HANSA 06-2021

SCHIFFSTECHNIK | SHIP

SCHIFFSTECHNIK | SHIP TECHNOLOGY From Insight to Action Come together – if right now is not possible, maybe later. HullPIC 2021 – the 6 th Hull Performance & Insight Conference had to be shifted, due to Covid-19, and was then merged with 2 nd In-Port Inspection & Cleaning Conference (PortPIC). By Volker Bertram The sister conferences are joining forces exceptionally this year. This may in fact be a blessing in disguise, as the two communities have much potential for cross-fertilization. HullPIC has its focus on insights into hull and propeller performance, using assorted sensor data, noon reports and increasingly machine learning to determine the current status of energy efficiency – one could say the ultimate EEXI decreasing in time with biofouling. Meanwhile PortPIC has its focus on inwater cleaning, the action to improve the performance (ideally back to its original state), but subject to scrutiny and constraints from assorted stakeholders, foremost port authorities and environmental agencies. In essence, we have insight and action for ship performance. And who would argue that having the two combined, at least on occasion, is a good thing. Insight without action is just as bad as action without insight. »Build it and they will come,« said Geir Axel Oftedahl from Jotun, the initiator and mastermind behind the concept of HullPIC back in 2016, and more recently, PortPIC. And indeed, they do keep coming (together) – people, companies and technologies, even if the effect of the pandemic is still palpable. Simple at first glance Some key countries like Australia and New Zealand have lock-down policies in force until the end of 2021. Some companies are struggling for survival or have already sadly folded their cards, at least in the business segment of interest at Hull- PIC and PortPIC. But the spirit in the industry is noticeably more optimistic than last year, and most of the traditional participants have announced their participation for the events planned from 30.8. to 1.9.2021 in Tuscany, Italy. Performance monitoring looks simple – at first glance: At a given speed, my ship has a certain power requirement. As the hull accumulates fouling, this power increases, respectively at that power my ship experiences a speed loss. Accordingly we can measure and express a performance loss. Before we complicate the matter by looking at changing ambient conditions and operational conditions, let’s go back to the beginning »at a given speed«. Hydrodynamically relevant is the speed through water (STW), but this is notoriously inaccurate in traditional speed log measurements and as a rule of thumb 1 % error in the speed measurement means 3 % error in the power. Sensor experts Miros and ship operator BW Dry Cargo joined forces to address this issue. Their new joint venture Miros Mocean seems to have cracked the nut. Using on-board radar to determine waves and currents, they present a con- 46 HANSA – International Maritime Journal 06 | 2021

SCHIFFSTECHNIK | SHIP TECHNOLOGY Miros Mocean uses on-board radar to determine waves and currents to get accurate speed through water measurements © Miros Mocean vincing approach to get accurate speed through water measurements. The measured power relation needs to be corrected for changing ambient conditions and then be compared to the ideal power at the given speed, draft and trim of the ship. This ideal condition is known for sea-trial conditions, not even 1 % of the operational conditions encountered in reality. We then need »baselines« expressing power as function of speed, draft and trim. These baselines are used to reconstruct a full hydrodynamic knowledge base from the small reliable fragments that sea trials furnish – one is reminded of the task of reconstructing a dinosaur from a single jawbone. You draw on experience, computer simulations, and fantasy. A frequently quoted aphorism in the community is that all models are wrong, but some are useful. And the suspicion, occasionally proven and published, is that some of the baseline models used in performance monitoring systems are wrong and not useful. Getting closer to the holy grail The baseline approach of the default method of ISO 19030 is quite correct and useful, but too expensive for most users in the industry. It would require systematic CFD simulations or systematic machine learning applied to the new ship. Hence the quest is on for a cheap and accurate approach. And in this quest, many fail – but that is no proof that we may not have reasonable accuracy for much lower effort. Sometimes semi-empirical methods work surprisingly well for ships, even if the theoretical base is questionable. I like to compare such methods to a knitted pullover – hole to hole and yet it holds. Richard Marioth from Idealship calls it »improving true lies – creating sophisticated baselines out of woefully little«. The short-term solution for some vendors seems to lie in avoiding looking too closely at just how high the errors in the model are at intermediate load conditions where bulbous bows pierce the water surface and massive wave breaking renders tradition ship design methods useless. Two trends giving hope Long-term, there are two trends giving hope for better models: (a) massively parallel CFD computations are becoming more accessible and cheaper, allowing systematic computations for hydrodynamic knowledge bases used both for trim optimization and performance monitoring. (b) more and more vendors use data fusion to improve data quality and derive cheaper, yet reasonably accurate surrogate models, as e.g. presented by Daniel Schmode from Wärtsilä Voyage Germany who recommends »blending data sources to economically predict hull fouling«. We may not have the holy grail yet, but we are getting closer to it in our quest. Even the best and most sophisticated monitoring does not save any fuel. Insight without action does not save any fuel, but action without insight is at best inefficient, and sometimes does more harm than Carsten Most Tel. 040/72003-120 | E-Mail: carsten.most@akzonobel.com HANSA – International Maritime Journal 06 | 2021 47