Mention “submarines” and most will think of the large nuclear vessels, capable of extended submerged voyages throughout the earth’s oceans or, by total contrast, the smaller, restricted-capability vessels of the tourist variety that barely dip below the sea’s surface to give non-scientific passengers a glimpse of what lies beneath the waves.

The more informed will also consider the term to include manned submersibles, the best known of which is probably the Alvin, operated by WHOI and capable of descent to great depths. There was also “Trieste” the famous bathyscaphe of Auguste Picard and the numerous manned submersibles employed in intervention tasks alongside divers in the early days of North Sea oil production. Their descendants are the one-atmosphere suits used for intervention tasks in relatively shallow working environments.

Somewhere in between these extremes is another type of vehicle that can offer an alternative yet proven technology for many of the tasks that currently use ROVs and their expensive DP support vessels. Enter the high-tech, non-nuclear submarines of the type operated by the U.S. based company, Kokes Marine Technologies, LLC. Their two vessels, the US Corsair and US Constellation are based on the previous success of the RS Series Design, in operation with a naval force for more then 12 years.

During the past twenty or so years, there has been a marked move from sending men into the water in machines and keeping them instead above the surface, controlling ROVs which are becoming ever more technically-complex and capable of doing almost anything demanded of them by their operators. The word “almost” is the critical one because at some point there is often a need or desire to have a human being directly view some task or phenomenon in 3-D rather than on a 2-D monitor several thousand meters away at the end of an umbilical. There is also often a need to have the human intervention closer to the task; that’s why one-atmosphere suits are still being used. No matter how smart the machine, we humans still have a competitive edge in rendering rapid assessment and judgement!

As befits an entry into the 21st. Century, we have recently seen amazing developments in Autonomous Underwater Vehicles. AUVs have been around for some thirty years but have had relatively limited usefulness: for much of that time there has been an ability to make the machines go from location to location, even avoid obstacles on their way, but what could they really do? It is only in very recent years that significant advances in power source technology (fuel cells and exotic battery materials), computer technology (particularly affordable, compact and reliable data storage) and sensor development that has enabled these vehicles to carry out useful observation and measurement tasks during their pre-programmed wanderings. Even with their improved power supplies, for the most part AUVs cannot yet achieve the type of energy budget that allows them to seriously undertake intervention tasks.

With all these technologies, even AUVs, it is still not possible to escape the need to use a surface vessel that can launch and recover the vehicle, support it and its crew during operation and be able to remain safely at sea at times of extreme sea condition. A submarine, able to proceed on the surface under its own diesel power can provide that measure of autonomy. The US Corsair and US Constellation have surface ranges of 400 NM at 8 kts with their air breathing diesel engines and can also submerge to escape surface wave action, using their snorkel systems, a feature which is shared with many military variants. Beyond snorkel depths, the vessels shut down their engines and run on battery power and can then go to full operational depth, at 3-6 kts, carrying up to six personnel for nearly a week, depending on the activity level. If remaining stationary is required, the vessels have additional vertical thrusters which are normally folded back into the aft section of the sail.

To further increase submerged autonomy, the US Corsair has an Argon-drive system that allows the diesel engine to run on a carefully metered mixture of oxygen (from on-board liquid oxygen tanks) and the inert gas argon. This is used as combustion air, the CO2 being removed by scrubbers and the mixture being recycled with additional oxygen. Using this system increases the daily operating costs considerably but can add valuable submerged time by allowing the diesel engine to be run for both propulsion and power generation whilst under water. During submerged operations, breathing air is recycled through scrubbers to remove CO2, and the crew lives in a relatively normal daily routine. They have a galley to prepare food, a head and a sleeping area for up to two crewmembers.

The vessels can operate at 200 and 300-m depths respectively. They can support a crew of six and can be independent of a large surface DP supports vessels, which significantly reduces overall operating costs. What can they usefully do while they’re down there? The short answer is, “Anything you want” but to do this requires an adjustment of thinking away from having only machines at depth, with distant reporting to human operators.

Kokes Marine Technologies’ submarines are capable of cost-effectively performing practical and necessary tasks at depth and benefit by having their operators onboard to assess and control the operation. Comparing them with unmanned Autonomous Underwater Vehicles, they have the advantage of being able to collect data and to have the operators assess it in real-time – the unmanned vehicles need to either deliver the collected data at the end of a 24-48 hour mission or transmit it using an acoustic modem. Either way there is a delay – one or two days whilst operating totally autonomously and anything up to half a second for the acoustic modem: whatever happens, the Laws of Physics cannot be modified and sound will always travel through water at around 1500 m/s!

Positioning on the surface is taken care of by GPS with integration of appropriate differential signals if survey standard accuracy is required. Once submerged, the surface position is updated by an on-board Inertial Navigation System interfaced with a Doppler Velocity Log. The perennial problem of system drift can be addressed if operating locally by having the submarine deploy its own seafloor transponder(s), calibrating the position from the surface, then using the beacons to correct and update position during operation. Once finished, the submarine can then pick up the beacons before moving on to a new location.

The vessels are equipped with hydraulic systems capable of operating at high pressure and ideally suited to their depth ranges. Fitting the optional six-function manipulators means that intervention tasks can be undertaken with direct observation via a large 1.1-m view port or via external cameras. Additional hydraulically powered equipment can also be added as needed.

The vessels have a forward-looking sector scan sonar as standard but can be fitted with a variety of additional sensors including side-scan sonar, multibeam bathymetry, sub-bottom profiler and magnetometer. The data from all of these can be processed on-board and integrated with navigation input using the HyPack acquisition system, which makes interpretation of ambiguous data easier and quicker.

Pipeline engineers can carry out touchdown monitoring if necessary and also observe freespan and other potential problems with as-builts and even be able to carry out the necessary intervention task to correct a problem without the need to surface and return. Pipeline and cable inspections can be carried out visually and acoustically at a higher rate than can be achieved by a surface vessel with ROV.

There are additional interesting possibilities in marine archaeology, environmental monitoring and protection, security related observation tasks, equipment and protocol testing – the list is limited only by the reader’s imagination.

Costwise, how do these vehicles compare with more traditional methods of acquiring data and providing intervention? The answer, of course, depends on what the client needs and for how long but, as a general rule of thumb, these vessels can provide services at a rate, which compares very favorably with towed and autonomous vehicles with surface support vessels. Ad to this the reduced sensitivity to Sea State and your likelihood of weather related down time diminishes, further reducing operational costs.

To find out how favorably, contact Kokes Marine Technologies and let them tell you what they can do!

BIO NOTES:

Brian E. Morr is President of Technosphere, Inc., a Houston based company, which provides representation, and consultancy to technology based companies in the offshore market sector.

He was educated in England and has a B.Sc. in Geology and Environmental Biology and has worked in the offshore survey industry in Europe and USA (Gulf of Mexico) for a total of some 23 years. He is Chairman of the Houston Chapter of the THSOA.