Ships can adjust their speed to arrive precisely. Image Credit: GMF

Shipping may be underestimating the emissions-cutting potential of slow steaming because current modelling often fails to account for port call optimisation, according to the Global Maritime Forum (GMF).

The shipping industry's assessment of slow steaming may be overly conservative because many studies assume vessels spend the same amount of time in port regardless of sailing speed, it said in a report published on Tuesday.

Slow steaming is the practice of operating ships at lower speeds to reduce fuel consumption.

GMF said under that assumption, ships travelling more slowly take longer to complete voyages, meaning extra vessels may be needed to maintain transport capacity.

But GMF said much of that lost time could be recovered through better port scheduling and just-in-time arrivals.

Ships frequently spend hours or even days waiting at anchor before berthing because of scheduling inefficiencies.

A recent study cited by the forum found vessels can spend 15-22 days each year waiting outside ports.

"With improved scheduling, information sharing, and contractual changes, vessels can adjust their speed to arrive precisely when a berth becomes available, rather than rushing to port only to wait offshore," GMF said.

The forum said operational measures such as slow steaming and port call optimisation can deliver near-term efficiency gains using existing technologies and better coordination across the maritime value chain.

While slower sailing and better port scheduling can significantly reduce bunker consumption and emissions, they are unlikely to eliminate the need for alternative marine fuels. Shipping will still require low-carbon fuels to meet long-term decarbonisation targets.