Introduction

The 2023 IMO strategy on reduction of GHG emissions from ships is to reach net zero close to 2050.

With Increase in Global awareness on Decarbonization to improve the climate conditions, multinational corporations across the globe are looking to decarbonize at a faster rate. Shipping being one of links in the global logistics supply chain, some of shipping companies have set ambitious targets and have taken necessary steps to reduce their global footprint either by investing in technological upgradation or by opting for low carbon alternative fuel.

One of the most direct ways to lower emissions is to reduce fuel consumption, which in turn cuts bunker costs. It is a common practice to cut fuel consumption by reducing ship speed but a far more effective alternative is to reduce fuel consumption via a well-maintained hull. A well-maintained hull will help in reducing emissions and thereby save fuel costs.

Hull management

Hull management is the maintenance of the ship’s hull in a smooth and foul-free state. Records show that a considerable amount of energy is required to overcome the frictional resistance between the submerged hull and water. This frictional drag impairs the ship’s speed, hence driving energy demand for propulsion and ultimately, fuel consumption.

This issue is worsened by hull roughness. Damage or decay or deterioration of hull painting on the hull structure causes hull roughness. This leads to uneven coating and hull plate corrosion, which affects the hull’s surface profile. The hull is prone to increase in fouling due to increase idle days,or deteriorated anti-fouling paint. The damages to hull paint or structural damage/deformation could occur for example when a vessel is alongside or at berth where paint and coating are most susceptible to abrasions. The growth and accumulation of marine creatures such as barnacles, algae or slime on the hull results in hull fouling.

These factors contribute to the effects of drag and diminish ship performance and energy efficiency- increasing carbon emissions.

Hull maintenance management

The most proactive and suitable way is to regularly monitor vessels hull performance with help of digitization and digitalisation, which helps in more accurate prediction of hull fouling and thus timely hull maintenance decisions can be taken to reduce fuel consumption which in effect reduces the carbon emissions. Through the utilization of our PAL tools for performance monitoring and analysis, we can inspect and, if necessary, undertake cleaning of the hull, propeller, rudder, sea-chest, and appendages. Undue cleaning can affect the well painted surface adversely. Undue cleaning can affect the well painted surface adversely.

Planned maintenance and hull cleaning

The most fundamental measure of hull roughness management is through the Planned Maintenance System (PMS). Hull maintenance includes a complete survey of the hull in dry dock twice in 5 years. Such dry-docking maintenance allows the inspection, repair, and cleaning of the underwater hull, which is not accessible during ship’s operations.

Hull cleaning is necessary in mitigating hull’s biological roughness. Proper cleaning of light slime can reduce fuel consumptions by 5% to 10%, while heavy slime cleaning reduces that up to close to 20%. Removal of macro fouling caused by barnacles can account for significant fuel savings of up to 30%.

Time-based maintenance is insufficient given the impact hull roughness has on dynamic CII ratings. It is prudent to continuously monitor ship performance with the help of data intelligence, hence condition-based maintenance is preferred. This involves sensor data, which is processed to provide a stream of normalized data, on which machine learning models provide necessary feedback. Based on this machine learning outcome, we have developed tools with predictive and forecasting ability which is the founding stone for developing our AI capabilities in future.

Performance-based systems track change in fuel consumption levels and main engine power through data collection to identify degrading hull conditions and timely maintenance. Consider the following when undertaking hull maintenance:

  • Data such as 24/7 voyage data monitoring and analysis
  • Current (voyage wise) and forecasted CII rating
  • Last drydock
  • Cost-effectiveness and potential savings

This system of monitoring allows effective evaluations to achieve continuous improvement.

Through such measures, operators can proactively manage structural defects and anomalies early to mitigate risks and avoid more costly repairs. These fuel savings satisfy decarbonization objectives and help in improving CII ratings.

Anti-fouling paint

Applying a coat of antifouling paint is another approach in preventing hull fouling and preserving its smoothness. At present, many environmentally friendly products such as low friction coatings and metal-free antifouling coatings are available. These high-quality paints keep the hull polished with minimum fouling for a longer period.

An alternative type of coating using silicone or fluoro-silicon base is also available. These paints utilise nonstick properties to mitigate adhesion of bio-organisms through its extremely smooth surface, shedding any micro and macro growth during the ship’s motion.

However, the degree of fouling reduction will vary with trading pattern and operational profiles, regardless of the coating type used. It is important to ensure regular maintenance and repainting of these coatings due to damage and deterioration over time.

Vessel operations

Apart from the technical aspects, good operational practices must be adopted to minimize hull fouling. Ships trading in warm waters and subjected to prolonged idle periods in ports or at anchorage are most vulnerable to fouling. Therefore, to reduce the risk of hull fouling, coordinated efforts between operators, charterers, and terminals are crucial to reduce the ship’s idle time. This includes providing a more accurate estimated time of arrival, timely loading / unloading and departure, and efficient berth planning.

Conduct efficient ballast operations to achieve lighter displacement while ensuring the stability of the ship and adequate immersion of the propeller. This minimizes the hull surface submerged which lowers the water resistance and further reduces fuel consumption.

Bulbous bow reduces wave-making resistance.

Hull design

In terms of hull design, key features of hydrodynamic optimization include lightweight constructions and the inclusion of the bulbous bow with other design extensions.

In newbuilds, light construction materials must be used in the manufacturing of the ship to reduce weight of the ship. A weight reduction of 20% has been seen to reduce engine requirements by approximately 5%. The addition of the bulbous bow, minimizes the interference caused by the incoming wave system to the bulb, improving the flow of water around its hull. This reduction in drag allows up to 20% less fuel consumption, significantly increasing the hull efficiency.

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