Danger in the SW Sunk Crossing

[tillergirl]

I have finally managed to upload a video onto Utube! This was shot during the survey by Larry (XO-Gladys) and I on 27th May. This shows us approaching the tide rip which is caused by the flood tide through the swatch colliding with the Barrow Deep flood. With plenty of height of tide we could go through the rip and over the top of the knoll. You can see the 'trace' of the bottom running along with video (I need better software for that).

The stranding position was generally off to the left as we reach the edge of the end of the rip. Please bear in mind, that is a long way away from the waypoints AND if your passage planning is for quick(ish) times, you wouldn't be there at that time of the flood.

Enjoy (PS I am sorry I don't have Tiller Girl anymore because of the arthritis so it has to be a.......... mobo ?)

 

[Daydream believer]

I do not understand how I found the water to be significantly less than the charted depth ( Note neaps so should be 1 metre more) when i was fairly close to route between the centre waypoint & the eastern one as logged in 2019.
My echo sounder is fairly accurate over hard sand ( i know from having touched on the Gunfleet in the past)
I cannot help wondering how the sands actually shift. Do they shift in shallow drifts or do they build up in "bumps" that move across the sea bed? We know the tide can run fast. I may have run over such a "bump" that was on the move that was feeding the infill of the old deep water to the south. This might explain why it was not seen on the soundings. I certainly do not doubt the accuracy Tillergirls soundings AT THE TIME.

Is it possible that the sands could shift that quick & then level out again. My friends said that the 2021 waypoints showed enough water 2 hours after LW but I would have been a bit to the south of them. But nowhere near( comparatively) the grounded yachts. The area I am adressing is the flat exit area heading east
The vessel that attended the yachts initially, could not get into the channel due to lack of water & I doubt it would draw more than 1.6 M being a wide rectangular shallow water dredger/under water operations, type of craft. This could support my depth readings, or a skipper being careful.

 

[Habebty]

This all underlines what a valuable service the CTTE team provide! Thanks.

 

[ex-Gladys]

I have finally managed to upload a video onto Utube! This was shot during the survey by Larry (XO-Gladys) and I on 27th May. This shows us approaching the tide rip which is caused by the flood tide through the swatch colliding with the Barrow Deep flood. With plenty of height of tide we could go through the rip and over the top of the knoll. You can see the 'trace' of the bottom running along with video (I need better software for that).


The stranding position was generally off to the left as we reach the edge of the end of the rip. Please bear in mind, that is a long way away from the waypoints AND if your passage planning is for quick(ish) times, you wouldn't be there at that time of the flood.

Enjoy (PS I am sorry I don't have Tiller Girl anymore because of the arthritis so it has to be a.......... mobo ?)

I can't emphasise enough how difficult it was to steer Seadog in that rip...

 

[tillergirl]

He ain't called 'XO-Gladys' for nuffin! ??

 

[LittleSister]

Should I be marking my chartlet 'Not for Navigation'?

What else do you suggest we should use it for?

Seriously, though, I can't remember quite how you express it, but surely it's enough to say something along the lines of 'depths are subject to significant change, your charts have limited accuracy and should be used with caution alongside all other relevant information'?

Your endeavours are greatly appreciated.

 

[AntarcticPilot]

What else do you suggest we should use it for?

Seriously, though, I can't remember quite how you express it, but surely it's enough to say something along the lines of 'depths are subject to significant change, your charts have limited accuracy and should be used with caution alongside all other relevant information'?

Your endeavours are greatly appreciated.

For TillerGirl's own protection, his charts should carry a notice outlining their limitations. For example:

While best efforts have been made to ensure that these charts are accurate, they were made using leisure equipment, and are in an area subject to rapid changes. They should be regarded as a guide to the actual situation, and users should not rely on them as their only source of information.

I am sure this could be improved on, but it parallels the notice we put on our maps of Antarctica.

 

[LittleSister]

For TillerGirl's own protection, his charts should carry a notice outlining their limitations. For example:

While best efforts have been made to ensure that these charts are accurate, they were made using leisure equipment, and are in an area subject to rapid changes. They should be regarded as a guide to the actual situation, and users should not rely on them as their only source of information.

I am sure this could be improved on, but it parallels the notice we put on our maps of Antarctica.

Are we saying anything different?

 

[tillergirl]

I was tempted to observe that obviously nobody ever looks at my chartlets since I have added such a caution for ten years or so. So I decided not to make such an observation and I know LS was merely being humerous. I was just trying to introduce an element of humour about the utterly rediculous note about 'not for navigation'. I stood outside the Post Office today in the queue to post a parcel. Through the window I could see there is a group of umbrellas inside the door and there is a sign saying that the umbrellas has been kindly donated by a local Post Office customer. Below the sign there is a sentence to the effect that 'the umbrellas are not provided by the Post Office and the Post Office has no responsibility for their use'!

 

[AntarcticPilot]

Are we saying anything different?

Not really - I am merely sharing my professional opinion.

 

[pks1702]

Fascinating - thanks for posting that.

Your efforts with all the charlets are sincerly appreciated.

 

[rgarside]

I do not understand how I found the water to be significantly less than the charted depth ( Note neaps so should be 1 metre more) when i was fairly close to route between the centre waypoint & the eastern one as logged in 2019.
My echo sounder is fairly accurate over hard sand ( i know from having touched on the Gunfleet in the past)
I cannot help wondering how the sands actually shift. Do they shift in shallow drifts or do they build up in "bumps" that move across the sea bed? We know the tide can run fast. I may have run over such a "bump" that was on the move that was feeding the infill of the old deep water to the south. This might explain why it was not seen on the soundings. I certainly do not doubt the accuracy Tillergirls soundings AT THE TIME.

Is it possible that the sands could shift that quick & then level out again. My friends said that the 2021 waypoints showed enough water 2 hours after LW but I would have been a bit to the south of them. But nowhere near( comparatively) the grounded yachts. The area I am adressing is the flat exit area heading east
The vessel that attended the yachts initially, could not get into the channel due to lack of water & I doubt it would draw more than 1.6 M being a wide rectangular shallow water dredger/under water operations, type of craft. This could support my depth readings, or a skipper being careful.

Movement of the sand may result in sand waves, depending on the conditions - of which there will be a considerable variety in any tide cycle:-
(PDF) On the formation of sand waves and sand banks

 

[Denek]

Very interesting and scary thread. We are off to Ramsgate next Wednesday next week but thankfully will be leaving from Harwich via Black Deep and Folgers Gat. We just yesterday had a cruise up north from Harwich and had a wind over tide situation and whilst I was not actually sick I came close. Hopefully we won’t have that next week. Will be watching the wind direction with interest. I’m glad all were safe. Will have a look at tillergirls waypoints.

 

[tillergirl]

Very interesting and scary thread. We are off to Ramsgate next Wednesday next week but thankfully will be leaving from Harwich via Black Deep and Folgers Gat. We just yesterday had a cruise up north from Harwich and had a wind over tide situation and whilst I was not actually sick I came close. Hopefully we won’t have that next week. Will be watching the wind direction with interest. I’m glad all were safe. Will have a look at tillergirls waypoints.

The waypoints we are talking about is for the SW Sunk. Harwich to Ramsgate has a completely different crossing point - at the Little Sunk. The Little Sunk is a pretty stable area, an even, plateau like top of the sand. I haven't done the Little Sunk this year yet but others have crossed there.

 

[Denek]

Thanks TG I think we will go around the top of the Black deep. At least that’s what I’m thinking at the moment.

 

[johnalison]

Thanks TG I think we will go around the top of the Black deep. At least that’s what I’m thinking at the moment.

The Little Sunk really isn’t at all alarming. I have never found less than about 3m at datum. As I said, the only thing is to keep well clear of the now invisible L Sunk beacon. The trip from Harwich to Ramsgate is then almost a straight line.

 

[Denek]

The Little Sunk really isn’t at all alarming. I have never found less than about 3m at datum. As I said, the only thing is to keep well clear of the now invisible L Sunk beacon. The trip from Harwich to Ramsgate is then almost a straight line.

So looking at navionics it looks like it would save about Half hour. It has been suggested ( and I am looking at this now) leave harwich 2 hours after hw to take the tide most of the way down. Agree?

 

[tillergirl]

Via the Black Deep is potentially the quickest e.g. at 5kts best time 7hr 31 minutes compared to the Little Sunk 7hrs 42 minutes. But, but, but. Bizarely, if you chose to go at 2hrs after HW Harwich, via the Little Sunk would take you 7hrs 50mins compared via the Black Deep at the same start time which would take you 7hrs 57 minutes. Sacrificing 20 minutes isn't a bad thing. If you took the quickest start time there is a risk that if your schedule slips that you would arrive at the North Foreland at the start of the adverse tide - which is good to avoid.

 

[Denek]

Via the Black Deep is potentially the quickest e.g. at 5kts best time 7hr 31 minutes compared to the Little Sunk 7hrs 42 minutes. But, but, but. Bizarely, if you chose to go at 2hrs after HW Harwich, via the Little Sunk would take you 7hrs 50mins compared via the Black Deep at the same start time which would take you 7hrs 57 minutes. Sacrificing 20 minutes isn't a bad thing. If you took the quickest start time there is a risk that if your schedule slips that you would arrive at the North Foreland at the start of the adverse tide - which is good to avoid.

Thanks for your help. This will be our first time across and our longest passage to date so I don’t want any dramas. Weather looks reasonable for wednesday with the wind in the north east to east so should be ok I think. Just an early start with the tides. Might have trouble getting the crew(wife) up?

 

[PeterWright]

- how serious could be grounding in such conditions. Yachts are rather strong, could they be destroyed by waves - so that liferaft mentioned earlier would be needed?
- how 'easy' is to get into such situation? I see by the map that it could be easy to see the contour of the edge

@tillergirl youtube video would be lovely

In answer to your 2 questions:
1. Boats are strong, but sand is very hard and the waves deliver a lot of energy. In the situation described, she will be lifted off the sand by each wave then dropped on her keel(s) as the trough arrives - after some time, this is likely to destroy the rudder and drive the keel through the bottom of the hull. When this happened to Edward Heath's Morning Cloud off the Sussex Coast, it actually split the hull along the line of the keel into two pieces, with loss of life. Never underestimate the risk of grounding on sand in a seaway. Imagine the consequence of your boat being lifted on a crane then dropped on her keel from 1 metre, repeating every 15 seconds for an hour or more.

2. If the charts you are using are out of date and therefore do not represent the actual state of the seabed, the features you are seeking to recognise may well not be there. A lifetime spent studying how to minimise risk in a high hazard environment has taught me to know that all humans make mistakes. It's all too easy to get into the circumstances Daydream Believer describes.

Thank you, Daydream Believer, for sharing your unpleasant experience, it's a great learning opportunity for us all and thank you again, Tillergirl for your wonderful contributions to this forum. I, for one, have great faith in your carefully conducted surveys.

Peter.