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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.


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 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.


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.


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.


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.

This information is subject to change without notice.