Goodwin Sands

Capt Popeye

Well-known member
Joined
30 Sep 2011
Messages
18,799
Location
Dawlish South Devon
Visit site
Drying out and visiting Sandbanks for fun or 'scrubbing off' used to be a regular occurance many years ago off Suffolk and Essex also in Herne Bay Kent.

Guess that over time these events have become less normal for many new into boating who get Rubbed Off in a Marina or Boatyard these days, so grounding out to do such tasks on their ownhas fallen through their learning or teaching ? What course does that RYA cover intentionally grounding in ?

At least up to 12 years ago at Herne Bay in Kent there was a craft who regularly took sight seers and holidaymakers out to part of the Margate Sands for a brief trip ashore there, went on a few times; the Skipper always approached the sands in deeepest waters side so getting away was safe and easy to do; we were encouraged to step onto the sands and stroll about, watching the Seals from afar or collecting sea shells untill Skipper called out for us to return to his boat; as far as I know he always took back same number as he deposited onto the sands, all safely; guess that he had researched the sands so knew and picked the right place to do it; noticed that on the opposite side of the Banks the water appeared to drop quickly into the depths so guess that side was scourged out by the tides and currents;

So guess that over time n tide the practice of intentional groundings has become a 'not to do task' in the newbies to boating; maybe the deep keels oft favoured has something to do with it ?

In the Mouth of the River Deben is Horse Sand right in the middle of the laid moorings, as a Youth i along with others from the Ferry used to row out and go ashore looking for shells and cay pipes etc never recollect there being any chance of being swallowed up by the Sands or Tides, we all lived to tell the tale (inc HM)

Yes no doubt that there are reasons that boats etc can and do get swallowed up into the sands just not sure how it happens though ?
 

Habebty

Well-known member
Joined
16 May 2001
Messages
4,458
Location
Norfolk/Suffolk
www.crittergetteronline.com
Now, I’m with Little Sister on this ”swallowing” business. I understand the liquefaction process and strongly suspect that vessels swallowed by the sand were holed as they hit or pounded on the sand, and flooded over 4-5 hours as the tide came in or otherwise flooded due to angle the vessel had reposed. A lot of old wooden vessels were often poorly maintained, and if settled on on a convex sand back would hog and open up seams and all sorts, again, letting enough water in to prevent adequate bouyancy. Whilst a good story, sand banks do not just swallow vessels unless a particular set of circumstances allow. I have parked my bilge keeler on many a sandy spot.
Do not confuse liquefaction with scour.
The risk also comes should any current scour sand away from under one keel (or even one end of a loaded barge?) and tip the boat thus rendering it liable to flooding and therefore at risk of settling down into the sand which as the tide came in would be a less dense medium. Scour can move a lot of sand into some pretty strange shapes very quickly without much current.
 

Capt Popeye

Well-known member
Joined
30 Sep 2011
Messages
18,799
Location
Dawlish South Devon
Visit site
Well I have experienced my feet being drawn down into soft watery sand in the past when standing still with feet covered by river water my guess at the time is that it was my weight assisting the drawing down process as the water appeared to be carrying the soft sedmented sand away from my feet

All in all percuilar
 

Habebty

Well-known member
Joined
16 May 2001
Messages
4,458
Location
Norfolk/Suffolk
www.crittergetteronline.com
Well I have experienced my feet being drawn down into soft watery sand in the past when standing still with feet covered by river water my guess at the time is that it was my weight assisting the drawing down process as the water appeared to be carrying the soft sedmented sand away from my feet

All in all percuilar
That is scour, not peculiar. Note the base of any pile or pier leg in a sandy bed.
 
Last edited:

Habebty

Well-known member
Joined
16 May 2001
Messages
4,458
Location
Norfolk/Suffolk
www.crittergetteronline.com
There is science being done about it. It mentions helical forces. For example, here.
There are lots bathymetric and sediment flow studies of the Thames Estuary as posted on Tillergirl's thread about anomolous sand formations. The link you posted is another, but does not allude to "mysterious" swallowing of vessels. It does however contribute to the explanation of sand/sediment erosion and deposition which if a vessel had already foundered, would explain it's eventual covering and possible uncovering due to wave/storm/tidal action.
 

tillergirl

Well-known member
Joined
5 Nov 2002
Messages
8,345
Location
West Mersea
Visit site
We were quite cautious when we went on the Buxey to look at a WWII airplane remains

P1010154 by Roger Gaspar, on Flickr

We could see that around the engine there was a depression in the sand by the scour of the tide and we feared it might be soft close to it. In a couple of small spots it was soft but fortunately not dramatic. The weight of the engine hasn't sunk it into the sand. Which strikes me as quite surprising after about 80 years. If the plane actually managed to land safely you would want to hope the dinghy was on board and held air!
 

Hallberg-Rassy

Active member
Joined
29 Oct 2020
Messages
246
Visit site
To be honest, I really didn't dig too deeply into researching it to win any "argument" but I think it make sense that there's more than just surface level erosion and deposition.

We're talking about a kind of slurry here, aren't we? Of which, again, there is a lot of study.

Of the tiny little I know about fluid dynamics, you will get a boundary level (bottom) dragging on wherever the solid part is, moving at a slower speed, and the more fluid (top) elements moving faster, consequently causing the particle-liquid to tumble in on itself, and I would guess heavier masses dropping down.

You'd also get effects before and after any vessels sitting on the sands, eg high pressure/density ahead of the vessel, low pressure/densities behind the vessel and lots of swirls and eddies caused by poor hydro-dynamic shapes that would erode the sand causing more liquidification on one side, leading to boats tipping, I would guess.

The latter is what you describe as "scour"?

Now, I'm not going to pretend to have anything more than a commonsense take on what is a serious area of science, but I think there's enough in that to be careful of not poo-pooing phenomenon as being "mysterious".

Big metal boats on the sands have tended to have their backs broken being half on, half off. No idea what of small boats being directly on it. But I'll be very surprised if someone has not studied them specifically. Perhaps just a long time ago and, hence, hard to find on the internet.

Fluidisation ....


"Bubbles" of lighter grains forming in sand, just as they can in other fluid, akin to the Rayleigh-Taylor (RT) instability in fluid dynamics. For what it's worth, before you embarass yourself with skepticism, this is pretty cutting edge stuff.

 
Last edited:

Habebty

Well-known member
Joined
16 May 2001
Messages
4,458
Location
Norfolk/Suffolk
www.crittergetteronline.com
To be honest, I really didn't dig too deeply into researching it to win any "argument" but I think it make sense that there's more than just surface level erosion and deposition.

We're talking about a kind of slurry here, aren't we? Of which, again, there is a lot of study.

Of the tiny little I know about fluid dynamics, you will get a boundary level (bottom) dragging on wherever the solid part is, moving at a slower speed, and the more fluid (top) elements moving faster, consequently causing the particle-liquid to tumble in on itself, and I would guess heavier masses dropping down.

You'd also get effects before and after any vessels sitting on the sands, eg high pressure/density ahead of the vessel, low pressure/densities behind the vessel and lots of swirls and eddies caused by poor hydro-dynamic shapes that would erode the sand causing more liquidification on one side, leading to boats tipping, I would guess.

The latter is what you describe as "scour"?

Now, I'm not going to pretend to have anything more than a commonsense take on what is a serious area of science, but I think there's enough in that to be careful of not poo-pooing phenomenon as being "mysterious".

Big metal boats on the sands have tended to have their backs broken being half on, half off. No idea what of small boats being directly on it. But I'll be very surprised if someone has not studied them specifically. Perhaps just a long time ago and, hence, hard to find on the internet.

Fluidisation ....


"Bubbles" of lighter grains forming in sand, just as they can in other fluid, akin to the Rayleigh-Taylor (RT) instability in fluid dynamics. For what it's worth, before you embarass yourself with skepticism, this is pretty cutting edge stuff.


i agree that vessel with compromised buoyancy aka broken backs/ opened seams etc. will flood and gradually sink into the sand.
Good video finds, and to me a perfect explanation of why a vessel/ball still capable of bouyancy or a less dense material will rise to the top and not sink in a liquified sand or other material.
 

Hallberg-Rassy

Active member
Joined
29 Oct 2020
Messages
246
Visit site
You first if you're committed to testing out your theory in practise. Make sure you get someone to upload the video afterwards.

So where did the 2,000 boats and planes (est) and bodies go, and how? You're saying they must float, when facts says they sunk and disappeared.

The specific gravity of GRP is, say, 1.4, about the same as the heaviest woods (oak is around 1.0). Of course, modern boats are greater than that, due to their metal keels (est 1/3rd). May be the quicksand effect (surface tension/viscosity) is strong enough to overcome the bouyancy in the first place, then once flooded with sand slurry (approx 2.5), sinks the boat, and the churn of the sands start to move them around?

 
Last edited:

Bru

Well-known member
Joined
17 Jan 2007
Messages
14,684
svpagan.blogspot.com
Odd things
i agree that vessel with compromised buoyancy aka broken backs/ opened seams etc. will flood and gradually sink into the sand.
Good video finds, and to me a perfect explanation of why a vessel/ball still capable of bouyancy or a less dense material will rise to the top and not sink in a liquified sand or other material.

And yet it is a documented fact that intact and seaworthy vessels have on occasions disappeared beneath the sands. And it must have happened with sufficient regularity (ie not so rare as to be forgotten between incidents) to become a known if inexplicable phenomenon in the past given the documented references to the Buxey being "hungry tonight", the Goodwin's "swallowing ships" etc
 

LittleSister

Well-known member
Joined
12 Nov 2007
Messages
17,545
Location
Me Norfolk/Suffolk border - Boat Deben & Southwold
Visit site
So where did the 2,000 boats and planes (est) and bodies go, and how?
I think you'll find that the 2,000 boats and planes were non-buoyant wrecks, and not relevant to what we're discussing.


May be the quicksand effect is strong enough to overcome the bouyancy in the first place,

How? The 'quicksand effect' is the sand acting like a liquid. An undamaged boat will float in a liquid.

And yet it is a documented fact that intact and seaworthy vessels have on occasions disappeared beneath the sands.

Is it? Can you provide a link to these documents? I'd love to read them.
 

Gargleblaster

Well-known member
Joined
16 Dec 2003
Messages
1,217
Location
Medway, Gillingham Reach
Visit site
In the Pathe film which I though was excellent, there is mention of 'Smugglers Tales' of the danger of the sands, both the Goodwins and the Buxeys. Both the Kent Coast and the Crouch/Roach were prime smuggling areas. So I wonder how much of the ships being swallowed was myth to keep the Customs cutters away.

The story usually starts: 'I know someone who was told of a ship that was swallowed on the Buxeys last week.' and so it spreads. witness statements particularly second and third hand are more often than not unreliable. In a court of law it is called hearsay.

I think Habebty's point of broken backs or sprung planks would be the only reason a ship could be swallowed.

I understand that it is impossible for instance for a person to sink in quicksand to such an extent that they disappear from view. Of course if you have sunk to such and extent that you are held and then overcome by a flood tide then you can drown. Notice in the Pathe 1948 film how easily the lifeboat person frees his foot by jiggling it causing the liquefaction of the sand.
 

LittleSister

Well-known member
Joined
12 Nov 2007
Messages
17,545
Location
Me Norfolk/Suffolk border - Boat Deben & Southwold
Visit site
I wouldn't like to try it, but I imagine it is quite easy to get your feet stuck and make things worse by thrashing about so both legs start to sink.

Indeed you would, but you wouldn't disappear below the sands: you'd sink only to about your waist (if you were upright) because you'd be floating in the liquified sand.

See my post #40 (reproduced below) and the link in it (which also advises how to escape it).

'Objects in liquefied sand sink to the level at which the weight of the object is equal to the weight of the displaced soil/water mix and the submerged object floats due to its buoyancy. . .

It is impossible for a human to sink entirely into quicksand due to the higher density of the fluid. . .

IN POPULAR CULTURE
Quicksand is a trope of adventure fiction, particularly in film, where it is typically and unrealistically depicted with a suction effect that causes people or animals that walk into it to sink and risk drowning. This has led to the popular perception that humans can be completely immersed and drown in quicksand; however, this is physically impossible.'

Quicksand - Wikipedia
 

Hallberg-Rassy

Active member
Joined
29 Oct 2020
Messages
246
Visit site
I think you'll find that the 2,000 boats and planes were non-buoyant wrecks, and not relevant to what we're discussing.
Larch and pine come in at about (I suspect most of the old boats were not made out of hardwoods) 0.5.
How? The 'quicksand effect' is the sand acting like a liquid. An undamaged boat will float in a liquid.
Try lifting your feet out of dry sand, quicksand, and water.

I read one calculation that put the force requied to pull one foot out was 104 newtons, equivalent to lifting a medium-sized car*. Last time I tried lifting my foot out a puddle, I'm pretty sure it wasn't that hard.

What liquid are you thinking about?

As I think I wrote, viscosity plays a role in the quation.

However, the discussion of how people die by being trapped in quicksand did add to my theorising of what happens to boats; they don't go right under, they get held half in, and then the high tide (of sand mixture) drows them.

I don't think your poo-pooing has add anything to our full understanding, or your credibility, at all.

* Khaldoun, A., E. Eiser, G. H. Wegdam, and Daniel Bonn. 2005. "Rheology: Liquefaction of quicksand under stress." Nature 437 (29 Sept.): 635. doi:10.1038/437635a
 
Last edited:

Habebty

Well-known member
Joined
16 May 2001
Messages
4,458
Location
Norfolk/Suffolk
www.crittergetteronline.com
Larch and pine come in at about (I suspect most of the old boats were not made out of hardwoods) 0.5.

Try lifting your feet out of dry sand, quicksand, and water.

I read one calculation that put the force requied to pull one foot out was 104 newtons, equivalent to lifting a medium-sized car*. Last time I tried lifting my foot out a puddle, I'm pretty sure it wasn't that hard.

What liquid are you thinking about?

As I think I wrote, viscosity plays a role in the equation.

However, the discussion of how people die by being trapped in quicksand did add to my theorising of what happens to boats; they don't go right under, they get held half in, and then the high tide (of sand mixture) drows them.

I don't think your poo-pooing has add anything to our full understanding, or your credibility, at all.

* Khaldoun, A., E. Eiser, G. H. Wegdam, and Daniel Bonn. 2005. "Rheology: Liquefaction of quicksand under stress." Nature 437 (29 Sept.): 635. doi:10.1038/437635a

I don’t think anyone is poo-pooing the established facts of liquifaction or non- buoyant objects disappearing into sand, far from it.

What is being treated with some scepticism, is that a well found vessel simply sitting on the sand will be swallowed up. It may well settle due to local scour but will not "sink" because it will always be more bouyant than the sand, liquified or not.

Your point about the density of hardwood (or any wood for that matter) on a wreck, does not take into account the heavy stuff like a keel bolted to the the hull. Some hardwoods (Greenheart) will not float Any holed wooden vessel will sink due to the mass of non-floatables exceeding the bouyancy ability of the wood it is built from. A sound vessel relies on internal bouyancy rather than material bouyancy.

The text quoted, again simply confirms the properties associated with super-saturated sand and does not indicate any downward "sucking" forces, merely gravity and agitation co-acting on a body heavier than can be supported by wet sand (up to the point of neutral bouyancy).
As a civil engineer, I have studied soil mechanics, and you will be (possibly)surprised at what will float. For example, engineers building petroleum pipelines across boggy ground, very quickly learned to "ballast" the pipeline to prevent it from rising up out of the ground due to the very much less dense than water, petrol contained within. There are numerous example of concrete basements simply "popping" out the ground before the upper stories were added due to bouyancy in wet ground.

Please don't think this is a put-down, poo-pooing, or argument, but any interesting discussion about the known facts of the behaviour of wet sand/sediment.
 
Last edited:

Bru

Well-known member
Joined
17 Jan 2007
Messages
14,684
svpagan.blogspot.com
Is it? Can you provide a link to these documents? I'd love to read them.

Already provided one quote and explained i don't currently have access to other sources I've come across (of which i haven't kept a record). Several references in old books i no longer have plus references in newspaper reports in the 19th century which i would have to pay to access.

In the case i quoted which i have researched, there was absolutely no suggestion that the barge was damaged and unseaworthy. Indeed, her mast and rigging was still standing

However, i am reminded of a known (and again documented) problem with working narrowboats drying out between tides in the channel below Brentford Lock off the Thames

It was not unknown when the tide returned for a boat to remain stuck in the mud and fail to float off and then inevitably fill with water as the tide topped the gunnels (the working boatmen used to sling a heavy rope under the hull before the boat dried out which could be dragged backwards and forwards to break the suction if necessary)*

So a hypothesis might be that with flat, or flattish, bottomed boats such as barges (and many coastal merchant ships - typically East Coast colliers were flat bottomed for example) a combination of scouring and liquefaction might initially cause the boat to sink into the sand to its marks

Then, as the tide rose, suction and/or the sand solidifying around the hull might prevent the vessel refloating leading to downflooding when the tide rose above the level of the deck or openings in the hull

Subsequent tides, now scouring around a waterlogged vessel, might then lead to further sinking into the sands

* Lest you doubt this... there are photographs and first hand accounts of it happening and i have personally experienced our motor initially failing to float off the mud in Brentford Basin when the basin was refilled after a paddle failure caused it to drain overnight. Whether she would have remained stuck and flooded is a moot point cos a combination of the flotation of our butty moored inside the motor and some serious grunt from a BW tug fetched her off into deeper water.
 

Other threads that may be of interest

Top