Chart Symbol explanation

[masonc]

I don't understand the symbol shown on the screengrab below. I understand that it relates to lighthouses or bouys, guess that it has to do with approaches, but I can't find a definitive explanation of the symbol, colours, and meaning. I am reading Calder's book but still can't find it explained. Any help please?

[John_Trusty]

US Chart #1 - $15 from Amazon, works internationally as well ... https://www.amazon.com/U-S-Chart-No-...2462427&sr=8-1

Screen shot does not show for me. Can you edit?

[enrigenna]

https://www.nauticalcharts.noaa.gov/...1/ChartNo1.pdf

[masonc]

Originally Posted by John_Trusty

Screen shot does not show for me. Can you edit?

How about now?

[Shrew]

I believe it indicates it flashes either White or Red. The color will be dictated by the angle of approach. The radius shows which color is presented based on the bearing.

It looks like it will be flashing either white or red 2 times every 14 seconds.

[knotstogo]

It designates a light, flashing white or red depending on the specified arc. The interval of the flash is 14 seconds, the height of the light is 18 meters. The white color is visible for 10 miles and the red color is visible for 6 miles.

[masonc]

Originally Posted by knotstogo

It designates a light, flashing white or red depending on the specified arc. The interval of the flash is 14 seconds, the height of the light is 18 meters. The white color is visible for 10 miles and the red color is visible for 6 miles.

What is the significance of the red and yellow areas?

[knotstogo]

An observer within the red arc (labeled "R") will see a red flashing light. An observer within the yellow arc (labeled "W") will see a white flashing light. The white color of the deep water contours necessitates the use of a yellow rather than white arc, unfortunately.

[masonc]

Thank you for the help, now I understand. I knew it was something to do with angles of view, did not get the light colours. What's the chances that it actually works as shown?

[knotstogo]

The general concept is known as a sector light. Such lights are usually employed to make the mariner aware of a possible hazard when approaching from a certain angle, or as a means to marshal traffic into designated approaches.

I wasn't familiar with that chart so I Googled it and it is somewhere in Anguilla, I think. Looking at a larger map of the area it appears there is a small island named Sandy Cay within the red arc of the sector light. In this case it seems the light is warning mariners of the potential hazard of Sandy Cay when approaching the light.

Within the light's charted visible range of 6 to 10 miles I'd say it can be expected to work well assuming good weather conditions.

[StuM]

Originally Posted by masonc

Thank you for the help, now I understand. I knew it was something to do with angles of view, did not get the light colours. What's the chances that it actually works as shown?

Very likely. It's common where approaches at certain angles are safe, but there are rocks or other obstructions in the "red sector". If you see ared flashing light, don't steer towards it

[StuM]

Archer Point off Cooktown in FNQ is one of my favourites. Seven sectors

https://webapp.navionics.com/?lang=e...%60se~A%7BpavZ

When transiting Gubbins Reef South to North at night, you need to keep in the narrow southerly white sector. If it changes to red or green, it's a good idea to change your heading slightly until you see white again.

[Zven]

Originally Posted by StuM

Archer Point off Cooktown in FNQ is one of my favourites. Seven sectors

https://webapp.navionics.com/?lang=e...%60se~A%7BpavZ

On a related note ...
I see electronic maps (or possibly just Navionics) use a lot of dotted lines, and it can be tricky to make out their meaning. Say, what's the meaning of the dotted line halfway between the island and the mainland above ...?

[Adelie]

Originally Posted by StuM

Archer Point off Cooktown in FNQ is one of my favourites. Seven sectors

https://webapp.navionics.com/?lang=e...%60se~A%7BpavZ

When transiting Gubbins Reef South to North at night, you need to keep in the narrow southerly white sector. If it changes to red or green, it's a good idea to change your heading slightly until you see white again.

8 sectors. 8th sector is unlit. Mostly that in the land side but some is water area.

[masonc]

Originally Posted by knotstogo

I wasn't familiar with that chart so I Googled it and it is somewhere in Anguilla, I think.

Correct, I live in Anguilla. Your analysis is excellent, I was not aware of the reason for the red sector, Sandy Island is the reason. It would be a real hazard if you didn't know it was there.

Originally Posted by knotstogo

Looking at a larger map of the area it appears there is a small island named Sandy Cay within the red arc of the sector light. In this case it seems the light is warning mariners of the potential hazard of Sandy Cay when approaching the light.

Within the light's charted visible range of 6 to 10 miles I'd say it can be expected to work well assuming good weather conditions.

I was more questioning whether the light worked at all, as I have sailed in at night a few times and didn't see it. However, now I will be looking for it so I may find that it works as advertised. I use GPS and a chartplotter, as everyone does, so I don't rely on shore based guides, but it's good to know what they are for and how they work. Of course, if they are not maintained and don't work, they are worse than useless.