Bimco is devising its own efficiency methodology to help owners of older ships deal with the International Maritime Organization's carbon-reduction framework.
The shipowners' organisation has teamed up with the Royal Institution of Naval Architects (RINA) after identifying a need for more accurate reference speed calculations in cases where sea trial data is unavailable.
For ships built before 2013, the IMO is introducing the Energy Efficiency Existing Ship Index (EEXI).
The intention is to force vessels to match the designed efficiency of new ships.
"While the EEXI guidelines are still in the making at [the] IMO, the regulation will likely affect around 30,000 existing ships, as many of these may need a technical upgrade to meet the new requirements," Christian Baekmark Schiolborg, the manager for maritime technology and regulation at Bimco, said.
Big numbers affected
Bimco and RINA believe there could be as many as 5,000 to 10,000 ships with inadequate documentation from the original sea trial.
"For many existing ships subject to the EEXI, such data simply does not exist any longer and is either lost over time for various reasons or has been measured in a particular loading condition which is neither relevant nor useful to the EEXI calculation," Schiolberg said.
He added that the IMO's preparatory work is far from simple and some of the parameters included in the calculation of EEXI will have a "high impact" on the outcome.
'Unrealistic' calculation
The current EEXI calculation guideline offers the option to calculate the reference speed, known as Vref, using an approximate formula.
However, this comes with an included "margin factor" of 5%, giving an unrealistic value for EEXI, in particular for well-maintained and energy-efficient ships, Bimco believes.
Bimco and RINA are suggesting a tweak to the IMO guidelines to calculate Vref based on "empirical data from actual in-service ship-performance measurements in a given loading condition".
Bimco's proposal has been submitted to the IMO's working group on reduction of greenhouse gas emissions ahead of its meeting in May.
Greek shipowner Okeanis Eco Tankers has said it expects older vessels will have to reduce their speeds by as much as 35% to meet new efficiency rules.
