11 visiblity of lights
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Navigation
NAU 102
Lesson 11
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R anges
Two objects, when in line, indicate aspecific line of position.
E.g. Mark when in the center of achannel
Can be lighted or day beacons.
Lights can be red, green, white or
yellow.
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R anges
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R anges
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R anges
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Lights
Major Lights
Primary Seacoast ± major lights thatgive early indication of landfall
High intensity lights on a fixed structure.
Secondary Lights ± mark harborentrances
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Lights
Primary Seacoast Light
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Lights
Minor Lights
Smaller, low-intensity lights within aharbor, marking a channel, etc.
Includes lighted buoys, range lights, etc.
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R ange Lights
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Lights
R ed = move to stbd.
Directional lights ± use colored lenses toshow narrow beams of colored lights.
Green = move to port
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Lights
Usually mark hazards.
Sector lights ± use colored lenses to showdifferent color at various bearings.
Stay out of the red sector!
Bearings stated in Light List as seen fromvessel.
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S ector Lights
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Lights
Bridge Lights
R ed lights ± piers and closed drawbridge.
Green lights ± deep channels and open
drawbridges.
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Light Characteristics
Lights have color and phasecharacteristics that aid
identification.
See Bowditch
Ch. 5
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V isibility of Lights
When will I see the light?
If you don¶t see it when expected, youcould be in trouble!
Current range of visibility must becalculated.
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V isibility of Lights
R ange of sighting a light depends on:
Intensity of the light.
Atmospheric conditions.
Height of light.
Height of observer.
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V isibility of Lights
To determine the range at whichwe¶d see a light, we need to calculate:
Geographic R ange
Luminous R ange
The smaller of the two is the distancewe can expect to see the light.
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V isibility of Lights
Geographic R ange
Maximum distance an observer could seea light if limited only by curvature of the
earth.
= distance of observer to horizon +distance of light to horizon
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V isibility of Lights
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V isibility of Lights
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V isibility of Lights
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V isibility of Lights
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V isibility of Lights
Horizon Distance
Horizon Distance (nm) = 1.17 * ¥height (ft)
Horizon Distance (nm) = 2.12 * ¥height (m)
Or
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V isibility of Lights
Geographic R ange = Horizon Distance of theobserver + Horizon Distance of the light
GR = 1.17 * ¥height of eye + 1.17 ¥height of light
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V isibility of Lights
Example:
What is the geographic range of alight that is 70 ft tall for an observer30 ft above sea level?
GR = 1.17 * ¥30 ft + 1.17 ¥70 ft
GR = 6.4 nm + 9.8 nm = 16.2 nm
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V isibility of Lights
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V isibility of Lights
Example:
What is the geographic range of a
light that is 70 ft tall for an observer30 ft above sea level?
Geographic range = 6.4 + 9.8 = 16.2nm
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V isibility of Lights
Luminous R ange
Maximum distance light will travel in
current visibility conditions.
Depends on intensity of light (nominal
range) and clarity of atmosphere(visibility).
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V isibility of Lights
Nominal range
Maximum distance light will be seenif visibility is 10 nm.
Stated in Light List, List of Lights, onchart.
A measure of light intensity.
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V isibility of Lights
3
6
0
ChesapeakeLight
3654 17N
7542 46W
Fl (2)W 15s
0.1s fl 2.9 sec
0.1s fl 11.9 sec
1
1
7
1
9
Blue tower on white square
superstructure on four
black piles,
CHESAPEAKE on sides.
Emergency light of lower intensity will
be displayed when main light is
inoperative.
RACON: N (- ).HORN: 1 blast ev 30s (3s bl).
Operates continuously.
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V isibility of Lights
Visibility
Particles in the air (fog, haze, smog, etc.)scatter and absorb light.
An estimate of the clarity of the
atmosphere.
On any particular day, light from a beaconmay travel more or less than the nominal
range.
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V isibility of Lights
Visibility can
be estimatedusing theInternationalVisibility
Code.
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V isibility of Lights
Entering arguments:nominal range &
visibility.
Luminous R ange iscalculated using aluminous range
diagram in the LightList.
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V isibility of Lights
Example
What is the luminous range of a lightwhose nominal range is 19 nm when
visibility is 5 ½ nm?
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V isibility of Lights
ANS: LR = 13 nm
Nominal range = 19 nm
Visibility = 5 ½ nm?
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V isibility of Lights
R ange of visibility is the smaller of Geographic R ange and Luminous R ange.
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V isibility of Lights
Example
What will be the range of a light that is 70
ft tall with a nominal range of 19 nm foran observer whose height of eye is 30 ft
when the visibility is 5 ½ nm?
GR = 16.2 nmLR = 13 nm
R ange = 13 nm
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I ntroduction to Navigation
Questions?