Slowing down on the approach to congested ports cut CO2 emissions by up to 11% on individual ballast legs, according to new research from Cargill Ocean Transportation analysed by the Global Maritime Forum (GMF) across terminals in Brazil and Australia.

The study covered 16 ballast voyages at three ports, each using different systems to match vessel arrivals with berth availability. The headline finding: savings depended less on the technology deployed than on how much waiting time a ship could realistically absorb before it hit its queue position.

What did the trials actually deliver?

At Cargill's grain terminal in Santarém, Brazil, a bespoke virtual notice of readiness arrangement let ships slow down without losing their place in the terminal queue. Across 10 voyages, estimated emissions fell by 222 tonnes of CO2 — 3% of ballast-leg emissions — with no disruption to berth schedules.

The Port of Newcastle's existing vessel arrival system performed better. Three voyages logged estimated cuts of between 6% and 11%, helped by favourable currents that allowed ships to drift toward the Australian port with engines stopped. Two other vessels registered zero savings. The reason was simple: berths were free when they arrived.

The sharpest single result came at Albany, Western Australia. A kamsarmax fitted with the Blue Visby Solution slowed from 8.6 knots to 7.4 knots, saving an estimated 10.73 tonnes of fuel and 33.4 tonnes of CO2 — 9.6% of ballast-leg emissions. The bunker savings were split between Cargill and grain handler CBH Group under the arrangement's cost-sharing terms.

Why does idle time matter commercially?

The report estimates commercial vessels spend 4% to 6% of their operating year — 15 to 22 days — waiting outside ports. Better arrival coordination can trim that idle period without extending total cargo transit time. For owners and charterers, that is fuel burned for nothing; for ports, it is anchorage congestion that better scheduling can dissolve.

What's blocking wider adoption?

The study identifies familiar commercial friction. Ports and terminals often must change their scheduling practices, while the fuel savings accrue to the ship operator — a split that gives terminals little incentive to move first. Charterparty provisions, commodity contracts and hold inspection requirements can also frustrate virtual arrivals, since early arrival often secures queue priority regardless of berth availability.

The researchers are candid about limits. Sixteen voyages is too small a sample to establish industry-wide savings figures, and most bulkers in the study were already steaming close to their minimum practical speeds. Squeezing out more would require engines suited to ultra-slow steaming, workable contractual clauses and berth systems that reward slower approaches rather than rewarding whoever shows up first.

The economics are proven in principle. The question the trials leave open is whether ports and charterparties will reprice waiting time fast enough for just-in-time arrival to scale beyond a handful of grain and bulk terminals.