Longitude: How do yo tell what the exact ships time is.
If the sun is directly over-head where you are at 18:00 hours GMT (for example) and your boat is at 42 degrees N latitude, you''re on Lake Michigan which is 90 degrees west. For every hour past GMT that the sun is over-head where you are, you''re 15 degrees west of GMT. It doesn''t matter what time it is at your location, it only matters when the sun is over-head and what time it is at GMT. One hour equals 15 degrees. Now get the hell out of my way, I''m on starboard tack!