THE DIVING BELL
Rudimentary forms of the diving bell have been in use since antiquity, although it did not come into frequent use until the latter 16th century. A typical diving bell is a hollow, watertight vessel, open at the bottom and containing a pocket of air within which swimmers can be lowered under water.
As it is easily entered and exited underwater from the open bottom, the diving bell is commonly used by scuba divers to rest or change air tanks while submerged. With some modifications, it is also used as decompression chamber which can be removed from the water while retaining a controlled atmosphere.
The first primitive submarine also appeared in the latter 16th century. Also called called a submersible, the submarine has a pressure-resistant hull which maintains atmospheric pressure regardless of depth. The difference between a submarine and submersible is that the former can recharge its own batteries and compressed air supply at the surface, usually by running deisel generators and compressors. The submersible however, must be removed from the water to have the batteries and compressed air bottles recharged or replaced.
While modern submersibles allow divers to go to greater depths than any other vessel, they are subject to tremendous pressure from the weight of the surrounding water (.445 lbs per square inch per foot of depth). This means they must be built to rigid - and expensive - specifications to ensure safety. Unlike the diving bell,
diver lockout (for submerged entry and exit) with these vessels pose additional
With the advent of the Self-Contained
Underwater Breathing Apparatus (SCUBA), prior to World War II, wet submersibles
became not only possible but practical. Scuba divers carry only a limited
amount of compressed air and to increase bottom time this air must be used
efficiently. The air consumption rate of a scuba diver during periods of
exertion, such as swimming to and from a dive site, is often two or three
times the average resting rate of 60 cubic feet per hour, drastically reducing
The Mantaray represents a unique marriage
of all three previous types of manned submersibles. Although relying on
the latest technologies related to submarine and scuba design, the diving
bell has provided the chief inspiration for the Mantaray.
When a bell-shaped vessel is lowered, mouth down, into a body of water, the pocket of air trapped inside remains equal in pressure to that of the surrounding water. The internal water level rises or lowers like a piston, compressing the air in relation to the external water pressure. This ambient relationship ensures:
If the hull of a diving bell is streamilned, self-propelled and freed of surface lines and tethers like a submarine, and supplied with on-board scuba air supply, a totally new class of submersible results. This unique "flying bell" concept clearly sets the Mantaray apart from other mini subs.
There will be no pressure stress on the hull at any depth.
Swimmers breathing the compressed atmosphere inside the vessel can enter or exit at any depth without the need of an air-lock, or diver lockout compartment.
The Mantaray Submersible combines the efficiency, safety and versatility of the diving bell with the freedom of scuba and the speed, maneuverability and comfort of conventional submarines.
The Mantaray has been designed for maximum stability to prevent it from tipping and releasing air. The center of gravity is at the bottom of the craft, directly below the center of buoyancy (a point on the internal water surface), at a distance equaling twice the height of the trapped air pocket.
The entrance to the Mantaray passenger cabin is at the rear, through the lower hull and below the interior water line. It is large enough to allow two swimmers, in full scuba gear, to enter and exit quickly and easily in a swimming position.
The forward compartment is the actual diving-bell section of the Mantaray. Once inside, swimmers assume a kneeling position, centering their weight at the bottom of the craft. Their heads and shoulders are above water, and they are free to talk and breathe naturlly inside the bubble of air trapped in the upper hull. The leading, planar surfaces in this compartment are made of clear acrylic to allow maximum visibility -- 310 degrees horizontally and 290 degrees
vertically. All operating and life-support controls are in the forward
compartment to ensure safety, convenience and ease of operation.
All peripheral systems on the Mantaray are modular, easily expandable, and interchangeable. This means the basic unit can be modified quickly and economically to perform a variety of special diving tasks.
While external air systems can be employed on the Mantaray, the basic system provided is scuba. There are quick-release mounts below the aft compartment to accommodate as many as six 100 cu. ft. air bottles, although any standard size bottles can be used and the number will depend on the user's needs and mission profile. The forward compartment of the Mantaray is large enough to acomodate two divers in full scuba gear.
The bottles in the onboard system are connected through standard first-stage regulators, with quick disconnect fittings. The system is designed for quick release of each bottle and has independent second-stage mouthpiece regulators and air pressure gauges.
Optional gas systems on the Mantaray include:
Surface supplied air.
Surface supplied mixed gas(helium/oxygen
Onboard mixed gas (helium/oxygen or nitrox).
Ballast and buoyancy are integrated into one system on the Mantaray. The ballast is "fixed", using a 3/4 inch, 300 pound stainless steel plate fastened to the bottom of the craft, plus droppable lead ballast weights for fine trim.
Buoyancy is adjustable by increasing or decreasing the volume of air trapped inside to achieve positive, negative or neutral buoyancy. For positive buoyancy, the volume of trapped air is increased, using a trigger-operated purge valve until the submerged weight of the Mantaray is less than its buoyancy. In this condition, the Mantaray will float on the water surface.
For negative buoyancy, trapped air is released from the hull exhaust port until the Mantaray submerged weight is greater than its buoyancy. In this condition, the craft will stay on the seafloor. This is controlled by means of a rotational acrylic "Constant Buoyancy Valve (CBV)" which covers the hull exhaust and is fastened to the inside of the acrylic viewport.
The CBV also has an exhaust port toward its outer edge. Rotating the CBV exhaust port above the internal water line allows air to escape. When the internal water level rises to cover the CBV exhaust and no more air is displaced, the Mantaray's buoyancy is fixed at a new, lower level.
The buoyancy range of the Mantaray is approximately four cubic feet of displacement, or 258.8 lbs. in salt water and 249.2 lbs. in fresh water. And with the ballast trimmed so neutral buoyancy is achieved with the CBV at the center of its arc, the Mantaray is capable of as much as 129.4 lbs. positive or negative buoyancy (124.6 lbs. in fresh water). It can float on the surface or sit on the bottom,
with a payload capacity of 129.4 lbs. in either direction.
Standard propulsion on the Mantaray
is supplied by two electric thrusters mounted to port and starboard and
providing a total of 82 pounds of static thrust. These are capable of 360-degree rotation about the lateral axis for depth control and speeds of up to three knots are possible.
Power for the thrusters is supplied from deep-charge sealed gel-cel lead-acid batteries. The batteries are pressure compensated in fiberglass battery boxes to retard the effects of pressure and water contamination. They are recharged through amphenol pressure connectors on the boxes. For added safety the battery boxes are fitted with collection bladders that store hydrogen expelled from the cells for release when the batteries are recharged.
The Mantaray was designed to be as safe and simple as practical. As a result its control systems are few and easy to operate:
This is a constant bleed valve which allows the operator to regulate
the free flow of air from zero to 180 cubic feet per minute.
Valve: This is a trigger valve
on the control stick which allows the operator purge air into the human
compartment from an air line regulated at 200 p.s.i. above ambient (the
surrounding water pressure).
This is a simple handle, at the intersection of the thruster shafts,
which allows the thrusters to be rotated a full 360 degrees.
This is a pressure-resistant box, housing the switches for the port and starboard thrusters. The thrusters have two speeds, forward and reverse, and a high-speed boost. They can be controlled separately or in unison and are "fail-safe" protected. Fuses can be changed in the water.
The most important single safety consideration
is operator certification. Because the Mantaray uses scuba as its primary
air system, only a qualified, licensed scuba diver can operate the craft
and their certification card must be presented before a vendor will fill
the craft's air bottles. In addition, there are rigid government safety
regulations controlling the manufacture and maintenance of scuba equipment,
and the Mantaray uses this equipment in precisely the manner for which
it was designed.
Beyond these considerations, the Mantaray was designed from the beginning with safety in mind:
Divers can leave the craft in seconds.
Complete scuba for both divers is immediately accessible from quick-release mounts.
The cockpit area has a 10-minute reserve of air if the primary air system fails.
The protected environment of the Mantaray
reduces the risk of panic and shields divers from sharks and other unwanted
Diver exhaustion from cold water and over-exertion
is dramatically reduced or eliminated.
POTENTIAL: Industrial Applications
Since the introduction of the Mantaray it has recieved enthusiastically from both local and national media. But the most exciting response has
been from the commercial diving industry and other related industries.
The consensus is that a product such as
the The Mantaray is long overdue. Some commercial divers have even told
us they believe The Mantaray is the first major development in the industry
A number of sales and lease arrangements
are currently being negotiated for a wide range of applications. These
Other possible commercial applications include:
Electrical cable inspection.
Hull cleaning and inspection.
Geoduck (clam) harvesting and fish farming.
Search and recovery.
Resting and decompression stations for deep-sea
Log salvage and scaling (sunken).
Boom chain salvage.
General marine salvage.
Insurance inspection and adjusting.
Propeller inspection and salvage.
Geographical submarine surveying.
National defense (subsea operations).
Marina float and dock inspection.
Communication cable inspection.
General subsea construction.
Pollution and environmental study.
Numerous subsea oil operations.
General usage in the forestry, mining and
In addition to their market appeal on screen, these submersibles have practical applications behind the camera as well. Providing an ability to maneuver large equipment under water, these versatile work platforms can serve double duty as mobile camera platforms and can be fitted with large arrays of underwater lights to increase your ability to provide more dramatic underwater cinematography.
The Mantaray Flying Bell can be configured for easy egress/exit for two or three cinematography technicians while underwater. Illustrated here with a closed hatch panel behind and below two passengers, the Mantaray provides ample room for lighting and other equipment within the cabin.
If required, up to 400lb submerged weight can be attached to the base of the craft. Neutrally bouyant payloads such as lighting arrays, cameras, and camera operators can be secured anywhere on the hull.
For large assemblies, additional thrusters can be added to hold station or to make way against prevailing ocean currents. Air and battery systems are also modular and additional scuba bottles and battery packs can be added as required to extend the Mantaray's capabilities.
Mantaray Video Animation
File Type: AVI, File Size: 4.10 MB, Clip Duration: 0:00:42
While the industrial market potential
more than justifies the introduction of the Mantaray, there is another
large, and as yet untapped, market for this exciting and innovative craft:
the sport diving, leisure craft and tourism industries.
The sport diving industry is growing faster
than almost any other leisure industry. There are now more than 3.5 million
certified scuba divers worldwide, most of them sport divers. Even in Canada,
with its frigid northern waters, there are more than 300,000 certified
scuba divers (about 1.2 per cent of the population).
These numbers are growing daily, despite
the fact that divers-to-be must spend hundreds of dollars on lessons and
rental equipment before they "get wet" for the first time and thousands
of dollars on new equipment once they become certified.
The Mantaray was designed from the outset
with the sport diver in mind. It is safe, simple to operate and based on
all the physical laws that are part of the sports diver's early training.
And now, for the first time, an experienced
diver can take a non-diver underwater in the Mantaray to experience this
beautiful silent world before committing time and money to lessons and
equipment. People who have dreamed about diving, but have hesitated because
of the initial costs, will have the opportunity to see first-hand why diving
is becoming such a popular sport. This can only help the sport grow with
a corresponding growth in the market for the Mantaray.
Price is another reason the Mantaray has
tremendous potential for non-industrial, as well as industrial use. It
can be produced and marketed at a price that is competitive with other
leisure craft such as ski boats, sail boats, motor bikes, snowmobiles,
sail planes, hang gliders, etc. The Mantaray will fill a large gap in this
The major non-industrial markets for the
Mantaray are expected to be in warm-water recreational areas such as:
There is a tremendous opportunity with the
Mantaray for commercial exploration within the tourist industry in these
and other tropical and sub-tropical regions. Distribution for sale, rent
or lease of the craft in these regions would most likely be through diving
shops and schools, major resort operations and marinas. Some possible applications
The southern United States and Hawaii.
The Bahamas and the Carribean Islands.
Fiji, Australia and New Zealand.
Tourist areas of Central and South America.
The Mediterranean Riveras and Islands.
The Pacific Rim Holiday Islands.
Mantaray Technical Specifications
Mantaray Prices and Equipment
Guest usage at hotels and resorts.
Marina services and maintenance.
Promotion for local tourist industries.
Intertidal shore patrols for sharks, barracuda,
© Copyright Midwest Engineering & Design 1979-2009, All Rights Reserved