The port, as seen from the beach

(a) Passages per year, by class

In the four full years (2022-2025), total passages ran 15,766-17,536 a year. Passenger and pleasure, the two largest classes, together make up 41-46% of that total every year, while cargo holds steadier at 3,040-3,299 a year.

(b) Cargo: inbound vs outbound per year

Inbound and outbound cargo passages are within 0.4-1.9% of each other in every full year (2022-2025) — the one-percent symmetry the detector should show if it isn't losing one leg of a round trip, and it doesn't.

(c) Cargo + tanker passages per month

Cargo + tanker traffic is nearly flat across the calendar year: 283-308 passages a month on average (2022-2025), from a low in September to a high in May — no cargo season to speak of, unlike the tour boats below.

(d) Reported draught, cargo passages, inbound vs outbound

Inbound median draught runs 0.1-0.4 m deeper than outbound in every year 2021-2025 — the laden-inbound / lighter-outbound signature of an import port — though the gap is small next to the roughly 3-4 m interquartile spread within either direction. AIS draught is crew-entered and often stale; read these as distributions, not per-ship truths.

(e) Dwell: inbound call to next outbound call, same vessel, within 7 days

Median dwell — an inbound call to that same vessel's next outbound call within 7 days — runs 23.3-28.2 hours across the four full years, on 6,516 matched inbound/outbound pairs (cargo and tanker only).

(f) Size drift: cargo vessel length by quarter

Median cargo length ranges 275.0-299.0 m across the window, from 286.5 m in 2021Q3 to 294.0 m in 2025Q4; the longest vessel recorded was 403.0 m, in 2024Q4.

(g) Tour boats: season, by month

Tour-boat passages peak in May (208/month average, 2022-2025) and trough in February (55/month) — about 3.8x more traffic at the season's peak than its low.

(g) Tour boats: day, by local hour

88% of all tour-boat passages happen between 11am and 4pm local time, peaking at 12pm with 1,552 passages across the whole window (2021-2025).

(h) Top 30 vessels by number of passages

None of the top 30 most-frequent vessels are bucketed cargo — repeat visits are dominated by tour boats and tugs under 40 m; the largest is CARNIVAL SUNSHINE, a 270 m passenger recorded 436 times.

(i) What this does not show

• 2021 is a partial year (2021-09-19 to 2021-12-31, about 3.5 months). Its row and passage counts are not comparable to a full year and are marked SKIP in validation.
• 2021-22 dredging-fleet loitering. The Charleston harbor deepening project ran dredges and support tugs in the polygon in this window; their loiter passages inflate tug/tow and service counts in those years relative to a year without a dredging fleet.
• Sampling changes across years, which is why passages are counted, not rows. Row counts per year (2021: 425,990; 2022: 410,830; 2023: 238,307; 2024: 238,864; 2025: 186,692) fall even though the harbor did not get quieter; the national network's coverage and sampling changed over the period. The passage is the unit precisely because it survives this.
• Two different receivers. These five years come from the national AIS receiver network, one position a minute. Since September 2026 the house has its own receiver, hearing several positions a minute. The two are never added together, and no comparison across them is drawn here.
• AIS type codes are set by the operator and are sometimes wrong. CAROLINA BELLE broadcasts as tug/tow but is a Charleston Harbor Tours boat; SPIRIT OF LOWCOUNTRY / SPIRIT OF CHARLESTON / SPIRIT OF CAROLINA are the Fort Sumter ferries. The operators table will carry per-MMSI overrides; the class buckets above are as broadcast.
• No predictions. This document counts what already happened. Forecasting is a separate, later capability, and only for questions a backtest shows skill on.

(j) Validation