So after watching Supersize Earth on BBC last night and seeing those gigantic ships, it got me thinking…

If you took out all of the ships currently in the oceans over the world, would global sea level fall? Thinking along the lines of law of Archimedes and all that…

Of course.

But if you put them all on the land, would the land sink?

Theoretically yes, but not in a way that anyone could measure as the sea has a habit of moving about a bit round the edges which would make measuring such a small effect impossible. While there are some ships that are very big but theres not really all that many ships in total (of any size) in relation to the volume of the ocean.

As an aside – the issue of sea levels rising in relation to global temperature isn’t about the ice caps melting into the sea, but of the whole ocean warming and expanding

But if you put them all on the land, would the land sink?

Hmm, good point. I seem to recall something from a geolgy lecture that referred to the weight of mountains pushing down on the earths crust. So maybe…?

Yup, water would be displaced so sea level would rise. No way of measuring accurately, if at all mind.

If you put them all on land then there would be some isostatic change because your loading the crust with weight (although I imagine you would have to put them all in one place to make that work).

Theoretically yes, but not in a way that anyone could measure as the sea has a habit of moving about a bit round the edges which would make measuring such a small effect impossible.

Sneaky edit there 😉

Anyway, I thought global sea level change was measured in m so why not?

Hmm, good point. I seem to recall something from a geolgy lecture that referred to the weight of mountains pushing down on the earths crust. So maybe…?

all the metal will have been mine/quarried on land so the land would only sink back to where it had been prior to the extraction – assuming you put everything roughly back where it came from and assuming that the quarried areas have risen as a result of the extraction. If you piled everything up on the island of Sark that would be different though (and the Barclay Brothers would be furious)

All the worlds oceans contain 1.3 x10^21 litres of water.

The worlds largest ever ship when fully loaded displaced 5.7 x10^8 litres of water.

When it was scrapped the worlds sea level will have fallen* by 0.00000000004% or 1.6 nm

You would need over 600,000 of these ships to register a 1mm drop in sea level. These boats would have a deck area 948 times the size of Wales covering 5% the size of the worlds oceans.

So to answer the question yes, the sea level would fall but by such a vanishingly small amount that you couldn’t even measure it, let alone notice any effect.

*I’m ignoring the land sinking beause it make the equations less fun and we’d never be able to compare anything to the size of Wales

These boats would have a deck area 948 times the size of Wales

Excellent use of the SI unit of size there

Oooh.. go on then.. I’ll do this one since it’s Friday.

1.12bn tonnes of shipping in the world fleet in 2009.

So that’s basically 10^12 kg

Mass of world oceans is about 1.4×10^21 kg

So the mass of shipping is 10^-9 x world oceans.

Which is 0.00000001%

Put another way, if you took all the ships out that would be like removing 10^12kg of water from the oceans, or 10^9 m3.

The surface area of the oceans is 3.6X10^8 km2, or 3.6X10^14 m2

So if you spread 10^9 m3 of water over 3.6X10^15 m2 you get a depth of 2.7×10^ -7 m

Which is 270 nanometers.

Or about a tenth the thickness of spider silk.

Given that the tide comes in and out anywhere between 1 and 10m, and even small waves are 0.1m high, you’re not going to notice 🙂

the sea has a habit of moving about a bit round the edges which would make measuring such a small effect impossible

They measure average sea levels very accurately with satellites. From Wiki:

From 1950 to 2009, measurements show an average annual rise in sea level of 1.7 ± 0.3 mm with satellite data showing a rise of 3.3 ± 0.4 mm from 1993 to 2009,[6]

So they can measure remarkably accurately but not, of course, accurately enough for this.

So not only have we answered a wonderful question re sea levels we’ve also had a definition of second best … Thank you Mols 😉

(and yes you’re right I wouldn’t have know where to start, but next time please use the SI unit in your working 😀 )

Perhaps naive of me to think this might run on and on. Instead a bombardment of complicated (to me) maths has answered the question.

STW does amaze me sometimes 🙂

I think the original Q stemmed from too much red wine and watching the programme where China (or was it Korea?) are knocking out those mega container ships at a ridiculous rate of something like every 3 weeks. I couldn’t quite comprehend the scale and speed of production of something so vast.

Edit: And why is it Wales is always used as a SI unit? Surely other principalities exist? 🙂

If only they could knock them out a bit quicker we could tie them together and build a road over the top……

I’m worried there may be a mistake in jfletch’s calculations – probably due to an error converting from SI to Imperial units.

If the ships occupy 5% of the ocean’s surface (which is what 948 Wales’s do) and raise the sea level by 1mm of sea water (and I agree that ~600,000 of these ships would do) then surely they are only floating with 20mm submerged. Are we not nearer 1 Wales for all these boats?

If the ships occupy 5% of the ocean’s surface (which is what 948 Wales’s do) and raise the sea level by 1mm of sea water (and I agree that ~600,000 of these ships would do) then surely they are only floating with 20mm submerged. Are we not nearer 1 Wales for all these boats?

You weren’t supposed to check the workings.

I think I might be out by a factor of 1000 with the boats to Wales conversion so its 0.948 Wales.

And that makes the boats ~20m submerged which is correct as the draft is 24m but the sides aren’t straight.

Even the biggest ships don’t have a draft of 24m…

Nice working out, chaps. You guys have seen http://what-if.xkcd.com/, right?

Even the biggest ships don’t have a draft of 24m…

http://en.wikipedia.org/wiki/Seawise_Giant

Read it and weep

Nice working out, chaps. You guys have seen http://what-if.xkcd.com/, right?

Yes, it’s my new favourite website and as I was doing the calculations I thought “what would happen if a cat just added some zeros”!

and with a draft of 24.6 m (81 ft), she was incapable of navigating the English Channel[dubious – discuss], the Suez Canal or the Panama Canal.

Fair enough. But totally useless…

and watching the programme where China (or was it Korea?) are knocking out those mega container ships at a ridiculous rate of something like every 3 weeks.

Are they still producing those ships even now – I needed to buy a shipping container this time last year and there were non to be had – completely non to the extent that all the dealers I’d bought from in the past had shut up shop. The shipping lines had apparently panicked about the economic climate and stopped manufacturing them. A couple of years earlier I was able to buy them by the dozen for £800 each (pretty much their scrap value) then all of a sudden there were only a handful in the country with asking prices in excess of £2k for a really ropey one. So if the shippers have stopped making containers its a surprise they are still making the ships.

If I had a time machine I’d be heading back to 2010 to buy containers to sell in 2011. 🙂

I think I might be out by a factor of 1000 with the boats to Wales conversion so its 0.948 Wales.

So to the nearest whole unit:

You would need over 600,000 of these ships to register a 1mm drop in sea level. These boats would have a deck area 948 times the size of Wales covering 5% the size of the worlds oceans.

It was meant to be.

I’m ignoring the land sinking beause it make the equations less fun and we’d never be able to compare anything to the size of Wales

If global warming causes land shrinkage, … Oh God, I daren’t even ask it 😯