E
ARTH’S DEEP OCEAN trenches have been, and are still
being, formed as the planet’s tectonic plates crash into
each other: one slipping beneath another during a process
known as subduction. Trenches are the deep furrows formed
at the boundaries between subducting and overriding plates.
The deepest is the Mariana Trench, near Guam in the North
Pacific and its deepest part is known as the Challenger Deep,
nearly a gobsmacking 11km below the surface. The pressure at
this depth, due to the massive weight of the overlying water, is
1100 times that at sea level: about 16,000psi (pounds per square
inch) compared with 14.7psi at the surface. It’s like the weight of
a locomotive engine stacked onto your fingernail. Extraordinary
engineering is therefore required to construct a vehicle that
can reach the so-called hadal depths and return in one piece.
The first of the three piloted vehicles to visit the Challenger
Deep was the bathyscaphe Tr ie ste, in 1960, piloted by Swiss
engineer Jacques Piccard and US Navy Lieutenant Don Walsh.
To the astonishment of the world, the ground-breaking expedi-
tion reached 10,911m down – the deepest any vessel, crewed or
uncrewed had reached.
Tr ie ste was a large steel sphere attached to a gasoline-filled ‘steel
balloon’. Because gasoline is lighter than sea water, it provided
sufficient lift to bring the bathyscaphe back to the surface. Tr ie ste
was designed and built by Jacques and his father, Auguste, a fellow
explorer, and was bought by the US Navy.
It took five hours to reach its destination and a further three
to return to the surface. Tr ie ste didn’t carry any scientific re-
search equipment or external cameras that could withstand
the pressure. When it touched down on the bottom it raised a
silt cloud so dense it was impossible to see out. Tr ie ste spent less
than 30 minutes on the bottom, but proved it could be done.
The US Navy persisted with the Nekton program, featuring
further Tr ie ste dives, for another six months before winding it
down. For the next 50 years, deep ocean science was the domain
of ‘landers’ – unpiloted robot vehicles that can collect biological
and geological samples and record video.
The next piloted DSV capable of reaching such depths was the
James Cameron-designed Deepsea Challenger, built by Australian
engineer Ron Allum and his team (see Legend of the deep, AG 110).
Technologically, it was a quantum leap from Tr ie ste. The core of
both vehicles was a steel sphere to protect the occupant from the
crushing pressure, but that’s where the similarities ended. Unlike
Tr ie ste, Deepsea Challenger could hold only a single pilot, in some-
what cramped conditions, but the technology was remarkable.
Allum had developed and patented a form of syntactic foam
called Isofloat to provide buoyancy for the 12-tonne vehicle.
Isofloat contains millions of tiny air-filled glass spheres em-
bedded in an epoxy resin – as strong as steel, yet it still floats.
Deepsea Challenger was orientated vertically to descend more
easily through the water column. And it was decked out in100 Australian Geographic
PHOTO CREDIT: GLENN SINGLEMANExtraordinary engineering is therefore required to
construct a vehicle that can reach the so-called
hadal depths and return in one piece.
Victor performs pre-dive
safety checks inside
Limiting Factor at the
beginning of his dive to
the bottom of the
Southern Ocean.