Above and beneath the waves

Uploaded 05 Jun @ 18:37pm

It has been conjectured that mankind’s earliest attempts at navigating the seas could date as far back as 45,000 years, to Neanderthal times, evidenced by the arrival of the first humanoids in Australia. Whether or not this is true, the history of man’s engagement with the sea, for transport and exploration, for food, for trade and, inevitably, for warfare and conquest, is an extremely lengthy and eventful one. Mel Dunkin reports.

Relying first on manpower alone, were the simple canoes made from hollowed out logs and coracles woven from reeds. These were followed, in time, by the massive triremes and quinqueremes of the Hellenistic era, propelled by three and five banks of oarsmen respectively. Though sails were initially limited to smaller vessels, wind-driven ships gradually began to dominate and reached a peak during the 7th to 19th centuries, beginning with the Arab age of discovery and continuing throughout its European counterpart.

The golden age of sail began its decline when, in 1819, steam was first used to augment wind power in an historic Atlantic crossing. Just 26 year later, in 1945, wooden hulls gave way to iron and the propeller replaced the sail for most commercial and military vessels.

Today, we live in an age of vast super-tankers and container ships; a time of massive aircraft carriers with a crew compliment of up to 6,000, and of nuclear submarines capable of remaining submerged for up to 25 years (although limited to carrying sufficient food for about 90 days). Advances in technology and the introduction of new construction materials have been the main factors responsible for the evolution of marine transport to date. Over the coming decades, driven even harder by mounting economic pressures, these same two factors will continue to influence the development of marine transport and to accelerate it as never before in the ongoing quest for bigger, stronger, faster and safer vessels for commercial, naval and exploratory use.

New materials for the marine environment
Even when it is as calm as the proverbial mill pond, the sea remains a harsh environment in which man is merely an intruder. Salt water and the elements take their toll both on the superstructure of vessels as well as on those parts hidden beneath the waves. This results in regular and costly downtime for maintenance and repairs. When afloat, the sea resists the passage of these massive and inflexible structures, demanding vast amounts of energy to permit their progress.

Future ships will overcome the problems of both damage and inadequate power to weight ratios with new materials that are stronger, lighter and less susceptible to the effects of impact, corrosion and biofouling. The strong, lightweight and anti-corrosive properties of polymer matrix composites, both traditional, such as epoxy resins and glass fibre, and the more advanced plastics reinforced with carbon fibre, will replace steel structures wherever feasible. Widespread use of the honeycomb format will allow even greater strength and weight-saving. Composites are also being used to manufacture more resilient mountings to help supress engine noise.

Miracle Metals
That said, metal, albeit in some radically different forms, will continue to account for the bulk of the material used to build tomorrow’s ships. By applying the process of nanoprecipitation, widely used in the manufacture of semiconductors and pharmaceuticals, it is possible to create new and improved alloys. The process modifies the internal structure and properties of metals by doping them with selected substances in the form of nano-particles.

Carbide and copper precipitates in steel promise increased malleability and resistance to corrosion while the introduction of calcium or magnesium nano-particles offers a means to strengthen crucial welds. Nanoprecipitation technology also offers an alternative to the zinc-based coatings currently used to limit corrosion. The use of graphene as the dopant results in enhanced anti-corrosive properties, as well as a coating with ductility that is more comparable with that of the steel parts to be coated.

Perhaps even more promising is the prospect of self-healing materials that could allow ships to mend themselves. Using composites in which capsules or tubes within their structure contain liquid components with the ability to solidify on contact with air, a similar principle has been applied to metals and involves the dynamic precipitation of trace substances at defect sites. For example, when including small quantities of gold in steel plate, it is precipitated in the cavities formed by high temperature creep damage, thus resulting in an autonomous repair.

It is possible, however that some future shipbuilders will seek ways to emulate nature with the development of ‘bio-inspired’ materials. Used to create composites and adhesives, nature’s tried and tested chemistry could be used to provide protection against icing and fouling and, being derived from natural materials rather than from petrochemicals, they will offer the added bonus of sustainability. As is usual with all new developments, cost will tend to determine the extent to which these various materials will be used and, despite rigorous testing, only their sea-going performance over time will reveal whether they live up to current expectations.

Whatever the outcome, new and advanced materials will continue to play a key role in marine engineering and this is no less true for naval vessels. Although a warship does have some requirements that go beyond those of commercial shipping such as stealth technology and variable geometry, the need for tough, lightweight composites and anti-corrosive, self-cleaning nano-coatings will remain a shared one.

Transforming propulsion
The diesel engine remains the principal means of marine propulsion as well as for the generator sets used to provide auxiliary power. Not surprisingly, while research into alternative propulsion technologies continues, the primary focus will remain on finding ways to improve the performance of these long-established workhorses.

Although accounting for less than 3 per cent of global CO2 emissions, shipping contributes up to 30 per cent of the nitrogen oxides and almost 10 per cent of the sulphur oxides released into the atmosphere. Consequently greener fuels and cleaner-burning engine technology are a priority.

Bio-fuels offer an option for some smaller vessels, but total production potential falls well short of that needed for any significant industry-wide impact. Among the more feasible of these is di-methyl ether, obtained from sources such as coal, oil residues, biomass and natural gas. In compression-ignition engines, it mixes easily with air to provide smokeless, low-noise combustion with high thermal efficiency.
The most promising option to date is liquid natural gas that is already in use by many of the tankers used to transport it. New pipes and tanks are required to convert from diesel and as the liquefied gas occupies more space than diesel, some cargo capacity may need to be sacrificed.

Efforts to make diesel propulsion more efficient have led to the development of ultra-long stroke engines. These operate at revolutions considerably lower than conventional units but, when paired with large diameter propellers, they show both improved performance and economy.

Given the marked improvements in containment technology, and its proven long-term performance in naval submarines and large surface ships, nuclear propulsion offers an opportunity for greater use in commercial shipping. Steam-driven turbines are inherently quieter than internal combustion engines and produce no carbon, nitrogen, sulphur, volatile organics or particulate emissions during operation.

The best prospect for the widespread adoption of nuclear-powered vessels lies in the perfection of thorium reactors. Far more abundant than other fissile elements, thorium requires no enrichment, produces up to 100 times less nuclear waste with a half-life about one tenth that of uranium and, ton for ton, it also yields about 200 times more energy. It is estimated that the known reserves of this element could supply the world’s energy needs for a thousand years or more. Conversions to existing ships, however, would require major design modifications and thus any nuclear propulsion option is likely to be limited to new builds.

Rather than the massive solar sail, envisioned by NASA to harness the power of photons and propel its spacecraft to another star system, rigid sails, composed of solar panels could provide a dual boost for surface ships. They would provide supplementary motive power from the wind and auxiliary electrical power from the sun. The use of a hybrid system such as this offers obvious benefits both in terms of operational cost and environmental impact.

Although none have as yet been fitted to a marine vessel, a high temperature superconductor motor was designed for marine use jointly by Northrop Grumman and the American Superconductor. Successfully tested on land, it is seen as a viable marine propulsion system that is compact and energy efficient with low exhaust emissions.
Not a new idea, magneto-hydrodynamic (MHD) propulsion holds the promise of a drive that is noiseless, pollution-free and has no moving parts, not even a propeller. Originally applied to gasses, electrically charged particles are accelerated along a tube by the action of a magnetic field applied at right angles to the desired direction of thrust. On a large scale, the need for outsized, super-cooled magnets, the huge power requirements and the associated high cost are problems still to be solved. However, MHD drives have been successfully employed in mini-subs and torpedoes as well as in the remotely-operated vehicles (ROVs) and autonomous underwater vehicles (AUVs) now widely used in salvage operations and deep sea research.

In the face of a steadily increasing demand, ships seem likely to remain the most cost-effective means to transport bulk cargo. To do so more safely and cost-effectively, they will rely, initially, more on existing rather than experimental technologies for short-term improvements. In the main, these will be drawn from those already proven on land and in the air.
In the manufacture of sea-going vessels, ‘big data’, fast analytics and improved human-computer interfaces will result in more efficient designs. In parallel, existing 4D printing technology [search Skylar Tibbits] offers a means to create components from composites with the ability to change their form in response to certain environmental changes, making variable geometry a real possibility.

Fully autonomous ships able to make decisions based on data from multiple sensors, satellites and the internet could eliminate all need for a crew on certain naval and cargo vessels. The same technology, when applied semi-autonomously on cruise ships, will serve to simplify the role of crew members enabling owners to reduce the number of those not directly required to attend to the passengers. Based on data gathered from sensors, computers will optimise fuel consumption, control power distribution and communication systems, monitor speed and position and make any necessary course corrections, simply recording them in a digital log.

For millennia, mankind has battled to gain mastery of the oceans only to be forced to bow to its unstoppable power. Could it be that, with these new materials and technologies, the mariners of the 21st century may finally realise that dream?

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