The IMO’s greenhouse gas reduction targets are designed to support global efforts against climate change. Short-term measures to improve energy efficiency on existing ships include the application of technical efficiency measures, known as EEXI. An information paper provides best practice guidance for managing the risks associated with the implementation and operation of Overridable Power Limitation (OPL) on existing ships has been released, reports OCIMF.
Understanding The Purpose and Scope
The IMO’s greenhouse gas (GHG) levels of ambition are designed to meet specific targets that support global efforts against climate change and are subject to ongoing reviews. The latest IMO strategy update concluded at MEPC 80 in July 2023.
A range of short-term measures has already come into force and these focus on improving energy efficiency. Short-term measures include the application of technical efficiency measures for existing ships. This regulation is commonly known as the Energy Efficiency Existing Ship Index (EEXI). Mid-term measures remain under discussion at IMO and, once selected, are expected to come into force in 2027.
Regulatory Background
EEXI Regulation The International Convention for the Prevention of Pollution from Ships (MARPOL) Annex VI amendments, which support the IMO’s GHG Strategy to improve the energy efficiency of ships, came into force on 1 November 2022. The requirements for EEXI and Carbon Intensity Indicator (CII) certification which are part of the GHG Strategy’s short-term measures, came into effect on 1 January 2023.
To comply with this newly introduced regulatory limit, the technical efficiency of existing (operational) ships will be assessed against the applicable Energy Efficiency Design Index (EEDI) reference line that is dependent on ship type and Deadweight (DWT) segment.
A ship’s EEXI would be calculated for each ship and benchmarked for compliance against the EEDI baseline (Phase 0). A reduction factor (% below that baseline) had initially been set at 20% for commercial tankers of 4,000mt DWT and above. Recognizing the challenges that the larger DWT segments of new tanker designs have under the EEDI scope and considering that older hulls would face an even greater challenge, the IMO agreed to adjust the target to 15% for all ships of 200k DWT and above.
OPL Guidelines
OPL guidelines including both engine power limitation (EPL) and shaft power limitation (ShaPoLi), can be implemented for a ship to comply with the EEXI requirement. The IMO MEPC issued accompanying guidelines to the EEXI regulations, including technical and operational conditions that the OPL should satisfy under the EEXI framework (MEPC.335(76) as amended by MEPC.375(80)).
Following the IMO guidelines, ShaPoLi will require sensors for measuring torque and rotational speed delivered to the propeller, a data recording and processing device, and a control unit for calculating and limiting the power transmitted by the shaft to the ship’s propeller(s). For EPL, electronically controlled engines can limit the power output (or access the power reserve) using software linked to the fuel index limiter or by directly limiting power in the engine’s control system.
The power output of a mechanically controlled engine can be restricted using a sealing device that can physically lock the fuel index via a mechanical stop screw sealed by wire or an equivalent device with a governor limit setting. OPL cannot be overridden without permission from the Master or Officer in Charge of Navigational Watch (OICNW).
Click here to read the entire paper.
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Source: OCIMF
