NAVIGATION TRAINING

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NAVIGATION TRAINING Section 8 Position Lines and
Fixes
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Table of Contents

• Section 1 Types of Navigation
• Section 2 Terrestial Coordinates
• Section 3 Charts
• Section 4 Compass
• Section 5 Nautical Publications
• Section 6 Navigational Aids

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Table of Contents

• Section 7 Buoyage
• Section 8 Position Lines and Fixes
• Section 9 Tides
• Section 10 Currents
• Section 11 Weather

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Position Lines and Fixes
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Position Lines

• Position Lines (P/L) - A single observation that
  does not establish a fix, but does mean that
  ships position is somewhere along that line.
• Label - After the position line is drawn from a
  charted object, a four digit time must be written
  above and parallel to the position line.

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Position Lines

• All Compass bearings that are to be plotted on
  the chart, must be corrected to True Bearings,
  allowing for any compass error, including
  deviation and variation, before plotting.
• All True bearings/ courses taken from the chart,
  must be corrected for any compass error to obtain
  Compass Bearings/compass before use on radar or
  vessels magnetic compass.

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Sources of Position Lines

• A visual position line can be taken, using
  charted fixed navigational aids such as tanks,
  water towers, church steeples, spires, radio and
  TV towers, day marks, fixed navigation lights,
  flagpoles, or tangents to points of land.
• In general fixing off floating objects,
  especially buoys, should be avoided, if there are
  fixed charted objects available.

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Visual Position Line
1000
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Radar Range Position Line
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Position Line Measurement

• Visual Bearings can be measured in
• 1. Degrees Relative ( 0R )
• 2. Degrees per Gyro Compass ( ºG )
• 3. Degrees Magnetic ( 0M )
• The navigator must convert any of these types of
  bearings to True before they can be plotted on
  the chart.
• Degrees True ( 0T)

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Plotting and Labeling a Fix

• Fix - The point where two or more position lines,
  taken at the same time, cross. This indicates
  the ships position on the chart.
• Label - Use the four digit time next to the
  fix,it should be parallel to the bottom of the
  chart. The times of the individual position
  lines are not written.

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Visual Position Fix
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Visual Position Fix 1
Compass bearing of Abode Island bearing
009Compass, deviation 1ºW, variation 23ºE,
gives 030 º True Bearing
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Visual Position Fix 2
Compass bearing of Grebe Island Light bearing 058
º Compass, deviation 1ºW, variation 23ºE, gives
080 º True Bearing
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Visual Position Fix 3
Compass bearing of Pt. Atkinson Light bearing
098ºCompass, deviation 1ºW, variation 23º E,
gives True Bearing of 120 º T
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Visual Position Fix 4
Insert fix circle on intersection of position
lines, and time of fix
1230
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Cocked Hats

• In a perfect world, with due allowance made for
  compass error, the three position lines will
  cross at one point.
• However depending on the speed of the vessel, the
  proximity of the object from which a vessel is
  being fixed, and the accuracy of the bearing when
  taken, and other factors, it is far more likely
  that a cocked hat will be obtained.
• The larger the cocked hat, the larger an error on
  one, two or all of the position lines is likely
  to be.

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Cocked Hat
In this example there is an error of 3ºE on the
compass bearing of Point Atkinson Light and a
cocked hat is formed.
1230
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Cocked Hats

• Where a plotted position is a cocked hat, and
  there is no obvious error (such as in
  calculation), it should be generally assumed the
  position of the vessel is the point in the cocked
  hat closest to the nearest danger.
• Another position should be taken a soon as
  convenient to check on the position.An

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Reducing Errors
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Reducing Errors

• When taking distances or ranges, always take the
  ranges ahead or astern first, to minimise errors
  (as these ranges will change quickest with the
  speed of the vessel) before taking ranges on the
  beam.
• When taking compass bearings, always take the
  bearings on the beam first, to minimise errors
  (as these bearings will change quickest with the
  speed of the vessel) before taking bearings ahead
  or astern.

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Radar Fixes
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Radar Fixes

• Radar bearings are subject to compass error.
• Therefore the best way to obtain a fix by radar,
  is to take three radar distances off charted and
  identified objects.

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Radar Position 1
Using radar Grebe Is Electronic Bearing Marker
showing 058 º M Variable Range Marker showing
0.82
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Radar Position 2
From radar, plot position circle Grebe Is
Distance 0.49 nm
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Radar Position 3
Grebe Is Range 0.82 A second range of 0.93 off
Eagle Is. would give fix Mark fix position and
time. Best fix would be have third range.
1000
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Radar Position 4
Radar bearing of Grebe Is. is 058 º
compass Deviation 1ºW Variation 23ºE True
Bearing 080 ºT which confirms ranges
1000
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Electronic Position
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Electronic Position

• The GPS can give an accurate electronic
  position.
• First check that the GPS information is live, and
  not on Dead Reckoning (which GPS reverts to with
  certain faults).
• Also check that the HDOP figure is low - 1 is
  best.

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Electronic Position 1
Note down Latitude and Longitude 49º 20.38N 123º
17.23W
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Electronic Position 2
Plot Latitude and Longitude 49º 20.38N 123º
17.23W
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Electronic Position 3
Insert fix symbol, and time
1000
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Transits
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Transits

• Transits are the most accurate type of position
  line, when two charted objects line up.
• Transits are one of the most valuable tools when
  close to dangers or the land.
• Some transits are man made (intentional) and
  others are natural (coincidental).

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Transits

• The main benefits of transits are
• 1. There is no compass deviation or variation.
• 2. They can be used when the vessel's motion
  interferes with the use of a compass.
• 3. They are instantaneous and can be monitored
  continuously.
• 4.They occur frequently when in confined waters.

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Transits

• Good transit - Beacon in line with lighthouse

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Transits

• Poor transit - Buoy in line with end of land.
  This may be inaccurate due to land changing due
  to tidal height and the buoy being set by tidal
  stream or current.

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Transits
0945
A transit can give either a position line, or as
shown, a heading to steer on from the northwest,
before altering to about 045T into Fishermans
Cove
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Labeling Fixes
Symbol Type Meaning
Accurate Visual Fix
Fix Fix DR EP
Accurate Fix obtained by electronic means
Dead reckon position, advanced from previous fix.
Estimated position. Most probable position of
ship.
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Dead Reckoning
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Dead Reckoning

• Dead Reckoning is the process of determining a
  ships approximate position by applying, from its
  last known position, a vector or a series of
  consecutive vectors representing the true courses
  steered and the distances run as determined by
  the ships speed and time, without considering
  the effects of wind and current.
• From a known ships position, predicted future
  positions are plotted.

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Dead Reckoning
DR 1245
From ships known position at 1230, a future
position is plotted for 1245, knowing vessels
course and speed.
1230
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Dead Reckoning

• Dead Reckoning is derived from DEDUCED, or DED,
  reckoning which was the process by which a
  vessels position was computed trigonometrically
  in relation to a known point of departure.

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Estimated Position
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Estimated Position
EP 1245
From ships known position at 1230, a future
position is plotted for 1245, knowing vessels
course and speed, and allowing for set and drift
of tide.
1230
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Parallel Indexing
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Parallel Indexing

• Parallel indexing is using the radar to monitor
  the track of a vessel along a preplanned course,
  maintaining a distance off a known charted
  object.
• Where using a magnetic compass input to a radar,
  the true bearing will have to be corrected for
  variation and deviation before setting the
  Electronic Bearing Marker.

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Parallel Indexing
Find a radar conspicuous object on the chart.
Draw a line parallel to the required course
touching the object. Measure the distance between
the course line and the parallel index line.
That is the Cross Index range.
015ºT
CIR 0.32
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Parallel Indexing
Course 017C VRM 0.18nm EBL 017C
Offset and set up the Variable Range Marker to
the distance off a conspicuous point of land that
is required, and set the Electronic Bearing
Marker to the required compass course.
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Parallel Indexing
Course 017C VRM 0.18nm EBL 017C
The VRM should run up the EBL if the vessel is
staying on track.
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Time-Speed-Distance Calculations
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Time-Speed-Distance Calculations

• These calculations can be made using a
• nautical slide rule, electronic calculator,
  set of
• pre-computed tables, or the speed nomogram.
• D S x T
• where
• D distance traveled
• note ( 1 nm 2000 yds)
• S speed in knots(nautical miles per
  hour)
• T time in hours

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Simple Rules

• 3 Minute Rule
• Distance traveled in 3 minutes (yards)
• Ships speed (knots) X 100
• 6 Minute Rule
• Distance traveled in 6 minutes (nm)
• Ships Speed (knots) divided by 10.