NOAA's nautical charts of U.S. waters are free: the coasts, the Great Lakes, and many rivers and inland lakes. This guide covers what they are, how to look at them in your browser, and how to take them on the boat for when there's no signal.
What NOAA ENC charts are
NOAA publishes its charts as Electronic Navigational Charts (ENC), in the international S-57 format. An ENC isn't a picture of a paper chart. It's data: soundings, depth contours, buoys and lights, hazards, bridges and their clearances. A chartplotter draws it at any zoom, and it can tell you things a picture can't, like the depth under a planned route. NOAA corrects its ENCs every week, and they're free to download and use.
View NOAA charts in your browser
The MarineOS web chart shows NOAA's charts in any browser, on a computer, tablet or phone, with no download and no account. Search for a harbour, a town or a buoy, or type coordinates to jump there. The address keeps the view, so you can bookmark a spot or send it to your crew.
With a free MarineOS account you can also plan routes on it, and they go to your boat: to the MarineOS app on your iPhone or iPad, or to a MarineOS Helm display.
Take them on the boat, offline
A browser chart needs a signal. On the water, charts need to be on the device. In the MarineOS app and on MarineOS Helm, Settings › Charts & Tides › Download Charts lists chart regions:
- NOAA: all the Great Lakes or each lake on its own; inland lakes NOAA charts (Okeechobee, Winnebago, Pontchartrain, Tahoe, Mead, the Finger Lakes, northern Michigan's lakes and more); NOAA-charted rivers (the Hudson, the Columbia and Snake, the St. Johns, the Sacramento, the New York State Canals); and every U.S. state.
- U.S. Army Corps of Engineers inland charts: the inland rivers, one region per river: the Upper and Lower Mississippi, Ohio, Illinois, Missouri, Tennessee, Cumberland, Arkansas and more.
Charts are compact: all the Great Lakes are 955 charts, about 58 MB. Zoom into a spot with no chart installed, and MarineOS offers just the charts for there.
Keeping them up to date
Once a week, when it's online, MarineOS checks NOAA's catalog (about 11 MB) and offers the corrections. It waits for Wi-Fi unless you allow cellular, and it removes charts NOAA has cancelled.
Charts for your home region are free. Every region, with updates checked automatically, comes with MarineOS Plus or a MarineOS Helm license; see pricing.
River charts: bridges, locks and clearances
River charts show river miles, locks with their chamber sizes, dams, and bridges and overhead cables labelled with their clearance. Tap a bridge for its horizontal clearance. Clearances show in your depth unit.
Lake depths beyond NOAA's charts
Many inland lakes have no nautical chart. For Michigan's, MarineOS adds depth contours from the Michigan DNR's lake surveys. They're useful for finding the deep water and the drop-offs, but they're old surveys (1929–1980), not nautical charts, and the app says so.
Using charts safely
Electronic charts are only as good as the survey behind them; some areas haven't been surveyed in decades. MarineOS isn't certified navigation equipment: keep a proper watch, check the chart's notes, and keep official charts on board.
Want the charts at your helm? See how to build a Raspberry Pi chartplotter.