In-depth | EEDI


FEATURE THEME Arrested development


Te impacts of current EEDI calculations for ro-ro cargo and ro-ro passenger vessels are once again under scrutiny


was a rocky, and at times, controversial undertaking. It ultimately ended with the adoption of a method in April 2014, but recent research and industry experiences are reopening the debate and adding weight to old concerns. Ro-ro cargo and ro-ro passenger vessels


T


were always difficult to include in IMO’s EEDI because of, in simplified terms, the huge diversity of technical and ship design characteristics of these ships and the varied nature of their operations. Tis diversity meant that every vessel would exhibit substantial variations in technical characteristics and mission profiles, and a wide EEDI scatter would therefore be seen when the data was grouped. As a result, correction factors were sought


to establish the required EEDI reference line for these vessel types. It is especially these correction factors (the so-called fjRo-Ro and the fjRoPax


factor factor) that are once again


under scrutiny, as according to research by Aimilia Alisafaki and professor Apostolos Papanikolaou of the National Technical University of Athens, and Hans Otto Holmegaard Kristensen, Head of Maritime DTU at the Technical University of Denmark, an alternative method that uses different exponents for calculating the f factors of EEDI for these ro-ro vessels is more suitable. Te new exponents in this method (Table


1 and Table 2) make it easier for shipowners to fulfil the EEDI requirements, which, at present, create infeasible goals and could potentially close ferry routes if vessels are unable to operate at the speed and efficiency


Table 1: Exponent values for ro-ro cargo ships


Exponent values


a b g


d e


18 Acc. to IMO


2.00 0.50 0.75 1.00


0.503


This study, non linear approach


2.80 1.89 1.26 -1.84 0.93


This study, linear


approach 2.00 2.00 1.50 -1.00 0.503


he formulation of a correct method for calculating EEDI for ro-ro cargo and ro-ro passenger vessels


Figure 1: Changing EEDI requirements for an example 1,500 passenger ro-pax ship from Kristensen’s study


required of them to function commercially and within regulations. In addition to the calculated EEDI values for the sample ships being lower, the statistical variance of the statistical sample is also reduced - an outcome that should be desirable for IMO. Speaking of his own calculations in a paper


entitled “Influence on attained EEDI for ro-ro ships using a revised formula for the f correction factor,” Kristensen says: “Using the revised power exponents proposed by Alisafaki and Papanikolaou decreases the attained EEDI for ro-pax ships by 15 – 27%, while the attained EEDI for ro-ro cargo ships is reduced by 12-19%, depending on the ship size, which means that it will be easier to fulfil the EEDI demands by using the revised exponents in the f correction formula.” It is important to note that a lowering of


EEDI targets is not aimed at prolonging higher pollution levels in the ferry sector or to rein in the setting of ambitious emission reduction targets; it is instead intended to prevent ferry route closures and the redirection of cargo


Table 2: Exponent values for ro-ro passenger ships


Exponent values


a b g


d e


Acc. to IMO


2.50 0.75 0.75 1.00


0.567


This study, non linear approach


2.79 1.97 1.40 -2.07 0.93


This study, linear


approach 2.00 2.00 1.50 -1.00 0.567


traffic through the more polluting automotive and aeronautical industries, and Kristensen emphasises that he is diagnosing a problem, not suggesting a definitive solution. An example of the results found in


Kristensen’s study can be seen in Figure 1 where the requirements for future EEDI targets of the current method are also plotted. The figure shows the obtained EEDI at different design speeds from 12 to 22knots using the present EEDI calculation procedure. The normal design speed for the ro-pax ship carrying 1500 passengers is approximately 21.3knots. Lowering the design speed lowers the EEDI until around 13knots where the EEDI increases due to the wrong definition of the fjRoPax revised fjRoPax


factor. Using the factor proposed by Alisafaki and


Papanikolau results in a more logical EEDI curve that shows EEDI is decreasing with decreasing design speed. Such results call for further discussion


of the current method of calculation for ro-ro cargo and ro-ro passenger vessels, and coverage of the EEDI debate will continue in Te Naval Architect’s April issue. NA


References ALISAFAKI, A.G. and A.D. PAPANIKOLAOU, On the Energy Efficiency Design Index of Ro-Ro passenger and Ro-Ro cargo ships, IMechE 2015 Journal of Engineering for the Maritime Environment, October 2015.


The Naval Architect March 2016


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