Clarksons warns against misunderstandings of CII speed Ship’s crew

Clarksons, a leading marine consultancy, urges its clients to reconsider their decisions regarding Carbon Intensity Indicator (CII) compliance and the calculation methods used.

The operational measure decided by the IMO came into force earlier this year and is expected to result in a significant reduction in sailing speed for a large part of the world fleet.

To address the inaccuracies of traditional CII methods, the Clarksons Green Transition team developed a velocity CII modeling tool that demonstrated that the potential for CII improvement through velocity reduction can be grossly overestimated and does not necessarily reflect the CII Ratings improved.

CII is a rating system for measuring the environmental efficiency of ships and evaluating how much carbon dioxide (CO2) a ship emits per unit of cargo transported a given distance. A lower CII rating indicates better efficiency, which means the ship emits less CO2 for the amount of cargo transported. The thought is that by reducing speed, a ship will use less fuel per unit distance traveled, resulting in a lower CII rating.

But the Clarksons Green Transition team did explained that the misjudgment is due to calculations based on standard speed-consumption curves that show exponential growth over the entire speed range. But when real-world variables and ship-specific conditions are factored in, the curve flattens out at lower speeds, says Jon Leonhardsen, the team’s lead analyst.

“This means that the marginal fuel savings decrease with the distance travelled, and that is ultimately what counts for CII performance,” adds Kenneth Tveter, Green Transition Team Leader. “So while some ships need to slow down significantly to comply with regulations, for others a speed reduction is not at all feasible and other costly measures and improvements need to be implemented.”

This understanding of the relationship between speed and CII can give a misleading impression of a ship’s CII and opportunities for improvement. To address these challenges, the Green Transition team introduced a CII evaluation modeling tool, which Clarkson’s says has proven to be up to 30% more accurate than traditional methods in predicting actual fuel economy and CII, especially at lower speeds.

Finally, Kenneth Tveter emphasizes the goal of providing the industry with an accurate and reliable approach to operate effectively within CII.

“It is only through clarity and standardization of approach that the industry can truly begin to make smarter and cleaner travel deployment decisions and fleet renewal strategies that will have a significant impact on decarbonization targets,” he said.

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