Why speed and propulsion control drives the biggest efficiency gains

Because the power required to move a ship rises with the cube of its speed, even tiny adjustments in propulsion can produce outsized fuel savings. This insight explains why speed is the single most powerful operational lever available to operators, and why the gap between recommendation and execution is where most of those gains are still being lost.

Many factors influence vessel efficiency and propulsion, but speed remains one of the most important operational tools available to operators. Naturally, fuel consumption is linked to vessel speed because the energy required to move a ship through the water increases with speed.

Small changes in vessel speed can result in large differences in fuel consumption. This is shown by the ‘cube law’, which is where the power required to move a ship increases with the cube of its speed. This means that small changes in speed (whether positive or negative) will always have an outsized effect on fuel consumption.

As a result, speed management is recognised as one of the most effective operational strategies for improving maritime energy efficiency. One of the central ways the industry is responding to emissions regulations is by reducing speed during voyages, whether through slow steaming or measures such as shaft power limitation.

Despite this, feedback from interviews conducted as part of this research suggests that speed optimisation is somewhat misunderstood, with a view that it is simply a matter of reducing speed wherever possible. In reality, the effectiveness of speed optimisation depends on how well crews adjust propulsion settings in response to changing operating conditions throughout a voyage.

“Speed optimisation is the low-hanging fruit. It is an easy way to get some percentage of fuel gains,” he explained. Achieving these gains depends on maintaining the recommended propulsion settings throughout a voyage. When speed recommendations are not followed throughout a voyage, the expected efficiency improvements are considerably reduced.

Despite advances in the advisory tools used onboard vessels, these alone cannot guarantee that the crew follows the recommended optimal operating profiles throughout a voyage. Bridge teams are required to interpret the information provided to them and make the propulsion adjustments they deem necessary while managing other operational factors.

“Route optimisation tools are widely available and can identify more efficient routes and schedules. However, without proper automation and monitoring to ensure these recommendations are applied in practice, the realised benefits are likely to fall significantly short of expectations,” explained Dr Timoleon Plessas, Founder of Sealion Engineering.

This highlights a gap between optimisation planning and real-world execution as even when crews intend to follow recommendations, doing so requires constant monitoring and a lot of manual adjustments.

Stavros Paschalakis, Chief Technology Officer at DeepSea Technologies, supported this view, stating that “Beyond a certain point, you cannot expect the captain to constantly adjust speed throughout a voyage.”

While guidance is useful, the inability to maintain ideal operating conditions is a drawback for operators looking to realise the full potential of speed optimisation. If optimisation tools are automated or semi-automated, propulsion control systems can adjust propulsion settings in the background, ensuring optimal performance.

This can free up crew as the need for manual adjustments decreases, allowing them to focus on more pressing tasks. Prateek Rana, Maritime Decarbonisation Consultant, Siglar Carbon, discussed this, stating that “automation can remove a lot of administrative hours, even saving one hour a day for crew makes a big difference over time.”

Read this and more about supervised propulsion control and how this leads to efficiency gains in our latest full report here.