OpenSeaMap (www.openseamap.org) is an open source, worldwide project to create a free nautical chart. There is a great need for freely accessible maps for navigation purposes, so in 2009, OpenSeaMap came into life. The goal of OpenSeaMap is to record interesting and useful nautical information for the sailor which is then incorporated into a free map of the world. This includes beacons, buoys and other navigation aids as well as port information, repair shops and chandleries. OpenSeaMap is a subproject of OpenStreetMap and uses its database.
Navigating to the site and selecting download charts
The below map downloads appear to no longer work as of 3/17/2022. You can get direct list of KAP files here:
https://ftp.gwdg.de/pub/misc/openstreetmap/openseamap/charts/kap/
The rest of the unzip and install guide below works.
Go to www.openseamap.org
On the left navigation sidebar, just inside the Nautical Chart box, choose “Download chart”
Scroll to the bottom of that page, and select “Download-Layer for KAP-Charts”
On the left of the chart map, you will see Download Type and a selection box. Make sure you pick KAP as the type.