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Sailing down the east coast we often came across Cardinal Markers that just 'didn't seem to be' of value without a chart. They make sense when approaching from the 'ideal' direction but sometimes had we not been using a chart showing the obvious obstruction I feel we could have made a mistake. I have attached an example. If we approach the East Cardinal marker from the east (Position 'A') then we are safe to pass on the east side... we cannot pass to the north or the south because we would end up on the west side (in the example shown the actual obstruction was actually on the south side of an east cardinal marker which doesn't make sense to me!). If I am not using a chart, how wide a berth or how big should the radius be if in the example my intention was to arrive at point 'X' ? (See greyed arc which I would gather would be the no go zone) Is there a standard that is used to place them a certain distance from a known obstruction or are they just not something you can navigate by without a chart? (or perhaps I am not reading them correctly?) Like I said with the luxury of a chart it is blindingly obvious but if you can imagine not having a chart I feel it could be quite confusing.
Two things come immediately to my mind.
1. You are using Navionics. If you zoom in, does another danger appear to the west of the cardinal?
2. What is the direction of bouyage (not shown on your screen shot)?
Ok. I did wonder about the ark as I hadn't seen it before.
When I asked direction of bouyage, I wasn't referring to your track. You will find on your Navionics map (but in my opinion more easily found on the paper chart) a magenta coloured arrow (possibly with two circles either side). This indicates the direction of bouyage (not your track) that the cardinals and channel markers are based on.
That is is to say... 'IF' you are travelling in this direction you will want to pass to the east (in your example) of this mark. If you are well north of that mark and you are sailing east to west than you should be fine, especially once you've identified the danger. I hope that makes sense.
The other day, I was looking at a chart for an area I am totally unfamiliar with. The port and starboard markers didn't make sense to what I was expecting. Once I identified the direction of bouyage as depicted on the chart it all fell into place (it didn't help that it reversed mid passage 
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You are right in that it is a compass quadrant. It made more sense in my mind 
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Your question I think was more "how much margin do you give the cardinal?".. that I don't know 
I will have a look at the chart in the morning 
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Seems to me that the chartmaker has cleverly put the Cardinal marker to the North East so when
approaching from Honeysuckle Point you don't just nick around the Cardinal and run into the hazard.
I think in this case the east cardinal mark is noting the danger of the marine farm directly to the west of it.
I think I understand the context of the cardinal mark - if you approach or from the east you are in safe water. If you want to go any further you need to identify the hazzard on a chart! The context also makes more sense with the zoomed out chart, as most people will be making for the marina rather than into the second fold of the bay. The east cardinal then identifys that they are in safe water on approach from the east.
Thanks for all your replies. I think as a few have said it makes more sense if you are travelling the most likely route to the most likely destination. I guess it would be wise to put all cardinal marks in this context when approaching. ie If I am travelling on a less taken route to a less popular destination this cardinal may not be placed ideally from my perspective. Lazzz, thanks for posting those three chart examples. May I ask if these are online charts? I would really appreciate the links if they are as I have only been using Navionics on the PC and would really benefit from a variety of charts to compare, etc. Thanks again.
I think you really do need situational awareness by charts or some other landmarks. Example: The middle of the channel to Brisbane Water near Hardies Bay has multiple sand bars and three channels and dozens of blinking navigation lights. If you dont know where you are they can easily make no sense at all.
At any given time you can see multiple greens reds and whites. I ran aground there on my first night trying to go up that channel because we couldn't tell which lights belonged to which channel. Fortunately it was a weekend so the Coast Patrol at the time was on duty and we called them.
They also ran aground on their way down the channel to pull us off also because of misreading the channel markers! We spent 3 hours waiting for the tide to rise to get their boat and my boat unstuck.
It is a good question.
There is a north cardinal mark off Drummoyne near Snapper Island. I often go for a motor near there and keep well clear to the east and west as well as south because I am unclear the size of the obstruction.
DS and others, just a short aside, that area of Twofold Bay (Eden) is a terrific stopover, whether from the land or the sea. I first went there in the early 80's on a Uni field trip to Edrom Lodge which is in the area just inside the southern headland of the bay. This lodge is an old and rambling 30's era californian bungalow which was donated for the use of educational institutions, it has lovely lawns running down to its own beach right beside the very large Naval wharf in what the chart lists as East Boyd Bay.
This wharf was open to the public the last time I was there 2 yrs ago and a few people were fishing off it, one guy used a golf buggy to cart his fishing gear to the end, as its about 1 km long, and as wide as a highway! When the Navy moved its munitions storage/loading from Sydney/Newington prior to the 2000 Olympics it was moved to Twofold Bay and this wharf and other infrastructure was built.
There is also the historic Sea Horse Inn just south of the 'X' in DS's original chart. This is a great place to have a few beers as you look across the lawns to the beach.you can also stay there.for a price!
These places are an easy drive out of Eden if you're visiting the area from the land, but are possibly a little exposed as an anchorage area in unfavourable weather, as the entrance to Twofold bay is very wide and much like Jervis Bay has few sheltered areas to run to except the wharf area on the north side of the bay.
Cheers. Greg.
Larger obstructions like Sow and Pigs inside Sydney's south head have more than one cardinal marks, this one has all four. The only one I'm aware of that does so.
i assume that a single mark indicates a small obstruction. It is how small is the question.
Cardinal marks are quite simple to understand.
If it is, for example, a north mark it is quite clear, it means pass north of it in a safe distance and you should come to no harm.
At sow&pigs it is quite clear again. It is marked by all four. Still, years ago some fool run into it, racing! 
(he obviously had problems defining the meaning of 'safe distance' )
If the danger is a single spot, like a peak of a rock which might not quite be visible at high tide, it would have the isolated danger mark. So one could pass it in any direction at a safe distance.
The cardinal mark in its place would send a different message, pass it in the marked direction in a safe distance and no other.
The drawn arch on the chart quite correctly suggest the area is to be avoided. It might mark a chain of underwater obstructions etc.
Why would anybody in his right mind would start a trip out of home waters without some sort of mapping this age, is beyond me.
The book section at Whitworts is holding a selection of useful books on the subject.
Paper charts and books supposed to be found on every yacht on passage.
In NSW by law one must carry a chart.
