Page 110 - AlertDiver_Spring2013

There is hardly anything that can compare
with taking that first breath of compressed air
underwater. It’s totally unnatural — contrary
to every human survival instinct — but
the resulting sensation is electrifying. One
experience that comes close is the first time one grabs the
handles of a diver propulsion vehicle (DPV) and sets off like a
fighter jet on an adrenaline-charged flyby of the reef. Effortlessly
carving high-speed turns while hugging the contours of the
bottom is serious underwater fun. Without a doubt, DPVs
redefine diver performance.
DPVs — or scooters, as many divers call them — come
in a variety of configurations. The most popular design is
the teardrop or torpedo-shaped rig with an aft-mounted
propeller and handgrips. The diver squeezes a trigger or
triggers to route power to the motor and adjusts his body
position to steer the DPV. Alternative configurations include
ride-on scooters, back- or tank-mounted models that free up
divers’ hands and even foot-mounted DPVs.
Matters of Efficiency
No matter the configuration, the trick to manufacturing a
high-performance scooter is to master efficiency at each level
of energy conversion. First, the battery must efficiently store
chemical energy, and then it must efficiently convert that
chemical energy into electrical energy. The control circuitry
and motor must then efficiently convert the electrical energy
into mechanical motion. Finally, the propeller must efficiently
transfer the rotary mechanical motion into propulsive force.
If the designer can shave a percentage point or two at each
conversion, the overall performance increases significantly.
Unfortunately, improved efficiency and robust design
translate directly to dollars, and so in general, the machines
that provide higher performance come fully equipped with
higher price tags. While an entry-level DPV might cost about
$200, more powerful (faster) models and those designed for
greater depths can range from $400 to more than $2,000.
One measure of a DPV’s capabilities is its run time — the
period the scooter will operate on a full battery charge. This
combined with speed, the other primary performance measure,
gives users an idea of the distance the DPV can take them.
It’s important to consider that over time battery capacity and
efficiency can degrade, so a better battery has a higher long-
term value. If you’re going to splurge on a particular aspect of a
DPV, a better battery is the place to do it.
Battery Technology
Unsurprisingly, battery technology is one of the limiting
factors in DPV performance. In this age of tiny gadgets and
environmental awareness, scientists and engineers are motivated
to constantly push the envelope with regard to battery
technology. The more energy they can store in a given weight
and volume, the more performance users can extract from
GEAR
B y R o b e r t N . R o s s i e r
Redefining Performance
Diver propulsion vehicles: manage the risks and enjoy the ride
108 | SPRING 2013
JAY EASTERBROOK
DAVID RHEA