Coloured circles on map by coast?

[grumpy_o_g]

There's two sources that tell you what all the (often totally obscure) symbols on a chart actually mean and how to interpret the numbers one is a book by Nigel Calder http://www.amazon.co.uk/Read-Nautical-Chart-Edition-Includes/dp/0071779825 and the other is technically a chart (Admiralty Chart 5011) but is actually a book. Of the two Nigel Calder's book is a probably better as it's a bit more than just a straight definition of each symbol but even that really needs a day skipper level book or CD to help you understand the full meaning.

I notice that the Singapore Chart 5011 is available to download as pdf here http://www.mpa.gov.sg/sites/pdf/chart1_jan13.pdf. It looks pretty similar to the UKHO version - anybody know if it is?

 

[andygc]

I've used Admiralty and Imray charts between 1980 and 2010 and have never seen light sectors on a chart, is it new or a different type of chart? What were on the charts were the lighthouse, it's range and and type of flash.

You perhaps need to look a little closer. Admiralty charts show the sectors as a black pecked line in an arc centred on the light with arrowheads at the endge of each sector and radial pecked lines showing the sector margins. Each arc is labelled "R", "W" or "G", sometimes more exotic - "QW", "QR", "QG" "Al.WG", "Al.RW" - Plymouth harbour's very pretty at night .

It shows the safe and dangerous zones from which you can approach the light / coast. The red light areas will have shoals or rocks in that segment. Yellow (white) and green light areas are safe.

Although it may be true that being in the green sector is often a safe place to be, the big disadvantage of being in that sector is you can't tell when you are about to leave it, and leaving it on the wrong side in Fowey will put you on Punch Cross Rocks or Lamp Rock, in Oban will put you ashore on Maiden Island, and in Dartmouth will have you going across the shallow bit of Castle Ledge - and even if you stay in the green you can still ram Kettle Point. The main purpose of the coloured sectors is to warn you when you are leaving the safe (white) sector - but that's only safe if you understand which safe area is being marked. Usually, when approaching the light, if it goes red you need to alter to starboard and if it goes green you need to alter to port - but not into Oban approaching from the north-west (because of the direction of buoyage up Kerrera Sound).

 

[KellysEye]

>I've used Admiralty and Imray charts between 1980 and 2010 and have never seen light sectors on a chart, is it new or a different type of chart? What were on the charts were the lighthouse, it's range and and type of flash.

>So how did such charts describe the sectors? The light characteristic will say something like RWR for a sector light, but no indication of which directions they cover.

I've just dug out an Admiralty chart for Mallorca and Corfu and they had no sectors just the range an type of flash, as I mentioned. The charts are very old so it's obviously changed.

 

[knuterikt]

There's two sources that tell you what all the (often totally obscure) symbols on a chart actually mean and how to interpret the numbers one is a book by Nigel Calder http://www.amazon.co.uk/Read-Nautical-Chart-Edition-Includes/dp/0071779825 and the other is technically a chart (Admiralty Chart 5011) but is actually a book. Of the two Nigel Calder's book is a probably better as it's a bit more than just a straight definition of each symbol but even that really needs a day skipper level book or CD to help you understand the full meaning.

I notice that the Singapore Chart 5011 is available to download as pdf here http://www.mpa.gov.sg/sites/pdf/chart1_jan13.pdf. It looks pretty similar to the UKHO version - anybody know if it is?

The different Hydrographic offices in the world do cooperate, after all they have an international audience, so for paper/raster charts the symbols are pretty much the same.
There might be some local variations so it's good practice to check.
The IALA system for is adopted by most countries (in to flavors A/B though) so the marking used is somewhat standardized at least.
http://en.wikipedia.org/wiki/International_Association_of_Lighthouse_Authorities.

For vector charts is't a little bit different because information is not stored graphically in the chart, so the display (MFD/plotter) maker can decide.
My MFD give me lots of options on displaying the data, the most important I think is the ability to use ECDIS symbols or the more "classic" looking symbols, I prefer to use the ECDIS symbols.
More on ECDIS or ENC symbols here https://www.ukho.gov.uk/Productsand...ents/Admiralty-Quick-Guide-to-ENC-Symbols.pdf

 

[prv]

I've just dug out an Admiralty chart for Mallorca and Corfu and they had no sectors just the range an type of flash, as I mentioned. The charts are very old so it's obviously changed.

The sector circles only appear on sectored lights. For Imray and Admiralty, anyway, I don't know what Navionics does.

Perhaps the lights on Mallorca and Corfu aren't (or weren't) sectored?

Pete

 

[scottie]

Having checked on various charts green is not safe but is a starboard indication when used with lights other than traffick lights

 

[macd]

The sector circles only appear on sectored lights. For Imray and Admiralty, anyway, I don't know what Navionics does.

Perhaps the lights on Mallorca and Corfu aren't (or weren't) sectored?

Navionics shows them in much the same way, with appropriately coloured sectors. I've just done a quick (but less than exhaustive) check and multi-sectored lights don't seem common in the Balearics, although they do exist, eg. Islota Botafoch, near Ibiza town harbour. Can't see any around Corfu.

 

[ghostlymoron]

ASFAIAA, the white sector is the safe place to be. Red means steer to starboard and green means steer to port.

Having checked on various charts green is not safe but is a starboard indication when used with lights other than traffick lights

 

[RichardS]

ASFAIAA, the white sector is the safe place to be. Red means steer to starboard and green means steer to port.

Yes, you and scottie are correct and I had mis-remembered.

I blame doing my Yachtmaster many years ago and then only ever sailing in a region where there are no sectored lights! :ambivalence:

Richard

 

[alant]

ASFAIAA, the white sector is the safe place to be. Red means steer to starboard and green means steer to port.

Correct, great tool for steering a safe course at night, without needing to rush below & check position.
When sailing up from Poole for example & hoping to use Needles Channel, its easy to stay in the white sector, until the white sector of Hurst Castle light is seen. Simply turn to port & in down into the Solent.

 

[knuterikt]

ASFAIAA, the white sector is the safe place to be. Red means steer to starboard and green means steer to port.

Can you explain using this chart?

 

[scottie]

Can you explain using this chart?

Not at this magnification you need to zoom out to se what corresponds with the sectors

 

[knuterikt]

Not at this magnification you need to zoom out to se what corresponds with the sectors

Assuming that white is safe sector the starboard/port rule in the OP don't make sense.

Is this better?

 

[andygc]

ASFAIAA, the white sector is the safe place to be. Red means steer to starboard and green means steer to port.

Like I said in post #22, that is not necessarily true. It depends on the direction of buoyage. I even provided an example - the northern approach into Oban. The direction of buoyage in Kerrera Sound is south to north, so the green sector is on the port hand when sailing into Oban from the north-west. If you steer to port in the green sector you stand a good chance of hitting Maiden Island. Likewise when leaving Loch Creran you could run up the shore on Eriska.

 

[scottie]

Assuming that white is safe sector the starboard/port rule in the OP don't make sense.

Is this better?

Out again please but yes you can see where the sectors relate to hazards

 

[Tryweryn]

Dafydd,

I guess from your previous postings you are an avid acquirer of sailing knowledge!

I need to learn as much as I can. The more I learn the better it gets so thanks everyone. I read loads but some times its better to get a simple answer from experienced ppl....big thanks.

 

[alan_d]

For the full directional light experience, try the approaches to Faslane on the Clyde. When going in the direction of buoyage you get a steady white if you are in the centre of the channel, alternating red and white if you stray a little to port, becoming steady red if you stray further. Similarly if you stray the other side you get alternating green and white and then steady green. Something to do with nuclear submarines, apparently.

 

[knuterikt]

Out again please but yes you can see where the sectors relate to hazards

I was't asking on help to do night navigation in my own backyard.
But here is a link to online map of the same are feel free to zoom as you like http://www.norgeskart.no/#13/252967/6642920/-land/+sjo

My post was aimed at this misleading statement

ASFAIAA, the white sector is the safe place to be. Red means steer to starboard and green means steer to port.

So assuming that the white sectors are indeed safe - the rule of thumb is dangerous

 

[ghostlymoron]

My statement is verified here http://en.m.wikipedia.org/wiki/Sector_light but perhaps I should have said "refer to sector info on chart and depends on direction of buoyage and only in uk system".

 

[knuterikt]

My statement is verified here http://en.m.wikipedia.org/wiki/Sector_light but perhaps I should have said "refer to sector info on chart and depends on direction of buoyage and only in uk system".

The page says

http://en.m.wikipedia.org/wiki/Sector_light#/issues

Using Wikipedia as an authoritative source can be a bit risky at times, the article you linked use a Finnish light as illustration so it's not about UK waters only.

So reading and using the information in the chart seems to be the best advice.

From the IALA AIDS TO NAVIGATION GUIDE (Navguide)

3.7.1.4 Technical Considerations for Sector LightsWhere a single sector light defines a navigable channel:
· There is no reference of the vessel’s lateral position within the channel
until a sector boundary is reached. This may cause a problem in
channels subject to a strong cross current. For vessels with local
knowledge, the zones defined by the angle of uncertainty can sometimes
provide a useful guide to the vessel’s proximity to a sector boundary;
· Where practicable, there should be a margin of safety between the sector
boundary and adjacent hazards. If an appropriate safety margin cannot
be achieved within the sector boundary, the hazards could be marked
separately.
· Zones defined by the angle of uncertainty should be considered an
additional margin of safety over the actual sector boundary;
· The design process for a sector light needs to consider the speed and
manoeuvrability of vessels likely to be negotiating the sector, how quickly
they can respond once they cross a sector boundary and the situations
that may develop when other vessels are in the vicinity;
· A sector design should take account of the spectral distribution of the light
source and the proportion of this light transmitted through the filter
material. The process should also check for potential for glare problems;
· The period of the light flash should be selected to provide ample time for
a mariner to recognise the transitional phases that occur at the sector
boundary47;
· A white light is normally the first preference for a lighthouse of beacon. If
a single coloured sector is added, the preferred colour for the sector is
red.
· If a white sector light is used to mark a navigation channel, coloured
sectors may be used either side of the white to indicate the lateral limits.
In such cases it is common practice to use red and green sectors that
follow the convention of the IALA Maritime Buoyage System;
· Multiple sectors can be used to provide a better indication of a vessel’s
lateral position within the channel but at the expense of complexity for
both the system designer and navigators.