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How to approach CII, EEXI, EU ETS, and other regulatory efficiency requirements?

Significant improvements can be achieved by installing energy efficient propulsion systems, relevant for both newbuilds and retrofit projects. This article will present some of the methods for increased efficiency available from the Brunvoll expertise and solutions.

Higher Propulsion Efficiency = Lower Fuel Consumption = Reduced Emissions = Improved Business Results

The Regulatory Landscape

The regulations set for the direction towards zero emission shipping in 2050 are many....

  • EEXI - Energy Efficiency Existing Ship Index - the technical energy efficiency of the ship
  • CII - Carbon Intensity Index - measured from the ship's operation
  • EU ETS - Emission Trading System - for CO2 quotas on voyages within EU
  • FEM - FuelEU Maritime - measuring carbon intensity on the energy used

.....are just some of the regulations - all with a commercial impact, where Energy Efficiency is an important working remedy.

Energy Efficiency

Complying with the standards will fundamentally change the lifecycle of vessels. Ships will need to improve efficiency to maintain or improve the CII-rating, a rating that will become increasingly stringent towards 2030.

EU ETS is also covering shipping from 2024. By increasing the Energy Efficiency the vessel will require less CO2 quotas.

FuelEU Maritime is measuring carbon intensity of the energy used, and a high Energy Efficiency will reduce required volume of alternative fuels.

Before the infrastructure and volume of zero emission fuels have reached a sufficient level, Energy Efficiency through available technology can contribute significantly to reduced emission.

What is EU ETS?

EU has decided to include shipping to the Emission Trading System (EU ETS). From 2025, ships must report greenhouse gas emission based on the MRV emission reports for the previous year. Shipping companies will acquire and submit allowances for their emission. In 2024 40% of EU-emission need to be compensated. In 2025 it will be 70%, and 100% in 2026. EU-emission is defined as emission from voyages between EU-ports (100%) and between an EU-port and a non-EU-port (50%). EU ETS applies to all vessels above 5000 GWT transporting goods or passengers.

What is CII?

IMO’s Carbon Intensity Indicator (CII) is an operational efficiency measure which target is to reduce emissions and make ships more efficient.

CII applies to all vessels above 5000 GWT transporting goods or passengers.

CII is a measure calculated in grams of CO2 per cargo-carrying capacity and nautical mile based on the aggregated operation for the previous calendar year. 2023 is the first year of registration, and the first annual rating will be issued in 2024.

The rating ranges from A to E, where A-C gives a Statement of Compliance (SoC), while D and E require a corrective plan to obtain level C as a minimum.

What is EEXI?

Energy Efficiency eXisting ship Index (EEXI) is a measure introduced by IMO to reduce greenhouse gas emission from ships, by improving the technical performance.

The EEXI regulations apply to all existing ocean-going cargo carrying vessels over 400 GWT. The measure must be carried out within the annual class inspection after January 1, 2023, and after any major conversion. An effect of the measures can be to operate at reduced speed and consumption.

Reduce the Energy Consumption

Reducing energy consumption is critical to reduce emissions, and further reduce the impact of increased energy costs of carbon-neutral fuels.

Propeller System with 6-20% Increased Efficiency

One of the remedies to meet an acceptable CII-rating will be to use low-carbon fuels. However, these are more expensive fuels, so it makes sense to invest in efficient propellers to reduce fuel consumption.

One of the answers to this is the Brunvoll Contra Rotating Propulsion System (CRP). A complete propulsion system with high propeller efficiency and thereby low energy consumption. It is a system consisting of known technologies in an efficient system configuration.

According to a study on "Energy efficiency technologies for ships" conducted by the European Commission Ecofys, there is a potential savings of 6-20% of the power consumption by using the CRP propeller system.

The Contra Rotating Propulsion System is ideal for vessels with electric propulsion and transit operation mode as main condition.

The CRP-product sheet

Well Prepared for Future Fuels

A propulsion system with propeller and reduction gearbox is a system of high flexibility - prepared for future fuels.

The gearbox can be connected to conventional combustion engines, dual fuel engines, electric motors powered by auxiliary machinery or from batteries or fuel cells, etc. The mix of energy options in each configuration leads to high flexibility and increased efficiency for the different operations.

A wide range of solutions for PTO/PTI/PTH units will further improve operational flexibility and optimise energy consumption and efficiency;
  • PTO: Power Take-Out - for power distribution to other consumers
  • PTI: Power Take-In - for boost and/or hybrid-electric propulsion
  • PTH: Power Take-Home - for emergency operation mode

The reduction gearbox – the unit that makes it all possible.

The wide range of gearboxes opens for a great variety in system configurations, and optimised systems for all ship types.

  • Module based gearbox design makes it convenient to upgrade the system for future requirements
  • PTO/PTI solutions can easily be integrated in the gearbox design, for an energy efficient hybrid-electric configuration
  • Gearboxes with multiple power inputs allows for optimised hybrid-electric propulsion
  • A CP-propeller can optimise the relation between rpm, pitch and power, and operate efficiently over a wider power range

The compact twin-in single-out gearbox in a configuration with two el. motors.
The propeller can be run by one or both el.motors. The gearbox can be connected to
up to four el.motors.
A vertical offset gearbox with two electric motors.


A twin screw configuration with twin-in single-out gearboxes connected to multiple combustion engines and el.motors ensure high redundancy and full flexibility for optimising power to the propellers. In such a configuration the propulsion system can be designed for several operation modes utilising one or multiple engines/motors.

Brunvoll ICP
- Integrated Costa Propulsion

The ship and her operating profile is the starting point when deciding upon the propulsion system configuration. For all ships it is essential to reduce fuel consumption by improving the flow around the propeller.

A device that will lead to such improvements for most ship types is the Brunvoll ICP - a rudder with Costa bulb and CP-propeller with hub cap acting as one system.

This system increases propulsion efficiency by up to 8%.

Without Brunvoll ICP: The vortex in the slip stream behind the propeller hub is causing resistance and loss of energy.

With Brunvoll ICP: The Integrated Costa Propulsion reduces the hub vortex and increases energy efficiency.

with Condition Monitoring System

  • Early warning of possible incident
  • Reduced cost when planning and performing service due to early identification of wear or possible malfunctions
  • Reduced cost and downtime through preventive maintenance trigged by the condition monitoring system
  • Reduces need for dry-docking of the vessel for visually inspection
  • Easier troubleshooting due to measuring equipment in operation

Energy Efficiency - 20% Reduced Fuel Consumption

Case study

Ship type: Multipurpose Cargo Vessel

Propulsion System: Twin screw, CP-propeller System, Reduction Gearbox with PTO/Shaft generator

Diesel Engine: 2 x 1600 kW @ 900 rpm

Main speed areas: 15kn, 13kn, 7kn

The operation profile of the vessel gives the basis for selection of propulsion configuration

Varying working conditions of a vessel require flexible solutions in order to execute all tasks efficiently.

In conditions requiring reduced power to the propeller you save fuel if your propulsion and energy production system is allowed to lower the main engine rpm and the propeller rpm.

Technically - operating the vessel at lower speed requires less power at sea. This can be obtained either by reducing pitch at full rpm, or by reducing the rpm and increasing the propeller pitch to a higher and more efficient setting - at the same time as the main engine output are at an optimum lower load. The benefits can be substantial.

These improvements give a high propeller efficiency, resulting in lower fuel consumption and reduced emission

The above figures illustrate the energy consumption for the different operation modes in fixed rpm, floating frequency 50-60Hz, and variable rpm.

To find the optimum configuration it is necessary to do an analysis of the operational profile and the different options in machinery and power production.  

Brunvoll has the tools to do such evaluations based on the following input data;

  • Vessel resistance curve
  • Main engine – type and mussel / FOC diagram
  • Brunvoll propeller curve
  • Operation profile, speed, time and required PTO power

In this case, the operation have three main speed areas; 15kn, 13kn and 7kn.

Furthermore it is necessary to evaluate the different ways to supply power from the shaft generator connected to the gearbox to the main switchboard.

Options are normally;

  1. Fixed rpm shaft generator
  2. Floating frequency 50 - 60Hz shaft generator
  3. Variable rpm shaft generator

The different options influence the choice of equipment onboard where option 2 requires power consumers that allows different frequencies. Option 3 requires the use of frequency converter between shaft generator and the main switchboard.

The short summary of this evaluation is a difference in fuel consumption pr year from 755 tons for fixed rpm operation, to 579 tons pr year with full variable frequency, a difference of 23,3 %.

The propulsion system has high potential for efficiency improvements

New build and retrofit  

  • Propulsion system optimised to the operation profile
  • Hybrid propulsion prepared for fuel flexibility
  • Energy efficient propeller systems
  • Integrated Costa Propulsion
  • Reduction gearbox - 2-speed gearbox, for multiple energy sources and PTO/PTI-solutions
  • Modern Control and Automation systems

Upgrade and retrofit pays off
up to 20-30% energy saving

Optimise the entire propulsion system to fit with the requirements of todays operation profile.

Contact persons

For more information, please do not hesitate to contact us.

See all contacts
Kirsti Gjørvad

Kirsti Gjørvad

Senior Sales Manager, Brunvoll Volda AS

+47 916 29 430

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