Article - June 26, 2019

ECO Insight hull degradation computation method goes beyond ISO 19030 standard

Hull cleaning
Hull degradation is one of the most important vessel performance levers in shipping, but is very often overlooked. The reason for this is the high level of difficulty in computing hull degradation properly.

Only a proper computation allows a shipping company to go away from current practices, i.e. troubleshooting after a charter party consumption claim or planned maintenance such as cleaning the hull and propeller, despite whether it is needed. Usually, the speed-consumption development is monitored rather than the hull index itself.

ISO 19030

Industry experts, ourselves included, have developed ISO 19030 to detail correct computation. This norm serves as a good basis for assessing the condition of the hull based on collected data. With more than 2,000 vessels using StormGeo’s ECO Insight Performance solution, we have discovered some shortcomings of ISO 19030:

  1. The standard method (ISO 19030 part 2) needs high frequency auto logging data, which most vessels today do not have.
  2. The current computation in most cases shows a dependency on speed—the faster the vessel sails, the lower the computed degradation.
  3. The computed hull condition changes when there are weather shifts, which does not happen in real life.

The main downside of the ISO 19030 is that it measures performance improvements rather than the absolute level of performance. So while you will see X% improvement of performance after dry dock, you won’t know whether you came back to 100% performance.

How to Assess Hull Performance

To explain the significant improvements to ISO 19030 that have been implemented, we will first describe the basic methodology for hull performance assessment. A main KPI can be the speed-power relationship, i.e. the power increase needed to move a fouled ship forward or the loss in speed when keeping constant power. We prefer to look at the power increase needed, due to the exponential relationship between speed and power.

Steps to assess hull degradation:

  1. Measure power.
  2. Correct it for environmental factors (weather, water, temperature etc.).
  3. Compare this value to the ideal power needed at the same speed, draft and trim as the measured power.
Prop power chart

As the hull performance index is a relation between ideal power and corrected measured power, it represents a simple way to understand the KPI for added resistance due to hull and propeller fouling. The hull performance index is approximately 100% for a ship with new paint and below 80% for a degraded hull.

Improving the Process

After assessing hull degradation continuously for many ships, we not only recognized the issues above, but also took the opportunity to solve them.

  1. In order to use low frequency data, we introduced snapshot reporting to the industry. This means speed, draft, trim, power and weather data are also taken at the same time as average noon data. We have also applied smarter filters, which do not reduce the amount of available measurements as much as strict ISO norm. Example: The wind filter takes into account where the wind is coming from and its influence on the vessels, also looking at the superstructure geometry.
  2. To get away with the speed dependency, you could model the difficult effects such as drifting at slow speeds, other propeller inflows, etc. While possible, this is very costly to do. Having a high amount of real performance data from actual sailing vessels on-hand, we can use machine learning to solve this issue.
  3. To reduce the weather dependency, we used a similar approach. The ISO 19030 wind correction factor uses the ISO standard for sea trials, which has been introduced by shipyards and tend to overcorrect high winds—an advantage for the shipyard. We also use machine learning here on the 2,000-vessel database to come to more realistic wind corrections.
The Results

Our aim is to show hull degradation as an absolute level and as a degradation trend, which is reset by a dry-docking or cleaning event.

Hull performance

Hull Performance Index – development over time

While this development work took about one year, how can we be sure our new approach is better than the existing ISO one?

  • We have significantly reduced the scatter of our results, which is a statistical measure for confidence.
  • Previous speed and weather dependencies from before have disappeared.
  • We continue comparing computed hull performance indexes with visual inspections, i.e. from dry docks, which we get from customers and our coating partners all over the world. Our method allows for assessment of the absolute level of hull performance.