IN Brief:
- Sea-Intelligence's analysis of vessel arrivals through September 2026 identifies more pronounced seasonal variations in schedule reliability.
- Weekly service-number variability increased across four major East–West trades, with Asia–North Europe showing the largest rise at 78%.
- Irregular vessel arrivals and service deployment complicate terminal resource planning, cargo collection, and inland transport scheduling.
Sea-Intelligence has identified greater seasonal variation in global container shipping reliability and more irregular weekly service deployment across major international trades. Its latest analysis shows that shipping operations have become less consistent since the pandemic, with the largest measured increase in weekly service-number variability occurring on the Asia–North Europe route.
The research draws on two datasets covering different aspects of liner shipping performance. Sea- Intelligence’s Global Liner Performance database records vessel arrivals and schedule reliability, while its Trade Capacity Outlook database tracks the services and shipping capacity deployed across individual trade routes.
The reliability analysis uses monthly vessel arrival data extending from July 2011 to September 2026. Comparing the period before the pandemic with subsequent years allows the research to distinguish established seasonal behaviour from changes in the timing and consistency of vessel operations.
Between 2013 and 2019, global schedule reliability generally followed a recognisable annual pattern. Punctuality tended to weaken during the opening months of the year, improve through spring and early summer, decline modestly towards the end of summer, and recover again during October and November.
Individual years have become less closely aligned with that pattern since 2020. The average seasonal fluctuation has also become more pronounced, with weaker reliability during the early part of the year and higher performance peaks during summer. The difference affects when cargo owners can reasonably expect changes in vessel punctuality.
Schedule reliability measures whether vessels arrive within a defined tolerance of their published arrival times. It provides a measure of punctuality, while average delay duration describes how late vessels are when they miss that threshold. The two measures must be considered together because the frequency of late arrivals does not, by itself, establish how long those delays last.
Sea-Intelligence examined how these measures have moved together over time. Its analysis indicates a change in their statistical relationship since the pandemic, with the relationship between falling reliability and longer delays becoming more pronounced. The results establish an observed pattern in historical data rather than a guarantee that future delays will follow the same progression.
A separate analysis examined fluctuations in the number of weekly liner services operating across four major East–West trades. The selected routes were Asia–North America West Coast, Asia–North America East Coast, Asia–North Europe, and Asia–Mediterranean.
The research accounted for changes caused by new service introductions, cancelled routes, blank sailings, schedule slippage, and seasonal or specialist services. These events alter the number of departures operating in a particular week, even when a carrier’s broader advertised network remains unchanged.
Sea-Intelligence calculated the annual standard deviation of weekly service numbers as a percentage of the average weekly number of services. This produces a measure of relative variability, allowing periods with different levels of service deployment to be compared without relying solely on the absolute number of departures.
All four routes recorded higher variability during 2020–2026 than during 2013–2019. Asia–North America East Coast showed the smallest increase, at 26%, while Asia–North Europe recorded the largest at 78%. The rise was particularly pronounced across the two Asia–Europe trades.
These percentages describe changes in the variability of weekly service counts. They do not represent equivalent falls in the number of available vessels, container slots, or on-time arrivals. A route can experience considerable week-to-week changes in departure numbers while still carrying substantial total shipping capacity over a longer period.
Fluctuating departures can alter the timing of cargo arrivals at container terminals. When several services are delayed into the same operating period, a port may face a concentration of vessel calls and containers requiring handling, even if the total volume over the month remains broadly consistent.
Terminal operators allocate quay cranes, yard equipment, storage positions, and labour according to expected activity. Clusters of vessel arrivals can place pressure on those resources, while periods with fewer calls can leave capacity underused. The distribution of work across individual days therefore influences operating performance as well as the total quantity of cargo handled.
Inland transport arrangements are connected to those vessel schedules. Hauliers and rail operators organise container collections around vessel discharge, terminal availability, and subsequent delivery commitments. A change in the arrival pattern can require revised collection appointments, different equipment allocations, or changes to warehouse receiving schedules.
The resulting changes can extend through several stages of a shipment. A container arriving later than expected may miss a planned rail departure or delivery slot, while cargo arriving earlier than the receiving operation can accommodate may need temporary storage. Actual outcomes depend on the available capacity and flexibility within each transport arrangement.
The latest variability findings accompany weak overall schedule reliability during 2026. Sea-Intelligence reported that global punctuality recovered to 50.6% in September after three consecutive monthly
declines. Average delays for late vessels stood at 6.65 days, confirming that missed schedules continued to involve substantial waiting periods.
Separate research published in late October identified unusually high deployed shipping capacity during October and November. Sea-Intelligence linked part of that increase to vessel bunching caused by congestion and delays in Asia, where ships originally scheduled for earlier departures were moving into subsequent reporting periods.
That capacity analysis measures the number of container slots deployed, while the latest service variability research examines how consistently departures occur. Both can be affected by disrupted vessel rotations, but they provide different information about the maritime transport available to cargo owners.
The distinction extends to published transport schedules. A shipping line may maintain a nominal weekly service while individual departures are cancelled, delayed, or moved into another week. Cargo owners planning shipments need the actual available sailing and its connection arrangements, rather than the nominal service frequency alone.
Sea-Intelligence’s historical comparison establishes a more variable operating environment across the principal East–West trades than before 2020. The continued movement of delayed vessels through the network, together with changing weekly deployment patterns, will determine whether service consistency improves during the remaining months of 2026.
