Houlder: Reducing emissions via slow steaming can have unintended consequences

Houlder’s research using Clarksons’ data indicates a noticeable trend in the reduction of average service speeds across different vessel types – oil tankers, bulkers, and container ships – from 2012 to 2024. Specifically, container ships experienced the most significant decrease, with a reduction of 1.50 knots (-11%) by 2024, followed by bulkers and oil tankers, which saw reductions of 1.01 knots (-9%) and 0.74 knots (-6%) respectively. 

Iebum Shin, Data Analytics Lead at Houlder cautioned:

Any speed reduction could result in a significant departure from a vessel’s original design parameters, so the benefit of corrective measures should be considered too.

For example, a simple hull retrofit or propellor optimisation to align with the vessel’s new operating conditions could be the difference between slow steaming delivering minimal or real benefits.

The analysed data shows that while subject vessel types have reduced speed, the rate of reduction varies, reflecting differing impacts of slow steaming across vessel categories. The associated speed changes from 2012 (figure 2) underscores the unevenness in speed reduction, emphasising the need for a detailed and tailored approach when considering slow steaming as a strategy for reducing GHG emissions.

Shin added: “It’s important to carry out a ship-specific analysis to establish what the real saving will be from a range of speed reductions and to consider these against the other, perhaps unintended, or unseen, consequences.” 

Slow steaming has largely been popular because it is relatively simple to implement. In theory, it doesn’t require extra capital expenditure (CAPEX) and, as long as the rest of the fleet is doing it to the same degree, then market economics should push the freight rate up to compensate the owner or charterer for the reduced annual cargo carrying capacity. 

Trafigura has also highlighted that slow-steaming is not an option open to everyone; some vessels are not designed to move slowly while others may need to pick up speed to compensate for lost time if disruptions have forced them to take longer routes.

Houlder highlights that, in reality, slowing down is not necessarily a no-, or even low-cost option. There is often hidden CAPEX for the ship to address the consequences of slow steaming, such as modification to the turbocharger – and if engine de-rating is considered (as opposed to mechanical/software power limiters), CAPEX should be expected to be more significant.

There can also be unintended consequences of slow steaming on operating expenditure (OPEX) meaning that the expected fuel savings (and resulting OPEX reductions) may never be realised.

Consistently operating outside the ship’s design parameters may mean costly engine maintenance is required more often – for example, cold corrosion, and fouling on the exhaust gas boiler, injector and piston rings.

Commenting on the bigger picture, Rupert Hare, CEO of Houlder said: “There is real potential for significant financial impact in additional days on hire or in reduced cargo revenue if the market doesn’t compensate with increased freight rates.

If you can improve the ship’s efficiency without a high cost and without slowing down, this will offer a competitive advantage in terms of earning capacity. 

“Ultimately, if the fleet slows down, it will need to expand to maintain the same cargo-carrying capacity. More ships can easily result in more GHG emissions for the same cargo miles, hindering progress towards IMO GHG reduction targets. While slow steaming can lower emissions in some circumstances, it can also deter investments in a more ambitious, long-term, sustainability strategy – including investments in energy efficiency technology, optimised operations and new fuels.”