HANSA 05-2017

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Schiffstechnik | Ship Technology How to optimize the propeller performance was the central discussion Photo: Thomas Wägener Next step for better hull performances At this year’s second Hull Performance & Insight Conference (HullPIC 2.0) in Ulrichshusen from 27 to 29 March more than 100 attendees discussed ways to make the ships hull more effcient. HANSA informs on the main results Many fuel-saving technologies (such as advanced coatings or energy saving devices) are not adopted, because the industry does not trust the promises or because contracts fail to create win-win situations. »Ship owners maintain a degree of skepticism around fuel and CO2 saving predictions. The lack of accurate and transparent supporting data underpinning statistics quoted has contributed to this mindset,« confirmed Barry Kidd (Akzonobel). ISO 19030 is expected to bring major improvements in this respect. The standard on hull and propeller performance for fleet in service was published in November 2016, moving the discussion from the smaller circle of experts in the working group to the wider public. HullPIC 2.0 brought developers and ship operators together to exchange experiences in the still evolving field of performance management, especially in the light of ISO 19030. The topic apparently strikes a nerve in the industry. »Since the beginning of the ISO 19030 development, many shipping companies and operators have taken interest in the standard,« said Beom Jin Park (KRISO). Despite the complex, technical challenges involved, the response to the conference was impressive. For those who could not attend, the proceedings of the conference can be downloaded free of charge from www.hullpic.info. References and quotes given below are all from Hull- PIC 2017. While there is wide consensus that performance monitoring is necessary and good, there remains controversy over the ISO 19030 standard approach. Is it too complicated and costly? Is it too simplistic and inaccurate? »ISO 19030 delivered on its stated aims, but that does not prevent us from having ideas for further work,« concluded Geir Axel Oftedahl (Jotun), secretary of the ISO 19030 working group. »[The ISO 19030] methods are […] not so easy to implement for ship operators. […] the accuracy of measurements [is lower than] considered in ISO 19030. [… And] even with built-in filters and long time span of evaluation and reference periods, continuous analysis of performance does not show much consistency,« said Park et al. (KRI- SO). In the open spirit of HullPIC, common ground was found between these positions. »More discussion is needed« was frequently used and might have been the unoffcial theme of the conference. What’s your baseline? From a distance, performance monitoring looks quite simple: You monitor how the power needed for a given speed increases over time due to fouling. »However, there are numerous challenges and pitfalls when discussing the absolute level of hull and propeller performance,« elaborated Andreas Krapp (Jotun). Raw data need to be corrected (»normalized« in expert jargon) for varying operational and ambient conditions. In essence, we need to make numbers comparable, correcting for differences to a standard reference condition. This task requires a model to determine for example differences in power requirements for different draft or different wind conditions. The model used in the evaluation of the performance data can be built on physical models (white box), derived directly from observed data (black box) or a combination of both (grey box), said Dafni Sofiadi et al. (ABS). Depending on the approach, models have largely varying accuracy. The problems start at the very core of performance monitoring: the speed-power relation or »baseline«. While measuring the 72 HANSA International Maritime Journal – 154. Jahrgang – 2017 – Nr. 5
Average Axial Velocity (normalized by w/o Fin) 1.000 0.983 0.982 Schiffstechnik 0.961 | Ship Technology Nominal Wake Gain (%) base 1.7% 1.8% 3.9% Looking from aft Hull Looking from aft Hull st 1 st fin nd 2 nd fin Propeller plane 1 st fin 2 nd fin Propeller plane Comparison of axial velocity distribution at propeller plane (left – black: w/ofins, red: withfins, right – difference of axial velocity) Source: Japan Marine United shaft power is relatively straightforward, the notorious speed through water (STW) remains an Achilles’ heel for performance monitoring. »We find two main categories of quality issues. First, the [speed] logs are often miscalibrated, i.e. the measured [speed] is constantly too large or two small in certain speed ranges. Second, sometimes [speed] logs will provide noisy and clearly erroneous measurements.« Eric Giesberg (NSWC-CD) contributed a scientific study on the (in)accuracy of logs, finding acoustic Doppler current profiler reliable and accurate, while electro-magnetic logs was found to have issues beyond calibration offsets. His work reopened the discussion on using GPS speed over ground data as input data for performance monitoring. Mi- HANSA International Maritime Journal – 154. Jahrgang – 2017 – Nr. 5 73
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