Marine Charts and Navigation Oceanography 2017 Earth Coordinate

Marine Charts and Navigation Oceanography 2017

Earth Coordinate System ► 1. 2. 3. 4. Latitude Parallels of arc 0º-90º N-S from the equator to poles 1º = 60’ (1’=60 sec) small circles ► 1. 2. 3. 4. Longitude Meridians of angle 0º (prime meridian) 180º E-W pole to pole Prime meridian is measured at Greenwich England great circles

Marine Charts Water depths ► Configuration of the shoreline in coastal waters ► Navigational lights, buoys, landmarks ► Chart title block ► Nature of the bottom (hrd, rky, g, sh, s, co) ► North is the top, latitude scale on side, and longitude on top and bottom ► Many charts cover less than a 1º of lat or long, so be careful when “fixing” a position ►

Units of Distance Statute vs. nautical miles ► 1 nautical mile = 1’ of latitude ► 1 nautical mile = 1. 15 statute miles ► 1º of latitude = 60’ = 60 nautical miles ► 1º = 60 nautical miles = 69 statute miles ► Use a drafting compass or dividers and spread points to apply to chart bar scale to determine distance ►

Units of Speed ► Knot = 1 nautical mile/hour ► 1 knot x 1. 85 = km/hr

Plotting a Course Magnetic vs. true (geographic) North ► Use the “Compass rose” on the chart ► The compass is graduated from 0º-360º and broken into 32 points on the compass ► Cardinal points (0, 90, 180, 270 degrees) ► Intercardinal points (northeast, southwest, northwest) ► Cardinal-intercardinal points (ie. east northeast = 67. 5º and southeast = 157. 5º) ►

Cont’ Course ► Intended direction of travel ► Expressed in degrees ► However, influenced by winds, currents, and pilot error Heading ► The direction in which the ship is actually traveling regardless of prescribed course Bearing ► Direction from one point to another ► Expressed as an angle from North ► Traditional expressed as relative parts of the vessel

Time and Earth’s Rotation ► Earth rotates on its axis once in 24 hrs = day ► Each rotation is 360º = 24 hrs ► Longitude 0º (prime meridian at Greenwich England) when sun is directly overhead is 12: 00 noon ► Therefore at 180º the time is 12: 00 am (midnight) ► Therefore, every 15º of longitude E or W of Greenwich = 1 hour of time (Zulu or Z. time) ► 360º/24 = 15º

D. R. Navigation ► ► 1. 2. 3. 4. ► Also known as Dead Reckoning or “Ded” Reckoning Method of navigating using the following from a KNOWN position: Time Speed Distance Direction Note: Does not account for error or currents

Formulas ► Distance ► Speed ► Time = Speed x Time D = Distance / Time = Distance / Speed Use 60 D = S * T (for minutes) S T