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Old 27 November 2007, 17:01   #1
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Navigation Aids question

Just looking at some of my charts and trying to brush up on my symbols and lights.

What does it mean when you look at a shore light for example:

Oc.G.5s7m10M

I understand the Occulting Green bit (more on the off) however...

with a normal buoy the 5s bit would mean a flash every 5 seconds however in this case what does 5s mean is it the length of time the light is on?

What does the 7m10M bit mean?

Chris
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Old 27 November 2007, 17:08   #2
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Off the top of my head.... and I am a bit rusty on coastal navigation.

7m = 7 metres above sea level

10M = visible from 10 Nautical Miles away in good visibility.

I'm not at all sure that is correct.

Cheers,
WMM
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Old 27 November 2007, 17:29   #3
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Originally Posted by whiteminiman View Post
Off the top of my head.... and I am a bit rusty on coastal navigation.

7m = 7 metres above sea level

10M = visible from 10 Nautical Miles away in good visibility.

I'm not at all sure that is correct.

Cheers,
WMM
Sounds right to me.

Quote:
with a normal buoy the 5s bit would mean a flash every 5 seconds however in this case what does 5s mean is it the length of time the light is on?
It is the time from when the light goes on until it comes on again.

SO

####-####-####-####-####-####-
<-5s->

[Edit - the time is always the time of each 'cycle' of lights]
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Old 27 November 2007, 17:45   #4
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Quote:
Originally Posted by Polwart View Post
Sounds right to me.



It is the time from when the light goes on until it comes on again.

SO

####-####-####-####-####-####-
<-5s->

[Edit - the time is always the time of each 'cycle' of lights]
OK I think I understand so in this case the light would shine continuously for 4 seconds then would be off for a second then on for another 4?

Chris
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Old 27 November 2007, 17:52   #5
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This is quite useful:

http://en.wikipedia.org/wiki/Characteristic_light
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Old 27 November 2007, 18:01   #6
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I feel it helps to think of it as a continuous light which flashes off. A bit like a light which blinks. Not to be confused with an isophase light which has the same time on and off.

The 7m is 7metres above MHWS.
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Old 27 November 2007, 18:04   #7
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OK I think I understand so in this case the light would shine continuously for 4 seconds then would be off for a second then on for another 4?

Chris
Possibly - but it doesn't need to be 4+1: it will be a total of 5, with the ON much longer than the off; but 3.5 ON + 1.5 OFF or 4.5 ON + 0.5 OFF or any other combination would also have a period of 5 secs.
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Old 27 November 2007, 18:06   #8
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The 's' is for period

Period - The time in seconds needed for one complete cycle of changes.

Hope that helps

Tim

PS.
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Old 27 November 2007, 18:34   #9
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This publication has it all.

http://www.admiraltyleisure.co.uk/chart5011.asp
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Old 27 November 2007, 20:37   #10
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