SØNDAG
2026-09-13
The Cloudy Brain

Too many projects, too many ideas, too few hours — one learning a day anyway

Havnetryk

When will there be a berth? Guest pressure in Danish harbors, read out of 17 months of AIS.

The Havnetryk front page: a MapLibre map of Denmark where every one of 673 harbours is a blue circle sized by guest pressure — the south-Funen archipelago, the Limfjord and the island harbours light up densely — under the headline stat of 198,345 guest arrivals by 20,312 AIS-visible sail and motor boats over 17 months.
FIG. 1 Every guest arrival in Danish waters on one map — circle area is 17 months of harbour pressure.
The harbour page for Anholt: the season chart shows July owning the year — 864 guest arrivals in July 2025 against near-zero winters — and below it the berth-window chart plots hourly arrivals and departures across 3,097 guest visits: the orange departure wave tops at 08–09, the blue arrival wave builds through the afternoon to 15–16, so the best chance of a berth is late morning, just after the departures.
FIG. 2 Anholt by season and by hour — July owns the year; departures top at 08, arrivals at 15.

I sail exactly the waters — Samsø, Tunø, Anholt — whose harbors overflow on July weekends, so the question is personal: where will I get a berth, and when should I arrive? Havnetryk answers it with guest pressure per harbor, by weekday, hour and season, computed from 17 months of AIS data.

The model is built on rules that keep it honest. Ferries are excluded as noise, and berth-holders are excluded by default — only guests compete for space. Because small craft are invisible to AIS, it claims relative pressure only: rush hours and trends, never absolute berth counts. And geography stays real — distinct harbor names never merge (Skagen is four harbors).

The public site at havnetryk.dk is aggregate-only by design: harbor stats, seasonality, arrival and departure hours, typical stay lengths — plain static HTML with one MapLibre map and small SVG diagrams, refreshed by a nightly anonymized export. The vessel-level layer stays private, permanently: no identities in any public artifact, ever.

CODElast 26 weeks · all-time 55 commits · +2k−691 lines
  • Nightly exports still running unattended
  • Named-vessel view gated behind Cloudflare Access
  • Coverage area and data freshness on every page
  • The site gets its Danish strapline
  • Soundings archive moves to R2 storage
  • Nightly export, privacy checks and auto-deploy
  • First anonymized harbour data export ships
POSTS1