Submitted by LilyFish- t3_10c73wv in askscience
Things like aircraft carriers and container ships are already so huge, I’m wondering if it would theoretically be possible to build a ship the size of an entire city, or even larger. What kind of problems might there be with that?
There is theoretically nothing stopping you from making a ship as big as you want it to be. Practically speaking, that ship still needs to fit into harbors, through canals and enter drydocks for maintenance.
Ship size is limited by the infrastructure necessary to support it, not any sort of engineering limitations.
There are engineering size limits if you want it to be seaworthy. This is a constraint imposed by how well the materials used can tolerate the stresses that the ocean applies to the hull. For example, wooden ships can’t be much larger than 400 feet. The largest wooden ship ever made was the Wyoming, and it required many pumps to keep it afloat, because the constant twisting and bending of the hull would create gaps between the boards, allowing seawater in. It eventually sank in heavy seas.
We don't build wooden ships anymore. There are no size limits for steel, and eventually the ship gets so big that weather just won't affect it much.
The Seawise Giant was 2.5x bigger than an American supercarrier. If there were a shipyard big enough to do it, there is nothing stopping us from building a ship 10x bigger, or even 100x bigger except the price tag and the lack of logical reasons to ever build such a ship due to how impractical it is
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Yes, there are upper limits, and things get difficult as you approach them. There are "softer" limits imposed by infrastructure capacities, "firmer" limits imposed by seaworthiness considerations, and finally hard limits due to material properties and the forces involved.
Others have covered infrastructure limits, so I'll begin with seaworthiness. Bigger ships are more fuel efficient due to the square cube law, and industry has pursued that advantage by increasing size dramatically. But bigger ships require more steerage way, and are less controllable at low speeds. They also need more power to overcome wind and current. They are hard to control in tight harbors and locations without sea room.
The final limit is materials. Humans approached the upper limits of wood ship size, and the biggest wood ships had considerable hull volume devoted to reinforcing frames, stringers, laterals etc. All necessary to deal with the unequal forces imposed on a ship's hull. Not only by wind and waves, propulsion, but by the inequal buoyancy inherent in making something pointy that will go through the water efficiently. There is less buoyancy at the thin ends than amidships, and over time and constant movement that causes wood (and metal) ships to "hogback", where the bow and sterm droop and the middle rises.
We never solved the issue with wood construction, we simply found stronger materials. First iron, then steel, and now higher strength steels.
But the bigger the ship, the bigger the forces, while the tensile strength of steel remains about the same. To prevent buckling under dynamic loads, more and more payload consuming reinforcement has to be added inside the hull, until like their wood forebears, it becomes impractical.
At that point, maybe we'll find a new material again, and start over with a brand new limit.
They already make ships that are as big as cities, have you ever stood next to a large cruise ship? They're way bigger than you think, larger than freight ships and air craft carriers, and they can house thousands of people.
The largest cruise ship in the world is a cruise ship called Wonder of the Seas, it's *1,187.8 feet long (that's almost 1/4 mile) and can carry up to 6,988 passengers.
The wonder of the seas is large, but not quite that big. 1188 feet instead of 1888, which is 362m. Still very long, but not the longest ship in the world.
Whoops, thanks for the correction!
You might also correct "almost 1/2 mile" to "almost 1/4 mile".
Wikipedia has a list of the longest ships and the longest is an oil tanker that was 458.46 m (1,504 ft) long.
Are there quarter-mile cities??
Defining what a city is, is a wee bit more complex than measuring its length. But to answer your question, the worlds smallest city that has record of its size is Hum, Croatia and its only a little more than 4 sq km so it reasonably could be as little as 1/4 mile long, and it has a population of 20 as of the 2011 census.
Vatican City is a bit more than half a mile long and just under 1/2 square miles area.
Just to save other europeans some time: 1,187.8 feet is around 362m (that's almost 0.362km)
To extrapolate very very far....
If you scaled up an ordinary shaped ship, to truly enormous bigger than would fit in any earth sea, you'd run into this...
https://en.wikipedia.org/wiki/Triple_point#High-pressure_phases
...where it's sort of no longer "floating".. it's bottom is resting on a somewhat weird solid.
There are material limits to how large you could make something. The compressive strength and the tensile strength of materials would be the main limiting factor. Going beyond those limits and the structure would collapse or fall apart under it's own weight. If you went to space you could theoretically make much larger ships, but they would have the same limits in their material properties and would have to be mindful of the inertial forces when maneuvering the ship. The wrong gravity well and everything would rip itself apart.
Just think about the largest buildings in the world, why is it so difficult to build the tallest building? Now imagine that building moving around bobbing on the ocean.
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I suppose one "floor" still has to carry the weight if all the floors above it, same as with any building. Just replace the ground with the hull.
Also, from what people have stated elsewhere, supposedly the distribution of the water pressure actually isn't all that even.
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It depends on what kind of ship. If you mean ocean vessel then yah there are limits. If you mean an airplane driven by fossil fuel then yah. If you mean a space vessel that uses gravity manipulation to create lift and gravity for thrust then there is no limit so long as it isn't within our atmosphere. The only limit then would be if we were talking something like...the moon size where it's own gravity would cause compression
ncc81701 t1_j4f4wyz wrote
It depends on what you call a ship. Theoretically you can just tie a bunch number of ships together and make it into a really big ship. Floating bases with some limited propulsion have been proposed before to pre-stage logistical items for the US military. In WW2 the British had the idea of either co-oping an iceberg or build one with ice+wood chips that would be the size of a small island to serve as an aircraft carrier (Project Habakkak). The question is whether you'd still consider these things as a ship, if you do count it as a ship then there's no reason why you can't tie enough ships together to fill all of the oceans theoretically.
Generally the limit to the size of a ship hull (and thus the upper limit of an independent ship hull) has more to do with the size of port facilities, dry docks and canals. You can really only build a ship hull to a size that will fit in your biggest dry dock because otherwise you wouldn't be able to launch the ship and put it into the water once it's done. Even if you build a ship that's bigger than any dry dock by building it in a temporary coffer dam or something, presumably you'll eventually need to bring a ship into a dry dock to perform maintenance and repairs on the hull so you don't really want to build a ship any bigger than what your biggest dry dock can support.