Energy sustainability in naval and aerospace systems through improved turbulence management

The global shipping industry has an enormous environmental and economic footprint. There are estimated to be over 90,000 ships operating worldwide, together consuming between five and seven million barrels of oil a day (up to 8 per cent of the world’s production). The oil that these ships burn is mostly of a low grade, with a sulphur content that can be thousands of times higher than is permitted in diesel fuel. The health impact of shipping pollution is difficult to quantify, but recent studies indicate there may be up to 60,000 deaths a year related to shipping emissions, with health bills running into the billions. 

Hull roughness and fouling is a major but unmeasured contributor to the energy expenditure of the world’s shipping fleet. This project aimed to improve the efficiency of ship operations by providing a means to quantify the penalty in emissions, financial cost and fuel use of hull fouling on an in-service vessel. This in turn would permit the maritime industry to make more informed decisions in terms of operations, either at a regulatory or operational level. 

Both Australia and Indonesia are uniquely reliant on long-haul shipping. Australia is a large continent, with diverse population centres, that is geographically isolated from major trading partners. A strong resource sector puts major demands on export bulk shipping. Indonesia is an archipelago of 17,000 islands, with a large population reliant on shipping for transport links. The President of the Republic of Indonesia, Joko Widodo has pledged to start a Sea Highway project involving new ports and consistently high high numbers of large transport ships between five of Indonesia’s main islands. Currently, it is more expensive to deliver goods from Jakarta to West Papua than to London due to lack of transport infrastructure. 

Hull roughness is an important but largely unquantifiable contributor to shipping’s energy expenditure. For any vehicle moving through a fluid, the optimal surface for minimising drag will almost always be a smooth finish. The degree of smoothness required to meet this optimum is determined by operating conditions. For a ship moving at 15 knots, this creates a target of approximately 20 microns (less that the diameter of a human hair) for the maximum permissible roughness height, beyond which performance will start to degrade. With the exception of racing yachts, ships rarely meet this optimum condition. 

Hulls have underlying roughness due to manufacturing imperfections, coatings, and, most importantly, biofouling – the settlement of marine organisms on to a ship’s hull. An earlier study used laboratory data to estimate that heavy fouling in a naval frigate could result in powering penalties of 86 per cent at cruising speed. In subsequent work, the economic impact of moderate hull fouling to the US fleet of FFG-7 frigates was calculated at $US1 billion over 15 years. When one considers that this calculation is for just 56 ships out of the 90,000 estimated to be operating, the magnitude of the economic and environmental impact of biofouling becomes clear. 

Despite the severity of the problem and the knowledge that rough surfaces are undesirable (hence the expenditure on anti-fouling technology), there is no reliable way for ship operators to quantify drag due to hull roughness for an in-service vessel. Almost all reliable estimates on hull roughness penalties have resulted from laborious laboratory experiments on replicated surfaces, precluding widespread regular monitoring. As a consequence, the scheduling of cleaning and re-coating remains suboptimal. 

Through underwater scanning techniques coupled with laser measurement of water flow over the hull, this project aimed to provide data on the increase in drag experienced by a ship under different fouling conditions. An Indonesian inter-island ferry was fitted with sensors, with detailed laboratory experiments used to validate the approach. The goal is to create a real-time monitoring methodology suited to widespread application. This is of particular importance to an industry under increasing pressure to mitigate emissions. Ultimately it is hoped that this project will lead to more informed decisions around hull-cleaning, regulatory guidelines and application of coatings.

The collaboration between Indonesia and Australia has been cemented and will be ongoing, with the interchange of staff between universities strengthened by the arrival of the first Institut Teknologi Bandung PhD student into the University of Melbourne fluids research group in 2016. The project attracted further support from Europe (the University of Southampton and the Danish marine coatings manufacturer Hempel A/S), and from Indonesia (the government shipping registry, Biro Klasifikasi Indonesia, and ship operator PT Dharma Lautan Utama).

Besides the obvious advantages of improved collaboration between Australian and Indonesian researchers, we firmly believe that the eventual outputs from this project will improve the overall efficiency of shipping. The economic and environmental penalty due to biofouling has, up to this point, been difficult to accurately quantify. By putting an accurate figure on this we believe that appropriate regulatory pressure can be brought to bear that will improve the overall efficiency of the world’s fleet. For an industry that burns such a large proportion of the world’s oil supply, the economic advantages of such an outcome would be far-reaching. 



Assoc Professor Hutchins was invited to departmental seminar at the University of Southampton, 2015.

Assoc Professor Jason Monty presented to the second ANZPAC Workshop on Biofouling Management for Sustainable Shipping, 2015.

Professor Ketut presented to RINA Conference in Surabaya, 2015.


Putting a window and lasers in a ship’s hull