The challenges of working subsea
The potential beneath the waves
Maritime Media Awards 2008 Brochure
Ian Gallett, Director of the Society of Underwater Technology, on one of the most promising fields of maritime endeavour
Photo: Barry McGill/MSP
We are all familiar with the truism that nearly 70% of the world’s surface is covered by the sea. What is not so well appreciated is that the underwater world is one of the most hostile and unknown environments in which humans operate. The deepest part of the ocean is the Challenger Deep, at the southern end of the Mariana Trench in the Pacific, 11,000 metres below the surface. It has only ever been visited twice. The first was a manned expedition in 1960 in which Jacques Piccard and Don Walsh descended to the bottom in the bathyscaphe Trieste, and the second was a visit by the Japanese research ROV (remotely operated vehicle) Kaiko, which went there in 1995. Contrast that with the plethora of manned and unmanned expeditions to the moon, the exploration of Mars, and the many fly-bys and descents to the surface of the planets of our solar system and their moons.
So difficult is through-water sight and communication, and underwater navigation, that we literally know more about the surface of the moon and the other planets than we do about what is in our oceans. Every time we put a camera into the deep oceans we see creatures, often quite large, which are unknown to science. This was particularly well illustrated by the deep-sea episode of the 2001 BBC series The Blue Planet. It is further exemplified by the fact that one of the largest creatures on our planet, the giant squid, was not seen in its natural habitat until 2004, and then only by camera.
Impenetrable darkness, high pressure
At the best of times light only penetrates the sea for the first few tens of metres, so below that is blackness. And in many places, for example where the seabed is disturbed, the visibility may be only a few centimetres – and divers often have to work by feel. In fact, it is not only light but most other electromagnetic frequencies which cannot penetrate far through sea water. For this reason, use is made of sound, both actively and passively, as sound waves can carry information much further than electromagnetic waves underwater. But even here there is a trade-off between data rate and distance. One result of this is that a true universal GPS system cannot work underwater, except in a very limited area. Unmanned aerial vehicles (UAVs), which we have become accustomed to seeing on the daily news operating in Afghanistan, are continually monitored and are in direct communication with their operators. This cannot happen underwater with a free-swimming vehicle, because of the limitations on sensors and communications.
Other challenges include the underwater pressure. Every 10 metres of depth is equivalent to approximately one extra atmosphere. This means that, at full ocean depth, anything which cannot stand the pressure (including a person) must be housed in something that will withstand 1,100 times atmospheric pressure, or approximately 11,000 tonnes per square metre. A further problem for designers of underwater equipment is that salt water is very corrosive.
Despite all the challenges, more and more equipment is being designed to work in the very difficult subsea environment. The impetus comes mainly from two directions: resources and science.
Exploiting the resources
We have long been familiar with utilising the living resources of the sea in the form of fish and other seafood. The pressure on our fisheries has led to the exploitation of fish species from deeper and deeper parts of the sea, but now interest is blooming in the many exotic sea organisms that can provide a source of biotechnological substances. Further, steps are now being taken to start farming the seas offshore rather than relying on capture (and much wastage) through wild fisheries. There are other resources that are again becoming of interest, such as seabed minerals, as the price of metals rises around the world – but the main investment taking place at present is in energy, both conventional oil and gas and more latterly renewable energy, and even some unconventional sources of gas.
As far as conventional oil and gas is concerned, the exploitation of underwater fields started in the Gulf of Mexico, when oil wells moved offshore into shallow water, with the wellheads (or Christmas trees, as they were called) on the platforms in the dry. This was followed by developments in the North Sea, where wellheads went subsea for operational and economic reasons, but still in relatively shallow water (less than 150 metres). By 1999, the Roncador field off the Brazilian coast had set a record for production at 1,853 metres using (wet) trees on the sea floor. Today, with depths now heading towards and beyond 3,000 metres, the requirement is increasingly for subsea developments. This means that the wells themselves (both for injection and production) are on the sea floor, as are the manifolds – where the output from several wells is brought together, and substantial lengths of differing-bore pipelines and umbilicals carrying chemicals, power and data are connected. This technology is also suitable for very harsh environments, such as the Arctic, where ice cover is a major consideration.
The construction and maintenance of all this hardware on the sea floor requires intervention by engineers and maintenance staff, and a key enabling technology is the ROV. In shallow water divers can do the work, but they can only operate effectively to about 200 metres, and even then they must use ‘saturation’ techniques, where the divers live, typically for a month at a time, at the pressure of their working environment even when resting between dives in the mother ship. Anything deeper than this needs underwater robots in the shape of ROVs. These vehicles are operated by a person at the surface, via an umbilical which supplies power and command signals to the vehicle and images back to the surface. The operator flies the vehicle to the site of the work and then performs the necessary tasks using purpose-designed tools. Modern ROVs are routinely designed to work at 3,000 metres, and they will soon be operating deeper than this.
A further development is the autonomous underwater vehicle (AUV). This is the exact equivalent of the UAV mentioned above, but it does not have the benefit of GPS or high-data-rate communications. This means that the vehicles have to have a very high degree of artificial intelligence (AI), enabling them to operate totally without interaction with a pilot, and to make quite high-level decisions about their task and programme of work. These vehicles are now finding a use in seabed survey for pipelines, telecommunications cables and field development sites, as well as for mine counter-measures (MCM) in the military.
AUVs are also of great use to the scientific community, used for measuring many aspects of the water column. Apart from the thirst for scientific knowledge for its own sake, there is also now the driver of global warming. The oceans play a major part in controlling the world’s climate, but we still know very little about this process, or indeed about how the oceans themselves work.
The first true oceanographic expedition was that of HMS Challenger in 1873–76. Since then a great deal of work has been carried out, but it is always hampered by the need to measure and understand the constituents of the oceans at all depths from surface to seabed. For many years this could only be achieved by the laborious process of lowering a weight from a research vessel to the seafloor on the end of a very long wire, often as long as 5,000 or 6,000 metres, and attaching sampling bottles to it. These would then be recovered and their contents analysed. The drawback to this was that the samples would be at single points and at a very limited set of discrete depths. Considering that the lateral extent of a piece of ocean ‘weather’ such as any eddy is an order of magnitude less than that of a similar event in the atmosphere, sampling was very poor. Satellites can now give a synoptic picture of the conditions at the sea surface, but only the top few millimetres. Some gross subsurface features can be inferred from these measurements, but subsurface data can really only be gathered by in situ measurements. Increasingly, these are provided by various remote devices such as buoys (e.g. the international Argo Float programme) that sink and then rise to the surface following a fixed programme, reporting back by satellite when at the surface, or by more sophisticated AUVs making their own decisions based on what they have measured to date. Some of these are capable of staying at sea for months or even years.
Problems and potential
Working under the sea, whether for the exploitation of resources or for scientific purposes, always presents a great technical challenge. Unfortunately most of the activity, being offshore and below the waves, is out of sight. The result is that in the current climate of a severe shortage of engineers and scientists, it is often forgotten that there are more than enough engineering and scientific challenges to satisfy anybody in the deep-water arena. This shortage of trained manpower is possibly the biggest challenge of all faced by the subsea engineering and science sector.
There are countless opportunities for innovative solutions in deep water. The real issue is not engineering capability, but the need to increase awareness of the opportunities that exist. The Maritime Media Awards will play their part in helping to highlight the potential for really exciting careers in the deep-water arena.
Cutting-edge underwater imaging
High-resolution multibeam sonar is now being used by one British company to survey shipwrecks and provide detailed three-dimensional images, either as interactive computer visualisations or as movie animations. By exploiting the full potential of subsea technology, ADUS (Advanced Underwater Surveys Ltd) originally aimed to bring images of historic wrecks to a wider public, but
the techniques are now more regularly used to investigate wrecks that are environmental hazards because of oil, ordnance or nuclear materials on board.
Recent surveys by ADUS using this technique include those of the battleship HMS Royal Oak, torpedoed in 1939 in Orkney, and the Russian nuclear submarine B-159, lost in 2003 in 250 metres of water off Murmansk. These surveys, undertaken for the Salvage and Marine Operations team of the Ministry of Defence, are examples of the forensic wreck investigations the company has undertaken for government agencies and other organizations.
In November 2008 ADUS launched a series of interactive wreck visualisations, to help sport divers with their dive planning. Eight popular dive sites – First World War German wrecks in Scapa Flow – are being offered as 3D images in WreckSight, the software specially developed by ADUS for viewing high-resolution multibeam sonar data. The viewer interacts independently with the representation of each wreck, and six preset animations show important features. Other features include the ability to set out dive routes and measure accurately the distance between any two points.