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Given current technology, ten years, and an infinite amount of money, would it be possible to build an aircraft carrier with a 7,000-foot-long (2,200 meters) flight deck? This is about seven times as long as typical aircraft carriers. Catapults and other equipment are not required.
I'm tagging this as military because most if not all aircraft carriers are military ships, not because this will necessarily be used for military purposes.
Yes, it's possible. WillK wrote the basic concept: line up separate units, connect them together and put a runway over the whole. However, this poses huge problems if you use normal ships, because of the way they heave in the waves. Even in calm seas this is a considerable amount of motion (it's hardly perceptible for a human because it's so slow, but that's no help for a plane trying to roll from one ship to the next).
In principle it would be possible to connect the ships rigidly together to suppress this, but that would require infeasibly strong joints, because such big ships have enourmous leverage. Probably the hulls themselves would need to be strengthened too. Flexible joints would be more promising, since they avoid having to fight all the force of the waves – but making those reliable would be a challenge of itself, and it would cause other problems for the aircraft.
Fortunately, the situation if better if the individual units are semi-submersible platforms: those generate most of their lift several metres below the surface, which means they're much less affected by waves.
Another advantage is that these platforms are already designed very heavy, since moving efficiency is much less of a concern than for military vessels. This means they're also less affected by the weight of the airliner. And oil companies already have a lot of experience in connecting such platforms together, so you'll be able to tap into that expertise.
The way I'd design this is like this: first create the runway as a relatively light barge, consisting of beams that are in the lengthwise direction only connected with thin-ish (like, 5 cm) steel plates and a tarmac layer. This way, the structure stays flexible enough so it doesn't need to fight the waves by itself – though of course it also wouldn't be able to support an airliner. Then, after towing it to deep enough waters, you rendezvous with the semi-submersibles, which would either dive underneath the runway to support it directly from below, or attach to the protruding beams on each side. It would possibly be best to make these connections still somewhat compliant, e.g. with air cylinders, but I'm not sure.
After making all the connections, you lift the runway above the level of the waves, either by pumping ballast out of the semi-submersibles, or increasing the piston pressure or with strand jacks. The end result is a runway that is supported strongly from the submerged lifting bodies, but with clearance in between so that the waves can harmlessly run underneath it – at least in calm waters. Whether this structure would be able to survive a storm on the open sea, I'm not sure about.
It would have a lot of similarity with a pontoon bridge. The largest such bridge, Evergreen Point Floating Bridge, has almost exactly the dimensions you envision. It does benefit from crossing only a lake, not open sea – but I don't think that's completely necessary. E.g. Nordhordlandsbrua crosses a fjord: still not open-sea level waves, but they can already get pretty rough in bad weather.
Of course, these bridges are anchored to the sea bed, but sufficiently heavy semi-submersible bodies should get you close enough.
See Project Habakkuk
That was to be 2000 feet long, which was huge for WW II. The aim was not to be as big as possible, but to be unsinkable. Torpedoes could knock lumps off it, but it could repair itself by mixing up and freezing more pykecrete. It could even be used for landings on coasts with cliffs, just by ramming the shore, and maybe leaving a few hundred feet behind when you were done.
There was no reason to make something 7000 feet long but it could be done.
You could even have a one-use device - omit the refrigeration unit, and build it somewhere cold in winter. Something that big would take a long while to melt.
There are problems here which are difficult even with "infinite" money.
Landing an A380 on a minimal-length runway is not easy, especially since it will also be narrow compared to a normal runway. Landing it on a moving runway is going to be harder, since it lacks the responsive low-speed handling that is mandatory for carrier aircraft. The C-130 has been landed on a carrier, but it also has good low-speed handling, required for its role as a tactical military airlifter.
The A380's wingspan is 80 metres (261'8"), which sadly makes HMS Conga impractical; you're going to need 100 metres (330') width at a minimum. If something goes wrong during the braking after touchdown, the aircraft is very likely to end up in the sea: normal carrier aircraft are restrained by arresting gear, but this one won't be.
What is meant to happen to the aircraft once it has landed? If you unload and refuel it, you then need to tow it back to the stern of your carrier for it to have a chance of taking off successfully. If something goes wrong and it's immobilised on the deck, the carrier is out of action, and you may well have to push the aircraft over the side. That's harder and more dangerous for the ship with a 285-tonne (empty weight, metric tons and American long tons are very close) A380 than a 15-tonne Hornet or 19-tonne Hawkeye. This is one of the reasons the C-130 is not used for carrier deliveries: if it broke down, it would have to be discarded, since it's too big to be got out of the way of other aircraft.
Building a ship this long is not impossible but would be difficult and time-consuming. If it is built as a single rigid hull, it will have to be extremely wide and tall to avoid being bent by waves. If it's built in several articulated sections, prototyping the pivot mechanism in a smaller ship will be necessary to make sure it's strong enough. In either case, you need to build the world's largest dry dock to assemble the carrier in, which will be quite time-consuming.
Getting the ship built within ten years looks doubtful, and the use you want to put it to looks difficult and risky. Finding another way to achieve your desired outcome looks like a good idea.
From a standpoint of just making the ship longer, there's no particular limit. It's certainly possible to make a ship much longer than current maximum sizes.
The limitations are not directly on building the ship. There are other constraints and limits.
It would certainly be possible to join up a lot of individually modest floating structures. It would have to be a fairly robust join between the segments so that the weight of the plane did not depress a segment too much. As long as the water was not too rough, and you did not need this thing to be easy to move, you could build a surface that could be used as a runway. It would be something like a pontoon bridge but not anchored to the shore. You might have to split it up into segments in rough weather. And you might need a lot of tugboats to move it.
So such a thing would not be great in battle conditions. It might be useful as a temporary airport in a place with ocean but no good land area to build an airport. 7000 feet is at the low end of jet aircraft runway length. Planes like a 747 with a heavy load will want more.
It took eight years to build the USS Gerald R. Ford aircraft carrier (Nov 2009 to May 2017). But that's not telling the whole story. It took 21 years to start with a blank sheet of paper and end with a commissioned aircraft carrier. And the Gerald R. Ford is only 1,106 feet long.
Can you get 6.3X the ship with only 25% more time with today's tech? I'm having trouble believing that. The problem is that infinite money doesn't make all the other resources you need infinitely available. Ignoring completely the mind-bogglingly devestating effect this kind of event would have on any economy (even planetary), you can only get (e.g.) steel so fast. You can only transport so much at a time. You only have so much asphalt to work with. You only have so many trained people and you can only get a finite number more regardless the amount of cash you have.
It isn't just the effort needed to build the ship. it's the development of technologies needed to move it, power it, steer it, stabilize it, and a great deal more. Your question limited the answers to today's tech. When CVN-78 began, the technologies that allowed the ship to be built didn't exist. The technologies today to build a successful ship of the size you're describing don't exist.
And if that's not enough, there's feeding those people and their families. Educating their children and providing health care. It's the entire supporting economy that must be engaged. It's a nice theory to think that throwing money at it will fix all the problems, but that simply isn't true. I remember the world-wide steel availability problems that existed while China was building the Three Gorges dam. Your ship will cause problems like that, that can't be trivially solved with more money in the ten year period (now, if you had 20 years before the ten year period to prepare for this and the many other problems... maybe... maybe... there isn't a shipyard on the planet today that can build a ship this long).
So, ignoring all the problems of having an ultra-long aircraft carrier (and those answers haven't even scratched the surface of the problems), no, I do not believe it's realistically possible to crank out a 7,000 foot aircraft carrier with today's tech. Money isn't the limiting resource. In fact, there isn't one limiting resource.
And if you start making concessions (e.g., "Let's assume the 13 years of technical planning are already in place...") then there isn't a reason to ask the question.
Line them up.
https://www.navylookout.com/what-are-they-for/
Depicted: the HMS Conga. You can make a superlong flight deck by lining up a bunch of your existing aircraft carriers. And you should.
I will accept my 1% share of the infinite amount of money, thank you.
One way would be to make a lot of smaller ships which had big flat sections in their middle between any forecastles and sterncastles they might have. They would have flight decks in the flat sections. And more flight deck on each side in the form of drawbridges which could raised or lowered.
So in calm weather the ships could all be in formation parallel to each other and lower their drawbridges to meet each other to form a long runway. Presumably drones could carry cables from the tip of one drawbridge and insert them into the tip of the neighboring drawbridge, which would then winch them closer and closer until they met.
Or possibly the sections of the flight deck for use betwen the ships would be carried folded up when the ships were separated and would unfold to meet the neighboring ships when they were connecting.
Or possibly the ship would be assembled out of many floating rectangular sections which would launched separately and then meet previously launched sections and attach to them.
Each section of flight deck, hanger deck, and other decks, might be supported above the ocean by several shafts leading to hollow watertight floats. And possibly the shafts might have sections which could slide up and down relative to each other as the waves lifted up the floats and lowered them again, keeping the flight deck level. And possibly the floats might turn like giant paddle wheels to propel the giant aircraft carrier.
You could reduce the length of runway needed for takeoffs by using JATO units.
JATO (acronym for jet-assisted take-off) is a type of assisted take-off for helping overloaded aircraft into the air by providing additional thrust in the form of small rockets. The term JATO is used interchangeably with the (more specific) term RATO, for rocket-assisted take-off (or, in RAF parlance, RATOG, for rocket-assisted take-off gear).
https://en.wikipedia.org/wiki/JATO
Forward facing JATO units have sometimes been used to slow down landing aircraft.
So possibly extensive use of JATO could enable your giant aircraft carrier to be a bit shorter than it would otherwise need to be.
Of coure the best way to shorten needed runway lengths would be to only use vertical take off and landing aircraft.
Folks seem to generally discount the fact that stuff like this requires planning, and planning takes time.
Consider the history of the A380:
Granted, the A380 faced numerous random hurdles, including coordination problems among half-a-dozen Eurozone partners, org changes at Airbus, and an economic recession. Unless your project takes place in a fictional society of perfect beings, it will face its own unique, stupid hurdles, all of which will slow it down.
Blueprints take time to design. People who design things aren't just drawing lines on paper -- they are thinking through problems, solving them, and then capturing part of the solution as a physical description of the construct.
Or consider the the latest US aircraft carrier, the "Gerald R Ford" class:
If your goal were a marginal increase over previous versions, my answer would be "yes": creating an aircraft carrier that's 5% bigger probably isn't much harder, so existing techniques will work, and we can assume this project will run similar to previous projects: just under a decade.
But you're not making a marginal increase. You're building something roughly seven times bigger. This will inevitably run into new problems. It will require vastly more planning, vastly more money, and vastly more time.
I doubt it could be done in under 25 years, and that's assuming an ironclad guarantee, evident from the beginning, that all necessary funding and materials will be available on time.
Skynet could probably do it. Independent organic beings could not, at least not the first time.
Oh, and the physics is hard, so it might actually be practically impossible. Other answers go into that in detail.
Another solution would be to make a concrete boat.
If we are trying to make a sea-going platform that does not have to defend itself, I feel it could be done in the time. You are not trying to make a capital ship that could survive any attack, but a big,box that floats, and can move itself or be towed.
The Phoenix caissons that made the Mulberry harbours for the D-Day landings were 60x20 metres, and over 200 were produced in a year or so. They were made to be grounded, rather than being fastened together at sea, but this would have been possible. Fasten 40x5 of these together and you would have something 2400 * 100 meters, and 15 meters high.
This is five times as long as the largest ship ever.
