Chart Symbol explanation

[Bleemus]

It is a sector light.

[Alan Mighty]

Originally Posted by Zven

Say, what's the meaning of the dotted line halfway between the island and the mainland above ...?

Do you mean the black dashed line that originates at the Archer Point light and runs 156 Magnetic (or runs to the Archer Point light at 336 Magnetic, should you prefer) and crosses Rocky Island?

That line is on paper charts and electronic charts. And probably on all of them (probably since the late 19th century).

That black dashed line is the centre line of a section of shipping channel, running between the coast to the W and coral reefs etc to the E, offshore from about Rattlesnake Point in the S to about Thomas Point in the N.

Zoom out the electronic chart to show that black dashed line (and the sector light) in context. One possible problem with electronic charts is that context can be missing or lost when zoomed in.

[masonc]

Originally Posted by knotstogo

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..

Here's the larger view showing the hazard.

[Kelkara]

Originally Posted by Alan Mighty

Do you mean the black dashed line that originates at the Archer Point light and runs 156 Magnetic (or runs to the Archer Point light at 336 Magnetic, should you prefer) and crosses Rocky Island?

I think he means the dotted line halfway between the island and the mainland, that separates two dark-blue shaded areas ... the linked Navionics web-app just labels it as "obstruction" which isn't very descriptive.

[Alan Mighty]

Originally Posted by Kelkara

I think he means the dotted line halfway between the island and the mainland, that separates two dark-blue shaded areas ... the linked Navionics web-app just labels it as "obstruction" which isn't very descriptive.

Mea culpa! I missed that one. Dotted lines surround an obstruction. SoThe chartlet StuM loaded used only dotted lines and did not use other line formats.

Here's a clip from my CM93v3 chart that should make the situation clearer.

[hellosailor]

I think it is priceless, that Amazon will sell you a $10 ebook which consists of....The same PDF file that the US government generously provides for free. Hell, they used to even give out the paper version of the booklet for free, might still do that too.

[JPA Cate]

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.

Just a comment here, really. Yes, most everyone uses GPS and some form of chart plotting. But, if you meant that you ignore shore based aids to navigation, you might want to reconsider that. If you were coming in from the sea towards that area, that white light, and following it would keep you safe, and the red, lead you into danger.

Just imagine a lightning strike taking out your electronics. Using Mark One Eyeball and basic piloting skills will save your bacon.

Ann

[knotstogo]

Thank you, that zoomed in chart makes it all really clear. I wouldn't want to run into any of those islands or shoals at night, or day for that matter! You are right to suppose that a light could be out of service. I am not familiar with the conditions of navigation aids in Anguilla (a place I dearly would love to see). I am also really not aware of how the authorities would alert mariners of equipment that is out of service. Your experience would provide more truth to the matter.

To change the subject, I am a pilot in the US and there is a protocol called NOTAM (notice to airmen) where local conditions can be relayed to aircrew. The governing body of aviation in the US, the FAA, also spends a lot of effort to verify the functionality of the air transportation system. However, there have been incidents of aircraft striking treetops with their landing gear because there was enough discrepancy in the reported minimums for an instrument approach.

The reason I bring that up is because you and I and a lot of others rely on technology to get us there safely. Even a cheap portable GPS can navigate us along a known course. Sure our navionics can fail but so can ground based systems. I'm curious about your light there in Anguilla and I hope you can investigate it.

Well, if it all goes pear shaped, that's a good place to get shipwrecked I'd say.

[knotstogo]

Now that is an awesome example!

[knotstogo]

Ouch...

[StuM]

Originally Posted by Adelie

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

Pedant

Seven light sectors

[StuM]

Originally Posted by Zven

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 ...?

According to the info I can tunnel down to when I hover over the line:
Great Barrier Reef - Nature Reserve - Restricted Area - Habitat Protection.

For more info, you need to look at the GBR MArine Park zoning maps.
Zoning maps - GBRMPA

[StuM]

Originally Posted by masonc

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.

Danger, Will Robinson!

Use all available aids including the mark one eyeball and lights/marks etc.
In the case of a constricted location like Gubbins Reef, the light sectors are a far better guide than GPS and chartplotter. At least you will be looking outside the boat and will see other vessels using the same route.

[masonc]

Originally Posted by JPA Cate

Using Mark One Eyeball and basic piloting skills will save your bacon.

Ann

Absolutely agree. I just meant that, as we are not in the US, I would be wary of expecting any equipment to be working. I don't trust Government moorings to be maintained, hazards to be marked correctly, or information to be accurate.
I asked the question because I am working hard to be better at navigation. When I can't find an answer I ask people who I know will have the experience.

[Adelie]

Originally Posted by StuM

Pedant

Seven light sectors

Yes, I am. I even do it professionally. ⚒🔨🛠⛏🔩