International VentureCraft Corp.
Tel: 604 436 5653
The Ambient Advantage
Definition
All of the submersibles manufactured by
International VentureCraft corp. are of the Ambient
Pressure variety. What this means is simply that the
pressure inside the hulls of our vessels is always equal
to the pressure of the surrounding water, no matter how
deep the sub goes. This is in contrast to the "One
Atmosphere" design which is common to most research
submersibles as well as tourist passenger subs and
military subs. One Atmosphere subs are completely sealed
and need to have the hull strength to withstand the
difference in pressure between their internal pressure of
one atmosphere, and the crushing pressure of the
surrounding water at depth. A third variety of
submersible is the "Wet Sub", which refers to a
vehicle that may or may not be enclosed, but in either
case water floods the interior so SCUBA equipment is used
to facilitate breathing. An ambient pressure submersible
provides an air-filled cockpit so that occupants can
breathe and talk normally without regulators, and they
don’t have to wear face masks. They will, however,
feel the changing pressure as they descend and ascend in
the water. We refer to our ambient pressure submersible
technology generically as the SportSub design, even
though the same technology is used in all our models.
Principle
The basic principle of the ambient
pressure submersible is the same as a diving bell. It’s
like taking a giant drinking cup and turning it upside
down and pushing it under water. The air trapped inside
stays there as long as you don’t tip it too far
sideways. The bottom is open to the water so the internal
pressure and the external pressure are always equal. The
SportSub design ensures that the air pocket trapped in
its cockpit never shrinks or expands as pressure changes
during descends or ascends. If the air pocket volume were
allowed to shrink or expand with changing pressure the
buoyancy would change, causing a loss of control. This is
regulated by the SportSub’s automatic buoyancy
control system which maintains neutral buoyancy
throughout a dive.
Neutral buoyancy does not equal neutral
stability however. The SportSub is kept in a stable,
upright position at all times because its center of
buoyancy and center of gravity are as far apart as
possible, causing a sort of pendulum effect. The bottom
of the SportSub is where the majority of its weight is
located and the top is where the buoyant air pocket is
located. This causes a very strong tendency for the
bottom of the sub to stay directly under the top and
prevents any air from spilling out of the cockpit.
Fresh air is continually circulated
through the cockpit during a dive. Air flow is regulated
by a flow meter which is set according to a formula,
depending on how many occupants are in the sub. This
formula was developed through extensive research done by
scientists and medical doctors using a SportSub cockpit
in a hyperbaric chamber.
The Experience
One major advantage to the SportSub
design is the intensity of the experience. A ride in a
One Atmosphere sub is a lot like sitting in a chair
watching a TV show about the underwater world. In a
SportSub the feeling is more like entering an alien
environment. Passengers describe it like a trip to a
foreign planet. You feel the pressure and hear the sub’s
automatic buoyancy compensation system working. If you go
deep enough your voice changes and you start to sound
like you’ve breathed helium or turned into Donald
Duck. You feel the air in the cockpit heat-up as you
descend and cool off as you ascend, following Boyle’s
gas law. The interior environment is very humid and
sometimes during the cooling effect of a quick ascent a
cloud forms in the cockpit.
Occupants are sitting in a cockpit that
is half flooded with water. At first this might seem
strange but all the windows as well as the control panel
and dashboard are above the water level. The dashboard is
nearly horizontal and is positioned to come right up to
the chests of the occupants. The water in the cockpit is
therefore generally below and behind the occupants' field
of view and it is hardly noticed once the dive begins.
Operating the SportSub is like flying
an underwater helicopter. The automatically maintained
neutral buoyancy means that all maneuvering can be done
using the thruster motors. These two motors can be
directed up and down to cause descent and ascent. Their
speeds are variable and they can be independently
reversed, allowing the pilot to turn, hover, move forward
and backward, or spin on the spot.
The balanced pressure hull allows
large, flat windows to be used because they don’t
have to withstand much pressure difference. Each occupant
has unobstructed views in all directions, including
straight down, which is where much of the marine scenery
and activity is located. Flat windows minimize the
natural distortion that occurs when water and air meet.
These are used for forward looking windows to permit
accurate visual navigation. The dome shaped side windows
exploit the distortion effect and provide a wide angle
lens effect allowing occupants to see a larger vista. The
SportSub design keeps light from above out of the cockpit
so reflection of interior objects is kept to a minimum.
The ambient pressure principle also
allows easy exiting of the sub without using a lockout
chamber. Occupants are always equalized to the
surrounding water pressure so it’s possible to land
the sub on the bottom, don SCUBA gear, and go out for a
swim. A SportSub can also be equipped with a SCUBA
regulator on an extension hose connected to its internal
air supply. This allows passengers to exit the sub and
walk around on the sea floor. With the right amount of
weight strapped on you can bounce along and feel like you’re
walking on the moon.
Safety
Safety is a major consideration in
every aspect of the SportSub design. Starting with a hull
that isn’t required to contain enormous pressure
makes this task a lot easier. No submersible is safe
unless it is operated within its design limits by well
trained pilots, but the ambient pressure principle is
somewhat more forgiving of errors. The two principal
safety advantages of the SportSub design over a One
Atmosphere design are; the hull can never be crushed by
external water pressure, and, occupants can readily
escape from the SportSub by swimming out, then up to the
surface. These are, of course, worst-case scenarios but
it is a relief not to have to dread the slightest leak.
The SportSub has many safety features
and backup systems to prevent resorting to a swimming
escape. If the operator runs out of air or has an air
supply malfunction there is a complete redundant air
supply system that can be engaged with the simple turn of
a valve in the cockpit. Even if all air supplies are
exhausted the SportSub can surface on electrically
powered thrusters alone. If electrical energy is
depleted, pressurized air can be added manually to cause
a controlled ascent. There are two separate ballast
tanks, in addition to the cockpit, where air can be added
manually to increase the buoyancy. In the unthinkable
event that electrical systems and both air supply systems
fail simultaneously it is still possible to cause the
SportSub to surface by manually dropping lead ballast
bars. If all else fails, and a swimming ascent is
required, a complete SCUBA breathing system is supplied
for each occupant. These can be removed from the sub and
carried while swimming to the surface.
Entry and exit from the SportSub is
accomplished by swimming through the lower aft opening
that remains open throughout the dive. Having to enter
the sub by swimming into the cockpit is a nice way to
help prevent passengers from taking a ride if they aren’t
comfortable under water. This gives the operator some
confidence that passengers will be capable of handling a
worst case emergency situation.
Usability
The SportSub is the "ultralight"
of submarines. In fact the ultralight aircraft revolution
of the 1980s was part of the inspiration for its design.
The intention was to develop a sub that could be safely
and easily operated and maintained by any competent
individual anywhere in the world.
The selection of standard SCUBA tanks
and equipment as the air supply was intended to simplify
the customary submersible air supply systems of pure
oxygen bottles and carbon-dioxide scrubbers.
Availability, cost, and maintenance of such systems would
create a level of complexity that would reduce the appeal
of a sub, especially in some of the remote tropical
locations where its operation is ideal.
The absence of stress on the hull also
reduces cost and complexity. A One Atmosphere submersible
is designed according to rules dictated by an association
such as the American Bureau of Shipping. These rules
require that every component be marked and catalogued and
that licensed technicians do all maintenance. They also
require that every sub be tested and inspected annually
by a representative of their organization. All of these
activities add cost and complexity while consuming a
considerable amount of time. The SportSub is designed to
be easy to operate, support, and maintain, using only the
type of systems required to support SCUBA activities.
This equipment is readily available worldwide and is a
fixture on many larger boats and yachts where diving is a
recreational or commercial activity.
Weight and Handling
The weight of any dry submersible is
dictated by its internal air volume. The weight of a sub
must always be exactly equal to its buoyancy, most of
which comes from the air inside it. If the internal air
volume can be reduced, the weight can be reduced. The
SportSub design provides a very small internal air
chamber because the occupants are half submerged in water.
This is not possible with a One Atmosphere design so they
are inevitably heavier.
Added weight increases the required
strength of all handling equipment. This in turn
increases the weight and cost of the handling equipment.
If the sub had twice the internal air volume it would
weigh about one thousand pounds more. If it did weigh one
thousand pounds more, the weight of a davit to launch and
recover it from a boat deck may also weigh a thousand
pounds more. The added weight carried by the boat would
probably double. What this means is that a significantly
larger boat would be required to carry, launch, and
recover the sub if it weighed more. This fact is
particularly critical when a boat is designed
specifically to carry a sub and passengers to a dive site
in a tourist operation. It also allows owners of smaller
boats to enjoy the advantages of taking their own
submersible wherever they go.
Cost
Another primary objective of the
SportSub design is to keep the cost low enough for
personal recreational use and for profitable tourist ride
operations. To meet this objective, consideration was
given not only to the initial purchase price but also to
the cost of ongoing maintenance as well as auxiliary
equipment required for operation, including launch and
recovery. One Atmosphere designs do not meet any of these
objectives for the reasons explained previously. They are
too heavy, require specialized air supply equipment and
maintenance, and they cost many times more to manufacture
due to their complexity. Wet Sub designs do meet the cost
objectives but are restricted to use by qualified SCUBA
divers and therefore do not provide the ability to offer
rides to friends and/or paying passengers. A Wet Sub also
doesn’t allow occupants to talk normally with each
other and share the dive experience.
Conclusion
The SportSub design using the Ambient
Pressure principle provides the ideal solution for
recreational submersibles and certain commercial
operations. The diving experience is superior,
maintenance is simple, the cost is minimal, handling is
easy, and operation is practical. These subs can be
enjoyed anywhere in the world, including tropical islands
or aboard yachts or commercial vessels.
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International VentureCraft Corp.
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