Swatchway N of London Array - not there!

Marmalade

Marmalade

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Coming back from hols last week we sailed from Boulogne outside the London Array wind farm and aimed for the swatchway that appears on my current versions of charts (Navionics) north of the wind farm. My older C-Map charts don't show this swatchway - ie a far smaller channel with less water. 51deg 42.4N; 1deg, 31.0E

Well - it's not there. We touched going in and felt around and there's certainly far less water than the chart says. Ended up working our way back through the wind farm to Foulgers Gat (should have stuck to that as normal) which cost us a couple of hours at least. With hindsight continuing up to Long Sand Head would have been quicker.

Email to Navionics on the way!
 
My up-to-date Admiralty chart is on board so I would need to see tomorrow. My UKHO Leisure Folio (5607.2) is 3rd June 2010; the latest is 15th December, 2011 so might have altered. But using the 2010 leisure folio I don't think I would have described your position as a 'swatchway' - i.e. v narrow, only sounding is 0.1m north side of the 'rill'. And it is 'downtide' of the London Array. There is significant scour round the the turbines and logic (on the grounds the ebb has the strongest tides) is that the sand will move towards the north.

Using the previous edition of Admiralty chart - 1975 which is the primary source data has an identical image of the 2010 Leisure Folio. But it shows the data is based on 2000 to 2003 Government sources and 2004 Commercial Survey (presumably the London Array commissioned surveys).

I would be interested by the Navionics swatchway but in honesty I wouldn't be brave enough to try that. Perhaps I ought to dig out my older Admiralty charts to see if the swatch is visible then.:confused:
 
I suspect Navionics is out of date. It may be since I haven't got the latest Admiralty chart on board. However if the Navionics looked like this:



it is out of date. This below is recent - er, significantly more recent:

[URL=http://s217.photobucket.com/user/rgaspar_album/media/P1050899.jpg.html]

The pencil cross marks the position you quoted (was wearing the wrong pair of glasses! Needed to get out the cheapo pair but the position is close enough).

I am probably trespassing over copyright beyond the licence permission I have from the UKHO but I hope this is ok on the grounds this is improving safety (and that buying a UKHO chart is probably a good idea - not trying to be sarcastic, just on the grounds of pushing the boundaries, the UKHO full chart is the most up to date [which reminds me to remind UKHO to alter the folio 5607.2 to cover the SW Sunk swatch]).
 
This is what my chart shows, last update was early May this year

17197ed1354a272c0805f531643eec7a.jpg
 
Here's the chart I was following - we touched right on line in the "white" ie in water surrounded by the 2m contour. With the tide I expected c. 3.5m (we need 2m) ie I wasn't expecting loads!
chart.jpg
 
That's clear isn't it. I'll go on board tomorrow and look at the latest UKHO edition. If it's like that, it would be valuable for you to submit a H102 to the UKHO; you will merit a 'Less water reported (2016)' NtM!

The VMH chart is the same as your Navionic; Little Grebe's Navionics or someone's else?

Personally I think it's a changeable area. Long Sand Head's extension has required the Black Deep to be the most frequently channel buoy to be the most moved in the Estuary and the change has been to extend to the north-est. Movement to the north-east because of the Wind Farm? Who knows? Presumably you went through the Wind Farm?
 
tillergirl said:
Presumably you went through the Wind Farm?
Click to expand...

Just snipped the corner off - ironically bags of water through the windfarm - mostly 10m plus. It was the last leg of a 3 week trip so I thought I'd save a mile. As you say - the sand shifts. I should have stuck to the known buoyed channel (which we used on the way out). Ah well - the Thames Estuary always has the ability to bite you in the derriere.
 
Marmalade, time for an H102! The Navionics chart matches the current UKHO chart, April, 2015:



But, BUT, BUT

The source says it is a 2013/2014 Check Survey - 500m line spacing. The chart note says "Depths within the area indicated in the sources diagram are taken from a single beam check line survey with lines 500m apart. Less water than charted will exst over the sandbanks". Note the chart contours in that part are broken lines which means approximate depth contours. The Chart Plotters don't appear to warn readers - well at that definition anyway. A curious process - well it seems to me. I collect a sounding every 1.5 seconds: 500m apart strikes me as a long distance apart. I would ahve thought the process would be continuous with absolutely no issue to cause a problem. I actually scan every line of soundings which is easy in a small defined area like the SW Sunk but you would think they would automate it to finding a problem. Not that I know how a 'Check Survey' works.

The history is 2002 - it's there, 2004 it isn't, 2014 it is, 2016 t'isn't. Can I suggest you make a 'Less water reported' report: to [email]sdr@ukho.gov.uk[/email], the form H102 is at [url]http://www.ukho.gov.uk/ProductsandServices/MartimeSafety/Pages/Hydrographic-Notes.aspx. Would be worthwhile plus the UKHO are interested in reports from leisure users.
 
Tillergirl, ghe cross on your latest chart is in a different place to the waypoint on mine, is the cross the position the OP gave ?
 
It's a bit further north of course. It is further into the 'swatch' but the contours are an assumption. Now is the swatch on a direct line between the 2.5 and 1.7?
 
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