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According to Statista, as of January 2017, there are approximately 52,000 ships currently operating in the merchant fleet and 11,000 of these are considered bulk carriers.

How many ships are there in the world? The number of ships in the world exceeds 50,000: As of January 2017, there were 52,183 ships in the world's merchant fleets. General cargo ships are ranked as the most common type of ship in the global merchant fleet, accounting for about a third of the fleet: There were almost 17,000 such ships in the merchant fleet as of the beginning of 2017.

According to Wikipedia, the Batillus class bulk carrier, unloaded, displaces 77,300 tonnes of water and 630,962 tonnes when under a full load.

  1. Assuming a range between 850,300,000 and 6,937,612,000 tonnes of displaced water, what would be the acceptable average range of water that could be displaced by the merchant fleet during daily operation?

According to Ocean's Depth and Volume Revealed - Live Science, the ocean's volume is approximately 1.332e+18 cubic metres

A group of scientists used satellite measurements to get new estimates of these values, which turned out to be 0.3 billion cubic miles (1.332 billion cubic kilometers) for the volume of the oceans and 12,080.7 feet (3,682.2 meters) for the average ocean depth.

  1. How much does that displaced water raise the sea levels?
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    $\begingroup$ You don't actually need the ocean volume. Just divide the total volume of displaced water by the surface area of the oceans and you have the answer to question #2. $\endgroup$
    – gerrit ♦
    Jul 4 '18 at 15:42
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    $\begingroup$ I don't believe that there are only 52k ships in the world. It probably means "...over a certain tonnage", or "...on a given set of registries", or some such. Interesting side-question, relevant to this one (but off-topic here): What's the size distribution of the world's shipping? Is the total tonnage dominated by the giants, or by the much larger number of smaller vessels? $\endgroup$
    – Semidiurnal Simon
    Jul 5 '18 at 12:35
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    $\begingroup$ The Statista report said the number exceeded 50,000 and 52k ships are in the merchant fleet. I agree there are likely many more as there are about 10k military war ships and a plethora of pleasure crafts. $\endgroup$
    – Chimera.Zen
    Jul 5 '18 at 13:13
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    $\begingroup$ The size distribution is also something I was looking into to try to determine a working range, but I settled on worst case and proceeded on the assumption that all 17k merchant cargo ships are supertankers and one fully loaded supertanker likely displaces the same as all of the smaller vessels. For curiosity sake, I'd really like to know the answers to your questions as well lol $\endgroup$
    – Chimera.Zen
    Jul 5 '18 at 13:17
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    $\begingroup$ This is now answered at what-if.xkcd.com/33 ! About 6 µm. $\endgroup$
    – gerrit ♦
    Jul 27 '18 at 18:41

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