Luxury Subs :: Tourist Subs :: Manned Submersibles :: Used Subs

The Tourist Submarine Industry:
A Summary Article

INTRODUCTION

While the construction of manned submersibles for scientific research and commercial application has decreased dramatically in recent years as a result of their replacement by remotely operated vehicles, a new type of undersea vehicle has been built in substantial numbers; the tourist submarine.

Approximately 48 purpose-built tourist submarines have been constructed in the last ten years and seven commercial deep submersibles have been converted to carry paying passengers as well. Today, tourist submarine operations span the globe, providing approximately 2 million passengers each year with the opportunity to view the creatures of the sea while contributing $150 million in revenue to the operators of these vehicles.

HISTORY

The first tourist submarine, the Auguste Piccard , was built for the 1964 Swiss National Exhibition. The 40-passenger vehicle was capable of diving to 610 meters, and in a 16 month period the submarine carried 32,000 people to the bottom of Lake Leman. After the Exhibition, regulatory difficulties precluded the use of the submarine for passenger carrying purposes in the U.S., and the submarine later was converted to commercial application. The vehicle was quite large, with a length of 28.5 meters and a displacement of 180 tons. Notably, it is still the largest and deepest diving tourist submarine yet built.

In the mid 1970's, Kawasaki Heavy Industries executed a design for a 40 passenger tourist submarine, but the vehicle was never constructed. It was not until the advent of a company named Research Submersibles in 1983, that true passenger carrying operations were established; however, the vehicles were converted commercial submersibles with a limited seating capacity of one pilot and two observers. They plied the depths of the famed Cayman Wall, often times to as deep as 600 meters. RSL still exists today and routinely operates its Perry class submarines to the 250 meter level.

In 1984 a British Columbia based company managed by people that had worked on modifications to the Auguste Piccard, designed and built a 28-passenger tourist submarine, the Atlantis I, which began operations the following year in Grand Cayman. The same company had placed two more vehicles in service by 1987, and at that time other companies began establishing operations of their own. Today, Atlantis Submarines International (ASI) remains the industry leader, having designed and constructed 12 tourist submarines with three different capacities; 28-, 46- and 64-passengers.

ASI has prospered due to their vertical integration. The company only builds submarines for themselves and their joint venture partners or licensees. In all cases they are directly responsible for the day to day operation of the vehicles. ASI is the only company that operates more than two tourist submarines. The remaining operators are all independents, having purchased their submarines from one of the many manufacturers that have existed over the past ten years.

The Auguste Piccard in 1964. CURRENT INDUSTRY STATUS

After a period of rapid growth the tourist submarine industry is "reorganizing" following the bankruptcy of two of the largest independent submarine manufacturers and in a financially related matter, several of their customers. Currently, there are several tourist subs for sale on the secondary market. The number of "orphaned" t-subs available at reasonable prices has adversely affected new construction sales, yet the overall industry activity level is high, with several new prospective operators considering entry into the business.

ECONOMICS AND RELATED FACTORS

The most successful tourist submarine operation maintains passenger load factors in excess of 90% on a 48-passenger vessel making 10-12 dives per day, 320 days per year with a ticket price of $95. This amounts to gross revenue of over $11,000,000 per year with a pre-tax annual profit of well over $7 million. In such optimum circumstances the entire capital equipment and pre-development expenditures can be amortized in a 12 month period, making tourist submarine operations potentially very profitable.

Typical start-up costs include approximately $3.7 million for a new 48-passenger tourist submarine and another $2 million in pre-development costs, operating capital reserve, support equipment, crew training, other capital equipment, pre-marketing and infrastructure.

As a rule of thumb a tropical location of limited geographic extent must have 125,000 incoming annual tourist arrivals for every 12 seats on a tourist submarine. A 48-passenger vessel would then require a location with 500,000 tourists. This significantly narrows the number of suitable locations for the larger size submarines. The author's comprehensive site feasibility analysis evaluates over 200 separate factors in an effort to predict the success of operations. The ten major categories are:

  • Dive Site Quality - (e.g. visibility, depth, features, marine life)
  • Dive Site Logistics - (e.g. currents, sea state, weather, proximity to shore)
  • Dock Site Facilities
  • Maintenance and Haul-out Facilities
  • Storm Refuge Plan
  • Passenger Facilities
  • Market Profile & Visitor Demographics
  • Maritime Law
  • Environmental Permits
  • Long Term Growth Potential

Several t-sub operators have ignored one or more critical factors, and have consequently seriously compromised their ability to be successful. Poor site selection and/or undercapitalization have accounted for virtually every t-sub operational failure.

This tourist submarine in Bermuda failed for logistics reasons

DESIGN AND ENGINEERING

All of the tourist submarines currently operating were designed by engineers from the manned submersible community as opposed to individuals with military submarine design experience. As a result, tourist submarines tend to be more analogous to manned submersibles in nature. They are solely battery powered, and as a consequence have limited speed, range and endurance. Because observation is an important factor the viewports are quite large and the vehicles operate at low speeds of less than 1.0 knot and possess excellent maneuverability, which includes the ability to "hover" over a given spot on the sea floor. Unlike military submarines, manned submersibles have many key mechanical components located outside the pressure hull, resulting in higher parasitic drag and increased maintenance requirements.

Tourist submarines range in capacity from 3-passengers to 64-passengers. The most common size for a tourist submarine is 46-48 passengers, followed by 26-28 passengers. Economics favor the larger vessels because the cost of maintaining the basic crew and support infrastructure is to a certain extent independent of vehicle size, while overall revenue is directly related to the number of passengers.

Pressure Hull & External Framework

The pressure hull resists the hydrostatic forces imposed by seawater and isolates the occupants from the external environment. The pressure hull is typically a steel cylindrical section mated to a forward steel hemisphere with integrated spherical sector viewport, and either an aft hemispherical or conical steel section. The pressure hulls are composed of fine grained, medium to high tensile steel with diameters on the order of 1.6 meters to 2.4 meters. Ring frames are either placed internally or externally and serve to stiffen the hull, while lateral viewports are sealed with o-rings and a retaining ring into forged steel inserts between the frames. However, one 40-passenger tourist submarine, the Comex Seabus, has a pressure hull composed almost entirely of polymethyl methacrylate (acrylic plastic) and provides superior viewing for the passengers.

Typical tourist submarine diving depths are 50 meters to 100 meters. Forward hemispherical sector viewports for the pilots tend to be quite large, from 1.1 meters to 1.8 meters in diameter, while the side passenger viewports, which are shared by two passengers, are normally 600mm to 800mm. Side windows are generally flat, but can also be spherical sectors which are more load resistent and provide better downward viewing. Two entrance trunk and hatch combinations are required and range in diameter from 700mm to 1.2 meters.

Tourist submarines have steel or aluminum frameworks attached to the pressure hull that provide support for the fiberglass deck and superstructure as well as attachment points for high pressure air and oxygen bottles, main ballast tanks, etc. A skid assembly provides a base that protects the bottom of the pressure hull and is used for securing hard ballast tanks, trim and drop weight assemblies, thrusters and other components. In some cases a pipework frame provides collision protection for forward and side viewports.

The pressure hull of a 36-passenger submarine.

Internal Arrangement

Tourist submarines are designed to provide passengers with a comfortable environment from which to view the subsea world, and the degree of comfort and the quality of the view are obviously critical to passenger acceptance of the vehicle and the experience as a whole.

The main design compromise is in finding sufficient battery storage space within the pressure hull while still prioritizing passenger comfort. Battery capacity is a key issue directly related to vehicle speed, range and endurance. Approximately half of the larger tourist submarines have long battery boxes that are situated in the center of the passenger compartment and form the basis for the molded passenger seats. This design is characterized by two aisles, and a seating arrangement that has the passengers situated back to back, with two passengers facing each viewport. The advantage of this approach is that it provides considerable space for batteries and these vehicles have ample capacity for 12 or more one-hour dives between battery charges. Other tourist submarines have smaller batteries placed beneath the slightly elevated floor of the passenger compartment, allowing for an uncluttered expansive interior with a central aisle. Two comfortable individual pedestal mounted seats face each viewport. Typically these vehicles have endurance limits of eight one-hour dives per day.

Again, approximately half of tourist submarines have dedicated machinery spaces in the aft section that contain electrical, mechanical and hydraulic equipment separated from the passenger compartment by a soundproof bulkhead. The remaining vehicles largely install the same equipment in spaces in side mounted cabinets and in areas below the floor in the passenger compartment while using the aft section as an area of additional passenger seating around an aft-facing large hemispherical sector viewport. In practice it has been found that passengers dislike seeing the sights moving away from the submarine and prefer other seats. The main manufacturer of this style of submarine is removing the aft viewport and changing the aft section to a machinery compartment.

Each tourist submarine has a pilot's compartment behind a large spherical sector acrylic viewport located in the forward portion of the pressure hull. All control and navigation functions are carried out from this area.

Interior of a 48-passenger submarine.

Ballast and Trim Systems

Tourist submarines have main ballast tank (MBT) systems composed of rectangular ballast tanks attached to the upper sides of the vehicle which are open to seawater at the base. The system includes a set of air injection and vent valves connected to main and reserve high pressure air tanks located within the framework outside the pressure hull. The purpose of the main ballast tanks is to provide the vehicle with the necessary freeboard, stability and buoyancy while in the surfaced condition. Main ballast tanks can also be blown at depth in an emergency, resulting in a rapid, uncontrolled ascent. MBT buoyancy is typically on the order of 15% of the submarine's weight in air.

Normally there are at least three MBTs on each side of the submersible which may be composed of fiberglass reinforced plastic (FRP), steel or stainless steel. In most cases the vent and blow valves are pneumatically actuated, although both electrical and hydraulic actuators have been used.

Variable water ballast tank (VBT) systems are designed to allow the vehicle to be neutrally buoyant regardless of passenger load. Typical VBT capacity is equivalent to the weight of the rated maximum number of passengers. For instance, a 48-passenger submarine with three crew would ideally have VBT capacity equal to the average passenger weight (70 kilograms) multiplied by 48, for a total of 3360 kgs. This would allow the submarine to operate with a total of only three crew on board, in which case the variable ballast tanks would be full, or with a full load of passengers and empty VBTs.

VBTs are usually one-atmosphere, pressure resistant tanks, two to six in number, located outside the pressure hull. In a few cases the VBTs are located inside the pressure hull beneath the cabin floor.

Water is pumped into and out of the VBTs with one or more high pressure pumps. When water is pumped out, air is injected into the tank to maintain pressure and prevent pump cavitation. In some cases only high pressure air is used to eject water from the VBTs. In either case it is critical to reduce the VBT adjustment time while the submarine is on the surface. Some early tourist submarines took up to 40 minutes to adjust ballast, resulting in a reduced dive schedule. VBT adjustment times are now typically on the order of 10 minutes or less.

Tourist submarines also have a provision for lead ballast that can be varied to compensate for differences in water salinity or additions or deletions of equipment.

Many tourist submarines are capable of using their VBT systems for pitch trim adjustment to compensate for differences in passenger loading, either by pumping water between forward and aft tanks or by differential filling. In addition to VBT trim capability some t-subs have hydraulically actuated track-mounted trim weights between the skids. These systems can quickly vary the pitch angle by up to 14°, allowing for rapid changes in not only the pitch angle, but also in the submarine's altitude above the sea floor provided there is sufficient forward motion to generate dynamic lift.

Each tourist submarine is also required to have one or more emergency drop weights which are mechanically or hydraulically actuated by the pilot.

Main ballast tank vent and blow valves.

Electrical Power and Distribution

All tourist submarines derive their power from lead acid storage batteries. In all cases the primary consumers; thrusters, hydraulic motors, air conditioner fans and compressors, scrubber blowers and underwater lighting are operated from 120VDC or 240VDC current. Navigation, control and communication systems use 24VDC or 12VDC current.

Battery selection and systems design is critical to a safe and successful vehicle, and up to 20% of the pressure hull volume may be relegated to battery storage. Batteries are selected to last a minimum of 1500 deep cycle charges or five years.

Standard lead acid traction batteries are common and are inexpensive and reliable with slightly higher power densities then the gel cell alternative. Drawbacks include increased maintenance requirements and a tendency to outgas hydrogen during discharge, as well as during charging. Because lead acid batteries are not sealed, accidental immersion in sea water can cause the dangerous production of chlorine gas.

Gelled electrolyte batteries are sealed and relatively maintenance free. Typically they can be deeply discharged and left in that condition without deleterious effect. However they are sensitive to charging rates and must be charged over at least a 12 hour period (C/12) while wet cell batteries can be charged at a more rapid 8 hour rate. These batteries are more expensive than their wet-cell counterparts and have slightly lower energy densities. Recommended regular discharge is to the 40% level, as opposed to 20% for wet cells. Most gel cell designs undergo no hydrogen outgassing during discharge.

Some wet cell systems in use have an automated distilled water top-off system as well as a provision to circulate the electrolyte between cells during charging. This cools the electrolyte and also prevents stratification.

Batteries inside the pressure hull are always isolated from the passenger compartment and monitors are installed to detect the presence of hydrogen. One tourist submarine model has the batteries situated in external one-atmosphere pods. All tourist submarines have a provision to ventilate the battery compartments during charging, but discharge is accomplished in three separate ways. Most common is the sealed battery compartment which is closed during submarine operations.

Hydocatylator caps are attached to the inside of the battery compartment, but care must be taken to insure that hydrogen levels remain low and in some cases dives have had to be aborted by vehicles using this system. Another approach is to continuously vent the battery boxes into the larger volume of the pressure hull so the resultant dilution eradicates the risk of the hydrogen concentration approaching the lower explosive limit level. Alternately, a platinum-based catalytic converter system can be used to reduce the hydrogen to water.

All tourist submarines have well designed electrical systems with extensive circuit protection and ground fault detection capability. Main power for the submarines is either 120VDC or 240VDC. Several submarines have sealed, pressure compensated AC thrusters and so power is converted from DC by the use of inverters.

Control and navigation equipment is powered by 24 V or 12VDC power from a separate battery bank. The emergency battery bank is also separate and powers the essential equipment in an emergency. Emergency electrical system design includes a trip switch that interrupts the main and control battery systems and switches critical equipment to the emergency bank. Some designs alternate use of the control and emergency banks to keep the batteries charged. Many t-subs also have a separate 24V/12VDC battery bank for communications equipment in order to mitigate electrical interference.

The battery container. The lid provides seats for the passengers.

Propulsion and Maneuvering Control

Tourist submarines generally have considerable parasitic drag as a result of the externally mounted components, including thrusters, main and variable ballast tanks, exostructure, high pressure air and oxygen bottles, external frames and other equipment. Speeds are quite low, with a typical maximum of 3.0 knots. Actual operating speeds are in the region of 0.5 -1.0 knot, as faster speeds tend to be the enemy of observation.

Forward and reverse thrust is generally provided by two to four, sealed, pressure-compensated electrical thrusters operating at 120V or 240V. Occasionally, hydraulic thrusters are used. Motive power output varies from 3.5 kW to 15kW per thruster. The thrusters may be fixed, variable incidence or rudder mounted. In a few cases a single electrical motor internal to the pressure hull provides power to a main propeller shaft. In all cases the propeller is contained in a Kort nozzle. Often the nozzle is screened to prevent accidental ingestion of foreign objects.

Tourist submarines are very maneuverable as a result of bow and stern mounted lateral thrusters and twin vertical thrusters. The t-subs can sidle sideways in either direction or rotate in their own length. Precision vertical control is also possible. In most cases these maneuvering thrusters are identical to the main forward/reverse thrusters to provide for interchangeable spares.

Maneuvering is accomplished through digital proportional joystick control. In most t-subs each thruster pair is controlled by one joystick. In more advanced systems all maneuvering control function is integrated into one F-16 style joystick. Rudders, variable incidence thrusters and steerable Kort nozzles are generally hydraulically actuated. Typical maneuvering control instrumentation includes thruster RPM gauges, a rudder/thruster angle meter and water contamination warning lights.

Pilot's maneuvering control console.

Life Support and Safety Systems

In a tourist submarine the cabin pressure is always maintained at very close to one atmosphere, regardless of the depth of the vessel. Life support is effected by injecting pure oxygen into the cabin to maintain 19%-22% by volume, while the carbon dioxide is absorbed by a chemical compound in a scrubber system.

High pressure oxygen is generally stored at 50 bar in individual bottles located outside the pressure hull, typically secured to the framework beneath the main deck. The main oxygen system provides sufficient oxygen for at least an entire day of operation. A second, independent emergency oxygen system is required to provide a minimum of 72 hours of life support for a full complement of passengers and crew.

The oxygen supply, reduced in pressure by a regulator, is either controlled manually by the pilot or is automated by a solenoid valve controlled by the oxygen analyzer. In the event of automated control, a manual backup is provided.

The carbon dioxide component of the air in the passenger cabin is removed through adsorbtion by circulation through a porous bed of soda-lime. A high volume blower forces the air through the scrubber cannisters. Carbon dioxide levels are thus maintained at levels below 0.5% by volume. Some t-sub designs provide for several scrubber/blower combinations located throughout the passenger cabin, while others rely on a single system with several duct-work linked pickup and outlet points.

Emergency scrubber compound is stored in accessible sealed containers within the pressure hull. In the event of emergency the scrubber compound can be replaced periodically. A 24V emergency scrubber fan is part of the emergency circuit. Carbon dioxide is monitored by the atmospheric monitor system and a manual gas monitor is also included in the emergency supplies.

Virtually all tourist submarines also have an air conditioning system to cool and dehumidify the cabin air.

Fire protection includes both active and passive fire systems. Passive systems include flame retardant materials, while the active systems include flame detectors, high temperature alarms and a pilot controlled Halon 1301 fire suppression system. Individual closed circuit emergency breathing systems with two hour capability are provided for each passenger for use in the event of atmospheric contamination by fire.

Emergency food and water rations, inflatable life preservers and first aid kits are included in the submarine emergency equipment.

Communications, Navigation and Monitoring

During tourist submarine operations a surface officer aboard a surface vessel that tracks the submarine remains in constant contact with the submarine pilot through an underwater telephone (UWT). It is the responsibility of the surface officer to make sure there are no vessel traffic conflicts when the submarine surfaces.

The UWT operates on two frequencies (8.8 kHz and 27 kHz), the appropriate frequency being condition dependent. Generally there are two upward facing and two downward facing transducers on the submarine. An emergency pinger locator is also integrated into the UWT system. In addition to the UWT there is a pilot controlled VHF radio for surface communications, and an internal intercom system as well.

Navigation is typically accomplished by reference to submerged objects and dead reckoning. Virtually all tourist submarines are constrained to one or two dive sites, and the pilots quickly become familiar with the subsea route which is usually less than one nautical mile in length. A fluxgate electronic compass is the usual heading instrument with a magnetic compass or aircraft style gyro as back-up. A Bourdon tube style depth gauge provides depth information while a depth sounder provides altitude data. Some t-subs also have high resolution color imaging sonar for obstacle location/avoidance. A forward facing depth sounder is a lower cost alternative.

Other instrumentation includes an alarm system for water egress, atmospheric monitors, motor over-temperatures, etc. In addition there are electrical voltage and amperage meters, oxygen and high pressure air pressure gauges, battery amp-hour meters, optional speed log and autopilot as well as a wide variety of control valves, electrical switches and circuit breakers. The result is an impressive array of switches and instrumentation in the pilot area.

Pilot's station with control and navigation equipment.

OPERATIONS

A typical tourist submarine operational day begins with the morning crew towing the submarine out to the dive site. The tow speed is virtually always limited to four knots, making this a time consuming endeavor if the dive site is any significant distance from the submarine base. Once on site pre-dive checklists are completed and the first load of passengers is ferried out to the submarine for the at-sea transfer. The passenger transfer vessel is always capable of carrying twice the maximum number of submarine passengers.

Transferring the passengers from a light displacement surface vessel to the submarine is very difficult in conditions over a sea state three, potentially making a protected dive site important as economic viability becomes difficult if 270 annual operating days are not implemented. Once the passengers are on board and briefed, the surface officer clears the submarine to dive. Usually, the submarine will dive in shallow water, gaining depth over the dive period, which is usually 40-50 minutes. During the dive the copilot or cabin attendant will provide a running commentary for the passengers. Once the submarine has surfaced, the passengers are discharged to the transfer boat which in the interim period has gone to shore for a new load of submarine passengers. The entire process then continues throughout the day and in some cases into the night. Night dives are very popular and the majority of t-subs are equipped with powerful external lighting systems.

At the end of the day the submarine is towed back into base and the maintenance personnel clean the cabin, recharge the batteries, high pressure air tanks, oxygen bottles and carbon dioxide scrubbers and also perform routine maintenance.

For a typical tourist submarine operation a staff of about 35 persons is required, including the general manager, marketing manager and staff, ticket sales staff, operations manager, chief pilot, pilots, copilots and attendants, surface officers and crew, divers, transfer boat captains and crew, training officer, and maintenance officers and staff.

A tourist submarine with tender and passenger transfer vessel.

TRENDS AND OPPORTUNITIES

ASI, the largest operator of tourist submarines has recently completed construction of a 64-passenger tourist submarine which is now operating in Honolulu, Hawaii. In terms of passenger capacity, this vehicle is the largest t-sub yet built, and certainly ASI will build other submarines in this size as the opportunity arises. They plan three submarines for a Miami, Florida based operation.

New construction has slowed as the supply of used tourist submarines available for purchase at reasonable cost remains excellent. The refit and refurbishment of used equipment is taking place, with one 48-passenger tourist submarine being rebuilt for a Florida location. There are no diesel electric tourist submarines currently operating, yet one U.S. company is offering several models. The advantages include greater speed, range and endurance and the ability to recharge high pressure air banks and the batteries while running on the surface. Transferring passengers from shore to the dive site aboard the submarine obviates the need for a passenger transfer vessel and crew while mitigating the number of weather related days where operations are not possible because of passenger transfer difficulty due to high sea states.

Today, worldwide, the tourist submarine experience is remarkably similar. New trends include smaller tourist submarines in the 16-passenger size range which are of interest to resorts requiring market differentiation from their competitors. Deeper diving t-subs, capable of dives to 300 meters or more provide a mechanism for a new and different experience at increased ticket prices. Meal and drink service on such vehicles is also possible.

Acrylic plastic is the latest material of choice for t-sub pressure hulls. The one acrylic tourist submarine in operation provides an experience far superior to that of its conventional counterparts. Two new, 44-passenger acrylic t-subs slated to operate at Ko Olina, Oahu, Hawaii are in the design stage now.

The opportunity to operate a tourist submarine in conjunction with an ocean activity center also exists in the design stages for two different clients. In one case, the floating, semi-submersible activity center with large subsurface glass-clad acrylic windows includes an underwater bar and restaurant, each with 40 seats, and a separate connected complex with underwater hotel suites. Each suite has a spiral staircase to an above-water lounge area with private deck. The fact that the unit floats means that construction costs are minimal and easily compete with the cost of waterfront real estate. The tourist submarine, gift shop, bar, restaurant, snack bar and water sports center each provide separate profit centers in one integrated floating unit.

And finally, perhaps the most ambitious opportunity is to construct and operate a cruise-ship style submarine. A vehicle on the order of 50 meters in length and 600 tons displacement could provide 15-20 luxury private cabins similar to those Pullman car style cabins found on the Venice-Simplon Orient Express. The trips would be of 24-hour duration and would include extremely high service levels and a per person ticket price in the region of $2,000.

Resort sized submarines like this are proving popular.

ABOUT THE AUTHOR

L. Bruce Jones is the President of U.S. Submarines, Inc., a company engaged in the design, engineering and construction of diesel electric submarines and conventional manned submersibles. For seven years, the author has provided a wide range of consulting services to the tourist submarine industry. Mr. Jones is the Chairman of the MTS Manned Submersible Committee and also sits on the American Bureau of Shipping's Special Committee on Underwater Systems and Vehicles.

REFERENCES

Allmendinger, E.E. editor. 1990. Submersible Vehicle Systems Design. The Society of Naval Architects and Marine Engineers.

Busby, R.F. 1976. Manned Submersibles, Office of the Oceanographer of the Navy

Busby, R.F. 1990. Undersea Vehicles Directory, Busby Associates, Inc.

Jones, L.B. 1993. The emerging undersea leisure industry. Sea Technology. 2: 37-42

Jones, L.B. 1990. Preparing the comprehensive business plan for underwater leisure projects. Proceedings of Tourist Oceanology International

Jones L. B. 1992. Design and Operational Developments in Tourist Submarines. Proceedings of MTS '92

Jones, L.B. 1994. Design Rationale of the Nomad 1000 Multi-purpose Diesel Electric Submarine. Viewports 4: 6-16

Pritzlaff, J. editor. 1992. International Safety Standard Guidelines for the Operation of Tourist Submersibles. The Society of Naval Architects and Marine Engineers.

Walsh, D. and L.B. Jones. 1996. The Worldwide Tourist Submarine Industry. In preparation

Copyright, 1996, Marine Technology Society