How much would sea levels fall if all ships were removed all at once from the oceans of the world? Far less than you might think.
To put this in content, according to UNCTAD, in January 2011, there were over 100,000 seagoing commercial ships in service, with a combined capacity of around 1.4 billion deadweight tons. According to calculations run by the “What if ” website, if all the worlds ships were to be removed at the same time, the sea level of the worlds’ oceans would fall by “about six microns—slightly more than the diameter of a strand of spider silk.” Click here to read more. Thanks to Brooks Rowlett for pointing out the article on the MarHist list.
Deadweight is more or less cargo carrying capacity of a ship for weight-limited cargo, ie, stuff that brings the ship down to her loadlines before cubing out. Actual displacement, which counts the total weight (ie volume displaced) of the ship would be greater because it includes the cargo plus the weight of the hull itself. OTOH, while tankers and ore carriers are weight-limited, container ships and car carriers are volume-limited. Anyway it doesn’t make any difference.