21 piloting

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Navigation

NAU 102

Lesson 21


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Piloting

Determining the position of the vessel by visual

reference to landmarks, by measurements of

depth or by radar. Duttons

Piloting involves navigating a vessel in

restricted waters and fixing its position asprecisely as possible at frequent intervals.

Bowditch


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Piloting

The task of piloting is to determine (fix) your

position at a certain time.

A Line of Position (LOP) is the building block

of a fix.

LOP a line along which you know you are

located.


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Piloting


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Piloting


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Piloting

LOPs can be obtained:

Visually

With Radar

By taking Soundings

Loran-C

Radio Direction Finders


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Visual LOP

Using a bearing or azimuth circle or a pelorus.

The bearing of a

charted object isobserved and the time

noted.

An LOP is drawn on

the chart to the

observed object.


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Visual LOP

Draw the line of the

correct bearing to the

object on the chart.

Label the LOP with

the time of the bearing.

No need to draw a

lengthy line


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Visual LOP

Visual Range Line

Two charted objects are

sighted in line.

Draw an LOP throughthe objects, extended

towards your probable

position.

No need to note bearing.


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Visual LOP


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RadarRange LOP

Distance to a charted

object is determined on

radar.

An arc of a circle

centered on the object

is drawn on the chart.

Radius = distance


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RadarRange LOP

Arc is labeled with

the time the rangewas determined.

No need to draw the

entire circle


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RadarRange LOP


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RadarRange LOP

Radar ranges are

more accurate thanradar bearings.

If possible, use visual

bearings vice radarbearings.


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Soundings

Compare charted depth (corrected for height of

tide) with echo sounder reading.

A depth contour can be used as an LOP.


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Soundings


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The Fix

A fix can be obtained where two or more LOPs,

taken at the same time, cross.

Your Fixed Position (Fix) is your known

location at a point on the earth at a specific time.

Sometimes referred to as a Simultaneous Fix.


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The Fix

1000


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The Fix


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The Fix

Minimize positional errors caused by a bad LOP

Three (or more) LOPs are better than two.


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The Fix

Where am I?


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The Fix

Option 1 In the center of the triangle.

.


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The Fix

Option 2 In the most dangerous position.


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The Fix

Ideally, well get a 3-point fix.


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Fix Geometry

If using 2 LOPs, navigation aids should be

approximately 90 apart.

To ensure accuracy and minimize errors, we must

choose our navigation aids carefully.

Ideally, 3 navaids would be separated by 120,

or 60 if all within 180.


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Poor Fix Geometry


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Good Fix Geometry


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Good Fix Geometry


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Good Fix Geometry


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The Fix

Unless you have several people on your

navigation team, this is impossible.

To be truly simultaneous all LOPs (bearings

and/or ranges) must be shot at exactly the same

time.

To minimize errors, first take the bearing or

range that is changing the quickest.


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The Fix

Ranges at fix time, mark the range of the

navaid ahead or astern.

Bearings at fix time, take the bearing of the

navaid closest to the beam.


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Introduction to Navigation

Questions?

21 piloting

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