Loran Lines on Penobscot Bay Chart
Many small scale charts provide Loran lines, which indicate the time difference expected between receipt of "master and slave" radio signals in the Loran electronic navigation system. This chart, Penobscot Bay and Approaches, #13302, has four different sets of lines, improving a navigator's chance of getting an accurate electronic fix. Loran receivers indicate by number which signals they are getting, and the navigator finds the numbers and uses them to plot a fix. Loran was state of the art electronic navigation, and modern Loran receivers read directly in latitude and longitude, but the system has been made obsolescent by GPS.
This chart is at a scale of 1:80,000 and is good for planning a route up Penobscot Bay but does not show harbors and sections in the detail of a 1:40,000 harbor chart . The green bar shows the start of the main ship channel up to Searsport, and its beginning between Allen and Monhegan Islands is a spot that is easily found.