tillergirl
Well-known member
I had the opportunity to conduct a re-survey of the SW Sunk early Tuesday morning. Bit nippy 
given the north-easterly but reasonable wind speeds to ensure flat enough conditions. A brisk spring ebb got me down there very promptly so I was able to start before local LW. With great visibility the whole of the SW knoll was exposed but nothing side of the Middle knoll was exposed although obviously shallow.
The result is that the swatchway is viable; comfortably viable. Indeed last year’s waypoints and rhumb line was viable. However, the rhumb line was uncomfortably close.
The swatchway has slightly narrowed and more a little to the north-east. Please download the revised chartlet at: http://www.crossingthethamesestuary.com/page29.html. This is the Downloads page: item 2. You can see the jpg or the PDF.
Any previous version of the chartlet should not be used. I have also revised the waypoints and the rhumb line. The west waypoint is further north (away from the SW knoll), the east waypoint is pretty close to its former position but I have also included a new ‘middle’ waypoint. To go straight west to east waypoint brings the rhumb line close enough to require caution close to the SW knoll so the middle waypoint gives a very comfortable ‘dogleg’.
I have added some notes on the chartlet:
1. The SW knoll is very steep-to (as before). With a north-easterly that morning as a lee shore, the edge was lively enough. When I attempted to get the closest run, the wind piped up (of course) to 18 kts and I declined to pursue the attempt. With the flood then starting onto the lee shore, I thought perhaps not. But there were no difficulties. I was content that the new rhumb line provides no particular hazard but do not wander south of the rhumb line. Coming either way having started at any of the waypoints, it is possible (with visibility) to mark either the Gunfleet Wind Farm or the London Array ahead but no visible back bearing. For those of you with chart plotters keep the X-track zero.
2. Opposite the SW knoll, the bottom shallows even and regularly so there is quite a lot of room to keep further to the north-east if you want. The Middle knoll does clearly intrudes eventually!
3. From the central new waypoint to the east waypoint, the bottom is very flat. As before it shallows 3 metres approximately from the deep west start of the swatch.
4. The edge of the Sunk Sand at this point by the edge of the Black Deep is pretty steep-to as well. When I first approached while there was a little of the ebb, there was a very distinct tide ‘popple’ (I wouldn’t call it a rip) about 400m wide and 30 to 40m ahead. I took a little bit more precaution thinking there might be a bar but there was no shallowing. Once I had come off the Sand, the depth dropped very quickly; very quickly indeed. There was no tide problem affecting the yachts direction. I do think there are slight signs of the eastern edge of the swatch having a modest flat bar.
5. To the north of the eastern side of the swatch had obvious sand waves or ripples. The visible depth sounder polls an average every 4 seconds so it looks on the instrument head flat and even. On the full record of the data the evidence of the sand waves was obvious: depth could change in three seconds and the sense of waves is obvious – e.g.
6. 1.6, 1.7, 1.9, 2, 2, 1.6, 1.9, 1.9, 1.8, 1.9, 2.1, 1.3, 1.7, 1.9, 2.3, 2.2, 2.2, 1.7, 1.8, 2.3, 2.2, 2.2, 2.2, 1.7, 1.8, 2.0, 2.1, 2.4, 1.7, 1.7, 1.8, 1.8, 1.9, 2.2 etc and again for that area. Note the soundings on the chartlet are the ‘worst case’. Deliberately so as peaks can reduce depth by over half a meter quicker than you can respond. Again don’t worry there is plenty of space and depth. Remember how shallow the 2012 swatch was – best 2.5m if I recall.
7. Obviously at LW I could not collect data over the knolls but the point is to help the floaty parts.
I didn’t intend to write quite so much but when you have an attack of anorakism then you have one.
I hope this detail hasn’t worried people. It is not intended for but to help. Of course navigational decisions are for you but I spent 2 hours 40 minutes over the Sand without any hazard. I do confess to being a DORK. I was going to try the GoPro Chinese clone £40. First I should have put it on the starboard side because it would have given a very clear view of the drying SW Knoll. Err, second – yeap I have to turn it on!
So here is me heading for home - for £40 a good little piece of kit - water proof etc:
But here is a dawn view – very chilly mind you:
[URL=http://s217.photobucket.com/user/rgaspar_album/media/P1050839.jpg.html]
So best now to have a cup of tea :encouragement::
[URL=http://s217.photobucket.com/user/rgaspar_album/media/Image2_1.jpg.html]
I hope this helps:
[URL=http://s217.photobucket.com/user/rgaspar_album/media/P1050820.jpg.html]
(Need a CTTE burgee)
given the north-easterly but reasonable wind speeds to ensure flat enough conditions. A brisk spring ebb got me down there very promptly so I was able to start before local LW. With great visibility the whole of the SW knoll was exposed but nothing side of the Middle knoll was exposed although obviously shallow.The result is that the swatchway is viable; comfortably viable. Indeed last year’s waypoints and rhumb line was viable. However, the rhumb line was uncomfortably close.
The swatchway has slightly narrowed and more a little to the north-east. Please download the revised chartlet at: http://www.crossingthethamesestuary.com/page29.html. This is the Downloads page: item 2. You can see the jpg or the PDF.
Any previous version of the chartlet should not be used. I have also revised the waypoints and the rhumb line. The west waypoint is further north (away from the SW knoll), the east waypoint is pretty close to its former position but I have also included a new ‘middle’ waypoint. To go straight west to east waypoint brings the rhumb line close enough to require caution close to the SW knoll so the middle waypoint gives a very comfortable ‘dogleg’.
I have added some notes on the chartlet:
1. The SW knoll is very steep-to (as before). With a north-easterly that morning as a lee shore, the edge was lively enough. When I attempted to get the closest run, the wind piped up (of course) to 18 kts and I declined to pursue the attempt. With the flood then starting onto the lee shore, I thought perhaps not. But there were no difficulties. I was content that the new rhumb line provides no particular hazard but do not wander south of the rhumb line. Coming either way having started at any of the waypoints, it is possible (with visibility) to mark either the Gunfleet Wind Farm or the London Array ahead but no visible back bearing. For those of you with chart plotters keep the X-track zero.
2. Opposite the SW knoll, the bottom shallows even and regularly so there is quite a lot of room to keep further to the north-east if you want. The Middle knoll does clearly intrudes eventually!
3. From the central new waypoint to the east waypoint, the bottom is very flat. As before it shallows 3 metres approximately from the deep west start of the swatch.
4. The edge of the Sunk Sand at this point by the edge of the Black Deep is pretty steep-to as well. When I first approached while there was a little of the ebb, there was a very distinct tide ‘popple’ (I wouldn’t call it a rip) about 400m wide and 30 to 40m ahead. I took a little bit more precaution thinking there might be a bar but there was no shallowing. Once I had come off the Sand, the depth dropped very quickly; very quickly indeed. There was no tide problem affecting the yachts direction. I do think there are slight signs of the eastern edge of the swatch having a modest flat bar.
5. To the north of the eastern side of the swatch had obvious sand waves or ripples. The visible depth sounder polls an average every 4 seconds so it looks on the instrument head flat and even. On the full record of the data the evidence of the sand waves was obvious: depth could change in three seconds and the sense of waves is obvious – e.g.
6. 1.6, 1.7, 1.9, 2, 2, 1.6, 1.9, 1.9, 1.8, 1.9, 2.1, 1.3, 1.7, 1.9, 2.3, 2.2, 2.2, 1.7, 1.8, 2.3, 2.2, 2.2, 2.2, 1.7, 1.8, 2.0, 2.1, 2.4, 1.7, 1.7, 1.8, 1.8, 1.9, 2.2 etc and again for that area. Note the soundings on the chartlet are the ‘worst case’. Deliberately so as peaks can reduce depth by over half a meter quicker than you can respond. Again don’t worry there is plenty of space and depth. Remember how shallow the 2012 swatch was – best 2.5m if I recall.
7. Obviously at LW I could not collect data over the knolls but the point is to help the floaty parts.
I didn’t intend to write quite so much but when you have an attack of anorakism then you have one.
I hope this detail hasn’t worried people. It is not intended for but to help. Of course navigational decisions are for you but I spent 2 hours 40 minutes over the Sand without any hazard. I do confess to being a DORK. I was going to try the GoPro Chinese clone £40. First I should have put it on the starboard side because it would have given a very clear view of the drying SW Knoll. Err, second – yeap I have to turn it on!
So here is me heading for home - for £40 a good little piece of kit - water proof etc:
But here is a dawn view – very chilly mind you
:[URL=http://s217.photobucket.com/user/rgaspar_album/media/P1050839.jpg.html]
So best now to have a cup of tea :encouragement::
[URL=http://s217.photobucket.com/user/rgaspar_album/media/Image2_1.jpg.html]
I hope this helps
:[URL=http://s217.photobucket.com/user/rgaspar_album/media/P1050820.jpg.html]
(Need a CTTE burgee)
