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-   -   Navigation Aids question (http://www.rib.net/forum/f8/navigation-aids-question-22353.html)

Chris 27 November 2007 16:01

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

whiteminiman 27 November 2007 16:08

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

Poly 27 November 2007 16:29

Quote:

Originally Posted by whiteminiman (Post 228651)
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]

Chris 27 November 2007 16:45

Quote:

Originally Posted by Polwart (Post 228653)
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

Andy Moore 27 November 2007 16:52

This is quite useful:

http://en.wikipedia.org/wiki/Characteristic_light

jwalker 27 November 2007 17:01

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.

Poly 27 November 2007 17:04

Quote:

Originally Posted by Chris (Post 228659)
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.

v666 27 November 2007 17:06

The 's' is for period

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

Hope that helps

Tim

PS.
PM sent

Biggles 27 November 2007 17:34

This publication has it all.

http://www.admiraltyleisure.co.uk/chart5011.asp

TonyC 27 November 2007 19:37

:/


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