The National Oceanic and Atmospheric Administration now
provides the public with free downloads of 1000 U.S. nautical
charts. Charts are available in 2 formats, raster navigation
chart (RNC) and electronic navigation chart (ENC).
Charts are not directly viewable, but rather require a
viewing program to use them. A variety of commercial programs
can view and manipulate RNC and ENC charts.
To download NOAA charts, visit
http://www.nauticalcharts.gov/