Improve CII ratings: Effective actions for shipowners and operators

To achieve and improve CII ratings shipowners will have to find ways to decrease CO₂ emissions, in relation to the transport work performed. In our previous CII article, we explained how the rating is calculated. 

The algorithm for attained CII describes the core issue:

Simplified, the attained CII for a ship is calculated as emissions of CO₂ divided by the transport (capacity) work performed. To improve the CII rating of a ship, we either need to decrease CO₂ emissions, get the ship to sail further without using more fuel – or do both. 

There are a number of technical measures that a shipowner can take to improve the CII rating of a ship. Other measures require more active involvement by the ship and fleet operators. Some measures are  more feasible and efficient than others. Most likely, a combination of measures will be required over time. 

Use a fuel with a lower carbon emission factor

CO₂ emissions are calculated based on fuel consumption times a carbon emission factor that is defined for each fuel type. Therefore, changing to a fuel with a lower carbon emission factor is one way to improve a ship’s CII rating. Fuels with radically lower emission factors however, will mostly be something to consider for newbuilds. The existing fleet will need fuels compatible with existing combustion engines and propulsion systems without too much retrofitting work.

The work of  establishing standard emission factors for alternative low or near zero carbon fuels has started but is still some time away before completed and implemented in the regulatory framework. Increasingly, regulations will focus on the Well-To-Wake rather than the Tank-To-Wake emissions of fuels. 

Minimize hull friction to improve CII ratings

Hull friction occurs when water comes into contact with the ship’s hull, as it moves through the water, leading to resistance that requires additional energy (fuel) to overcome. Here’s an overview of various strategies to reduce hull friction and ultimately lower fuel consumption in order to improve CII ratings:

• Hull design and shape optimization: A streamlined, hydrodynamic hull shape can significantly reduce friction. Smoother curves, reduction of sharp angles, and minimizing appendages like protruding propeller shafts can help streamline the flow of water around the ship, as can a bulbous bow.
• Anti-fouling coatings: Marine organisms such as algae, barnacles and mussels can attach to the hull, creating roughness that increases friction. Anti-fouling coatings reduce growth. 
• Hull surface smoothness:  A smoother hull surface reduces turbulence and friction. Sanding and polishing the hull during dry dockcan help maintain smoothness. Intermediate hull polishing while the ship is in operation is also gaining ground with new technologies and equipment developed. 
• Air lubrication systems: These systems inject air bubbles or a thin layer of air under the ship’s hull, creating a boundary layer that reduces friction between the hull and water. This technique is still in development but has shown promising results in reducing fuel consumption.
• Regular hull inspection: Regular inspection of the hull’s condition and cleanliness helps detect and address fouling and damage to maintain fuel efficiency.
• Maintaining the ship’s trim and draft within optimal ranges. Improper trim and excessive draft can lead to increased drag. By distributing the cargo properly on the ship you can maintain optimal stability and trim. Unevenly distributed weight on the other hand, will increase resistance and fuel consumption.

Reduce the need for any non-propulsion power generation

The use of the auxiliary power generator adds to fuel consumption without contributing to transport work. A number of measures can be taken to minimize its load and fuel consumption:

• Choose energy-efficient lighting, HVAC systems, and appliances to lower power consumption.
• Utilize waste heat from propulsion systems or other onboard processes to generate electricity through heat recovery systems and to provide heating and hot water. 
• Install energy storage systems, such as batteries, to capture excess power during low-demand periods.
• Implement an intelligent load management system to distribute power efficiently among different ship systems. Prioritize essential systems and minimize simultaneous high-power operations to prevent peak demand. Real-time monitoring and data analytics can be used to track energy consumption and identify areas for improvement.
• Integrate renewable energy sources like solar panels and wind turbines to generate power during daylight hours and when the ship is stationary.
• Use shore power instead of the onboard generator whenever possible.

Add rotary sails for supplementary propulsion power

Although not practical or possible for all ships, rotary sails offer a possible solution for reducing fuel consumption and emissions. By harnessing wind energy through spinning sail designs, ships can supplement their traditional propulsion systems. These sails capitalize on the power of wind at various angles, enabling ships to sail more efficiently even against headwinds. 

Optimize propulsion efficiency to minimize fuel consumption

Monitor the ship’s engine performance and optimize settings for the operational conditions to minimize fuel consumption. Propulsion systems should be fine-tuned to operate efficiently across required load ranges and the engines should then be operated within their optimal load range to decrease fuel consumption. Ensure the propeller is properly maintained and aligned. A well-maintained propeller and shaft system can significantly impact fuel efficiency.previous