Nassau bad charts / Green Cay-Sandy Cay

[Falbala60]

Green Cay is one of the most popular snorkeling site with the lot of turtles feeding there.

If you go there TAKE CARE and choose the passage just at the EAST end of Sandy Cay. Both Garmin and Navionics are wrong.

We went there from West Rose Island end and chose the south passage around the central reef there. I choose at low tide to stay in 6-10 ft of water. See my real course on the picture of my Garmin.

In the red circle with a 4ft draft wew touched the coral 2 times but just the tip and was not stopped.... in 6-10 ft of depth.

I was amazed and sent a message to Garmin with all pictures in a way to help them to correct their maps, at least inform there is a PROBLEM THERE. The answer was "This is not our department that take care of..."

I made a superposition of Garmin and Navionics in this area and they ARE BOTH WRONG !!! At Palm Cay Marina, other chaptains told me they also touched the bottom there.

Maybe the best way to PUSH the chart companies to IMPROVE would be to have their faults made public on a special forum in Cruisers Forum to help everybody.

[Shrew]

A 2 foot threshold is just too tight for me. The numbers are based on MLW. LLW can be lower. Wind can push water and make it shallower. I try not to assume that 6-10 means 8, or that everything will be 10. I assume 6-10 means there will be spots that are 6. A Rock could make that one spot 5. Which, incidentally I see many of, including directly in the path and location where you indicate a bump occurred.

So if you already have a threshold of 2 feet, and there are known rocks on the chart, you're theoretically, starting out with a potential of 12 inches of draft. That is not enough space to account for the variables of wind, LLW, or a few extra cans of beans in the holds and a low waterline.

[Bean Counter]

Please advise the Lat and Long of where you hit, then we can all add a marker to our chart.

[Bean Counter]

In terms of chart meanings, those little dotted lines joined together with the "+" s inside = "Danger Line in general" if I understand the US Nautical Charts symbols guide correctly - the course taken goes through the middle of this area noted on the Navionics chart. The Garmin chart is just blank in this area.


http://www.seasources.net/PDF/ChartNo1.pdf

[StuM]

Do you know what the arrow is pointing at?
What is the curved dotted line indicating?







Hint, look up the words "rock" and "obstruction" in a dictionary.

[Falbala60]

Originally Posted by StuM

Do you know what the arrow is pointing at?
What is the curved dotted line indicating?
Hint, look up the words "rock" and "obstruction" in a dictionary.

Don't kill the messenger ... (some people are often prone to)

For sure, but those X was not on the Garmin chart I only have on my GPS.
I checked lot ot time the x coral head and on Garmin they are quite precise. In the passage from Nassau to Highborne when crossing the coral head region, they where precise to 6-10ft and if it is just a x it is more than 6ft clearance and with a blue circle, less than 6ft.

This event was the first time I had a surprize with the Garmin charts.
The x you mention are on the Navionics chart... I will need to follow both in restricted zone.

[Bean Counter]

I agree, Garmin charts are usually more accurate in the Bahamas, in this case not so given the lack of soundings marked in this area you refer to, We run two plotters simultaneously a Garmin and a Raymarine with updated Navionics through the Bahamas and avoid the rocks marked on both and any hazard zones marked with dotted outlines. We also run an ipad with active captain as many of the warnings are useful. Same for Caicos banks. I have marked the section you ran aground with a hazard symbol on my plotter, but I doubt I would sail through the dotted line hazard area unless really slowly under motors only in good light.

[Falbala60]

Originally Posted by Bean Counter

Please advise the Lat and Long of where you hit, then we can all add a marker to our chart.

We where so amazed to hit something there where Garmin displayed no marks, that I just can find it on our actual course from the GPS. It was not just a coral head. My wife at the bow shouted me that we where in a very very shalow area, a large one like what we see on GE, not a small spot.


I am not on the cat now but on Google Earth it should be :

25° 5'43.19"N 77°12'47.18"O
but don't pass there take the narrower but deeper passage at the east end of Sandy Bar.

[MartinR]

I am sorry, but is the OP trolling?

I mean, corals grow, sands shift, the survey is probably done a long time ago. In coral waters, you navigate by sight or you run aground. If in doubt, you go slow. A little basic seamanship goes a long way.

[AiniA]

A few things to say. First and most importantly don't assume that charts are 100% accurate, because they just aren't. I can remember one lovely spot in Indonesia where we anchored in a river mouth, the Navionics chart showed us a quarter mile inland - on land. The paper chart did not even show the small river. The wonderful thing there and in the Bahamas is that the water is almost wonderfully clear and the Mark I eyeball navigation devices work really well. Some people just get so focussed on their electronics that they forget that the chart, paper or electronic, is just a representation of the real world just beyond their vessel.

Second important consideration is what accuracy you can expect with a chart. When we were at Pitcairn with paper and electronic charts it was a similar situation. The paper chart was from surveys in the 1880s as I remember and the location of the island was off by something over one km. It said this on a note on the paper chart. Why they didn't fix this rather than adding the notification I have no idea. The Navionics chart had the island in the right place but little detail. When we were last in the Bahamas Garmin charts had Explorer Chart data (which is wonderful) along with government data so they were better than Navionics which only had government data. In the eastern Caribbean, Navionics had Imray-Iolaire data and Garmin did not. You need to read the fine print. In both places the water is clear enough that eyeball nav works well. Even in good hydrographic data countries like the US you can get stuck because the charts are not perfect. We anchored in a small bay in Naushon Island in New England in a spot that showed 12' of water (we drew 5'). The sounder showed about 15' and the water was most definitely not clear. We settled in for a BBQ and a quiet night but realized as the tide dropped that we were most definitely aground. Turned out there was a triangle shaped mound of sand there that was only about 4'. Explained why no one else was anchored in the lovely spot I guess. Even when we were firmly aground and a foot or so above our normal waterline the depth sounder (transducer in the bow) showed we had over 9'. No harm, no foul we just waited until some tide came back and moved. It was a nice weekend day and we had about half a dozen small motor boats come by and ask us if we knew we were aground. Well yeah.

If you are in a questionable spot you just need to go slow enough that you don't damage anything or get stuck if you 'miscalculate'. I have been on boats for 50 years or so and learned navigation before electronic aids other than RDF I guess (certainly couldn't afford LORAN and SatNav when they came out). A lot of it is just common sense, which is a big part of the fun.

[Falbala60]

My main objective was to have a sub-forum where the charts faults can be reported and discussed.

That way the charts companies would have "the cloud" over their head because everybody can know.


If there is a place, I did not find it, please tell because the constant checking I made during 10 weeks in the Bahamas with my Garmin 7412 where dead right, the coral heads where precise...



... but now I fear of other places.

[skipmac]

Originally Posted by Falbala60

My main objective was to have a sub-forum where the charts faults can be reported and discussed.

That way the charts companies would have "the cloud" over their head because everybody can know.


If there is a place, I did not find it, please tell because the constant checking I made during 10 weeks in the Bahamas with my Garmin 7412 where dead right, the coral heads where precise...



... but now I fear of other places.

Maybe not fear other places but you should highly, highly suspect charts, any charts: paper, Garmin, Navionics, Explorer or any other, especially in places like the Bahamas.

The surveys just cannot be that accurate. There is no way that any company or government could survey and chart an area that large down to that level of detail. The main focus of most charts is to show safe channels for large commercial vessels. Recreational boating and the shallower waters and channels they use is generally an afterthought if they are specifically considered at all.

Bottom line, in shallow water, reef or rock areas, narrow channels or any other place where hazards might exist do not blindly trust and follow charts!!!

In the Bahamas charts are a good for planning and following a general course but your eyeball navigation is the ultimate, final answer to where you go. From many trips and years in the Bahamas I know of many areas where all the charts say something like "scattered coral heads" or "shifting sands" and specify visual navigation only in good light.

[stevo_002]

Of misleading charts, the entrance to North Bimini comes to mind

Channel markers, depth plots on charts and guide lines are guaranteed to take you aground it would seem.

Certainly sandbars shift in storms and anchored markers get dragged but one expects a certain responsible government to maintain to a safe(ish) standard.

Active Captain seems the best medium for sharing local knowledge and un-obvious pitfalls. Thankfully it still exists.

[Bean Counter]

Originally Posted by Falbala60

My main objective was to have a sub-forum where the charts faults can be reported and discussed.

That way the charts companies would have "the cloud" over their head because everybody can know.


If there is a place, I did not find it, please tell because the constant checking I made during 10 weeks in the Bahamas with my Garmin 7412 where dead right, the coral heads where precise...



... but now I fear of other places.

If you subscribe to Active Captain (can see the AC symbols on your) chart you can add a warning comment on-line, so that it will be recorded there for others to see when they do an update. This achieves part of your objective. However for the chart makers to respond to every small boat hazard identification it would need double checking from an independent and certified source, and some form of quality control, a legal liability assessment etc etc etc - that would be extremely expensive and would need to be passed on to users like us.

[Shrew]

Originally Posted by Falbala60

My main objective was to have a sub-forum where the charts faults can be reported and discussed.

That way the charts companies would have "the cloud" over their head because everybody can know.


If there is a place, I did not find it, please tell because the constant checking I made during 10 weeks in the Bahamas with my Garmin 7412 where dead right, the coral heads where precise...



... but now I fear of other places.

This is a single thread in the "Navigation" Sub-forum. Reporting a single incident doesn't establish this as a placeholder for chart discrepancies. No siongle thread will never become that regardless of how hard would would like it be so.

In all honesty, I'm not sure this is truly a 'chart discrepancy'. You traversed the area at low tide and experience exactly what the chart warns of. The entire area is surrounded by a hazzard warning with rocks/coral heads.

It appears to me that there are alternative, albeit longer, courses to be followed. You chose that one, were optimistic and kissed the ground.

I don't see how the chart is to blame here. Own the results of the actions and learn from them. choose a different departure time, or plot a different course.