New Predictions for Hull Roughness
Philip Stenson, Technology Leader at International, AkzoNobel’s marine coatings business, discusses the first major re-evaluation of average hull roughness (AHR) prediction methodology in almost 30 years:
Frictional resistance linked to hull roughness has always been a major factor in determining ship efficiency. For many years sustained high fuel prices gave shipowners and operators cause to investigate and introduce measures to mitigate hull roughness in order to unlock heightened levels of efficiency. Although fuel prices are dropping today, new environmental legislation has forced an increase in the use of more expensive distillate fuels. This, combined with pressures from shippers and charterers to improve sustainability, has placed significant onus on shipowners and operators to deliver more environmental and operational efficiencies. For many it is the key to unlocking competitive advantage.
In recognition of this, International has established the principles of a new AHR calculation, building on the landmark work of Dr Bob Townsin, the first researcher and academic to establish the important link between hull roughness and ship powering in the 1980s. While Townsin’s methodology is upheld by the shipping industry today, trends in hull coatings, ship yard practices, environmental changes and regulations, as well as vessel design and operation have altered considerably over the past 30 years. Consequently, there is a real requirement for an updated model that reflects the changing dynamics of the shipping industry.
In its latest research International has established the foundation of a new methodology that predicts AHR both at dry dock after a coating scheme application and during the subsequent dry docking cycle. Initial analysis is based on a new dataset of 845 individual hull roughness surveys carried out between 2003 and 2014.
The study reached new conclusions based on the dynamics of today’s shipping industry, which questioned the validity of some existing principles upheld previously. Importantly International found that vessel age is no longer a key parameter triggering hull degradation. Conversely, based on its current dataset, International found that vessels over 25 years old, through careful hull management, can still achieve low AHR, and increases in AHR over a dry dock cycle are lower than predicted previously.
Through analysis of its current dataset, International has concluded that increases in AHR during dry docking cycles are increased by a combination of factors, with key influencers including substrate preparation (i.e. whether the vessel is blasted or not), coating technology and vessel type. Correlations between these parameters exist and will be investigated in more detail as International develops its methodology. However data already available for the container and tanker sectors indicate that the impact of AHR is lower when a coating, such as International’s advanced biocide-free foul-release range, Intersleek, is applied to a vessel, as opposed to a biocidal antifouling.
While the economic importance of hull roughness mitigation as a means to deliver more environmental and operational efficiencies is undisputable, proving the AHR of a vessel or fleet is a more abstract challenge and one synonymous with all eco-efficient technologies. Through its new average hull roughness prediction methodology, International maintains that it can play a key role in wider efforts by the shipping industry to adopt transparent and highly accurate methodologies that measure fuel savings generated by eco-efficient technology, including hull coatings. Such clarity will provide an important tangible demonstration to ship owners of the rate of return on investment, helping to build trust between manufacturers and owners and driving shipping efficiency and sustainability.
Editor’s Note: The opinions expressed herein are the author’s and not necessarily those of The Maritime Executive.
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