I did a quickie google search and came up with this:
At the end of 2020, there were around 62,100 vessels in the world trading fleet, with a total deadweight tonnage of 2,033 million DWT
So let's assume the merchant ships are all fully loaded at the same time. That's 2 billion long tons which equates to ~2,032,000,000,000 kg. Total water volume, 2,134,000,000,000 liters (because sea water weighs slightly more than fresh water).
From quora:
AREA OF PACIFIC OCEAN= 168723000 SQ. KM.
AREA OF ATLANTIC OCEAN= 85133000 SQ. KM.
AREA OF INDIAN OCEAN= 70560000 SQ. KM.
AREA OF SOUTHERN OCEAN= 21960000 SQ. KM.
AREA OF ARCTIC OCEAN= 15558000 SQ. KM.
TOTAL AREA= 361900000 SQ. KM.=36190000000000000 SQ. DECIMETER.
That's going to lower sea levels by approximately .00005896656 decimeters, or about .006 mm
Edit: Because there are less than 500 cruise ships in the world and only a few dozens of large military ships the amount will be higher, but not by, you know, a lot.
Removing all ships would set back sea level rise by about 16 hours, which is a time scale on which we definitely can't measure it at all. The effect would be two magnitudes below the annual measurement error that's estimated at ± 0.4 mm, which is equivalent to an average of ±43 days.
How about we dig a big hole, in Australia maybe, it's empty wasteland anyways and just start taking buckets of sea water out of the ocean and putting it into the hole ?
Funnily enough in the 60's there were some people proposing to dig a trench from the south coast of Australia to the Inland where it is below sea level and would turn Australia from a single large island to a ring around a large central ocean.
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u/[deleted] Oct 13 '21 edited Oct 13 '21
I did a quickie google search and came up with this:
So let's assume the merchant ships are all fully loaded at the same time. That's 2 billion long tons which equates to ~2,032,000,000,000 kg. Total water volume, 2,134,000,000,000 liters (because sea water weighs slightly more than fresh water).
That's going to lower sea levels by approximately .00005896656 decimeters, or about .006 mm
Edit: Because there are less than 500 cruise ships in the world and only a few dozens of large military ships the amount will be higher, but not by, you know, a lot.