s the swimming propulsion system (usually propellers or water jets) that provide thrust and control authority when swimming. 

AUTOMATION

Unlike previous amphibious designs, the next generation of amphibians are entirely automatic.

When you are ready to come out of the water, there’s a button that simply says ‘land,’ and the vehicle transforms. 

“We’re trying to make this where the driver doesn’t’ have to make a lot of decisions under high pressure. When you hit the dashboard button that says ‘swim,’ everything changes automatically. The wheel works like a regular steering wheel, but it’s now attached to the swim system,” Hunn said.

Automation will enable future variants to incorporate driver-assist technologies, such as “autopilot” while in swim mode. This automatic system also helps with safety, too. If something isn’t quite closed enough, it lets the driver know. 

“I think what we’re going to see initially is commercial amphibian variants that are made for rescue operations—flooding situations that occur and you need to be able to get in to rescue people at a moment’s notice.”

LOOKING AHEAD

So, will the everyday person ever get a chance to take one of these new amphibians for a spin (or swim)?

Maybe someday, but Hunn sees a more near-term opportunity for amphibious vehicles that support rescue and relief efforts, especially after disasters like hurricanes or tsunamis.   

“I think what we’re going to see initially is commercial amphibian variants that are made for rescue operations—flooding situations that occur and you need to be able to get in to rescue people at a moment’s notice.”

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Published September 21, 2015