THE LOADED BOX · VSSI MONTHLY December 2025 · Vessel Schedule Stability Index

The window didn’t decay. It kept moving.

Where in the planning horizon the window actually moves - and what that means for commitments still open.

Published April 23, 2026 · Framework TradeLanes VSSI Monthly v1.1 · Companion publication DTB Monthly Dec 2025

1. The Reading

December did not get calm. It became mid-horizon. The median cargo receiving window at T-4w measured 129 hours across the U.S. export network. By T-0d, the median measured 137 hours. On aggregate, the window expanded across the planning horizon. Volume told the opposite story. Schedule revisions grew roughly eightfold across the quarter - from 459 in September to 3,779 in December. More motion. Earlier motion. Less time where it mattered. 57.6% of December revision events landed beyond T-7, outside the zone where exporters, terminals, and carriers usually fight over the window. The window is still moving. What changed is where it moves. Volatility migrated out of the 72-hour compression zone - the zone the system is designed to catch - and into the mid-horizon planning window where commitments are being priced. The window became more visible. It did not become more actionable.

2. The Mechanism

Sustained Churn · USSAV Garden City as terminal anchor The Execution Decay Curve that framed earlier VSSI readings - false stability, hidden decay, compression, collapse - describes a window that holds through the planning horizon and breaks inside the 72-hour zone. September and October fit that pattern. December does not. The decay framing is not the dominant explanation for this month. December’s mechanism is Sustained Churn. Roughly one in four December voyages - 24.8% - showed sustained, unsettled revision activity. Sustained mid-horizon movement. No stable endpoint. These vessels didn’t drift late or jump at the end. They never stopped moving long enough for a plan to settle against them. And Sustained Churn was not evenly distributed. It concentrated heavily at USSAV Garden City - one terminal carried the overwhelming majority of the month's Sustained Churn voyages. Many carriers, one place. The mechanism is cross-carrier but terminal-specific. The alliances didn’t produce the pattern independently and happen to converge there. They converged there because Garden City is where the pattern operates. The median at T-4w sat at 129 hours, held through T-3d, and finished at 137 hours. The shape on the chart is not decay. It is a plan that didn’t settle - and kept moving until the calendar caught up with it.

*

Fig. 1 - Median window width at each snapshot horizon across December 2025. The reference line (dashed) shows the typical decay shape when late-stage compression dominates. December’s line runs flat through T-3d and finishes higher than it started - the signature of Sustained Churn, not decay.*

The three-element read

Contradiction. If the window expanded, the system improved. It did not. Nearly one in four voyages never had a stable moment to plan against - and nearly all of them were at one terminal. The median rose across the network only because the aggregate hides where the mechanism operates. Operator implication. Exporters are no longer planning against a decay curve they can buffer. They are planning against a window being rebuilt between T-14 and T-3, inside the same horizon where rail commits lock and dispatch chains begin to warm. The information is arriving before the plan closes, but not before the commit chain opens. Failure mode. Plan committed at T-4w. Mid-horizon revisions arrive in paired cascades at the terminal. The window moves forward, sometimes by many days - MSC VANESSA at USSAV translated +23.0 days on both ERD and CY Cut; CMA CGM CALLAO at USSAV translated +11.0 days in lockstep across 35 revisions. By T-3, the window the operator committed against no longer exists. Re-dispatch is the remaining option.

3. Key Metrics

Two metrics reinforce the same finding. Revisions per voyage climbed. Late-stage share fell by proportion. Every move carries the same signature: earlier, not safer.

The first two rows are the conventional VSSI reading. The third row is the reconciliation the DTB Monthly flagged: share-based metrics show late-stage volatility easing, but absolute-volume metrics show compression-zone activity growing more than threefold since October. The system wasn’t quieter in December. It was more active by every absolute measure - and the new activity concentrated mid-horizon.

*

Fig. 2 - Change arrival distribution across the December planning horizon. 57.6% of events arrived beyond T-7 - the mass of schedule movement sits squarely inside the planning horizon, well outside the 72-hour compression zone.* The breakdown matters more than the aggregate. 28.9% of events arrived beyond T-14. 28.7% between T-14 and T-7. 21.7% between T-7 and T-3. The mass sits between T-14 and T-7 - the zone where rail commits and drayage dispatch are being finalized. This is the same voyage universe producing more revisions, earlier in the horizon.

4. VSSI-P - Port-Level Snapshot

Where the mechanism operated The redistribution did not arrive evenly. Two ports carry High bands, driven by recurring multi-vessel convergence events at specific terminals. One port carries Elevated. Three carry Moderate, one of which is under active data pipeline review.

Note on Norfolk. The Norfolk band for December reflects the port’s overall voyage distribution. A subset of MAEU voyages at USORF shows a CY Cut revision pattern currently under data pipeline review (documented in DTB Monthly Dec 2025, Section 4 methodology note). If confirmed as a pipeline artifact, the corrected band will be reissued in the January edition.

5. Representative Vessel-Level Movements

Supporting sample · curated by the month’s pattern · not a ranking The following vessels illustrate how receiving windows moved in practice in December. Each card shows the published window at T-4w, the actual window at T-0d, and the classification of what happened between those two points. The mix reflects December’s redistribution - Late expansion is the dominant outcome, with Compressed and Mixed cases showing the structural complexity beneath the network-level expansion.

| CONTI CONTESSA · USNYC · ONEY / ADHOC / 022E/W Original CRW: ERD Nov 18 | CY Cut Nov 29 Actual CRW: ERD Nov 21 | CY Cut Nov 28 Shift: +3.0d ERD / −1.7d CY · Late-stage: Yes (inside 72h) Outcome: Compressed - collapsed See this vessel in DTB Weekly → | |---|

| MSC VANESSA · USSAV · MSCU / INDUS2 / IV539 Original CRW: ERD Nov 14 | CY Cut Nov 20 Actual CRW: ERD Dec 7 | CY Cut Dec 13 Shift: +23.0d ERD / +23.0d CY · Late-stage: Yes (inside 72h) Outcome: Late expansion - shifted after commitment See this vessel in DTB Weekly → | |---|

| YM TRILLION · USSAV · YMLU / PEC2 / 017W Original CRW: ERD Nov 30 | CY Cut Dec 6 Actual CRW: ERD Dec 20 | CY Cut Dec 26 Shift: +20.0d ERD / +20.0d CY · Late-stage: Yes (inside 72h) Outcome: Late expansion - shifted after commitment See this vessel in DTB Weekly → | |---|

| CMA CGM CALLAO · USSAV · CMDU / CAGEMA / CAIWS Original CRW: ERD Nov 15 | CY Cut Nov 21 Actual CRW: ERD Nov 26 | CY Cut Dec 2 Shift: +11.0d ERD / +11.0d CY · Late-stage: Yes (inside 72h) Outcome: Late expansion - shifted after commitment See this vessel in DTB Weekly → | |---|

| HMM VANCOUVER · USTIW · ONEY / 302W / 0302 Original CRW: ERD Dec 4 | CY Cut Dec 4 Actual CRW: ERD Dec 16 | CY Cut Dec 28 Shift: +12.0d ERD / +24.0d CY · Late-stage: Yes (inside 72h) Outcome: Late expansion - shifted after commitment See this vessel in DTB Weekly → | |---|

| ONE WREN · USORF · ONEY / EC5 / 028W Original CRW: ERD Nov 29 | CY Cut Nov 28 Actual CRW: ERD Nov 27 | CY Cut Dec 2 Shift: −2.0d ERD / +4.0d CY · Late-stage: Yes (inside 72h) Outcome: Mixed - directional conflict See this vessel in DTB Weekly → | |---|

| ONE EAGLE · USNYC · ONEY / EC4 / 036-2 Original CRW: ERD Nov 19 | CY Cut Nov 24 Actual CRW: ERD Nov 21 | CY Cut Nov 25 Shift: +2.0d ERD / +1.0d CY · Late-stage: No (outside 72h) Outcome: Moderate drift - drifted within tolerance See this vessel in DTB Weekly → | |---|

| CAPE AKRITAS · USSEA · MSCU / CHAMPION / 549R Original CRW: ERD Nov 26 | CY Cut Dec 2 Actual CRW: ERD Nov 26 | CY Cut Dec 2 Shift: 0.0d ERD / 0.0d CY · Late-stage: No (outside 72h) Outcome: Stable - held See this vessel in DTB Weekly → | |---|

6. What This Means for Planning

The decision horizon changes under this pattern. When late-stage volatility dominates, exporters can buffer. Commit at T-4w, recheck at T-3, absorb the last-72-hour shift through reserved equipment and pre-booked appointments. The decision is sequential. The system is designed for it. When mid-horizon volatility dominates, the buffer moves inside the commit window. The plan is moving while it is being committed. The 57.6% of December events that landed beyond T-7 arrived while rail commits were being placed, labor was being scheduled, and drayage was being reserved. In absolute terms, both zones got worse. Compression-zone activity grew from 238 events in October to 782 in December - more than threefold. The share fell only because the denominator exploded. Reading share-only obscures this: the compression zone got louder, while the mid-horizon got much louder still. Both zones demand operator attention; the mid-horizon demands more new attention. The planning-horizon choice is no longer “commit early at T-4w, recheck at T-3.” It becomes: wait for the voyage’s trajectory to settle before committing, or accept that the commitment will be revised mid-flight. For a voyage whose schedule hasn’t settled by T-7 - visible in its revision activity - the plan committed at T-4w will not be the plan that executes. Cost is created when action is taken against a window that hasn’t stopped moving. The window at T-4w is not a fiction. But if the same voyage is showing mid-horizon churn, every dollar priced against that T-4w window is priced against a plan that will be rewritten.

7. Bottom Line

December did not resolve the cargo receiving window. It relocated where the window’s instability arrived. Volatility that used to land inside the 72-hour compression zone - where the system is built to catch it - now lands between T-14 and T-3, before the commit chain closes. The mechanism is Sustained Churn, concentrated heavily at USSAV Garden City. The window became more visible, and less actionable. Visibility improved. Decision quality did not. The Execution Decay Curve - the framing that carried September and October - is not the dominant explanation for this month. What remains is the question it replaces: if churn holds, the problem is no longer when the window closes. It is whether a plan can be made at all.

TRADELANES · VSSI MONTHLY · DECEMBER 2025 tradelanes.co

Appendix A - Measurement Layer

Band vocabulary

Stable - window held through execution. Moderate - window moved within planning tolerance. Elevated - window structure under stress. High - window not reliable for commitment. Used consistently across DTB Weekly, DTB Monthly, and VSSI Monthly.

Outcome classification

Compressed, Mixed, Late expansion, Moderate drift, and Stable describe how each window moved between its first and final snapshot. The exact classification thresholds live in the internal methodology appendix and are not published.

Sustained Churn

Voyage-level volatility pattern describing windows that keep moving through the planning horizon without settling. The classification thresholds live in the internal methodology appendix and are not published. Orthogonal to the Outcome classification above.

Late-stage qualifier

Inside 72h, inside 24h, or outside 72h, measured as the time between the latest revision event and ERD_final.

Methodology note

Analysis covers December 2025 U.S. departures with observable schedule revisions between October 22, 2025 and January 1, 2026. 3,779 events across 572 voyages after suppressing the MAEU/USORF-norfolk-terminal cyCut pipeline artifact documented in DTB Monthly Dec 2025 Section 4. September baseline: 459 events. Outcome classification applied to 761 voyages with complete T-4w snapshot data. Sustained Churn classification applied to 142 voyages meeting the published criteria. VSSI-P bands computed from voyage-level distribution using the current methodology; classification thresholds live in the internal methodology appendix and are not published.

Reconciliation with DTB Monthly Dec 2025

The December event volume (3,779), September baseline (459), and Sustained Churn cohort definition (24.8%) align with the DTB Monthly Dec 2025 edition. This edition standardizes on the post-suppression methodology so VSSI Monthly and DTB Monthly cite the same numbers. Earlier drafts also cited a “phantom window” framing (incomplete T-4w windows filled in by departure) that was replaced with the Sustained Churn mechanism read after additional review.