Marine Charts and Navigation Oceanography 2014

Earth Coordinate System Latitude Parallels of arc 0º-90º N-S from the equator to poles 1º = 60’ (1’=60 sec) small circles 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, southeast, southwest, northwest) Cardinal-intercardinal points (ie. east northeast = 67.5º and south 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 24hrs = day Each rotation is 360º = 24hrs Longitude 0º (prime meridian at Greenwich England) when sun is directly overhead is 12:00 noon Therefore at 180º the time is 12:00am (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 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 x Time Speed = Distance / Time Time = Distance / Speed Use 60 D = S * T (for minutes) D S T