There are designated routes, but you can pretty much go where you please on the lake. If you really want to know the trails purchase a Garmin Montana GPS, and buy trail maps for it. Just like using your cars GPS. here's an interactive map to get an idea of the trails system in New England. Just pan in to find Lake Winnipesaukee.
http://www.gpstrailmasters.com/conte...now-map_E.html