low-resolution 2D imagery
by shooting beams from its
transducers up to 1,000 me-
ters at 23 kHz both outward
and downward. The Petrel
crew then commands the
AUV to crisscross the des-
ignated search area in a grid
pattern, hoping it will send
images that match their de-
sired target back to them in
the ship’s control room.
Once an object is located
and the AUV is put in posi-
tion, the AUV uses a multi-
beam sonar at 75 kHz to
produce high-resolution 3D
images that can map a target
with extreme detail.
The AUV mapped an
area around 0.4 by 0.45 nau-
tical miles. It produced an
image that confi rmed what
Petrel was looking for: a vast
debris fi eld that included the
aircraft carrier’s main sec-
tion, bow, stern and bridge,
as well as 11 aircraft, includ-
ing seven Douglas TBD -1
Devastator torpedo bomb-
ers, three Douglas SBD -3
Dauntless dive bombers and
one Grumman F4F-3 Wild-
cat fi ghter.
“Once you start seeing it
on sonar, that’s kind of the

fi nal piece of the puzzle,” says

Paul Mayer, the pilot and re-

searcher for Allen’s crew, in a

video interview. “After that,

it’s getting a good survey of

the area and ROVing.”

ROV refers to the ship’s

remote operated vehicle, in

which a joystick-controlled

unit descends to the seafl oor

to capture video and photos.

Once those came back to the

surface, the ship’s crew had

no doubt they had found the

long-lost Lexington.

EYES

UNDERWATER

The ROV the Petrel crew

uses is an Argus Bathysau-

rus, also capable of descend-

ing over 3 miles below the

surface. It has the look and

shape of a large genset with

robot pincer arms, weighing

in at nearly 6,400 pounds.

When lowered into the water

using Petrel’s heavy-duty da-

vit, it remains tethered to the

ship with an umbilical cable

that both provides power

and a connection to the con-

trol center. It too uses sonar,

in this case short-band sonar

Once you

start seeing

it on sonar,

that’s kind

of the  nal

piece of the

puzzle. After

that, it’s get-

ting a good

survey of

the area and

ROVing.”

“

Once ynce

start seeinstart see

it on sonit on son

PHOTOS: COURTESY PAUL ALLEN

96 | BOATINGMAG.COM | JUNE 2018