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.
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.
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
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.
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.
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 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
http://mikes.railhistory.railfan.net/r008.html
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.
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:
