How much does idling at anchorage cost in fuel and emissions?

A vessel idling at anchorage burns a significant quantity of fuel even at minimal power settings. Depending on vessel size and engine configuration, daily fuel consumption during anchorage waiting can range from several tonnes for smaller vessels to well over 20 tonnes per day for large container ships running auxiliary engines and maintaining hotel loads. Those figures translate directly into operating costs and emissions that accumulate with every hour of delay.

Port congestion, berth unavailability, and scheduling misalignment are the most common drivers of prolonged anchorage waiting. For terminals and shipping lines alike, understanding the true cost of that idle time is the first step towards addressing it. The sections below work through the fuel burn figures, the financial exposure, and the emissions consequences in practical terms.

How much fuel does a vessel burn while idling at anchorage?

A vessel at anchorage typically burns fuel across two categories: auxiliary engines powering onboard systems and, where applicable, a main engine running at low load to maintain position or manoeuvre. For a large container vessel, auxiliary engine consumption alone can reach 5 to 15 tonnes of heavy fuel oil per day. At low main engine load, total consumption can exceed 20 to 30 tonnes per day depending on vessel class and conditions.

Smaller feeder vessels consume proportionally less, but the principle is consistent: there is no such thing as zero fuel consumption while a vessel is crewed and operational. Hotel loads, ballast pumps, navigation systems, crew accommodation, and cargo refrigeration units all draw power continuously. The engines supplying that power burn fuel whether the vessel is moving or stationary.

It is also worth noting that vessels burning low-sulphur fuel oil or liquefied natural gas under current IMO regulations may face different cost profiles, but the underlying consumption pattern remains. Anchorage waiting does not pause fuel burn; it simply relocates it away from productive transit time and into a period that generates no cargo throughput.

What are the financial costs of prolonged anchorage waiting?

The financial cost of anchorage idling combines fuel expenditure, crew time, vessel hire or operational overhead, and the downstream consequences of schedule disruption. For a large container vessel burning 15 to 25 tonnes of fuel per day at anchorage, and with bunker prices varying by fuel grade and region, daily fuel costs alone can run into tens of thousands of dollars. Multiply that across a multi-day wait and the exposure becomes operationally significant.

Beyond direct fuel spend, prolonged anchorage time affects vessel utilisation. A ship waiting at anchor is not generating revenue from cargo movement. For liner operators on fixed schedules, delays at one port cascade through subsequent port calls, potentially triggering demurrage charges, missed slot agreements, and repositioning costs. For terminals, repeated congestion that forces vessels to anchor also carries reputational and commercial consequences, as shipping lines factor port reliability into their service route decisions.

Charter party agreements often include demurrage clauses that activate once a vessel exceeds agreed waiting times. Those costs are contractually defined and can be substantial. When anchorage waiting is a recurring pattern rather than an isolated event, the cumulative financial drag becomes a material concern for both terminal operators and their shipping line customers.

Reducing fuel waste from anchorage idle time is therefore not simply an environmental consideration. It is a direct operational and commercial priority. We work with terminals to analyse capacity and scheduling challenges that contribute to vessel waiting, using simulation to identify where operational adjustments can reduce congestion and improve berth utilisation.

How does anchorage idling contribute to CO₂ and NOₓ emissions?

Anchorage idling contributes directly to CO₂ and NOₓ emissions because combustion continues regardless of whether a vessel is under way. Every tonne of heavy fuel oil burned produces approximately 3.1 tonnes of CO₂. For a vessel consuming 15 tonnes per day at anchor, that represents roughly 46 tonnes of CO₂ emitted daily without any productive cargo movement. NOₓ emissions follow a similar pattern, generated through high-temperature combustion in diesel engines.

The regulatory context makes this increasingly consequential. The IMO’s Carbon Intensity Indicator framework, which came into force in 2023, rates vessels on their carbon intensity relative to cargo carried. Fuel burned at anchorage counts against a vessel’s annual carbon intensity score without contributing any cargo transport work. A vessel that spends significant time waiting at anchor will accumulate a worse CII rating than one with equivalent main engine performance but better port turnaround times.

NOₓ emissions carry additional significance in port areas and near coastal zones, where local air quality regulations are becoming more stringent. Vessels at anchorage in or near Emission Control Areas are subject to sulphur and NOₓ limits that apply regardless of operational status. Extended anchorage periods in these zones increase cumulative local pollutant exposure and can attract regulatory scrutiny.

For terminals, the emissions generated by vessels waiting for a berth are increasingly visible in sustainability reporting frameworks and port environmental performance assessments. While the vessel operator bears direct responsibility for onboard emissions, the terminal’s scheduling and throughput performance directly influences how long vessels wait. Improving berth productivity and reducing congestion are some of the most direct ways a terminal can contribute to lower total emissions across the port system.

If you want to understand how simulation and capacity analysis can help your terminal reduce vessel waiting time and its associated costs, get in touch with us to discuss your specific operational context.

Frequently Asked Questions

How can terminals practically reduce vessel anchorage waiting time?

Terminals can reduce anchorage waiting through a combination of improved berth scheduling, real-time vessel traffic coordination, and simulation-based capacity planning. By modelling berth occupancy, cargo handling rates, and vessel arrival patterns, terminals can identify bottlenecks before they cause congestion and adjust scheduling windows accordingly. Proactive communication with shipping lines about expected berth availability also allows vessels to slow-steam en route rather than arriving early and waiting at anchor, cutting fuel consumption without disrupting port throughput.

What is slow steaming and how does it help reduce anchorage idle time?

Slow steaming is the practice of deliberately reducing a vessel's speed during transit so that it arrives at a port closer to the actual time a berth becomes available. When terminals share accurate, real-time berth availability data with vessels and their operators, ships can adjust their speed profile at sea, where fuel consumption is more efficient per tonne-mile, rather than burning fuel unproductively at anchor. This approach requires reliable communication between the terminal and the vessel operator but can significantly reduce both waiting hours and total voyage emissions.

Does a vessel's CII rating recover if anchorage waiting is reduced in subsequent voyages?

Yes — the Carbon Intensity Indicator is calculated on an annual basis, so improvements in port turnaround time and reductions in anchorage idle hours will positively influence a vessel's CII rating over the course of the reporting year. Since fuel burned at anchor counts against CII without contributing any cargo transport distance, even modest reductions in average waiting time across a fleet can produce a measurable improvement in rating outcomes. Vessel operators and terminals working collaboratively to reduce port congestion therefore share a direct interest in the CII performance of the vessels calling at that terminal.

Are there any onboard measures vessel operators can take to reduce fuel burn while waiting at anchorage?

While no onboard measure eliminates fuel consumption entirely, operators can reduce anchorage burn by shutting down non-essential auxiliary loads, consolidating power generation onto fewer, more efficiently loaded engines, and switching off refrigeration units for empty reefer slots where cargo conditions permit. Cold ironing — connecting to shore power where port infrastructure supports it — is the most effective option for eliminating onboard combustion at berth, though its availability at anchorage is limited. These measures reduce the cost and emissions of unavoidable waiting but are not a substitute for addressing the scheduling and congestion issues that cause the waiting in the first place.

How do demurrage costs interact with fuel costs during extended anchorage periods?

Demurrage and fuel costs are separate but compounding financial exposures during prolonged anchorage waiting. Demurrage clauses in charter party agreements typically activate after a defined laytime threshold is exceeded and are charged at a fixed daily or hourly rate, regardless of what the vessel is actually consuming in fuel. This means that during an extended wait, a vessel operator may be simultaneously accruing demurrage liability to the charterer and absorbing direct fuel costs — two distinct financial drains running in parallel. Understanding both components is important when quantifying the true cost of a congestion event or negotiating service agreements with terminals.

What data should a terminal collect to start analysing the impact of vessel waiting time?

The most useful starting point is a structured dataset of vessel arrival times, berth request times, actual berthing times, and departure times across a representative period — typically 12 to 24 months. Combining this with vessel class and size data allows a terminal to calculate average and peak waiting durations by vessel type, time of day, and season. Layering in berth occupancy records and cargo volume data then makes it possible to identify whether waiting is driven by berth capacity constraints, handling rate variability, scheduling clustering, or a combination of factors — which is the foundation for any meaningful simulation or operational improvement work.

Are emissions from vessels waiting at anchorage included in a port's environmental reporting?

This depends on the reporting framework in use, but increasingly, yes. Many port sustainability frameworks and environmental performance indices — including tools aligned with the Environmental Ship Index and the Port of Call reporting standards — are expanding their scope to capture emissions from vessels within the port's operational influence, including anchorage areas. Even where formal inclusion is not yet mandatory, anchorage emissions are attracting growing scrutiny from port authorities, regulators, and sustainability-focused shipping line customers. Terminals that proactively track and work to reduce vessel waiting time are therefore better positioned as environmental reporting expectations continue to tighten.

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