From an economic perspective, shipping remains an indispensable and efficient means of transporting goods and supporting the world economy. However, many issues are taking a toll on maritime logistics and increasing the rate of ocean freight. For one, initiatives to make the shipping sector more environmentally conscious have long been in motion, with authorities like the International Maritime Organization (IMO) and many others already enforcing stringent regulations on improving sustainability, decarbonisation, and pollution reduction.
The pressure to go green is just one of the many factors contributing to the steady increase in fuel costs to date, which has been on the rise following the post-pandemic demand recovery while supply continued to lag. This was then exacerbated during the outbreak of the war in Ukraine last year, in which marine fuel spiked to its historic $1,000/ton mark. With fuel costs accounting for as high as 60% of the total operational costs of shipping, it is clear why the need for improved fuel efficiency is greater than ever. Otherwise, ship owners risk not just fuel costs cutting into their profits but also the consequences of failing to comply with environmental regulations.
Many solutions are being explored in response to these pressing issues, mainly using energy-saving devices, improving ship structure, and optimising voyage planning and execution.
Implementing Energy-Saving Devices
There are now numerous energy-saving devices for ships being developed and tested that focus on optimising their design or improving their existing design elements to reduce emissions and fuel consumption. An example of this is propulsion-improving devices (PID). Ultimately, the efficiency of a marine vessel’s propeller, regardless of class, all comes down to having low energy loss from propeller rotation and favourable wake flow.
Many of the different PIDs available today are designed to recover as much of this lost rotational energy and promote favourable wake flow that maximises propeller thrust, saves energy, and reduces fuel consumption. Implementing a PID entails modifying the hull or propeller with different fins, ducts, bulbs, nozzles, or other modifications to improve efficiency. When added in front of the propeller, these devices are known as pre-swirl devices that work to improve the propeller inflow conditions. If placed behind the propeller, they are classified as post-swirl devices that help recover some of the lost rotational energy in the propeller slipstream.
Besides optimising a ship’s normal functioning, other innovations take a different approach, such as Michelin’s Wing Sail Mobility (WISAMO) project that uses a ‘wing’ that resembles and functions similarly to the masts used by sailing ships during the Age of Exploration. However, this wing uses a smarter design that leverages variations in air pressure to generate lift and propel the vessel forward.
According to Michelin, the WISAMO project is designed to improve ship fuel efficiency by as much as 20% as per their technical tests and simulations. For large container ships, this would entail saving tens of thousands of litres of fuel a day and significantly cutting down on cargo ship fuel costs. The project is just one of many “wind-assisted propulsion” initiatives currently being developed, and the most effective designs may become widely adopted sooner rather than later.
Reducing Hull Resistance
A ship’s hydrodynamic performance largely depends on the pressure and frictional resistance acting on its hull as it moves through the water. Hull optimisation is incredibly important to reducing fuel consumption since hull performance directly affects a ship’s speed and power consumption.
Reducing pressure can be accomplished through retrofitting improvements, specifically hull form optimisation techniques, or by creating new designs that reduce wave resistance. For frictional resistance, surface improvement methods like using anti-fouling coatings and implementing air lubrication techniques are key to reducing turbulent flow in the boundary layer.
Ultrasonic anti-fouling is an established means of deterring marine bio-fouling, the undesirable build-up of biogenic structures and living organisms on a ship’s hull that increases drag and fuel consumption. Meanwhile, air lubrication is an alternative approach to reducing frictional resistance that improves the viscous behaviour of the water that makes contact with the hull. This is achieved by injecting low-pressure air into the wetted surface to either form a cushion or blanket of air or a microbubble interface between the water and the hull, reducing drag and resistance on the ship.
Optimising Voyage Planning and Execution Decisions
Many shipowners and technical managers have looked towards optimising their voyage planning and decision-making to contribute to their energy efficiency efforts. As it turns out, no single shipping organisation or department has full control over the energy efficiency of their maritime operations, and there are two aspects to consider when improving such efficiency: commercial and nautical.
The commercial decisions in voyage planning, which typically relate to matching ships and cargoes and speed and route choices, have a much greater impact on energy efficiency than nautical decisions. The scheduling and chartering managers are the ones who make such decisions in close dialogue with cargo owners, and their choices are largely dictated by market conditions like cargo ship fuel costs, freight markets, cargo-owner transit time preferences, and so on.
Thus, indices that aggregate the weather/sea, commercial, and nautical aspects of energy efficiency into a single metric cannot provide well-grounded measures of energy efficiency in shipping operations, a shortcoming that both the IMO’s Annual Efficiency Ratio suffers from.
Since observers cannot effectively separate the effects of the various nautical and commercial and unpredictable sea and weather conditions on these two metrics, their value for benchmarking ship energy efficiency and performance is usually limited.
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