Accelerating Maritime Decarbonisation Through Energy Efficiency Unlocking the Impact of Propeller Boss Cap Fins (PBFC) and Advanced Anti-Fouling Coatings in Reducing Emissions

1: ACCELERATING DECARBONISATION: THE IMMEDIATE IMPERATIVE OF ENERGY EFFICIENCY FOR SHIP OWNERS

With advancing regulations and technology, the imperative is clear: stakeholders across the maritime landscape must act now. For ship owners, there are multiple pathways to consider—such as preparing for future fuels—but the immediate priority for “acting now” centers on improving energy efficiency. By optimising vessels for peak efficiency, owners can achieve significant gains today while laying the groundwork for a more sustainable future. 

Efficiency improvements largely depend on the strategic adoption of energy-saving devices (ESDs). When implemented effectively, ESDs enhance environmental performance, reduce fuel consumption, and lower emissions, while also allowing vessels time to prepare for future fuel transitions. These gains translate to immediate cost savings, improved GHG ratings, and future-ready vessels for ship owners and managers. 

In this report, we will examine the adoption and impact of some energy-saving devices, providing a roadmap for maximising their benefits and accelerating the industry’s journey to net zero. 

 

Energy Saving Devices: Trends in the Bulk Sector 

RightShip’s GHG Rating has provided the commercial shipping industry with valuable insights into vessel efficiency since 2013. Offering the A-E rating scale, allows selection of the most efficient vessels by charterers and provides a metric for shipowners, charterers, ports and terminals and finance institutions to collaborate on as the industry progresses on their respective decarbonisation journey. 

The GHG Rating has incentivised investments in energy-saving devices (ESDs), driving meaningful progress toward industry-wide decarbonisation. With over a decade of data, RightShip can identify clear trends in these investments. Focusing on the bulk sector, in particular, we observe a steady increase in ESD adoption over the past ten years, signaling a growing commitment within the segment to improve energy efficiency and reduce emissions. 

2: EXPLORING KEY ENERGY-SAVING DEVICES: PROPELLER BOSS CAP FINS AND ADVANCED LOW-FRICTION COATINGS 

 

Data collected over the past decade through RightShip’s GHG Rating review process highlights the energy-saving potential of Propeller Boss Cap Fins (PBCF), which can enhance vessel efficiency by approximately 1.5%. While this gain may seem modest, it’s significant given the low cost of PBCF installation. Ironically, the expense of conducting a Computational Fluid Dynamics (CFD) study to quantify this benefit often surpasses the cost of the device itself. As a result, vessel owners seldom submit CFD data for PBCF installations, meaning these improvements often don’t count toward reductions in the Existing Vessel Design Index (EVDI) or the Energy Efficiency Existing Ship Index (EEXI), thus having no direct impact on a vessel’s GHG Rating.  

Another promising but under-utilised technology is advanced low-friction anti-fouling coatings. Marine organisms—such as barnacles, algae, and molluscs —accumulate on hulls over time, increasing drag and frictional resistance. This results in decreased speed at constant power output, or, conversely, increased fuel consumption to maintain speed. Traditional antifouling coatings control hull fouling, but advanced low-friction coatings reduce drag more effectively, which can enhance operational efficiency and reduce emissions. Recent data from RightShip highlights an encouraging upward trend in the application of low-friction anti-fouling coatings across vessels, with many opting for repeat applications as coatings reach the end of their lifespan. 

However, these coatings are difficult to evaluate under current frameworks, and their high cost makes it essential for owners to see a return on investment through enhanced ratings and recognition in the commercial market.

 

The Challenge of Measuring Efficiency Gains in Advanced Coatings 

While existing frameworks, such as CFD analysis, reliably evaluate traditional energy-saving devices like PBCF or Mewis Ducts, they fall short in accurately measuring the efficiency gains of low-friction coatings. These coatings are a relatively recent innovation and were not widely available when sea trial standards were developed in the 1980s. Though ship operators recognise the coatings’ potential for efficiency gains beyond fouling control, a standardised measurement method is lacking, making it challenging to capture their benefits within the GHG Rating framework. 

This leaves ship owners and managers of vessels with advanced coatings seeking ways to validate their investment. Current guidelines provide a clear methodology for hardware devices, but the unique hull-fluid interaction in low-friction coatings makes results challenging to replicate through simulations alone. Instead, actual sea trials are required to demonstrate their impact—but even here, factors like hull deformation complicate results. 

To fully leverage the decarbonisation potential of these coatings, establishing a crediting mechanism within RightShip’s GHG Rating is essential. Recognising owners who invest in advanced hull coatings not only rewards their efforts but also serves as a powerful incentive, encouraging more operators and managers to adopt these high-performance anti-fouling solutions. By making the benefits of such coatings visible, we can foster wider adoption across the industry, aligning individual contributions with the broader push toward net zero emissions. 

 

3: HOW RIGHTSHIP IS CREDITING PBCF AND ANTI-FOULING PAINT

 

The study on the data led to the conclusion that vessels installing PBCF will be given a 1.5% power reduction to achieve the same speed (Vref) at 75% nameplate MCR without the need to conduct a new sea trial or CFD studies. The new Vref can be derived using the formula:  

New Vref = Vref,original * {(1/0.985)^(1/3)} 

Nevertheless, if an actual sea trial or CFD study is done showing higher improvement, that will be credited upon verification. The above calculation needs to be detailed in Section 4 – Estimation Process of Speed-Power curve, of the EVDI Technical file and the adjusted Speed-Power curve needs to be presented together with the original Speed-Power curve therein at the EEDI draft by the submitter. 

 

Meanwhile, quantifying the impact of low-friction anti-fouling coatings on a vessel’s speed (Vref) presents unique challenges. RightShip has engaged in discussions with coating manufacturers (such as HEMPEL, JOTUN, and PPG), industry experts, and naval architects to better understand these complexities. One major challenge is that a ship’s hull deforms over time due to factors such as contact with barges, fenders, material degradation, and exposure to harsh weather. Although these deformations remain within safe operational limits, they can disrupt smooth water flow along the hull, masking the performance improvements achieved by coatings. Often, these coatings effectively compensate for the efficiency loss caused by a non-smooth hull profile, meaning that if these in-service impacts were absent, the true effect of the coatings would be more apparent in sea trials.  

The 1978 ITTC Performance Prediction Method (7.5-02-03-01.4), which guides the scaling of model test results to full-scale vessels, includes allowances for hull roughness in resistance predictions. However, it acknowledges the potential of advanced coatings, noting in Section 2.4 that “for modern coatings different values will have to be considered.” Unlike systems such as air lubrication or wind-assisted propulsion, which can be activated or deactivated for testing purposes, coatings are uniformly applied across the hull’s wetted surface, making it difficult to isolate and measure their exact impact. 

To address this challenge, RightShip leverages established guidelines focusing on demonstrating performance improvements in vessels as designed.  

 

Proposed Solution 

ITTC 7.5-02-02-03 – Resistance and Propulsion Test and Performance Prediction with Skin Frictional Drag Reduction Techniques specifically speaks of the difference between homogeneous and inhomogeneous categories of techniques that work by reducing the skin friction drag. Since the effect of coatings cannot be switched on and off it would require two identical models for studying the with and without skin reduction effect of coatings which is impractical. Hence, it suggests that such evaluations need to be performed with flow around simpler geometries such as towed flat-plates or floating-element measurements in a circulating water tunnel (Section 3). 

A framework for quantifying the impact of low-friction coatings on ship performance (Vref) was proposed by HEMPEL and HYDRUS, who also submitted experimental results, evidence and calculations for a test vessel approved by an IACS class member. In contribution to the review of these guidelines by RightShip following the procedure described in the ITTC 7.5-02-02-03 – Resistance and Propulsion Test and Performance Prediction with Skin Frictional Drag Reduction Techniques, feedback was received from coating manufacturers, HEMPEL and JOTUN and other industry bodies.  

It was demonstrated that there could be power reduction of around 7 - 9% for the same speed achieved at varying operational speeds. Such an improvement may vary from ship to ship as the calculations are specific to a vessel’s design.  

This approach has its own challenges such as scaling from simple geometry to full-scale ship, full scale sea trial records, and hull roughness contribution. The key challenge of the absence of hull roughness in the proposed calculations is addressed in Sections 5.3 and 5.4 of the ITTC 7.5-02-02-03 which explains omissions of roughness allowance, ∆Cf. However, hull roughness is a qualitative visual measure of the effectiveness of the coating application hence needs to be monitored as defined by the NACE SP0616-2022 - Standard for Hull Roughness Measurements on Ship Hulls in Dry Dock. 

Similarly, hull preparation is the most significant step in a coating’s application. If the surface has not been prepared as per the need for each specific coating it can fail to perform as expected sooner or later. Therefore, the mechanical and chemical foundation for coating application is very important and can be monitored as per the Blast cleaning grades (Sa) of ISO 8501-1 or equivalent standards. 

By establishing the guidelines accepting modifications to a vessel’s Speed-Power curves in Existing Vessel Design Index (EVDI) calculations upon the application of low-friction coatings, RightShip aims to position itself as a facilitator in advancing discussions on vessel efficiency improvements. Through its established environmental review mechanism, RightShip seeks to move beyond the conventional view of coatings as merely anti-fouling agents, recognising them instead as integral to a vessel’s overall performance and decarbonisation efforts. 

 

Read more about Propeller Boss Cap Fins Guidelines here: https://rightship.com/technical-information?nid=105  

Read more about Low Friction Coating Guidelines here: https://rightship.com/technical-information?nid=106