Take a tour of one of the longest-serving
deep-sea submersibles in ocean scienceInside Alvin
means the pressure equals the weight of an
elephant balancing on a postage stamp. To survive
that, deep-sea craft need to be extremely tough.
The outer shells of subs and ROVs need to be
made of a substance that won’t buckle under the
astonishing pressure. Titanium is often used,
because it’s incredibly strong, corrosion resistant
and is also able to withstand both the freezing
depths of marine trenches and the soaring
temperatures of hydrothermal activity.
The pressure hull of a submersible is the area
that needs to be hardiest of all, keeping the
internal pressure comfortable for human
occupation. A sphere is the most common form, as
with this specifi c shape the pressure is applied
equally. Many submersibles feature sphericalpersonnel pods constructed of one element, with
no joins that may weaken the structure. DOER
Marine’s Deepsearch submersible employs this
technique, with their sphere made out of
incredibly tough glass.
One submersible that uses a radically different
pressure hull is Virgin Oceanic’s sub. This features
a cylindrical compartment made of 13-centimetre
(5.1-inch) -thick carbon fi bre, capped with a
see-through v iew ing dome constructed of
incredibly strong synthetic quartz.
A nother key element of submersible design is
buoyanc y. The craft needs to descend, ascend and
be able to ‘hover’ in the water column at the pilot’s
direction. Many submersibles, both manned and
remotely-operated, use water bladders to prov ideballast. These can be fi lled or dumped at will to
ensure that the craft can manoeuv re w ithin the
water column.
To make submersibles and ROVs fl oat, many
possess ceramic spheres fi lled with air, packed in
to their body. The spheres are often fi tted
alongside sy ntactic foam, a light substance made
of glass microspheres mixed in epox y resin. These
features work alongside the ballast and also
function as a safety feature. If the submersible
encounters problems at depth, any expendable
weight can be dropped and the buoyanc y w ill lift
the sub to the surface.
Remotely Operated Vehicles (ROVs) come in
many different confi gurations, with a large range
of depth capabilities and uses. Many are used byThrusters
Seven reversible
thrusters power Alvin
through the depths of
the sea at a cruising
speed of around
1.85km/h (1.15mph).Cameras
and lights
High-defi nition
cameras are present
on Alvin to record
dives, as well as LED
lights to light the way.Sail
Known as the sail, this
holds the hatch where
the pilot and
passengers enter the
submersible before
the pressure hull.Ballast spheres
The variable ballast
system pumps
seawater into or out
of the tanks to alter
the sub’s total weight.Battery tanks
Two battery tanks
power Alvin to
provide up to six
hours of dive time.Personnel sphere
Alvin’s new personnel
sphere is larger, with
improved ergonomics
and fi ve viewing ports.
Sample basket
This allows Alvin to
take equipment to its
destination, or bring
samples and artefacts
back to the surface.Manipulator
arms
Hydraulically powered
manipulators allow
Alvin to carry out
tasks such as
collecting samples.Number of dives in
Alvin’s 50-year history
SEA