Measure1 CPF09 v1.3 Copyright © BSAC 2010 Chartwork and Position Fixing Measurement Basics

Chartwork and Position Fixing Measure 2 CPF09 v1.3 Copyright © BSAC 2010 Outline Direction ●bearings ●magnetic variation ●compass rose ●measuring at sea Chartwork instruments ●drawing on charts ●bearings ●distance Speed time and distance ●relationships ●measuring at sea

Chartwork and Position Fixing Measure 3 CPF09 v1.3 Copyright © BSAC 2010 Direction Nautical direction terms ●heading - direction in which the boat is pointing ●course - direction in which the boat is (or should be) steered ●track - direction in which the boat is moving ●bearing - direction of an object Direction expressed as an angle Heading Course Track Bearing

Chartwork and Position Fixing Measure 4 CPF09 v1.3 Copyright © BSAC 2010 N Bearings Bearings in degrees ●relative to North = 0° ●clockwise ●360° = 0° ●precise Cardinal points ●often used for approximate direction ●‘due’ N, S etc if precise Understand both W E NE SE SW S NW 0° 180° 45° 90° 135° 270° 225° 315° (360°) 237°

Chartwork and Position Fixing Measure 5 CPF09 v1.3 Copyright © BSAC 2010 Magnetic North Charts aligned to North Pole Compass points to Magnetic Pole ●angle between true and magnetic is ‘variation’ ●different in different places ●changes slowly with time ●currently about 3-5°W in UK Variation not significant for us Distinguish between ●chart measurements - °T ●compass measurements - °M vertical lines on chart North Pole (True North)

Chartwork and Position Fixing Measure 6 CPF09 v1.3 Copyright © BSAC 2010 Measuring bearings at sea Fixed compass ●shows boat’s heading ●smallest graduation 5° ●deviation ○error from nearby ferrous metal, magnets, electrics ○not usually considered on small boats Hand bearing compass ●used to measure bearing of objects ●smallest graduation 1° ●can distance from sources of magnetism – less deviation Record as °M

Chartwork and Position Fixing Measure 7 CPF09 v1.3 Copyright © BSAC 2010 Drawing on a chart Paper charts ●soft pencil (2B) ●draw gently ●plastic eraser for corrections Laminated charts ●indelible marker pen ●clean with solvent Exercise ●draw a line from slipway/harbour to {first waypoint on chart}

Chartwork and Position Fixing Measure 8 CPF09 v1.3 Copyright © BSAC 2010 Measuring bearings on charts Parallel rules ●line up on along direction of travel ●walk rules to centre of nearest compass rose ●read bearing from true scale Portland plotter ●line up along direction of travel ●twist circular scale to line up grid lines with grids on chart, north pointer to North ●read the bearing from plotter Record as °T Exercise ●measure the bearing of the line just drawn, enter on voyage plan

Chartwork and Position Fixing Measure 9 CPF09 v1.3 Copyright © BSAC 2010 Reciprocal bearings Bearing ●direction of island from boat Reciprocal bearing ●direction of boat from island ●add 180° (or subtract 180° if answer > 360°) ○90°→270° ○350°→170° ●your bearing from object ●your way home Add reciprocal to voyage plan Bearing = 30° Reciprocal = 210°

Chartwork and Position Fixing Measure 10 CPF09 v1.3 Copyright © BSAC 2010 Measuring distance on charts 1 Nautical Mile (nm or Nm or NM or M) = ●1´ latitude ●1852m ●1.15 statute miles ●1/10nm = 1 cable (ca) Measuring length of line ●span using dividers ●or set dividers to one nm & walk length of line Convert to distance ●read off distance in nm from latitude scale ●latitude scale widens towards poles so use scale at same latitude as line Exercise: measure line on chart and add to voyage plan

Chartwork and Position Fixing Measure 11 CPF09 v1.3 Copyright © BSAC 2010 Speed, time and distance Speed ●1 knot (kn) = 1nm / hour = 1.15mph Speed, time and distance are related ●Distance (nm) = Speed (kn) x Time (hr) ●Speed = Distance / Time ●Time = Distance / Speed ○for Time (min) use Speed (kn) /60 ○or Time (min) = Time (hr) x 60 ●or use triangle, if easier ○cover required item, read the others ●or use look-up tables ○nautical almanac ○easy to use at sea Dist Time Speed

Chartwork and Position Fixing Measure 12 CPF09 v1.3 Copyright © BSAC 2010 Examples and exercise Examples ●how long to cover 0.5nm at 15kn? ●how far after 30min at 12kn? ●how long for 7nm at 21kn? Exercise ●complete details for 1 st leg on voyage plan 2min 6nm 20min

Chartwork and Position Fixing Measure 13 CPF09 v1.3 Copyright © BSAC 2010 Measuring distance & speed at sea GPS ●distance travelled ●calculates speed Ground track v water track Tide Distance in 1 hour through water Distance in 1 hour over ground

Chartwork and Position Fixing Measure 14 CPF09 v1.3 Copyright © BSAC 2010 Summary Direction ●bearings ●magnetic variation ●compass rose ●measuring at sea Chartwork instruments ●drawing ●bearings ●distance Speed distance and time ●relationships ●measuring at sea 14 of 33

Chartwork and Position Fixing Measure 16 CPF09 v1.3 Copyright © BSAC 2010 Compass Rose One or more on every chart True bearings on outer circle Magnetic bearings on inner circle Variation at given date plus annual change variation 4°30’W 2003 (9’E) outer - true inner - magnetic

Chartwork and Position Fixing Measure 17 CPF09 v1.3 Copyright © BSAC 2010 Calculating variation variation now = variation chart ±(years elapsed X change annual ) Variation is 4° 30’ W in 2003 (9’ E) what is it in 2010? ●variation chart = 4° 30’ W ●years elapsed = 2010 – 2003 = 7 ●change annual = 9’ E ●years elapsed X change annual = 63’ E = 1° 3’ E ●variation now = 4° 30’ W – 1° 3’ E = 3° 27’ W Exercise: get variation from your chart & write on your voyage plan Change VariationWE W+- E-+ ± Same: add Different: subtract

Chartwork and Position Fixing Measure 18 CPF09 v1.3 Copyright © BSAC 2010 Bearing conversion Chart ●bearings recorded are true °T ●bearings measured are true °T Compass ●bearings displayed are magnetic °M (or °C) ●magnetic bearing required for steering Conversion ‘CadET’ ●C ompass to T rue A dd E ast ●or subtract West ●vice versa for °T to °M (or °C)

Chartwork and Position Fixing Bearing conversion examples CadET Bearing 330°T, variation 4° W, what is °M? ●compass to true add east/subtract west ●true to compass subtract east/add west ●330°T + 4° W = 334°M Bearing 170°M, variation 4° W, what is °T? ●compass to true add east/subtract west ●170°M - 4° W = 166°T 359°T, variation 4° W, °M? ●003°M 117°M, variation 3° E, °T? ●120°T