[Evgeniy Podolskiy]

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?

[lyner]

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?

[chris]

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

[lyner]

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.

[Chemistry4me]

Here is a similar question:

How much is the sea displaced by boats?

[daveshorts]

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.

[lyner]

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 ??