Lights
 

1 pt each

What is a range, and how are two lights used to establish a range?

Why would three lights be used?

What are the factors that determine a single light's visible range?

How are red sector in lights used?

Why are lighthouses all designed differently?

At night, what danger should a helmsman be aware of when
steering for a lighted bouy that is being used as a way point?

What is a Morse Code "A" light mean?

Lights
 

1 pt each

What is a range, and how are two lights used to establish a range?

To mark a direction, usually a channel, at night. One higher than the other,
then line 'em up.


Why would three lights be used?

Don' t know.

What are the factors that determine a single light's visible range?



How are red sector in lights used?

Keep clear.

Why are lighthouses all designed differently?

Identify location by color scheme or other attributes.

At night, what danger should a helmsman be aware of when
steering for a lighted bouy that is being used as a way point?

don't hit it or the jackass tied to it using his BBQ; keep to the appropriate
side.


What is a Morse Code "A" light mean?

safe water at center of a channel

Lights
 

Subject: Lights
From: (Bobspirt)
Date: 06/30/2004 07:35 Pacific Standard Time
Message-id:

1 pt each

What is a range, and how are two lights used to establish a range?

To mark a direction, usually a channel, at night. One higher than the other,
then line 'em up.

Day or night markers, used to mark the preferred line for a marked channel (may
or may not be centerline).


Why would three lights be used?

Don' t know.

Never seen this, but would guess it might used to show the edges of a narrowing
channel, to a certain point.


What are the factors that determine a single light's visible range?

G will leave this for someone else.



How are red sector in lights used?

Keep clear.

Why are lighthouses all designed differently?

Identify location by color scheme or other attributes.

At night, what danger should a helmsman be aware of when
steering for a lighted bouy that is being used as a way point?

don't hit it or the jackass tied to it using his BBQ; keep to the appropriate
side.


What is a Morse Code "A" light mean?

safe water at center of a channel

This is on the first buoy (or last, depending on your direction) you will
encounter at major ports. Can NORMALLY be passed on either side, but this is
not always true .... check your chart and local regs....called the "Sea Buoy"

Shen

Lights
 

Shen44 wrote:


Why would three lights be used?

Don' t know.


Never seen this, but would guess it might used to show the edges of a narrowing
channel, to a certain point.

Don't think that's what he's looking for....

What is a Morse Code "A" light mean?

safe water at center of a channel


This is on the first buoy (or last, depending on your direction) you will
encounter at major ports. Can NORMALLY be passed on either side, but this is
not always true .... check your chart and local regs....called the "Sea Buoy"

Shen

Not the only placed you could see this buoy, but the place most will
encounter it.

otn

Lights
 

Bart Senior wrote:

1 pt each

C'mon, I want more than one measly point!



What is a range, and how are two lights used to establish a range?

A range is two markers that should be kept in line with each other to
follow a channel, like looking down a gun sight. The upper light is the
further marker.

Care should be taken when following a range to know the marks for
*leaving* the range, I have seen plenty of range markers on dry land.




Why would three lights be used?

?? Dunno, maybe to mark a danger bearing?


What are the factors that determine a single light's visible range?

The height and the brightness




How are red sector in lights used?

To mark a danger zone or a "no-approach" zone.


Why are lighthouses all designed differently?

You mean why do they have different colored & patterned stripes etc on
them? So you can tell which is which, and thus where you are, if your
GPS is broken! However many lighthouses do have the same colors or
pattern.


At night, what danger should a helmsman be aware of when
steering for a lighted bouy that is being used as a way point?

Be wary of hitting the darn thing. Also, in some places, be wary of
hitting unlit markers along the same channel, or old out-of-service
marks. It can be a real PITA.


What is a Morse Code "A" light mean?

Sea buoy, the outermost channel marker entering a larger port. Small
sea channels won't have this.

Good questions Bart. Thanks

Fresh Breezes- Doug King

Lights
 

DSK wrote:

Bart Senior wrote:


1 pt each


C'mon, I want more than one measly point!



What is a range, and how are two lights used to establish a range?


A range is two markers that should be kept in line with each other to
follow a channel, like looking down a gun sight. The upper light is the
further marker.

Care should be taken when following a range to know the marks for
*leaving* the range, I have seen plenty of range markers on dry land.




Why would three lights be used?


?? Dunno, maybe to mark a danger bearing?


What are the factors that determine a single light's visible range?


The height and the brightness


To be more precise, the height determines the geographic range while
visible range is limited by conditions as well as luminosity and colour.


Cheers (call me Nav)

Lights
 

Nav wrote:

(call me Nav)

There are those on this ng who would call your Nav but you didn't
give his/her phone number.

--
Flying Tadpole

-------------------------
Break Away, Sail Away and putz away
now at http://music.download.com/internetopera

Lights
 

Nav wrote:

To be more precise, the height determines the geographic range while
visible range is limited by conditions as well as luminosity and colour.

Very good. But you jumped ahead, when you mention geo range you should tell
about luminous range.


Cheers (call me Nav)

OK, Navvie

Fresh Breezes- Doug King

Lights
 

5 points to you Bob.

Bobspirt wrote in message
...
1 pt each

What is a range, and how are two lights used to establish a range?

To mark a direction, usually a channel, at night. One higher than the
other,
then line 'em up.

How are red sector in lights used?

Keep clear.

Why are lighthouses all designed differently?

Identify location by color scheme or other attributes.

At night, what danger should a helmsman be aware of when
steering for a lighted bouy that is being used as a way point?

don't hit it or the jackass tied to it using his BBQ; keep to the
appropriate
side.


What is a Morse Code "A" light mean?

safe water at center of a channel

Lights
 

Good descriptive answers Doug, but not quick enough for points.

Not enough information for the one below. No points awarded for it yet.
Care to expand on it?

DSK wrote in message
...
Bart Senior wrote:

1 pt each
What are the factors that determine a single light's visible range?

The height and the brightness

Lights
 

Same for you. Need a little more detail to get a point for the one
question listed below.

Nav wrote

DSK wrote:

Bart Senior wrote:


1 pt each
What are the factors that determine a single light's visible range?

The height and the brightness


To be more precise, the height determines the geographic range while
visible range is limited by conditions as well as luminosity and colour.


Cheers (call me Nav)

Lights
 

1 pt each

Why would three lights be used?

Don' t know.

This is a tough one. I'll reveal the answer.

It it fairly common to find three lights constituting
two ranges, at the bend of a channel. The first
range is the normal type.

The second range uses one of the first lights and
is a "look behind you" range. After the bend in the
channel.

Does that make sense?

I mentioned it because it is something some of my
student have had trouble with in chart work

However, my question was, perhaps, confusing.

Perhaps I should phrased the question.

How can three lights be used to establish two ranges?

Bart

Lights
 

Bart Senior wrote:

Good descriptive answers Doug, but not quick enough for points.

Not enough information for the one below. No points awarded for it yet.
Care to expand on it?

Well, you can get quite dogmatic about determining a light's visible range.
The two keys are height & brightness.

Because the earth (and thus the surface of the sea) is spherical, the
higher the light is, and the higher the observer's eye, the further away it
will come over the horizon. There is a formula for determining this, adding
the two heights and multplying by a factor to get whatever distance units
you like. This is called the geographic range.

Brightness is also specified for major & minor lights, this is the reason
for the elaborate Fresnel lenses on lighthouses... to increase the
effective brightness. Obviously a tiny bulb connected to a AAA battery is
not going to be seen as far away as large halon floodlight connected to
high amp 120VAC. This is termed luminous range, and is usually the limiting
factor. It is affected very much by atmospheric conditions. In most nav
references there are tables for determining the luminous range of a given
light in given conditions.

The visible range of a light is the lesser of the geographic range and the
luminous range under prevailing atmospheric conditions.

If one is navigating towards a landfall, and expecting to see a light
during the approach, it is good practice to work out the visible range of
the light under current conditions, plot it against one's future DR, and
tell the watch on deck when to expect to see it. If a long time goes by and
no light, then it's time to work on an alternate approach... and a good
excuse...

Fresh Breezes- Doug King

Lights
 

2 points to you Doug--an extra point for the lengthy detailed
description.


DSK wrote
Bart Senior wrote:

Good descriptive answers Doug, but not quick enough for points.

Not enough information for the one below. No points awarded for it yet.
Care to expand on it?

Well, you can get quite dogmatic about determining a light's visible
range.
The two keys are height & brightness.

Because the earth (and thus the surface of the sea) is spherical, the
higher the light is, and the higher the observer's eye, the further away
it
will come over the horizon. There is a formula for determining this,
adding
the two heights and multplying by a factor to get whatever distance units
you like. This is called the geographic range.

I'm not entirely sure I understand your method. But you hit thed key
points,
height of eye for the observer, and height of the light are both limited by
the curvature of the earth and the horizon--even if the light is luminous
enough to be seen at greater distances.

I typically calculate the horizon for my height of eye, and also for the
light
based on it's height and add the two together, and check this against the
specs on the light, which is usually greater. The horizon is usually the
limiting
factor for major lights that are visible at greater ranges.

Brightness is also specified for major & minor lights, this is the reason
for the elaborate Fresnel lenses on lighthouses... to increase the
effective brightness. Obviously a tiny bulb connected to a AAA battery is
not going to be seen as far away as large halon floodlight connected to
high amp 120VAC. This is termed luminous range, and is usually the
limiting
factor. It is affected very much by atmospheric conditions. In most nav
references there are tables for determining the luminous range of a given
light in given conditions.


Fresnel lenses are amazing techonology. Have you seen one up close?

The visible range of a light is the lesser of the geographic range and the
luminous range under prevailing atmospheric conditions.

If one is navigating towards a landfall, and expecting to see a light
during the approach, it is good practice to work out the visible range of
the light under current conditions, plot it against one's future DR, and
tell the watch on deck when to expect to see it. If a long time goes by
and
no light, then it's time to work on an alternate approach... and a good
excuse...

Fresh Breezes- Doug King

Lights
 

Bart Senior wrote:

2 points to you Doug

Yeehaw, does this mean I'm winning?!?



I'm not entirely sure I understand your method. But you hit thed key
points,
height of eye for the observer, and height of the light are both limited by
the curvature of the earth and the horizon--even if the light is luminous
enough to be seen at greater distances.

Right... in which case, you might see the "loom" of the light's glow over the
horizon. Very reassuring to see this!



I typically calculate the horizon for my height of eye, and also for the
light
based on it's height and add the two together, and check this against the
specs on the light, which is usually greater.

IIRC you should add the heights first, then calculate the horizon. There is an
exponent in the formula which will throw you off. I'm usually in a hurry and
just interpolate from the tables in the appendix....


Fresnel lenses are amazing techonology. Have you seen one up close?

Yes, been inside one of the big ones. They are amazing.

One of the mysteries of history is what happened to the Cape Hattaras lighthouse
Fresnel lens at the outset of the War of Northern Aggression... some
Confederates thought it would be a good idea to swipe it, since it was very
expensive and, in place, could only benefit the Union Navy. Sketchy research
indicates that they hid it somewhere far inland, possibly on a farm in Vance
County (which means it's most likely under Kerr Lake now). There are still only
a few 1st-order Fresnel lenses on US lighthouses, IIRC the Cape Hatteras light
was only given a 2nd-order after the war.

Fresh Breezes- Doug King

Lights
 

No, of course not!

You're Winnie!

DSK wrote

Bart Senior wrote:

2 points to you Doug

Yeehaw, does this mean I'm winning?!?

Lights
 

For additional information. The first thing you see on a very clear night,
when the clouds are reflective overhead of the light source, and/or when the
distant light is very strong, is 'light loom.' That's the reflection of the
light up into the sky and what you are seeing is not in direct line of
sight. Altitude off the surface of the water still counts though so the
higher you are the better off you are. The reflection can be of lights 30
to 50 miles off depending on the source. For example the lights of Miami,
NewYork, Los Angeles or any other big city. On a good viewing night loom
from Miami area can be seen out as far as the Bahamas. Normally though you
are seeing light loom from a ship and the brightest lights are, invariably,
fishing vessels. They use strong deck lights when night fishing for these
reasons. Illuminate the deck working area, show they are 'shooting nets'
and sometimes to attract the fish. As the light source draws near we see
the source directly from our 120' vantage point out a bit further than 24
miles due to the combined heights. The higher the light source the farther
we see it. One light, on the top of a mountain in the Canary Islands can be
easily seen from our bridge wings at 40 miles and that's further than our
radars will operate. Of course the light is many hundreds of feet above us.
Light loom, under good viewing conditions, is a good advance indicator of
things to come. Early warning device as it were. Multiple light looms
often help us navigate between those rock filled waves (straits for
example) or give warning of increased surface activity ahead (such as the
fishing fleets around the entrance to the Med, both ends of Suez, the Red
Sea etc. On a lower to the surface sailboat I couldn't hope to see at those
distances BUT by using light loom reflections I can increase my range of
visibility in many situations beyond simple direct vision. A useful tool at
the very least.

M.


"Bart Senior" wrote in message news:EW%Fc.13086$kz.3
...
You didn't account at all for the curvature of the earth.

Yes, I do prefer more complete answers. The idea here
is to pass on information to other readers. Details count.

Nav wrote
It is remarkable that you prefer a long winded yet incomplete answer to
that which gives _all_ the factors without being longwinded. Was may
answer not precise enough?

Bart Senior wrote:
Same for you. Need a little more detail to get a point for the one
question listed below.

DSK wrote:
Bart Senior wrote:

1 pt each
What are the factors that determine a single light's visible range?

The height and the brightness

To be more precise, the height determines the geographic range while
visible range is limited by conditions as well as luminosity and
colour.

Cheers (call me Nav)

Lights
 

You forgot COLOR!!!!

Cheers

Bart Senior wrote:
2 points to you Doug--an extra point for the lengthy detailed
description.


DSK wrote

Bart Senior wrote:


Good descriptive answers Doug, but not quick enough for points.

Not enough information for the one below. No points awarded for it yet.
Care to expand on it?

Well, you can get quite dogmatic about determining a light's visible

range.

The two keys are height & brightness.

Because the earth (and thus the surface of the sea) is spherical, the
higher the light is, and the higher the observer's eye, the further away

it

will come over the horizon. There is a formula for determining this,

adding

the two heights and multplying by a factor to get whatever distance units
you like. This is called the geographic range.


I'm not entirely sure I understand your method. But you hit thed key
points,
height of eye for the observer, and height of the light are both limited by
the curvature of the earth and the horizon--even if the light is luminous
enough to be seen at greater distances.

I typically calculate the horizon for my height of eye, and also for the
light
based on it's height and add the two together, and check this against the
specs on the light, which is usually greater. The horizon is usually the
limiting
factor for major lights that are visible at greater ranges.


Brightness is also specified for major & minor lights, this is the reason
for the elaborate Fresnel lenses on lighthouses... to increase the
effective brightness. Obviously a tiny bulb connected to a AAA battery is
not going to be seen as far away as large halon floodlight connected to
high amp 120VAC. This is termed luminous range, and is usually the

limiting

factor. It is affected very much by atmospheric conditions. In most nav
references there are tables for determining the luminous range of a given
light in given conditions.



Fresnel lenses are amazing techonology. Have you seen one up close?


The visible range of a light is the lesser of the geographic range and the
luminous range under prevailing atmospheric conditions.

If one is navigating towards a landfall, and expecting to see a light
during the approach, it is good practice to work out the visible range of
the light under current conditions, plot it against one's future DR, and
tell the watch on deck when to expect to see it. If a long time goes by

and

no light, then it's time to work on an alternate approach... and a good
excuse...

Fresh Breezes- Doug King

Lights
 

It is remarkable that you prefer a long winded yet incomplete answer to
that which gives _all_ the factors without being longwinded. Was may
answer not precise enough?

:P

Cheers


Bart Senior wrote:

Same for you. Need a little more detail to get a point for the one
question listed below.

Nav wrote

DSK wrote:


Bart Senior wrote:



1 pt each
What are the factors that determine a single light's visible range?

The height and the brightness


To be more precise, the height determines the geographic range while
visible range is limited by conditions as well as luminosity and colour.


Cheers (call me Nav)

Lights
 

You didn't account at all for the curvature of the earth.

Yes, I do prefer more complete answers. The idea here
is to pass on information to other readers. Details count.

Nav wrote
It is remarkable that you prefer a long winded yet incomplete answer to
that which gives _all_ the factors without being longwinded. Was may
answer not precise enough?

Bart Senior wrote:
Same for you. Need a little more detail to get a point for the one
question listed below.

DSK wrote:
Bart Senior wrote:

1 pt each
What are the factors that determine a single light's visible range?

The height and the brightness

To be more precise, the height determines the geographic range while
visible range is limited by conditions as well as luminosity and colour.

Cheers (call me Nav)

Lights
 

Hah! If the earth was not curved height would not be the primary
determinant of geographic range. You've still ignored the question of
color which has a very large effect.

Cheers

Bart Senior wrote:
You didn't account at all for the curvature of the earth.

Yes, I do prefer more complete answers. The idea here
is to pass on information to other readers. Details count.

Nav wrote

It is remarkable that you prefer a long winded yet incomplete answer to
that which gives _all_ the factors without being longwinded. Was may
answer not precise enough?

Bart Senior wrote:

Same for you. Need a little more detail to get a point for the one
question listed below.


DSK wrote:

Bart Senior wrote:


1 pt each
What are the factors that determine a single light's visible range?

The height and the brightness


To be more precise, the height determines the geographic range while
visible range is limited by conditions as well as luminosity and colour.

Cheers (call me Nav)

Lights
 

Nav wrote:

Hah! If the earth was not curved height would not be the primary
determinant of geographic range. You've still ignored the question of
color which has a very large effect.

You are free to explain at length, if you wish. Or, if you don't like it
here, you're free to go away. Your call.

DSK

Lights
 

Michael wrote:
For additional information. The first thing you see on a very clear night,
when the clouds are reflective overhead of the light source, and/or when the
distant light is very strong, is 'light loom.'

I mentioned that. Good post though. I wonder why Navvie hasn't
complained that you also failed to explain how color affects visible
range? He must like you more!

DSK

Lights
 

On Tue, 06 Jul 2004 12:56:04 -0400, DSK wrote:

Nav wrote:

Hah! If the earth was not curved height would not be the primary
determinant of geographic range. You've still ignored the question of
color which has a very large effect.

You are free to explain at length, if you wish. Or, if you don't like it
here, you're free to go away. Your call.

You are all failing to take into account the effect of doppler shift
and how it affects color. As you sail towards a light source, the
wavelength will be shorter, and as you sail away, longer.

I'm sure this is a serious problem, worthy of an extended thread all
its own.

Lights
 

That is a fast boat you have. Must be a Catamarran.

A. Diesel Vents wrote

On Tue, 06 Jul 2004 12:56:04 -0400, DSK wrote:

You are all failing to take into account the effect of doppler shift
and how it affects color. As you sail towards a light source, the
wavelength will be shorter, and as you sail away, longer.

Lights
 

DSK wrote:

Nav wrote:

Hah! If the earth was not curved height would not be the primary
determinant of geographic range. You've still ignored the question of
color which has a very large effect.


You are free to explain at length, if you wish. Or, if you don't like it
here, you're free to go away. Your call.


You didn't know that for equal luminosity that red lights are less
visible than green?

Chees

Lights
 

DSK wrote:

Michael wrote:

For additional information. The first thing you see on a very clear
night,
when the clouds are reflective overhead of the light source, and/or
when the
distant light is very strong, is 'light loom.'


I mentioned that. Good post though. I wonder why Navvie hasn't
complained that you also failed to explain how color affects visible
range? He must like you more!



Color also affects loom strongly but few pople know that -even ocean
yachtmaster instructors!

Cheers

Lights
 

A. Diesel Vents wrote:

On Tue, 06 Jul 2004 12:56:04 -0400, DSK wrote:


Nav wrote:


Hah! If the earth was not curved height would not be the primary
determinant of geographic range. You've still ignored the question of
color which has a very large effect.

You are free to explain at length, if you wish. Or, if you don't like it
here, you're free to go away. Your call.


You are all failing to take into account the effect of doppler shift
and how it affects color. As you sail towards a light source, the
wavelength will be shorter, and as you sail away, longer.

I'm sure this is a serious problem, worthy of an extended thread all
its own.

Especially as you tack out of the solar system with your light sail!

Cheers

Lights
 

Well, it's all relative.

--
"j" ganz @@
www.sailnow.com

"Bart Senior" wrote in message
et...
That is a fast boat you have. Must be a Catamarran.

A. Diesel Vents wrote

On Tue, 06 Jul 2004 12:56:04 -0400, DSK wrote:

You are all failing to take into account the effect of doppler shift
and how it affects color. As you sail towards a light source, the
wavelength will be shorter, and as you sail away, longer.