ENC's are vector image files (file format IHO S-57, extension .000) containing geographical data normally found on nautical charts. The information about various charts is stored in seperate classes, a description of which can be found in the links below. There is an open source library for reading data from many types of vector image files which can also be found below along with a sample S-57 file. Many open source S-57 viewing programs can be found on the web such as Fugawi which can be found on the PC side of the Mast desktop. This may be usefull for checking the accuracy of a parser. In order to get gps locations for a sailboat it will be necessary to read the gps coordinates out of the relative classes (parse them) and store them in some form of data structures (perhaps a list of arrays each containing the points in a polygon outlining the feature) which the boat will be able to 'easily' store and check intersection courses with. Charts are available for purchase or can be refered from the Canadian, U.S. and British hydrographic services.
Pretty good; http://www.gdal.org/ogr/drv_s57.html
Some thesis ideas involving S57;
Gov. Chart Information;
A catalouge of features stored in S57;
Really usefull links;
An open source library for reading and using vector files such as S57 in C++ (Bingo);
Sample zipped S57 file;