20 Dead Reakoning

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Navigation

NAU 102

Lesson 20



Dead Reckoning

From Deduced (ded.) Reckoning

Abbreviated DR



Dead Reckoning

The process of determining present position by

projecting course and speed from a known

past position.

Definition

Or, the process of determining future position by

projecting course and speed from a known

present position.



Dead Reckoning

Doesn¶t take into account any other factor.

Considers only course and speed.

Leeway (movement downwind)

CurrentSteering errors

Compass error



Dead Reckoning

Determining course of advance

Speed of advance

EstimatedTime of Arrival

Uses

Voyage planning



Dead Reckoning

Uses

Keeping track of location in th

e absenceof other positional information.

Out of piloting range.

Overcast sky.

GPS acting up.

Approximate location between fixes.



Dead Reckoning

Determining outside forces.

Uses

If you know the forces, you can

compensate for them.

Wind

Current

Bad steering



Dead Reckoning

Plan future movements after a fix

Uses

DR to determine course and/or speed

necessary to regain track or avoid a hazard

Compare position to desired location



Dead Reckoning

DR Symbology

Use of standard symbols is important

Anyone else (Captain/Relief) caninstantly understand the situation.



Dead Reckoning

GPS fix ± diamond

R-fix

DR position ± h

alf circle

Estimated position ± square

Running fix ± circle labeled ³R-fix

Visual fix ± circle

Electronic fix ± triangle



Dead Reckoning

R-fix

TimesWritten horizontally for fixes and EP¶s

Written diagonally for DR¶s

1447

08121932

2000



Dead Reckoning

Courses

Labeled ³C´

3 digits

True degrees unless otherwise markedWritten above the track line

Speeds

Labeled ³S´

Written below the track line



Dead Reckoning



Dead Reckoning

Rules of DR

4. After plotting a single line of position (LOP)

3. After every course or speed change

2. After every fix or running fix

1. At least every hour on the hour

Plot a DR:



Dead Reckoning

Draw a line in the direction of the course

L

abel!

Using the mid-latitude, mark off the distance

Calculate the distance to next DR point

(using the Rules of DR)

(Use True directions only)

Constructing a DR

Start from a known position (a µfix¶)



Dead Reckoning



Dead Reckoning



Dead Reckoning

Departure from Plan

Between fixes, you may fall off your planned

track.

From your latest fix, DR to regain track and/or

avoid navigation hazards.

Wind

Current

Bad steering



Dead Reckoning



Dead Reckoning



Dead Reckoning

Fix Expansion

A DR is an approximation of position

based on very limited information.

There will always be inaccuracy and positional

error in every DR.

The longer the time since your last fix, the

greater the error.



Dead Reckoning

Be extra vigilant when a navigational hazard

falls within your error circle.



Dead Reckoning

Alternative format

for voyage planning.

Each turn point

(waypoint) is

labeled with ETA to

the point and

distance to

destination.



I ntroduction to Navigation

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20 Dead Reakoning