Humans are terrible
swimmers, converting roughly 3 percent of their kicks, strokes and
general underwater exertions into forward motion. We can boost our
efficiency to 10 percent by adding fins, but dolphins, by comparison, can
turn 80 percent of their
energy
into thrust. Not to be outdone, the Pentagon’s research wing, DARPA, is
developing a contraption that lets Navy SEALs and other combat divers swim
faster, and with less effort.
Instead of kicking, PowerSwim calls for a kind of undulation as its hinged
foils pivot up and down. Similar to the way a dolphin or tortoise pumps
its fins, this motion generates both lift and thrust. And while artificial
fins operate within the swimmer’s own wake (they form a kind of
expanding cone, starting at a swimmer’s shoulders), the PowerSwim’s
lead foil—or propulsor foil—sweeps through the water just outside that
wake.
When used properly, the device allows swimmers to cover a given distance
up to 150 percent faster than with fins, while using the same amount of
energy. Much of that boost in metabolic efficiency is due to the muscle
groups used. As DARPA program manager Barbara McQuiston explained, the
swimmer is essentially relaxing into a slightly bent position, instead of
forcing or pushing the foils through the water. This takes the emphasis
off the small muscle groups used to kick, and allows larger muscle groups,
such as the glutes and quads, to take over. During tests, it typically
took around 2 hours for Navy SEALs to fight the urge (and years of
training) to move forcefully and learn the PowerSwim’s unique motion.
If the device is widely used, it could be a huge benefit for combat
divers, letting SEALs
reach
coastal targets without becoming over-exhausted. The goal isn’t to
increase the total distance that personnel can cover, but to get them
there more quickly, and with more energy. Depending on the mission,
swimmers might dump the PowerSwim, along with
rebreathers
and other gear, before setting foot on land.
And
unlike
many DARPA programs, PowerSwim is coming soon—McQuiston says that
the device is at the packaging stage, as researchers determine how to
possibly fold or otherwise reduce its overall footprint, to allow for
more
efficient
transport. Full production units could be deployed within a year.
How It Works
The seesaw movement of the foils creates rolling currents, called shed
vortexes, that sweep back and around to push the foil forward. It’s a
phenomenon exploited by various aquatic species, such as penguins and
dolphins. (Illustration by Gil Ahn)