Image courtesy Fathom cTech
From 1 January 2013, all ships over 400GT on international voyages will be required to carry a Ship Energy Efficiency Management Plan (SEEMP), detailing the operational and technical measures that will be implemented on board to improve efficiency and therefore reduce fuel consumption.
As part of a series of articles examining some of the viable SEEMP measures identified by the IMO-commissioned study, ‘Assessment of Mandated Energy Efficiency Measures for International Shipping‘, Fathom cTech looks at the impact of hull and propeller monitoring and cleaning on fuel efficiency in the second of the Fathom-CTech series of reports.
By Fathom cTech
Vessel performance deteriorates in direct proportion to reductions in hull and propeller performance. Numerous studies including those by the IMO, academic institutes, and investigations on the part paint manufacturers attest to this.
A recent report from the Clean Shipping Coalition (CSC), which was submitted for consideration to the MEPC 63/4/8 in 2011, estimated that inadequate hull and propeller performance could reduce the entire world’s fleet efficiency by 15-20% over a typical 4 to 5 year sailing interval. For ships that maintain steaming speeds, this equates to a directly proportionate increase in bunker consumption and GHG emissions.
The figures put forward were based on an expansive study conducted by the paint manufacturer, Jotun, which covered analysis of hull and propeller performance on 32 vessels of varying class and subtype across 48 sailing intervals. The results showed that across an average sailing interval of four and a half years, a total speed loss of 10.6% was recorded, equating to an average 16% reduction in vessel efficiency.
The results are substantial enough to suggest that taking continuous action to remedy hull and propeller issues across a full sailing cycle is more beneficial than allowing gradual deterioration to set in, only to be rectified at the end of that 4 to 5 year cycle.
Typically, the deterioration that occurs in hull and propeller performance between dry-dockings is mainly the result of biological fouling and mechanical damage. Regular hull cleaning and propeller polishing can assist in negating these effects between dry dockings.
There are a number of options for hull cleaning; the most common is the use of diver-operated machines fitted with rotating brushes. With this methodology, it is very important that service providers choose the least aggressive cleaning brush that will effectively remove the fouling to avoid excessive anti-foul paint wear.
Other options emerging on to the market include the use of diver-less Remote Operated Hull Cleaning Vehicles (ROHCVs). This can be performed either at anchor or at berth – the ROHCVs only require 1m between the hull and quayside to operate.
One such provider of ROHCVs, CleanHull AS based in Norway, which uses a patented high-pressure water cleaning technology, give typical costs of between $15,000 and $30,000 per cleaning dependant on vessel size. This is for a partial hull cleaning (vertical sides and 2m of flat bottom), which the company claims has helped customers to report between a 5 and 12% increase in fuel efficiency post-cleaning.
Other emerging hull cleaning technologies include the Hull Surface Treatment system developed in Australia by Commercial Diving Services Pty Ltd. This system uses a containment device attached to the hull that pumps out hot salt water which is said to kill the foul-creating marine organisms; these then wash off under normal operating conditions.
Rudders and propellers, intrinsically more complex structures, require divers to carry out the service. Typical costs are in the range of $6,000-12,000 per polishing.
The frequency of underwater hull cleaning is dependent on the performance of the anti-foul paint. The performance of such paints and the fouling rate can be affected by many factors including time in operation, season of the year, and the geographical region of vessel operations.
In order to assist with assessing the scale of propeller and hull malfunction, a host of monitoring systems exist, which can offer advanced and computerised performance analysis of an entire ship’s operational and mechanical framework. Many of these energy monitoring systems compartmentalise a vessel’s performance into separate segments, including condition based monitoring of the hull and propeller.
One problem associated with assessing the value of such monitoring tools is that their success is dependent upon the alterations and amendments made in light of the information and analysis provided. However, ship owners and operators are prepared to vouch for the success of these tools in providing the data needed to instigate appropriate measures for improving hull and propeller condition.
In the case of one large tanker company that has employed the CASPER software, it was happy to declare that 1-3% efficiency savings were made from opportune hull and propeller cleaning, which was conducted on the basis of calculations provided by the software. The annual cost of $700,000 incurred by the company for subscribing to the CASPER package is more than adequately offset by annual fuel savings of $4 million across its fleet of 90 vessels that have access to the software.
CASPER software, developed by Propulsion Dynamics in the USA, enables ships to undergo the hydrodynamic mapping that is needed to acquire the appropriate dimensions and baseline data for comparison with in-service performance data. This baseline data then enables calculations to be formulated, for example for the resistance experienced by a vessel in-motion, by comparison of in-service data with its baseline equivalent. The software has been in action aboard commercial vessels for ten years and its success is testified by the fact that at least 50% of its contractors are ship owners who have won either the Green Ship or Clean Air Award.
Kyma and Force Technology are other companies that have developed performance monitoring systems with a particular focus on hull and propeller condition monitoring. Kyma states that its system can analyse the economic consequences of effects to propeller and hull condition separately from other potential performance effects; in addition, the system can appraise the impact of individual actions taken to improve their conditions. The focus of Kyma’s Ship Performance application has gravitated mainly towards tankers, LNG carriers and container vessels during its commercial life, with a client reference list that has greatly expanded over the last decade or so.
Force Technology has likewise developed a system that possesses hydrodynamic modelling capabilities for assessing hull and propeller condition. Seatrend, which is one element of Force Technology’s ‘SeaSuite’ products, provides general on-board performance information in addition to its focus on hull and propeller monitoring. As with many similar systems in the industry, the company does not attribute any specific savings potential to the product; it does however receive endorsement from the foul-release paint manufacturer, Hempel, whose first-yearly guarantee of 8% fuel savings is only tendered if results are measured by the Seatrend software.
However, stand-alone propulsion and hull monitoring systems are available that have a unique and undivided focus on these areas rather than a general performance focus. MacSea, whose applications have been tested extensively with the US Navy, are patents of a software programme called Hull Medic, which specifically detects underwater fouling on both the hull and propeller. The programme is also useful for providing advice to on-board personnel regarding optimal hull cleaning and foul coating intervals.
Wartsila and ABB, on the contrary, have both developed proprietary Propulsion Condition Monitoring Systems (PCMS), solely devoted to measuring the impact of external factors such as marine bio-fouling on propeller performance. Both recent additions to the market within the last few years, the systems have been developed in supplement to the propulsion units that both manufacturers supply. However, neither system is exclusively programmed to monitor their own systems; both offer retrofit options to vessels that have other propulsive systems already in place. Celebrity cruise line was the first to pilot the ABB system back in 2008 and has reported favourably on the system’s implementation.
Whether or not monitoring systems are put in place, hull cleaning and propeller polishing are measures that can be included within a Ship Energy Efficiency Management Plan with relative ease.
For further insight to current specialist hull cleaning operators and energy management systems, including ones that are specifically tailored to monitoring and advising on hull and propeller performance, Fathom-CTech provides profiles and case studies on the full range of systems.
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