Tackling the EEXI and CII Chal­lenge with Hydro­dy­namic Optimization

On January 1, 2023, the Energy Effi­ciency Existing Ship Index (EEXI) and Carbon Inten­sity Indi­ca­tor (CII) will come into force, creating new chal­lenges for oper­a­tors of com­mer­cial vessels. Ship owners and managers must prepare for these require­ments by assess­ing and improv­ing their vessels as needed. This is crucial in order to earn the proper cer­tifi­cates, allowing them to continue sailing and trading internationally.

EEXI and CII

These new manda­tory measures have been intro­duced by the Inter­na­tional Maritime Orga­ni­za­tion (IMO) to cut the carbon inten­sity of inter­na­tional shipping, setting shipping on a course to meet green­house gas reduc­tion targets estab­lished in the 2018 Initial IMO Strategy for Reducing GHG Emis­sions from Ships.

The EEXI is a tech­ni­cal index that deter­mines a vessel’s energy effi­ciency purely on the basis of the ship’s design para­me­ters. It has to be cal­cu­lated one time for the initial cer­ti­fi­ca­tion and is based on the same method­ol­ogy as the Energy Effi­ciency Design Index (EEDI) for new­builds. In a sim­pli­fied way, the EEXI esti­mates CO2 emis­sions per trans­port work (grams of CO2 per ton-mile). Emis­sions are computed from the installed power of the main engine, fuel oil con­sump­tion, and a con­ver­sion factor between fuel and the cor­re­spond­ing CO2 mass. Possible reduc­tion factors and energy-saving equip­ment are considered.

The CII is a recur­ring oper­a­tional require­ment, cal­cu­lated as the ratio of the total mass of CO2 emitted (from actually consumed fuel) to the total trans­port work (from the distance traveled and the ship’s capacity) in a given calendar year. A vessel’s annual carbon inten­sity per­for­mance will be compared against the IMO’s rating system which cat­e­go­rizes ships into A, B, C, D and E. Vessels which receive a D rating for three con­sec­u­tive years or an E rating for one year are required to submit a cor­rec­tive action plan to demon­strate ways in which they will improve their performance.

Several options for tech­ni­cal and oper­a­tional improve­ments are avail­able for ships that must mod­er­ately or sig­nif­i­cantly minimize emis­sions and improve fuel con­sump­tion. These include switch­ing to low-carbon fuels, limiting engine power, reducing speed, and retro­fitting vessels with energy-effi­cient technology.

Cor­rec­tive Measure and Hydro­dy­namic Optimization

One subset of the cor­rec­tive measures that can be taken to achieve EEXI and CII com­pli­ance is related to improv­ing the hydro­dy­namic per­for­mance of the ship by means of dif­fer­ent retro­fits. These measures have in common that their effect is to either reduce the required power and there­fore fuel con­sump­tion, or alter­na­tively, to increase the vessel’s speed for a given power, as both cases will equally lead to an improve­ment of the indexes. Some­times, they make sense in com­bi­na­tion with other measures, e.g., in the case of a poorly per­form­ing bulbous bow for a ship that is operated at a sig­nif­i­cantly reduced speed. Typical examples for retro­fits are: bulbous bow replace­ment, pro­peller mod­i­fi­ca­tion, air lubri­ca­tion systems, wind assisted propul­sion systems, and energy saving devices like wake ducts, pre-swirl stators and pro­peller boss cap fins.

As most of these retro­fitting measures require serious invest­ment, it is crucial to maximize the improve­ment they are able provide, also under con­sid­er­a­tion that their impact with regard to the vessel’s annual CII com­pli­ance should last as long as possible. This can only rea­son­ably be achieved by means of hydro­dy­namic opti­miza­tion based on CFD simulations.

CAESES® allows the design­ers to thor­oughly explore the avail­able design space by ana­lyz­ing many design variants in an effi­cient auto­mated process. It combines unique para­met­ric geometry modeling and vari­a­tion capa­bil­i­ties, a com­pre­hen­sive opti­miza­tion envi­ron­ment, and flexible inter­fac­ing capa­bil­i­ties to connect to external sim­u­la­tion tools (mostly CFD, but also struc­tural analysis, if required). This provides design­ers with a complete toolset to achieve a truly opti­mized design, shorten the devel­op­ment time frame, and under­stand the influ­ence of all involved para­me­ters on the design’s performance.

More Infor­ma­tion

See this overview to learn more about the capa­bil­i­ties of CAESES® for the design of ship hulls, appendages, and pro­pellers. Contact us to discuss your indi­vid­ual require­ments and our solu­tions in more detail.

Also, take a look at this pre­sen­ta­tion about how our customer DNV uses CAESES® for the opti­miza­tion of bulbous bow retrofits.