CCGA 08 Position Lines

8/13/2019 CCGA 08 Position Lines

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CANADIAN COAST GUARD AUXILIARY - PACIFIC

NAVIGATION TRAININGSection 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 LinesPosition 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, includingdeviation 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.


7/53CANADIAN COAST GUARD AUXILIARY - PACIFIC

Sources of Position Lines

A visual position line can be taken, using

charted fixed navigational aids such as tanks,

water towers, church steeples, spires, radioand 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.



Visual

PositionLine

1000



Radar

RangePosition

Line


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Position Line Measurement

Visual Bearings can be measured in:

1. Degrees Relative ( # # #0R )

2. Degrees per Gyro Compass ( # # # G )

3. Degrees Magnetic ( # # #0M )

The navigator must convert any of these

types of bearings to True before they can beplotted on the chart.

Degrees True ( # # #0T)


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Plotting and Labeling a Fix

Fix - The point where two or more positionlines, 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 notwritten.


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Visual Position Fix


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Visual

PositionFix 1

Compass bearing

of Abode Island

bearing

009Compass,deviation 1W,

variation 23E,

gives 030 True

Bearing


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Visual

PositionFix 3

Compass bearing

of Pt. Atkinson

Light bearing

098Compass,deviation 1W,

variation 23 E,

gives True

Bearing of 120 T


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Visual

PositionFix 4

1230

Insert fix circle

on intersection

of position

lines, and timeof fix


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Cocked Hats

In a perfect world, with due allowance made forcompass error, the three position lines will crossat one point.

However depending on the speed of the vessel,the proximity of the object from which a vessel isbeing fixed, and the accuracy of the bearingwhen taken, and other factors, it is far more

likely that a cocked hat will be obtained.The larger the cocked hat, the larger an erroron one, two or all of the position lines is likely tobe.


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CockedHat

1230

In this example

there is an errorof 3E on the

compass

bearing of Point

Atkinson Lightand a cocked

hat is formed.


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Cocked Hats

Where a plotted position is a cocked hat, andthere 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 closestto 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 takethe ranges ahead or astern first, to minimise

errors (as these ranges will change quickestwith the speed of the vessel) before takingranges on the beam.When taking compass bearings, always take

the bearings on the beam first, to minimiseerrors (as these bearings will change quickestwith the speed of the vessel) before takingbearings 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 andidentified objects.


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RadarPosition 1

Using radar:

Grebe Is

Electronic

Bearing Marker

showing 058 M

Variable Range

Marker showing

0.82


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RadarPosition 2

From radar, plot

position circle:

Grebe Is

Distance 0.49 nm


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RadarPosition 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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RadarPosition 4

Radar bearing of

Grebe Is. is 058 compass

Deviation 1W

Variation 23E

True Bearing 080 T

which confirms

ranges

1000


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Electronic Position


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Electronic Position

The GPS can give an accurate electronicposition.

First check that the GPS information is live, andnot on Dead Reckoning (which GPS reverts towith certain faults).

Also check that the HDOP figure is low - 1 isbest.


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Electronic

Position 1

Note down

Latitude and

Longitude

49 20.38N123 17.23W


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Electronic

Position 2

Plot Latitude

and Longitude

49 20.38N

123 17.23W


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Electronic

Position 3

1000

Insert fix

symbol, and

time


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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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Transits0945A 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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Symbol Type Meaning

Labeling Fixes

Fix

Fix

DR

EP

Accurate Visual Fix

Accurate Fix obtained byelectronic means

Dead reckon position, advancedfrom previous fix.

Estimated position. Mostprobable positionof 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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DeadReckoning

1230

DR 1245

From ships

known position at

1230, a future

position is

plotted for 1245,knowing vessels

course and

speed.


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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 trigonometricallyin relation to a known point of departure.


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Estimated Position


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EstimatedPosition

1230

EP 1245

From ships

known position at1230, a future

position is plotted

for 1245, knowing

vessels courseand speed, and

allowing for set

and drift of tide.


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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 chartedobject.

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

CIR

0.32

015T

Find a radar

conspicuous object on

the chart. Draw a lineparallel 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.


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Parallel

IndexingThe VRM should run

up the EBL if the

vessel is staying on

track.

Course 017C

VRM 0.18nm

EBL 017C


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Time-Speed-Distance

Calculations


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Time-Speed-Distance

CalculationsThese 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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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.

Simple Rules

Date post:	04-Jun-2018
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CCGA 08 Position Lines

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