Last I checked there AISHub was the biggest reusable source of AIS data. Coverage map here: http://www.aishub.net/coverage http://www.aishub.net/coverage. They

Last I checked there AISHub was the biggest reusable source of AIS data. Coverage map here: http://www.aishub.net/coverage http://www.aishub.net/coverage. They are used by various sites like https://www.vesselfinder.com/ https://www.vesselfinder.com/ MarineTraffic has a more comprehensive monitoring network but they keep the data to themselves. Details at https://www.marinetraffic.com/en/p/expand-coverage https://www.marinetraffic.com/en/p/expand-coverage As noted by another comment, AIS signals are being broadcast line-of-sight from the ground so you need more receivers than you do to track airplanes. OTOH you only need the receivers on the coastlines and on major inland waterways, not over the whole earth's surface. (If you want to track a ship mid-ocean, you'll need a satellite. Those exist but cost $$.)