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Let's say Earth suffered some technological catastrophe and the planet is now entirely or almost entirely only water and at today's commercial technological level. Putting aside the reasons and consequences of the apocalypse, people now live exclusively on ships, specifically big tanker/oil ships, that which concerns me is if linking/joining/tying a lot of such ships together is a good idea? I have been told it won't be such a good idea due to storms, but I want to know are there any potential benefits to such an action, as this allows people to be closer together and dramatically decreases travel time between ships (keep in mind - post catastrophe, no land, etc.).

Also is it better for ships to be long or short when faced with a heavy storm?

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Your question's title: "Is building giant ship-cities in a water world a good idea?" demands an answer that's sort of orthogonal to the actual question you elaborate, and to the answers you've gotten so far.

This rogue answer: Creatively, it's a brilliant idea. In terms of storytelling potential you have amazing scope if you can get this right.

  • In terms of contextual humans-vs-nature stress, this amps up the storytelling tension. The sea can always provide plot-driving difficulties and drama.

    I've been there personally: I was a working sailor (submarine, tugboat, and bluewater sailboat.) Scary things can happen in a big hurry.

    On the other hand, sometimes trouble can take a long time to build. When a big storm is coming, you have time to wait and worry and doublecheck and trice everything down... and then watch it start to happen. This is some of the best dramatic tension you can get.

  • When it comes to human-vs-human conflict (not just in the obvious sense of physical combat, but social, political, psychological, and familial competition and antagonism), your opportunities are huge. You have people doing the best they can in a tough situation. You have individuals of piratical mindset. You have possible conflict for scarce resources.

    After all, protagonist/antagonist conflict is the heart of just about any story.

  • As a beautiful, harsh, and dramatic setting, the image of rafted vessels out at sea, establishing a survival society when the land has become unavailable, is really a great one. The sea is both beautiful and terrible, and ships in the kind of situation you describe have a haunting power all their own.

There. A powerful, beautiful creative concept. Just so we're clear. :-)

Now, to, you know, actually answer the question you're asking...


Previous answers have done a pretty good job of considering practicalities. I'll add my US$0.02 on some of these:

  • @PeterMaisar:

    "And of course with no dry docks and no repair facilities it will be only a matter of time until your ship will sink, one after another."

    This is an extremely important consideration. Until you've seen it at work, it's hard to grasp just how incredibly corrosive salt water is to steel. Since we're talking steel ships here, it's very hard to see how this concept of building your infrastructure out of tankers and aircraft carriers would be sustainable.

    You could posit some kind of floating dry dock that would be a part of your flotilla/raft/floating city, but that's got a couple of severe drawbacks.

    • First, it's a terribly difficult engineering problem. All of these big ships are built and refitted in huge-ass shoreside graving docks. A floating dock big enough to accommodate these huge ship hulls is not very practical:

      • It has to be even bigger than the ships it services;

      • It will probably have major seakeeping issues. Large oceanic waves would create twisting stresses on the comparatively fragile hulls characteristic of floating drydocks. Making them big enough to accommodate huge ships will make them fail and break up in short order.

    • Second - and most fundamentally important - floating drydocks only kick the can down the road, because they themselves are subject to rust.

      This is perhaps some virtuous Worldbiolding.SE bait. Hopefully some of the good people here will want to come up with some good answers. However, until this one is solved, the entire project is doable only in the short run.

      Of course, if that's OK for your storytelling purposes, it becomes a feature not a bug. :-) MOAR DRAMA is good.

  • @CortAmmon:

    Well rafted ships survive better

    Rafting does two important things. One is that it decreases the distance any boat can travel before smashing into another boat. This is counterintuitive, but it works like leaning into a punch in boxing. It decreases the distance the other boat has to accelerate before it hits you. Your boat will be peppered with smaller hits, but hopefully avoid a fellow boat being smashed into you.

    Yes, absolutely. A good description.

    However, it's not all fair skies and following seas.

    Rafts are good for big waves, up to a point:

    A raft of vessels has one huge advantage compared to single hulls when the waves start getting big: A raft is flexible. you can have a raft that covers acres and it will conform to the surfaces of even immense waves.

    That said, there's a limit: If the steepness of the wave face exceeds the working tolerances of the vessel-to-vessel flexibility of the raft, there would be a catastrophic failure. I'm not conversant enough with naval engineering to make any suggestions about how that limit is computed; but it seems likely that gales and hurricanes would exceed the integrity of big ships rafted together, no matter how cleverly it was done.

    And then, there's also the occasional Rogue wave to worry about... really, rafts of large vessels in the open ocean would not survive too well, over time.

    Rafts are awful for big waves:

    The other thing about rafts, which can be a huge disadvantage in a heavy seaway, is that they cannot maneuver as a unit. What this means is that the ability to turn your bow into the wind/waves is no longer there when you're rafted. Each vessel is going to have to take the waves however they come:

    • bow-on (good),

    • dead astern (not too bad),

    • off the bow or on the quarter (worst forces on the cabling joining adjacent ships), or

    • on the beam (very bad.)

    Another concern: an independent ship under way has the option, not just of maneuvering to put the bow into the wind, but of turning to run before the storm. If you've got a 90 knot wind, and your vessel can make 10 knots, then running downwind you are only dealing with an 80 knot wind.

    That might not sound like much, but it's actually a pretty big deal in terms of moderating the forces on your vessel.

    (Note that this may not be good: sometimes running downwind in a storm will change the way the waves stress your hull in a bad way. Still, any ship captain will tell you that it's a good thing to have the option...)


All in all, I'm starting to have serious concerns about the feasibility of your idea.

I think that the fundamental creative vision is (as mentioned above) pretty wonderful. However, strictly interpreted, your particular scenario - lots of very large ships rafted together - seems unworkable.

There are some things you could do to fix it from the standpoint of practical shipbuilding and seamanship, if you're willing to relax some of your requirements. For example:

Raft dedicated components rather than big ships

It's not at all hard to devise modular floating structures that would raft together nicely. Because they wouldn't have the initial design constraints as independently operable ships, they could be incredibly superior for rafting purposes.

  • Really, these could be little more than floats with strong frameworks. Probably with decking or other minimal superstructure.

  • You could raft them together to create very rugged floating docks, even ones that sprawl out over a lot of area. It would be possible to dock smaller vessels at such a raft; and therefore possible to have the tankers and such keeping station (or remotely ingeniously moored), with small craft going to and fro. This would leave the big ships free to move away and operate independently in the event of a storm. This would preserve that particular conceptual element (of which I remain very fond.)

  • They could be built of a range of materials that wouldn't be as vulnerable to rust as steel hulls.

  • They could, and should, be small. They would accordingly not require the same massive drydocking capabilities as preexisting tankers/aircraft carriers/container ships.

  • This would make an excellent at-sea rendezvous/port for inexpensive small sailing vessels.

Consider semi-submersible large vessels/structures

Semi-submersible hull design is capable of amazing stability in high seas. This is achieved by having all significant buoyancy in the craft concentrated in underwater pontoons. The buoyancy provided by the pontoons remains the same when big waves pass overhead: submerged is submerged.

The pontoons are joined to a free-standing superstructure that remains above the water's surface at all times. Superstructure and pontoons are joined by strong struts that

  • do not show much net buoyancy change as the waves pass among them;

  • do not provide much of a surface for waves to break against, minimizing wave impact and the dynamic stress of wave action against the vessel.

I have personally seen this principle in action. Working on a submarine doing scientific experiments with FLIP, I was lucky enough to see FLIP holding dead still in heavy seas. ("Lucky" in relative terms. We, diesel-electric and therefore operating on the surface most of the time, were rolling all over the damn place.) There's a bit of footage in this video starting at around 3:40. Yes, it really was like that: FLIP holding stock still in big swells.

Made a believer out of me. :-)


Yes, you can do this, sort of.

You need to make at least the following changes to your premise:

Don't raft big ships together in open ocean. Have them together as a flotilla, working together, acting as motherships for smaller working vessels.

Treat the oil-tanker floating city/colony as a temporary thing, working towards something that can be sustained over time. That in itself could be a dramatic decades-long process.

A set of modular rafting floats, with some semi-submersible vessels at the center, could, over the long term, be the kind of floating city that you are asking about.

I hope?

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  • $\begingroup$ Gosh! I am definitely surprised I am the only one who up voted this answer. You put a lot of effort into it. $\endgroup$ – JDSweetBeat Mar 18 '15 at 18:12
  • $\begingroup$ Thanks @DustinJackson; sometimes the answers just demand to be busted out. ;-) $\endgroup$ – Bill Blondeau Mar 18 '15 at 21:45
  • $\begingroup$ Go-o-o-o-o-od, DAYUM! I'll be damned if that is not one of the best, most elaborate and well thought-out answers i have ever seen in the whole exchange! :D I'll cerainly accept some of your suggestions and make some amends to my original idea. It is really nice to have some input from a person with hands-on experience with the subject. $\endgroup$ – mathgenius Mar 19 '15 at 10:14
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Better starter floating city than tanker would be nuclear-powered aircraft carrier. It already has living quarters for some 5-6K people and own electricity.

You are right, storms would break any chains/links between such linked boats. In storm you want to face towards waves, and any jerk from other boat to side could be deadly.

Longer ships with higher deck (farther from the water) like aircraft carrier should be able able to deal with storm better than ships like tanker with less above-water supersturucture. You point nose of the ship toward waves to split them, you don't want to get wave from one side.

And you can also build fields to grow some potatoes on that huge deck.

After thinking some more: with no land, hurricanes would be devastating, and waves they whip would circle the globe multiple times with no shores to stop them. So rogue waves would be more common, and much more devastating. Just fair warning.

And of course with no dry docks and no repair facilities it will be only a matter of time until your ship will sink, one after another.

You can build dry land using artificial reefs - biorock - artificial coral reef in shallow seas like Saya de Malha Bank: "bank covers an area of 40,808 km2 with depths from 17 to 29 m"

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  • $\begingroup$ I'd question the hurricane thing, because their typical path is to curve from the tropics to northerly lattitudes. So a hurricane starting in the eastern Pacific doesn't often run all the way to Asia, gaining strength all the way. Here's a link to some nice images of hurricane tracks: wunderground.com/hurricane/ep2013.asp $\endgroup$ – jamesqf Jan 2 '15 at 21:06
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    $\begingroup$ I am aware that hurricanes curve north (or south on southern hemisphere). But the waves they whipped up will circle the globe, and interact with other waves. $\endgroup$ – Peter M. Jan 2 '15 at 21:10
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    $\begingroup$ I don't think that would happen. A hurricane is a fairly localized disturbance (they don't have a great 'fetch: en.wikipedia.org/wiki/Fetch_(geography) ). That is, an eastern Pacific hurricane doesn't usually contribute much to waves in the western Pacific, even though there isn't much land between. You might get big waves from winds constantly blowing in one direction, like the 'Roaring Forties' (en.wikipedia.org/wiki/Roaring_Forties ) of the southern hemisphere. but I don't think you'd see them at lower latitudes. $\endgroup$ – jamesqf Jan 2 '15 at 23:29
  • $\begingroup$ That's exactly my point. Constant winds from 'Roaring Forties' would whip waves (and we would have also northern forties), and these waves would interact with waves whipped by hurricanes into unpredictable rogue waves. Today, continent extinguish lot of wave energy. In OP's world, such wave energy would accumulate and rogue waves would be substantially bigger danger than it is now. $\endgroup$ – Peter M. Jan 2 '15 at 23:38
  • $\begingroup$ I think, though, that you would only get those winds in the '40s (and higher), not in more tropical latitudes. After all, we do not get greater wave/storm action in the tropical & subtropical Pacific than in the much more constricted north Pacific, or north Atlantic. But you'd really need a good global climate model to get an accurate answer. $\endgroup$ – jamesqf Jan 3 '15 at 19:17
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Two questions to answer:

Large ships fare better in heavy weather

The thing which sinks a ship is not the height of the waves, but how the waves act on the ship. The larger you are, the more you can ignore small waves, and the more you are in a position to be able to right yourself afterwards. Life on a carrier is surprisingly smooth because there's just so much mass damping out the waves, and so much length averaging out the small waves.

Captains are taught to turn the bow into a wave if reasonable, because it makes their boat effectively longer, and thus more stable versus that wave.

Well rafted ships survive better

Rafting does two important things. One is that it decreases the distance any boat can travel before smashing into another boat. This is counterintuitive, but it works like leaning into a punch in boxing. It decreases the distance the other boat has to accelerate before it hits you. Your boat will be peppered with smaller hits, but hopefully avoid a fellow boat being smashed into you.

I don't have any google research to defend this, but I think a raft could also act much like a larger hull, providing extra stability. A wave which might be sufficient to capsize a single vessel might be held upright by its fellow boats. However, I am less certain of whether this affects the edges.

The major advantage of rafting is sticking together

A powerful storm at sea is well beyond anything we land lubbers can comprehend. When a storm like that comes your way, you will yield to it. Storms like this can tear fleets asunder and scatter them across hundreds of square miles, if not thousands. Reconvening could be a monumental effort.

This was a much larger issue before GPS and radio, but it's still an issue for a city that needs to be interdependent to survive.

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  • $\begingroup$ Regarding your point about storms: I don’t know about you, but this landlubber is used to tornadoes passing through the city fairly frequently. $\endgroup$ – Molag Bal Jan 2 '15 at 19:57
  • $\begingroup$ @yellowantphil: I have to admit, as I wrote that, I was curious if it would qualify as flamebait for someone who lives in a tornado region. Tornado are so... precise, compared to the average storm off the Cape of Good Hope. They're tricky to compare! $\endgroup$ – Cort Ammon Jan 2 '15 at 20:02
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    $\begingroup$ Decent size hurricane can completely devastate several thousands of square miles or ocean (remember that ocean ADDS to hurricane power, after landing hurricane starts dissipating), and might contain a dozen of tornadoes. On such water-only planet hurricanes would be devastating, and waves would circle globe multiple times with unpredictable results. $\endgroup$ – Peter M. Jan 2 '15 at 20:13
  • $\begingroup$ Yes, tornadoes are tricky to compare to other storms. But a hurricane spawning tornadoes on a water planet sounds... worrying. I think I would want a submarine to get out of the way of that storm. $\endgroup$ – Molag Bal Jan 2 '15 at 20:22
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There's a big unknown in the specification "entirely or almost entirely only water" of the planet and that is: the depth of this water.

I'd argue that with a low depth (say a few hundred meters or so) it is both feasible and useful to build sturdy constructions founded firmly on the ground and with a height well above any major waves to be encountered (the issue of large waves and never slowing winds are covered in the other answers). Those structures could be the size of reasonable large cities. An example of this type of structures made with todays technology are fixed platform oil rigs. As a sidenote: a variety of oil platform types, e.g. offshore platforms, semi-submersible platform and large gravity-based structure could give valuable insights with respect to the question (see Wikipedia).

If the depth of the water prohibits such structures it's also conceivable to build submerged structures that at least do not have to face the issues of monster-waves and hurricanes. This of course comes at a high additional engineering cost. However since mining of raw materials will most likely have to be done at sea floor this field might develop faster than now.

Also maintaining "today's commercial technological level" if living only aboard some ships will be quite a challenge, e.g. putting a semiconductor fab and its whole supply chain on ships...

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