SW Sunk Passage Coordinates Crossing the Thames vs Imray

kocha44

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Good evening,

Still planning for the trip from Burnham-On-Crouch to Ramsgate next week and just wanted to check on the infamous SW Sunk passage. For the sake of having the tide with us, we are planning to leave at HW or HW-1 from Burnham to then reach SW sunk west side in 3-3.30 hours.

The map on http://www.crossingthethamesestuary.com/SW%20Sunk%20Drawplus%202014%20V4.jpg seems to provide more than sufficient depths for our crossing from one waypoint to the other (assuming they are LAT), but the coordinates on my Imray C1 bring me right across the bottom part of Middle Sunk. Does this mean that Middle Sunk has moved upwards and I am safe using the coordinates from the above mentioned site or do I not need to bother as much as I am now as we will be passing at HW+3?

Any advice would be much appreciated for our first Thames Estuary crossing. And yes, I have the crossing the Thames Estuary book, which is the source of my probably/hopefully unfounded confusion with Imray C1.

Thank you in advance,

Conrad
 

Marmalade

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Trust the CTTE route - which appears to take you over the green stuff - many on here have (I am one) and have found the waypoints and the route as described. Yes - the swatchway has moved since the chart was published.
 

philiphurst

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Trust the CTTE route - which appears to take you over the green stuff - many on here have (I am one) and have found the waypoints and the route as described. Yes - the swatchway has moved since the chart was published.

+1

Counter-intuitive it may be but there's plenty of water. Trust the CTTTE co-ordinates and don't deviate too far from them. As I passed through last month on my way south there was a sandbank and breaking water off my starboard side. Don't let this bother you. As always, the coordinates are spot on.
 

Tiller Girl

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Marmalade and Philip are entirely correct. Imray C1 has not yet been reprinted but if you were going to the expensive of using UKHO Chart 1975 you would have found it reprinted in April this year to show the swatchway illustrated in my chartlet. Chart plotter charts are, as far a I can ascertain, even further behind as at least one person from this parish has found this summer. This unfortunately is an area that really does change frequently making it difficult for chart makers - having said that this swatchway position has been with us for two years now and as yet is showing no signs of closing (the previous swatchway gradually closed over a period of about 3 years). If it makes you feel better, I sent my survey of 2014 to the UKHO who asked the PLA to survey the area which they did in February this year and there was pretty much 100% correlation with my survey. As a result the UKHO reissued their chart (kindly they sent me a complimentary copy). Other chart makers now have to catch up.

I went through twice in July using the waypoints quoted on my site and my data still looks compleely valid. Lovely and deep on the Barrow Sand side, the lower depths come on the Black Deep side - indeed just as you are thinking you are approaching the Black Deep. Feels a little counter intuitive for a moment but still with it; I found no less than 13ft of water LWS. As Philip says, at low water you will see a sandbank (Mystique's Knoll!) but the sand is really steep-to on the swatchway side and though you may see seals keep to the waypoints and the rhumb line twix them and you will be fine.

Oh, and all my chartlets show depths at LAT, the depth reductions being based on live data from either the PLA or the BODC.

Enjoy the trip.
 
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Supine Being

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It was absolutely fine when I used the route three weeks ago. It is pretty disconcerting when your chart plotter tells you that you should be firmly in the agricultural business, but the water was deep by east coast standards. I don't think I saw less than 5.5m at about 1.5 hours after HW, the "shallowest" being towards the SE end of the route.
 

kocha44

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Thank you, very pleased to hear the CTTE coordinates can be trusted. I will let you know how it went, should be crossing next Tuesday.
 

Tiller Girl

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Thank you, very pleased to hear the CTTE coordinates can be trusted. I will let you know how it went, should be crossing next Tuesday.

Please do let us know. It all helps. Enjoy your crossing. That day is RTIR day for Mersea - a hundred or so dinghys racing round the island (including over the road). So a lot of people will be hoping for reasonable winds.
 

toad

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A group of us went through last weekend, It is very disconcerting to see breaking water and sand both sides but we never had less than 19ft at around low water neaps. Plot the waypoints right and stay on the line, a big thank you to Roger.
 

toad

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One question if I may, how did you find that gap. Did you just drive up and down in the hope of finding a hole because looking at the breaking water and sand sticking up I would keep clear or was there other clues to the gut way. I am very pleased you did I just wondered how you found it.

Perhaps we should rename it Rogers Gut.
 

Tiller Girl

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Nobody needs a reminder of my 'Gut', thank you!:encouragement:

Pretty much it was found like that. Pick a calm day (pretty tricky), get down there around low water so the banks are exposed, look, look and look again at the surface - frequently there are some clues and then follow gently round the edge of the exposed sand watching the depth-o-meter like a hawk (obviously trying to make progress across rather than along the sand). Once you get across on one line (which I then have shown on the laptop running Imray's/Meridien chart flotter) then I return on a parallel leg and then criss cross until I find the other side. The NMEA data logger on the laptop is hoovering up a sounding a second with its lat/long. I try to listen in to London VTS to get the height of tide data at 15 minutes to and 15 past the hour. They give the height of tide at Walton, Margate, Shivering Sands and Southend - Margate is on a direct tidal line with the SW Sunk and Shivering Sands is about 0.1m further to the west. I note this for later reductions of soundings to chart datum and gives me the advantage that I can ignore any atmospheric pressure issues - well at least they will be minimal being that close - if anyone is giving themselves an inch clearance over the Sunk Sand I would suggest they don't!:encouragement::encouragement:

I keep going until I feel I have covered the area sufficiently or the conditions make collecting data worthless. For example on the last occasion I was about to explore a bit further on the Black Deep side and a bit of a sea breeze built from the south-east that induced quite a roll. There was no issue about safety; it wasn't much of a sea but try as could, I couldn't seem to stop the roll (and explore in a sensible direction) and so I stopped. In other places such as the Barrow No 2 crossing I have been able to get round this problem by changing the course and then doing a series of runs at 90 degrees and then checking for correlation between the data - which takes a bit of time back home.:confused:

It all takes a bit of time. Typically I will be over the Sunk Sand for a minumum of three hours and usually nearer 4 by which time you really get a feel for where the water is - and isn't. My trick is to get out from West Mersea - 3hrs, survey - say 4 hrs and return 3hrs, and get back to Mersea while the Club launch is still running! Usually means overnighting on the mooring and leaving early. It's nice when Colin (Essex Lad) can come along which isn't always, 4 hours over the Sunk is quite lonely enough and there is a fair bit to do for just one. I always feel I've done it that bit better when Colin has been with me.:D

You may be interested in this image. the PLA were kind enough to send me their data from their survey this February. I have overlaid their data in Magenta on my chart. First note the high level of correlation between the two sets of data in the Gut, second you will see the area I couldn't collect data because of the rolling, third, I am pretty pleased with my freehand drawing of Mystique's Knoll to the south-west. The 5m contour is a bit rubbish. The drying 0.5 sounding due east of the Barrow No 6 is I think a genuine change since my survey in 2014 upon which my chart is drawn. And have I ever touched - 'fraid so but never hard aground.

 
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pks1702

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It must be a labour of love but much appreciated by us East Coasters.

In my view you should never be buying beer in our company :encouragement:

Its a greatly appreciated resource.
 

Tomahawk

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When we are off to jolly Ramsgit, we punch the tide to arrive at Crouch No 3 than about HW -1 turn hard right.... straight across the top of Foulness sands... With the boards up we draw 1.1. The first few minutes is heart thumping as the echo sounder comes up like a rocket but as soon as you reach the top it is very flat thereafter. Remembering that everyone is quite happy to go across the Ray Sand it is very similar.

The distance saving is worthwhile.
 

Tiller Girl

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You remind me that in Irving's book of the 1920's (the forerunner of East Coast Rivers) he lists half tide routes across Foulness (and the Buxey). I've always been tempted to have a go and then to see if the old Barrow swatchway works. Do you do that bit as well?
 

Supine Being

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When we are off to jolly Ramsgit, we punch the tide to arrive at Crouch No 3 than about HW -1 turn hard right.... straight across the top of Foulness sands... With the boards up we draw 1.1. The first few minutes is heart thumping as the echo sounder comes up like a rocket but as soon as you reach the top it is very flat thereafter. Remembering that everyone is quite happy to go across the Ray Sand it is very similar.

I did a similar thing in 2012 on the advice of an old salt of my acquaintance, but I haven't had the nerve to try it again since. Our route was slightly different - turn right at Whitaker No.6 on to a course that clips the bottom of East Barrow. We draw 1.5m and, from memory, we saw a similar depth under us all the way across back then, so around 3m at HW-1. I was (even more) inexperienced at the time, and now I worry about uncharted obstructions... And possible explosions from the MOD... And dragons.
 

Bru

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I'm rather put off the idea of taking a short cut across Foulness by this note on the Admiralty chart ... "Numerous posts and stakes, sometimes submerged, may be encountered on Foulness/Maplin Sands"! Erk, no fear!!
 

Tiller Girl

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You'll be amused then by Irving's warning "It is well to remember when crossing the Maplins that artillery practice takes place over them" He recommended a half-tide course from Blacktail Spit to the West Buxey (then in the Ray Sand); how anyone followed the sailing directions for that is beyond me.
 
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