# What is the viability of trains on planets covered in water?

I want to write a science fiction book on a planet mostly covered by ocean, but I also want to incorporate trains into my story. However, it seems that with advances in ship and plane technology, trains may become obsolete. So, my question is, what role could trains possibly play in a world mostly covered by water?(It is not all water, but roughly 85%)

P.S. This is my first question so I might have gotten this wrong.

• How is it relevant how much of the planet is covered by water? Planets are huge and 15% is enough for train tracks. Trains are commonly used in sci fi, just do it. New colonies should even be pretty low tech because the lack of infrastructure, e.g. to build those nice flying cars. Maybe though it would help to know what the trains are for. Also do you mean literal trains or just long and heavy things that can get things from point a to point b? What kind of Trains? Apr 11, 2018 at 5:44
• For reference Earth itself sits at 71% water. You could probably simply sink a continent and meet your parameters as stated - some scoping down to a 'known world' and describing the shape of your landmasses (archipelago, pangaean, literally Water World, etc.) would likely greatly improve the quality of your answers Apr 11, 2018 at 6:13
• You question reminded me about "Spirited Away" where heroes go on train over water. Apr 11, 2018 at 10:40
• What we need to know is how large your average landmass is. If all the land is a single continent then there's no problem. If there's nothing more than sandy spits 200metres long then trains are less viable. Apr 11, 2018 at 13:41
• Makes me think of the Sea Train in One Piece. Apr 11, 2018 at 16:38

## 17 Answers

from wikipedia: "About 71% of Earth's surface is covered with water, mostly by oceans." So take away a couple of continents, and you have 85%.

If only Europe existed, that would mean roughly 98% of the Earth covered in Oceans and there would still be trains in it.

ETA to address comments: trains in a world mostly covered with water would have the same viability/purpose as trains have in our world. Unless all your land masses are islands with only space for one village on them.

• @Legisey Mostly just means over 50%. So, Real Subtle is just pointing out that our own world is mostly covered in water. You could have a world which was mostly land, but with no contiguous land masses larger than 16km² (about twice the size of Alderney), all seperated by at least 2km from the next parcel of land - that could be more of a trouble for trains Apr 11, 2018 at 12:51
• @Legisey, that means your real problem is with the question being badly worded and constrained rather than with the answer. Apr 11, 2018 at 13:13
• But maybe I'm the one that didn't get the question right, and the OP will be very happy with this answer. "Great I can use trains because 15% land is enough, having exactly 85% water is central in my story". Apr 11, 2018 at 13:31
• @Legisey The 85% isn't central to this answer. There isn't really a percentage at which trains stop being useful. Even if the world were 99.9999% water, that still leaves room for NYC's subway system. Apr 11, 2018 at 15:28
• Even single-village islands would have use for trains: the earliest railways were short lines connecting mines to smelters or docks.
– Mark
Apr 11, 2018 at 23:56

It largely depends on the size of the landmasses, as long as the islands are larger than coral atolls trains can be useful. Many small islands on Earth have or had trains despite people being able to walk across them in a few hours.

The Channel Islands have short railways that follow the coastline between the main port and the one or two other towns on the islands. These are generally about 6-24km long.

Some Caribbean islands have or had railways as well. The smallest one being 12km on St. Kitts.

Oceania has island railways as well, largest obviously being in Australia and New Zealand. But there are several small railways, working and abandoned, on smaller islands.

So while trains would be seen as a relatively unimportant means of transportation compared to boats and planes, they would still be useful for transportation.

I think that a specific train is going to outmatch your planes and boats: The Vacuum train.

By creating a tunnel, which seems pretty necessary anyway, and putting a maglev train into it (maglev so it doesn't create friction with the surroundings), then sucking it as vacuum as you can you can make trains go at 7000km/h through them. That kind of beats plane's 900km/h.

Build these tunnels at one specific height from the surface with as little altitude change as possible, but anchor them to the sea-floor for stability. The water deeper below the sea surface is extremely uniform between around 0 to 4 degree's (celsius), this means you suffer far less from expansion/retraction of the tubes heating up and cooling down across the day, which is kind of important when your tube spans the sea's. Since you are already sucking it vacuum anyway, it's going to be designed to withstand the larger pressures around your chosen depth so the extra waterpressure doesn't seem too problematic for a spacefaring organisation. Power it with tidal-generators at the surface and you've got a clean, solid system.

Example of proposed rail systems in large oceans found here: https://en.wikipedia.org/wiki/Transatlantic_tunnel

• I don't know enough about sucking trains to tell if anything you wrote otherwise is incorrect, however I want to comment on the 4°C because that's a common misconception. Pure water is densest at 4°C, so intuitively one would think water at low depths is 4°C when in fact it depends on where you are and how deep you are and many other factors. Here is an wikipedia article about the topic: en.wikipedia.org/wiki/Thermocline It's maybe a bit nitpicky, but if the OP wants to write a book about it, he/she better gets the facts right Apr 11, 2018 at 7:26
• Building them near the sea floor would be disastrous, complex and expensive. You want them to be at a standard depth so that the "tube" is straight and relatively near to the surface where pressure is lower and building and maintaining the tube easier and cheaper. Makes malfunctions much less instant death as well. Basically it is a floating tube that is anchored to the sea floor. I think some engineers did work on connecting Europe and North America like this, adding a link to an article about that would improve the answer. Apr 11, 2018 at 8:08
• @VilleNiemi Yeah I forgot about that when posting. I changed the post to reflect it (and Raditz his input) Apr 11, 2018 at 10:20
• Atmospheric Pressure => Vacuum = 1atm. Underwater pressure => Vacuum = 10->100->1000atm, potentially many orders of magnitude difference. Just because something is built to withstand a vacuum, doesn't mean it's built to withstand underwater pressures. This is a very non-trivial difference in possible pressures Apr 12, 2018 at 4:16
• Just for some more concrete numbers, every 10m down is 1 additional atmosphere of pressure. So at 10m down, it needs to be 2x as strong as at surface level. 100m down, it needs to be 11x as strong. From an engineering perspective, that's a huuuge difference in strength and material requirements Apr 12, 2018 at 4:45

You didn't specify how deep the water is. There was an early electric railway built in the tidal area of Brighton that ran with the rails under the sea and the cars above the surface:

http://volkselectricrailway.co.uk/history/the-daddy-long-legs/

It was very vulnerable to storms and the shifting of the coastline.

Trains are very efficient at moving things from one place to another - efficiency measured in amount of fuel required.

The limitations are that they require infrastructure (tracks) and they are most efficient the fewer stops they have (fewer points of embark/disembark).

So to make them viable in your story, the infrastructure needs to be cheap, fuel expensive, and having few points you need to connect or travel between. Building a separate transportation structure which does last mile delivery, and which can't easily replace trains will boost train usage.

The infrastructure is the difficult aspect of your water world, but if the world has shallow water between landmasses, trains on trestles over water will be faster and more efficient than boats.

So if you can design your world with shallow water, or peculiar landmasses that provide a place to put tracks (undersea ridges at continental plates - still below water, but shallow enough for tracks) then you may find that trains are a viable means of transportation of people and goods over large lakes and small oceans.

In these cases, though, ocean weather and waves become very important, and could result in some exciting scenes. Perhaps the trains may attach to the tracks more securely and are water shedding if not submarine, and perhaps the tracks are 10 meters above calm water so waves rarely reach the trains.

Yes, trains can work in a world with oceans. Like they do. Ho; hum. What is needed is awesomeness.

I propose a train which runs on a short pontoon bridge that reassembles itself in front of the moving train.

The schematic:

1: Train rolls along short bridge floating on pontoons.

2: Rearmost segment rolls forward along sister segments.

3: Moving segment overtakes train.

4: Moving segment clips in front, ready to receive train. New rearmost segment detatches and begins to move forward.

These moving segments of pontoon bridge would have submerged rudders which would swing parallel to axis of travel for motion, perpendicular to axis of travel when the train is atop.

I have depicted this with 3 segments in the interest of simplicity. A bridge with more segments would be safer and also present the spectacle of multiple segments moving along each side of the bridge at any given time.

What advantage does this have over a boat, the skeptical might ask. This system uses a train, with all train awesomeness, and which rolls along tracks as trains are wont. It does not know anything untoward is going on below. And the self-extending pontoon bridge would be great for a steampunk-type anime where you did not have to actually build it.

• So it has all the disadvantages of trains, with all the disadvantages of boats, coupled with the mechanical nightmare of connecting two tracks so the joint can withstand tons of force along with the ocean waves bending the pontoons... I like it! Apr 11, 2018 at 15:10
• While this is very imaginative, it would probably not work. I expect the whole pontoon to move in the opposite direction both because of very fast moving of the pontoon pieces to the designated place in front of the train and because of the acceleration of the train. Remember any force applied on an object causes equal reactive force in opposite direction. Sure there is some friction with water, but the whole thing would be highly inefficient. Apr 11, 2018 at 16:37
• +2 Brilliant. This could have some real world utility in a marsh world. The pontoons are light and float when unloaded and sink to the bottom when the train travels over them. They could be used to connect two land masses with a Porta-Bridge that is capable of carrying the mass of a fully loaded train in very shallow water to many destinations like a ferry rather than just one like a bridge. Apr 11, 2018 at 18:44
• @brett - my hope was that the submerged rudders would offer enough resistance to backwards movement to prevent that opposite direction movement thing. Apr 11, 2018 at 19:00
• I feel like this scheme is somewhat undermined by how if your train breaks down, as long as it's all on one bridge, it arrives at the destination anyway Apr 11, 2018 at 23:31

You could have underwater trains. Think hyperloop and such. Since your world is covered in water you cna have underwater dome stations and maybe cities as well that juts out to the ocean surface. Makes for an interesting social hierarchy as well but that's outside of your question so yeah maybe toy around with the idea for underwater trains.

• An underwater tube, tethered to the ocean floor by cables, or just suspended with giant momentum absorbing sinkers/floaters/both with very long curves & tolerance for flexing those long curves back and forth to accommodate advection forces. Feasible, assuming advanced material science capability. Apr 12, 2018 at 6:13

You didn't say your entire planet was underwater, so I assume there are landish areas.

Trains are far and away the most efficient way to move people fast.

Boats won't have speed much over 30 knots, Europe has tried with the ferries across the Baltic, Black, North and Irish seas.

If the sea is shallow, trains can cross it, as the Florida East Coast railway did to Key West.

The French have had no trouble running regular trains at 300 mph (500 mph). On a lark and with little preparation, Americans stuck jet engines on an old passenger car and shot it up to 200mph on some old track that was due for replacement.

The small size of your land area isn't a huge impediment, since railways struggle when they're too long. The Trans Siberian is an awkward operation, railways work better at 1000 miles long tops. Passenger railroads work better at 100-200 miles. That's why they work so well in Europe: countries are just the right size.

• There might even be ... (drum roll) out-landish areas Apr 12, 2018 at 6:13

There is one potential problem that has not been mentioned in the other answers and that is the amount of available resources. You will need a lot of steel (about 100 tons per kilometer for the tracks alone). Compare this to a lightweight plane or a boat which can be mostly made of wood.

Now if most of your world is at low elevation and close to the coast, any mining operation will either be rather superficial or has to deal with large amounts of groundwater seeping in from the sea. Using modern pumps and a lot of work this should be a solvable problem, however metals will be more expensive and less readily available in your world. The same holds for coal, which will hamper any sort of industrial revolution until you are able to locate and drill for oil in the sea.

Trains are not made obsolete by boats and planes, they are made obsolete by cars and trucks. Use tunnels rather than bridges to connect your land masses, as all the longest tunnels use rail. (see Channel tunnel and Seikan tunnel)

It may not fit, but what about a storm world with relentless winds and violent storms that prevent air travel and make travel using small vehicles dangerous. The rough water would also make ships dangerous and small boats impossible. You could use submarines, but trains would be more efficient.

A flat topography with few mountains to block prevailing winds could be the setting.

You could have small landmasses connected by isthmuses. cities would only be possible in the lee of rare mountains. Trains would connect those cities.

Trains require relatively flat terrain to operate most efficiently. That's because they haul huge weights with relatively little power, and so climbing gradients is relatively difficult.

Now, the sea surface is relatively flat, and its action on coastlines is often to level them, producing beaches, and in many places, shallow estuary-like areas. As ice ages come and go, the sea level changes so a common land pattern is a "raised beach" - relatively flat low-lying land a few metres above the current sea level. So seas can produce a range of terrain ideally adapted for efficient railway building.

Railways can run on or just inland from beaches, and crossing marshes, estuaries and shallow seas on causeways or bridges on stilts. Deeper water in sheltered areas may be bridged with pontoon bridges, though weather would destroy any built over deep oceans. Thus you can probably link island chains, with only a few miles between islands, with a railway running from one continent to another.

Historically, sea also tends to concentrate human populations along the shoreline - boats were a much easier form of travel than pre-railway land transport. Still works, though rail is faster if it goes where you're going. So most towns and cities were already built along the most convenient railway routes, making railway adoption easy.

A few examples from island nations:

Singapore's metro system has 200km of railway lines

https://en.wikipedia.org/wiki/Mass_Rapid_Transit_(Singapore)

The UK invented the railway and has an extensive domestic network. It is now possible to take the train to France via the channel tunnel on a Eurostar passenger train, or even take a car or truck across on board a Le Shuttle train. It was decided not to allow vehicle owners to drive through the channel tunnel, but they can drive onto the train and cross that way. I'm not sure of the reasons why this method was chosen, but I suspect accidents, breakdowns and disposal of exhaust fumes would be issues in such a long road tunnel. Freight trains have also been important in the UK, both as shuttles in the mining industry and for long distance travel, and routes through the channel tunnel connect the UK with the rest of Europe.

https://en.wikipedia.org/wiki/Channel_Tunnel

Japan's Shinkansen was/is one of the most advanced trains in the world. The map on the linked page shows only the Shinkansen lines (not the extensive local railways or metro systems.) Note that all major islands are linked by Shinkansen, though Hokkaido looks underdeveloped compared to the rest of the country.

https://www.japan-guide.com/e/e2019.html

More examples here

As castor says, the golden age of the railway was ended by motorised road transport, not boats. Prior to the invention of the motor vehicle, the railway was king.

For shallow water, an elevated track on pylons (either maglev or more conventional) would work quite well for crossing between landmasses.

For deep water..less so, but one concept that occurs would be something closer in principle to a real-world Land-Train.

Land Trains are essentially a conventional articulated truck with a particularly powerful cab and a daisy-chain of trailers behind them. They operate similarly to a train but don't use tracks to guide themselves.

I envision a system where you have an extremely powerful Tugboat pulling a series of barges on long-haul cargo trips.

The advantage over a more regular cargo ship is that it can operate in shallower water, can be split up at a port to unload without requiring specialised facilities and if something disastrous happens you only may only lose one of the barges rather than the whole payload.

Disadvantage is that its lower displacement and light/flexible nature makes it more vulnerable to extreme waves, so it might be more useful in calmer inland seas or on a planet with less tidal action.

• Ever towed another boat? If close coupled, the first trailer (barge) is in your propwash and you're going nowhere. Which is why tugs towing a large ship operate in pairs, port and stbd..Your idea is used on large rivers - but with a pusher. Apr 13, 2018 at 6:20
• I admit to knowing very little about boats. but it seems to me that having the props out on outriggers or widely spaced on a wider craft than the barge would negate that, have the prop-wash on either side of your trailers rather than straight into them. Alternately, have the barge a lot shallower than the tug and position the engines to thrust underneath the train. Apr 13, 2018 at 9:31
• Propwash spreads out, so outriggers are still draggy (and going deep eliminates the shallow water advantage). Pushers don't destroy your basic idea though, and handle up to 40 barges according to en.wikipedia.org/wiki/Pusher_(boat) Apr 13, 2018 at 11:37
• Certainly interesting. I'd imagine you would want some form of linked thrusters or rudders attached the "Tow" itself to provide a measure of additional control. You're essentially balancing a broomstick on your hand and trying to guide its path. But yes, this would certainly fit my suggestion better than my own description! Upvoted for improvement! Apr 13, 2018 at 15:15

Perhaps the planet has a backbone of landmass around its entire circumference. One of Saturn's moons, Lapetus, has an equatorial ridge of 20km tall mountains around 3/4 of its circumference.

If it was a connected ring you could imagine having an endless circle of trains encircling the planet.

Remember that the train powered by a locomotive was invented and first saw widespread use in... Britain, an island.

This gave the British a big economic advantage, as a train is a faster and much less expensive method of transportation, as compared to the alternative at that time... horse drawn wagons. Rails were less expensive to construct and could go more places than the other alternative at that time: canals with horse drawn barges.

So, yes, trains could play an important role in a planet that has even less landmass than earth... if the islands were large enough.

Some ideas:

• Possible on an ice covered planet (see The Ice Company).
• It has been reported that burning penguins is a good fuel for a steamer.
• Metallic nodules at the bottom of the sea can be collected to build the rails.
• It is possible to make ice structures using some king of refrigerated ice made concrete (see Pycrete).
• Burning penguins... you monster! Apr 13, 2018 at 14:34