Kukri
Well-Known Member
If someone has already posted this I must apologise:
http://gcaptain.com/how-many-shipping-containers-lost-at-sea/
http://gcaptain.com/how-many-shipping-containers-lost-at-sea/
The number of containers lost at sea annually (it's fewer than you expected)
- Thread starter Kukri
- Start date
JumbleDuck
Well-Known Member
How many of them managed to float just below the surface in flagrant disregard of the laws of physics?
pvb
Well-Known Member
All depends what was in them. Containers full of electronic goods in foam-padded packaging can be surprisingly buoyant.
Regardless, it's still far too many lost containers.
Davegriff
Well-Known Member
What a confused shambolic list of figures! In any event I'd have thought that a container lost was a container lost - why differentiate losses and 'catastrophic' losses at all?
pvb
Well-Known Member
Perhaps they're trying to make the dismal figures look better than they are?
JomsViking
Well-Known Member
That is not in disregard of the Laws of Physics - Actually the Laws of physics explains exactly why this happens for some objects - Cold Water is more dense than hot Water and typically (but not always depending on the Waters salinity) the temperature falls with depth. So a container of a given bouyancy may sink in the upper layers of Water then stop. To make this even worse as conditions change e.g. Wind/currents mixes Water said container will move up and Down.
Hadenough
Well-Known Member
Ahh, that'll be one full of Yoyo's then :encouragement:
Rhyddid
Well-Known Member
It has been said to me, and I have no facts to back it up, that the refrigerated container units lost over board are likely to be more buoyant due to the insulation afforded to them. Therefore take longer to sink.
JumbleDuck
Well-Known Member
The coefficient of linear expansion of water at 20C is about 2 x 10-4 / K, so the volumetric coefficient is about 6 x 10-4 / K. A forty foot container has a volume of 77m 3 and therefore displaces 79 tonnes in typical surface seawater. The change in buoyancy with water temperature is therefore about 47 kg/K at 20C, falling to zero at 3.98 C.
However, that's not the law of physics which is troubled by claims of containers floating below the surface. Like any other floating hollow object, a container is vertically unstable because of pressure effects on the container itself. The maximum density of seawater at great depths is around 1050 kg/m3, which is only 2% higher than the normal surface density. Containers are far more compressible than that: one a container is submerged the water pressure reduces its volume, reducing the buoyancy available, causing it to move downwards where the pressure increases more, the volume decreases more, the buoyancy reduces further and so on.
To have a container float in equilibrium at any height below the surface, the container would have to have a bulk modulus greater than that of water, which is 2.2 x 109 Pa.
Some containers will float. Some containers will sink. Some containers will float, then sink. However, the notion that containers will float in equilibrium just below the surface is hard to reconcile with physics.
All_at_Sea
Well-Known Member
Lost at sea
Going north between Naples and San Stefano.......couldn't believe our eyes
Going north between Naples and San Stefano.......couldn't believe our eyes
onesea
Well-Known Member
Not going to argue there but for all your science it seems to me that with vents and holes and leaking door seals the most likely way for a container to float (if its going to) is just on the surface. Which I am sure that could be considered just below the surface (glass or container half full 1/2 empty).
Think of trying to sink a beer can (when we used to do such terrible things), you could punch holes it stick things in it but 1/2 the time the bugger remained just bobbing about 99% below the surface....
No science in my statement just an observation....
JumbleDuck
Well-Known Member
No problem there ... it's just the idea that they lurk at keel depth which I think is a but dubious.
Sailfree
Well-Known Member
Surely the term semi submerged is really describing a floating container with only say one corner on the surface similar to the hull of an upturned dinghy. Then the dinghy is mostly submerged and hard to spot. A container in a similar state would be harder to see. Therefore not semi submerged just below the surface but floating but only a small part visible.
Aeolus
Well-Known Member
Thanks to the OP - very interesting. So the chance of running into a container is much less than we hitherto thought - good!. And those evil ones lurking just below the surface, they're ever rarer - double good.
I suspect that trees and chunks of timber are a much greater threat than containers. I've certainly seen (and so far have successfully avoided) tree trunks, branches and beams that would damage my boat if I hit them whereas I've never seen a floating container.
I suspect that trees and chunks of timber are a much greater threat than containers. I've certainly seen (and so far have successfully avoided) tree trunks, branches and beams that would damage my boat if I hit them whereas I've never seen a floating container.
JomsViking
Well-Known Member
Agree, exactly why I said they might move up and down, same happens with deadlogs in BC. Btw. some of those containers are full of Styrofoam (as someone else noticed) so very hard to calculate the actual buoyancy w/o all the data - just too many parameters..