Trans RINA, Vol 152, Part A4, Intl J Maritime Eng, Oct-Dec 2010


life cycles are not taken into account, and all technical features of ships A and B are assumed to stay constant for the sake of comparison. A more detailed, second- order analysis could try to predict future technological improvements in both A and B that may effect life cycle emissions in both vessels. This was considered as outside the scope of this paper (however, see some further discussion on this point in the concluding section of the paper).”


This assumption is not based on a realistic scenario, as also pointed out by Denmark at MEPC 60. It is assumed that the three ships of type A and the two ships of type B are built without any technical improvements at all.


At MEPC 61 the Working Group on energy efficiency measures for ships agreed on draft regulations on energy efficiency for ships, where a reduction rate of 30 % in year 2025 is proposed for bulk carriers. Further reduction rates can be expected in the following decades and such reductions will be possible due to the development in the energy efficiency technologies forced by the general requirement for reducing CO2 emissions in order to reduce the impact on the climate.


Furthermore there is a general trend in the industry to look for increased energy efficiency.


Accordingly it is obvious that ship number two of both type A and type B will be more energy efficient than ship number one and that ship number three of type A will again be more energy efficient than ship number two of both type A and type B.


In the study it is further stated that the additional CO2 emissions from steel fabrication, shipbuilding, repairs, recycling and transport of raw materials and steel will also be the same when building the three ships of type A and the two ships of type B, respectively.


It is again obvious that these CO2 emissions will be less for ships built


in the future. The transport of raw


materials and steel will be more efficient due to the energy efficiency design index, etc., and the steel fabrication, shipbuilding, repair and recycling will be more energy efficient due to the general requirements for reducing the CO2 emissions in order to reduce the impact on the climate and the general trend in the industry to look for increased energy efficiency.


Finally, it is assumed that ships of type A will have considerably more idle days/yr than ships of type B. Panamax ships of type A are assumed to have 14 idle days/yr, whereas ship of type B will have 6 idle days/yr (downtime due to dry-docking and steel repairs).


In the calculations of the downtime, in table 9 in the appendix to the study, a steel replacement rate of 7 tonnes /day is assumed. This seems very low, especially for the calculated repairs for 18-year-old ships of type A.


It does not seem probable that shipowners will use the average of 143 days, more than one third of a year, for dry-docking and steel


repairs (1.5 year before it


is


assumed taken out of service), and consequently the “additional ship factor” used in the calculations for the ships of type A should be lower.


If the study “Life-cycle CO2 emissions of bulk carriers: a comparative study” should be used as an argument to build ships with a life cycle of 30 years instead of 20 years, it is clear that the technological development resulting in more efficient ships, more efficient shipyards, more efficient steel fabrication, and more efficient recycling must be included in the calculations. This again would most likely give the result that, based on the CO2 emission, it will be better to have three energy-efficient and more modern ships through the 60- year period than two less efficient and less modern ships.


J Sun, Zhejiang Maritime Safety Administration of People’s Republic of CHINA


I had been always entangled in a question-whether in shipping safety and energy efficiency are contradicted or compatible. Gratsos and his colleagues give me a clear and perfect answer-both could be achieved simultaneity. The paper, from a holistic perspective,


through a


const/benefit analysis, shows convincingly that a robust ship built with sufficient corrosion allowances will have better environmental performance or less CO2 emission than so-called “energy efficient” ship which have a lower Energy Efficiency Design Index (EEDI). It provides a very


evidence not only for shipping and ship-built industries, but


also


important, for


governments, particularly persuasive those


and timely message or for


negotiators and policy-makers on emission reduction from shipping.


AUTHOR’S RESPONSE


First of all, we would like to thank all five respondents for taking the time to read the paper and provide their comments, all of which we found very interesting.


Responding to Nikos Mikelis’s comments first, we note that steel is manufactured mainly in blast furnaces or electric arc furnaces (EAF). Scrap is used as a feedstock in both processes. The more scrap used in steel production the less energy is required;


therefore the


emissions generated per tonne of steel produced through the use of scrap are less.


It is true that most scrap steel used as feed stock for steel production is exported by industrialised economies, which seem to have a surplus. It follows that India and Bangladesh would use the scrap from ships they recycle for their own needs, instead of importing similar quantities. The scrap imported by


steel producing countries comes from longer distances than those from


© 2010: The Royal Institution of Naval Architects


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