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General Science => General Science => Topic started by: Evgeniy Podolskiy on 07/03/2009 12:30:01

Title: Do ships raise sea level?
Post by: Evgeniy Podolskiy on 07/03/2009 12:30:01

Evgeniy Podolskiy  asked the Naked Scientists:
   
Every ship has few thousand tons displacement. How large the contribution of all ships to the global sea level rise? Is it really negligible?

Of course it is incomparable to the size of icebergs but still interesting...

Cheers,

Evgeny Podolskiy
Nagoya University
Japan

What do you think?

Title: Do ships raise sea level?
Post by: lyner on 07/03/2009 13:07:26

A finite amount but very very small - a molecule or two, I should imagine.

It made me think of the situation on a canal aquaduct. How does the load vary when a boat is going over an aquaduct? When do things change, if they do?

Title: Do ships raise sea level?
Post by: chris on 07/03/2009 16:30:20

That's an excellent and intriguing point - what does happen to the load on the aqueduct when the boat goes over? Presumably it stays the same?

Chris

Title: Do ships raise sea level?
Post by: lyner on 07/03/2009 18:34:08

Yes but, when the lock opens to let a boat through, the level may rise or fall and then the load may change a bit. But I don't think the presence or absence of boats in the lock will make any difference either.
It must make life a lot easier for engineers planning the carrying capacity of aquaducts.

Title: Do ships raise sea level?
Post by: Chemistry4me on 07/03/2009 21:50:12

Here is a similar question:

How much is the sea displaced by boats? (http://www.thenakedscientists.com/forum/index.php?topic=19626.0)

Title: Do ships raise sea level?
Post by: daveshorts on 10/03/2009 09:43:50

Quote from: chris on 07/03/2009 16:30:20

That's an excellent and intriguing point - what does happen to the load on the aqueduct when the boat goes over? Presumably it stays the same?

As a boat goes over the load stays the same as the water displaced is the same weight as the boat. But when you put the boat in the water even if it is miles away this will push up the level of the canal slightly which will increase the load on the whole canal, including the aquaduct.

Title: Do ships raise sea level?
Post by: lyner on 10/03/2009 09:54:45

The level of each canal pound is controlled (though, of course, not to fractions of a mm in practice) using weirs* so, when a canal boat is launched, the displaced water would theoretically overflow, leaving the level the same as before.

* i before e except after c ?????