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I have a huge planet with two continents separated by a wide ocean. Inhabitants think that their continent is the whole world because the other side is too far and they never visited it. What if people try to travel the ocean without turning back just for the sake of knowing what lies beyond? Remember they don't know how long they have to travel (even until death) so they might want to make the ship of their lifetimes, possibly the best possible ship they can make.

Please don't mind the gravity, or super-earths being gas giants, or other physical laws that might make life impossible. I'll probably make something up. Something magical. Something that can make gravity feel the same as our earth.

The circumference of the planet is around 120,000 km. The two continents are 50,000 km apart (opposite to each other on the planet).

Also, I want to make the trip very hard. No one has ever reached the other side. So maybe no islands to replenish supplies. Possibly many shipwrecks beached. Each more advanced than the other.


EDIT:

Thank you all so much for these good answers and questions. Here are my thoughts about them:

  • Challenges about the ocean's vastness, like the size of the waves, the storms they will encounter, etc., are hard for me to answer right now, since I have not planned that in detail yet. However, it is a fantasy world so there will always be a way to cross. Your ideas about what the ocean might look like is really helping me shape the travel.
  • I do already have a plan for what they will see on the other side. For those who are curious, the plants and animals will be significantly different. Yes there will be humans there, but they will also be... different. How they got there will be a secret. The story will show perspectives of humans from both continents.
  • I do have ideas for their motivations for the big voyage. They are important, but for now they remain flexible.
  • It's actually important that they reach the other side without the knowledge of what is in there. Yes, satellite/orbital technology might strongly affect how this goes. But keep in mind I have not revealed the cultures and capabilities of humans in this super-earth. I just wanted to have a good reference of what humans on our earth can do with their knowledge level in different eras, then steal ideas from them. You guys have been helping me form good arguments to justify how different tech can fail/succeed.

I know specifying more can help you answer more clearly but please bear with me. Many aspects of this world aren't actually fixed yet, so it's hard for me to add those details. I really enjoyed reading all your answers and comments. They have really helped me evolve my ideas and decide more about what the world should be. Thank you so much for your help so far!

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  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – James May 11 '18 at 16:40
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    $\begingroup$ Do birds migrate to the other continent or anything that lets the first continents navigators think that there is any land there at all? Lots of answers talking about Polynesians but Polynesians didn't just go sailing into the blue without a clue. $\endgroup$ – Kilisi May 29 '18 at 9:20

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Since you ask specifically for a technology level, I will answer only considering this aspect.

At a cruising speed of 22 knots (roughly 40 km/h), a ship needs 52 days to sail 50 000 km, so a current era cruiser ship can do it without any problems.
Probably any ship built in the second half of the 1900's, if designed with that goal in mind, can do it.

Now the problem is that they don't know how long the trip is, which has the effect to make the calculation hard on how much food and water you need to take with you. Luckily some of the food is in the water and it is not too difficult to have a desalination plant on board to produce water to drink and for the hydroponic cultures (vegetables). This way you can stay in water for longer than 52 days (maybe up to 100 days if the ship is really slow).

While this trip probably is not doable with an 1800's technology level ship, a relatively modern ship can be built with this goal in mind and be doable with current era technology without too many problems.

Update for clarification
I am thinking about a nuclear powered ship, so the range is not a problem, but probably a custom designed ship (something like a light tanker) can embark all the necessary fuel.

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  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – Monica Cellio May 4 '18 at 15:49
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    $\begingroup$ Given the tech level you described, surveying equipment would allow people toe get a fairly accurate estimate of the planet's circumference. Knowing that, and with good navigation devices, you can get a good estimate of travel time around the equater as if there's no other continent and plan the rations accordingly. Worst case, you'll have enough rations to bring you around the planet back to your own continent $\endgroup$ – ChP May 4 '18 at 16:28
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    $\begingroup$ @ChP True, but on a merchant ship you have a lot of space for cargo. For a trip like this, for example, you can get a merchant ship and convert all the cargo bay to fuel tanker and to store other necessary items, if you don't want to go nuclear $\endgroup$ – Gianluca May 4 '18 at 19:39
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    $\begingroup$ A Napoleonic-Era Coal-powered ship could move at 12 knots and faster in the wind. I'm not certain about how long such a ship could be out at sea, but 100 days of supplies does not seem unreasonable to carry. Based on your own math, i think it's pretty clear that a ship of that era would be able to make the trip across this mega ocean. $\endgroup$ – Kaosubaloo May 4 '18 at 22:32
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    $\begingroup$ In 1845 for Franklin searching of north east passage ships were loaded with food for 3 YEARS. I would say that for such ships it would be doable. en.wikipedia.org/wiki/Franklin%27s_lost_expedition $\endgroup$ – Shadow1024 May 5 '18 at 9:40
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Stone Age Tech

The pacific Islanders were able to colonize the most remote islands without any technology you might consider 'advanced'. In fact, their sailing technology has been quite sophisticated for a very long time. They can effectively live at sea indefinitely. There's a good argument that the Ancient Egyptians sailed to the Americas, too:

https://www.ancient-code.com/3-discoveries-that-suggest-ancient-egyptians-traveled-to-america-thousands-of-years-ago/

The limiting factors in crossing a large ocean are not technological.

Wind Conditions: Are there prevailing winds that allow for travel in both directions? The more consistent the wind, the easier the trip.

Sea State: How rough is the trip? Rough winds and waves can make a trip much, much harder. For example, for a long time, it was more difficult to round the Cape of Good Hope in S. Africa than it was to cross the Atlantic.

How frequent and how strong are storms? Is there a hurricane season? If storms are infrequent, it will be relatively safe, but the more frequent the storms, the more dangerous the trip.

How cold could it get? Again, the colder it might get, the more dangerous the trip. The Vikings could cross to Greenland in the summer, but had a hard time getting to England in the winter.

How abundant are fish? Pacific islanders can feed themselves on the go by catching fish. There is (was) a lot of life in earth's oceans.

How frequent is rainfall? Stores of fresh water can be harder. With frequent rainfall, they won't have to worry about fresh water. It's also possible to collect water from condensation every morning, but this takes up a fair amount of space, so its hard to do on a ship.

Most importantly: Does anybody feel like making the trip? People need reasons to make such a journey, especially when there might not be a destination. The Chinese could have discovered & colonized N. America whenever they felt like it, but they didn't for cultural and economic reasons.

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    $\begingroup$ I don't feel that ancient-code.com is really a legitimate source... $\endgroup$ – walrus May 3 '18 at 21:10
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    $\begingroup$ That link is pure junk science. Even if such sources could be the basis for a fun story, it is being presented here as supporting a historical precedent. $\endgroup$ – Harabeck May 3 '18 at 21:53
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    $\begingroup$ I'd upvote this if you removed the nonsense about Egypt. $\endgroup$ – curiousdannii May 4 '18 at 1:29
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    $\begingroup$ A diet of fish alone is likely to be lacking in certain vitamins. Scurvy was a serious problem on European sailing ships before they learned to take citrus along. But I admit I don't know how much of their diet was fish versus carried supplies. $\endgroup$ – Paul Sinclair May 4 '18 at 14:05
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    $\begingroup$ @James I think you're assuming a Polynesian craft is self sufficient. While we don't know how they did it, we have some good ideas. While food was supplemented by fishing and water was supplemented by rain, they had to carry most of their food and water. Food could be dried and fermented. Water was stored in gourds, bamboo, or they drank from coconuts they brought with them. For example, the Kon-Tiki expedition carried 1000L of water, 200 coconuts, and rations. $\endgroup$ – Schwern May 4 '18 at 22:19
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Doable: Space age tech: USA / USSR 1970's tech.

Lucky: 1840's tech.

Let's take a look at some ships, 1 knot = 1.852 km/h, 50,000 km distance, one way trip, best case, no detours.

To know where you are going, you will need satellites and imaging of foreign shores. Also weather forecasts are very useful. Yes, you can plot your way due East or West, but no guarantee to get to a place where you can land. But you might get lucky

And, you will want to get back to your home. And spend some time at the other side. So let's go with 5 times a one way trip. Say an even 10 months to go there, meet and greet, and come back. Doable, but a very large project. Akin our moon landings.

Option 1: single nuclear carrier:

Rebuild / custom build a ship for this mission. Make it large with nuclear power so no refilling and fresh water. And pile in the food. Lots of it. No, pack in more I tell you!

Option 2: the grand fleet:

So go and find your other continent with a (large) fleet of ships. Container ships and Carriers. Supply ships, fishing ships, repair ships, scouting ships, hospital ships... what ever you think you need. Big nuclear ships to reduce the need for fuel and fresh water. And much of it build just for this mission.

Option 3: the mad navigator (Columbus):

Pile in as much food as you can and get lucky you don't starve before you hit landfall. Columbus took 5 weeks (35 days) in his first trip.

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    $\begingroup$ I actually was talking about this with a friend earlier and brought up traveling from Fiji to Hawaii in wooden boats and said "Hawaii may as well be on the moon in relation to Fiji." Seriously, that's a lot of empty ocean between them, even for a very adapt seafaring people. $\endgroup$ – Anthony May 3 '18 at 10:20
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    $\begingroup$ Once you get up to nuclear tech level you could have launched satellites telling you exactly how far away any landmasses are, so OP probably wants to go a little more primitive than that. $\endgroup$ – sirjonsnow May 3 '18 at 12:27
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    $\begingroup$ A sailing frigate would need impossible wind to sustain 12kts for 93 days straight. You'd be lucky to cover the distance in six months. $\endgroup$ – J... May 3 '18 at 12:32
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    $\begingroup$ @Chromatix I think historical data is ample to demonstrate that sailing ships with 12-14kt maximum speeds did not make that pace on average on trans-oceanic voyages. Winds do vary, subtract leeway on any sort of tack, and consider especially a voyage across an unknown ocean (with nothing but compass, clock, and sextant) which has never been charted and "just pick the right latitude" seems a bit naive, I should think. $\endgroup$ – J... May 3 '18 at 13:46
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    $\begingroup$ @sirjonsnow Depending on the nature of the magic working on gravity, getting to orbit on a super-earth may be implausible. $\endgroup$ – Yakk May 3 '18 at 13:52
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The Franklin expedition, launched in 1845, was provisioned for 3 years. That would be adequate for a 50,000km voyage under sail. Fishing might provide additional food.

One of Franklin's ships, the HMS Terror, was built in 1813.

Magellan 3-year voyage circumnavigating the earth covered 69,800 kilometers, and that was from 1519-1522. His journey might be a source of inspiration for you, as only 18 members of the 270-person expedition survived! That's about as difficult a voyage as it is possible to imagine.

Of course, Magellan made many stops along the way. Looking at the greatest fictional sea voyage, Homer's Odyssey, again one finds he made landfall repeatedly in his decade-long journey. I would respectfully suggest some islands along the way would be a good idea. Regardless of how heroically difficult it would be, months or years of sailing across featureless open water sounds pretty boring.

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    $\begingroup$ The old man and the sea with friends? lol $\endgroup$ – ggiaquin16 May 3 '18 at 20:02
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    $\begingroup$ To be perfectly fair, the existence of islands may make the voyage easier if you know where they are. The Pitcairn Islands were discovered and then lost, because they were plotted in the wrong place on charts, only to be rediscovered by the crew of HMS Bounty. $\endgroup$ – Chromatix May 4 '18 at 5:46
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    $\begingroup$ Magellan's was a rough voyage, but within decades (mid to late 1500s) the Spanish were routinely sailing the breadth of the Pacific on trade routes between Indonesia and Mexico. This would have been about a 20,000km voyage with few to no options for stopping en-route. $\endgroup$ – J... May 4 '18 at 18:15
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Circa 1800 - Age of Sail

The (fictional) Horatio Hornblower made a voyage of roughly this magnitude of distance, with orders to stay out of sight of land until arrival, in a typical Royal Navy frigate (with a full crew), in the very early 19th century. The journey was from a West of England naval port to the western coast of Central America, via Cape Horn, and made a precisely accurate landfall. Though fictional, C. S. Forester's novels are well-regarded concerning historical plausibility.

In your scenario, I assume both continents have been sending out expeditions to each other and would have evidence of this, in the form of wreckage washed up on shore. This would constitute sufficient evidence (together with astronomical observations and the successful introduction of celestial navigation) that such a voyage was possible, even if nobody had yet succeeded, and probably also indicate the correct latitudes to pick up favourable trade winds.

NB: celestial navigation requires good knowledge of mathematics, an accurate observation instrument (eg. sextant), and an accurate timepiece (marine chronometer) if longitude is required as well as latitude. These were all available and in regular naval use by 1800.

Possibly even evidence of the length of voyage required could be obtained from the wrecks. If some of them failed only due to shortage of supplies, the ships might reach land intact but with nobody alive at the helm. Medical knowledge would be sufficient by then to approximately determine the time of death of the last survivors, and correlate this with the size of the crew and the quantity of supplies they set out with.

The ship's logs and charts would also be very valuable to future expeditions.

A civilian expedition would probably take a much smaller crew than a naval frigate, which would help to extend their supplies. Not carrying a large gun armament and not requiring a manoeuvrability edge in combat substantially reduces crew requirements. Adopting a schooner (or topsail schooner) rig also helps, though it may reduce sailing speed in tradewinds. Since the winds and waves are likely to reach similar magnitudes as in the Roaring Forties on Earth, a schooner rig is almost certainly adequate.

Storing large quantities of preserved food on board is not a problem - salt pork and hardtack was the standard of the day, and would keep almost indefinitely. In roughly this period, pemmican was also introduced to expeditionary rations. Catching fish en route is a possibility, but probably should be regarded as relieving the monotony of diet rather than a primary source. Avoiding scurvy requires carrying a source of Vitamin C, probably derived from citrus fruits; concentrated lime juice became standard in the Royal Navy, and is not especially difficult to make.

The major problem is likely to be fresh drinking water, which is difficult to keep drinkable over a period of months, even if a sufficient quantity is taken on board. Depending on your planet's climate patterns, it may be possible to collect enough rainwater to sustain a small crew. The key technological advance that makes the expedition successful might be a relatively efficient solar-evaporative distiller, which could be made with a glass lid. Carrying spare lids would be advisable.

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  • $\begingroup$ Welcome to WorldBuilding Chromatix! Interesting first answer. Looking forward to your future contributions to the site! If you have a moment please take the tour and visit the help center to learn more about the site. Have fun! $\endgroup$ – FoxElemental May 3 '18 at 15:50
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    $\begingroup$ Agreed and I think chains of supply ships interspersed every X hundred kilometers with shuttles running between them could be established. $\endgroup$ – Sentinel May 3 '18 at 19:34
  • $\begingroup$ @Sentinel well oceans are large and a bit o wind and currents will make middle ocean rendevous impratical without a GPS on top of that no age of sail if we don't have the need for navy tech anyway so OP must rule why we will care to build big ships and develop navigation if we only got a single (know) continent $\endgroup$ – jean May 4 '18 at 14:31
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    $\begingroup$ @jean It still makes sense to build ships for coastal trade, not to mention fishing - to some extent even with railways, ships are still good for moving bulk cargoes. There are probably some islands and subcontinents offshore too. $\endgroup$ – Chromatix May 4 '18 at 23:03
  • $\begingroup$ @Chromatix I agree in ours wolrd coastal trade is a thing but OP said nothing about isles and even don't ruled about climate, etc. In that regard I did the assumption (based on the size of the super-sea) sea will be hell with gigantic waves, absurd erosion, unthinkable tides, and Jupiter like stormy. Of course we can or not get big isles, channels, archipelagos, bays. That will rule if coastal trade is intense, non existent or something between. But even coastal trade can do little to help development of navigation in high super-sea (with the complications and danger a super-sea provides) $\endgroup$ – jean May 7 '18 at 11:02
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You need the Industrialisation

To put a definite upper bound, I would say mid-19th century. Take Brunel's SS Great Eastern, launched in 1858, originally designed to ferry 4000 passengers from Britain to Australia without refueling. That is already about half the distance you require. If you replace the passengers, their supplies and their amenities as well as the cargo with more fuel (and supplies for your crew) instead, a range of 50000km or more should not be a problem.

To put a lower bound, there are two technological advances made in the late 18th/early 19th century that allowed for this ship to exist and in my opinion are necessary to attempt such a trip.

The first is related to size. It is easy to see that a larger ship is preferable, especially a long ship. Roughly speaking, the capacity to carry supplies increases with volume, that is cross-section times length, while the resistance to traveling through water only increases with the area of the cross section.¹ Larger ships also tend to need less crew per tonnage.

Now the thing about wooden ships is that they are kind of limited in size. The iron-hulled Great Eastern, mentioned in the beginning had a length of 211m. Wooden ships of half that length already had big structural problems. So what you need is a ship with a metal hull. And while metal working was done since ancient times, the large scale precision engineering needed to build them just arrived at this time.

The second is related to propulsion. The reason people were able to routinely cross large distances in the age of sail is that they knew how the trade winds generally were blowing. And even then there always was a lot of luck involved as there might be no wind for weeks or a storm which is to strong to effectively sail. In transatlantic distances, this is already dangerous. At the distance you are thinking about, these uncertainties are simply deadly.

So in short, you will need an alternative to sails, the first feasible of which were steam engines.² While there were some experiments earlier on, the first practical seagoing steamships were built around the early 19th century.

¹ Yes, I know the reality is more complicated, yet the general idea still stands.

² There are oars as an alternative to sails, however they are not really feasible for long distance voyages.

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  • $\begingroup$ You need both steamships and compact energy supplies; coal may not be dense enough. Which pushes you to the age of oil, aka post-WW1. $\endgroup$ – Yakk May 3 '18 at 13:54
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    $\begingroup$ @Yakk: Apparently coal is just enough, see the example I gave. From what I googled, the Great Eastern apparently was able to travel half the distance with 12k tons of coal. If you replace it 6k tons of cargo and the passenger sections with even more coal, it can travel the full distance. And you could probably even reach a bit further with a more purpose-built ship, or go "multi-stage" by towing a tender for half the trip and then dropping it when it is empty. The tech was there at the time, there was just no reason to use it, since UK to Australia was the longest commercial distance anyway. $\endgroup$ – mlk May 3 '18 at 14:31
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    $\begingroup$ The thing is that for them to venture 50K Km, that distance has to be at most their no-return point. That means that they should prepare for a trip of at least 100K Km to be sure, and that's almost going all around the planet, so my guess is that they would only discover the other continent if they are prepared to sail a complete turn (120K Km minus whatever their continent's width is - which presumably is around 10K Km). So.... a LOT more coal. $\endgroup$ – tfrascaroli May 3 '18 at 16:43
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    $\begingroup$ You are right about that, although the question was for a one way trip. But even for the whole way, as I mentioned, with some ingenuity the technology was there. Build an even larger ship or tow a barge. You could even create a succession of swimming supply drops. Navigational accuracy back then was good enough to locate them again and in theory this will get you anywhere. $\endgroup$ – mlk May 3 '18 at 17:00
  • $\begingroup$ I don't know about that Britain to Australia voyage, but I assume that they sailed fairly close to Africa a large part of the way. Does not stopping to refuel mean not stopping at all (for any supplies like food)? $\endgroup$ – Anthony May 3 '18 at 17:08
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Sailing

As everyone has stated, sailing takes you a long way. Sailing allows fast circumnavigation of planets because winds and currents form specific patterns due to atmospheric circulation. A major challenge to circumnavigation in 1500 was that land kept getting in the way, and sailors had to cross through alternating ocean and wind currents as they sought paths around continents. If there isn't a land mass in your way, you can sail on a raft or canoe for as long as your food supplies last, as evidenced by ancient Polynesian travel patterns.

Larger planets have more belts in their circulation; Jupiter has 7 belts per hemisphere while Earth has 3. Yours is 3x earth, but still 1/3 Jupiter, so you might have 3-5 belts of atmospheric circulation.

Preventing Sailing

So, assuming a rotating planet with Coriolis effect and a star that creates equatorial heating and circulation of ocean and atmosphere, there need to be other specific barriers to finding the other continent.

Polar Continents

Both continents could be polar, with several bands of winds and currents, plus equatorial doldrums to cross. Equatorial oceans would have doldrums, air is heating and rising, so no wind currents.

Hot oceans

If your continents are polar, the world could be 20-30C warmer, so the poles are temperate, but the equator is a hot ocean, 40-50 C, which is hypoxic, so no sea life. A hot, dead, stormy belt that is uncrossable without (pick your tech and bravery level).

Storms

The planet, especially with continuous equatorial oceans, could (with a little stretching) form large, semi-permanent storms, like the eye of Jupiter, which create a dangerous band of storms combined with doldrums. Storms could be so powerful that modern airplanes can't cross, or an intrepid explorer in a small craft could thread the storms and make it through. Space travel would definitely make it over any obstruction, but increased gravity could make it harder to build orbital launch systems.

Dangerous shoals

Some crazy plate tectonics could be in place that create a ring of shoals and uninhabitable volcanic islands that make seafaring dangerous. Clouds of sulfur gas, boiling seas, rocky islands that rise from and sink into the ocean, etc, etc. These could be akin to the mid-Atlantic ridge, only way shallower and more active.

Continentality affecting winds and currents

Without being strictly polar continents, large continents shape ocean and wind currents by changing thermal patterns. The right shape could create currents in which the world is circumnavigable, but you won't reach the other continent. There would obviously be a blank spot on maps, maybe explainable by some cultural phenomenon. Explorers sail, ride the waves and wind, and end up back on the other side of where they started.

All of these have different tech requirements. Sea impediments could stop ancient rafts and canoes, sailing ships, or even modern ships and submarines. Atmospheric impediments would stop aircraft and dirigibles. You'd have to have extreme gravity or some crazy radiation and magnetic field issues to stop orbital technology. Or there could be a cultural explanation why the maps all end at a certain point and no one tries to go further.

Shipwrecks

Shipwrecks could be common in the doldrums or mid-areas, where explorers from each side find strange and unusual wreckage. You could even have two cultures at different tech levels finding eachothers' wrecks.

Hot oceans or poisonous volcanic gases could also kill crews but allow ships to drift, so shipwrecks occur on each continent, but no survivors tell the tale of the other land.

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    $\begingroup$ Loved this one +1 for the poles and wind $\endgroup$ – jean May 4 '18 at 16:45
  • $\begingroup$ Not really an answer but still some very good points $\endgroup$ – bendl May 7 '18 at 3:50
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    $\begingroup$ My point is that a water world is really easy to circumnavigate. Prehistoric tech could do it with enough food stores (like the prehistoric Polynesians). Maybe no one would try it, but a ship blown out to sea by storms would end up drifting completely around to the other side of a water world planet. If it had large stores of food and water, survivors would find the other continent, otherwise shipwrecks would occur. What you need is a barrier that matches the need of the story line. $\endgroup$ – user15741 May 7 '18 at 17:42
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Change some of the assumptions. The biggest single issue is water - so make the ocean freshwater. Next, forget the talk of steam power - that is daft, steam or oil power requires fuel. Go for sail. If you want a truly long-lasting voyage, choose a propulsion method that doesn't need fuel. Choose sail.

A sea-going people can fish as they go. The real limitations are therefore water supply and withstanding storms. Relatively small vessels, well built, can withstand major storms as well as large storms. Some of the whaling ships of the previous century would spend a year or more at sea.

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  • $\begingroup$ That's a mighty convenient assumption. I'm also a little surprised no one has suggested a submarine yet. Not that it has significant advantages, but if it was oar based it could probably go faster than on the surface. $\endgroup$ – Anthony May 3 '18 at 17:06
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    $\begingroup$ If you have trouble keeping yourself in fresh water, then maintaining a fresh air supply would be problematic for a submarine. $\endgroup$ – Chromatix May 3 '18 at 17:23
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    $\begingroup$ Fresh air can be done with a snorkel. While that was invented pretty late, there's no modern technology needed. It could have been invented decades earlier. But an oar, underwater? The idea behind an oar is that it travels forwards through air and back through water. Plus, the energy consumption of oars is massive. Food isn't efficient. If coal is a problem, oars are right out. $\endgroup$ – MSalters May 4 '18 at 13:38
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So maybe no islands to replenish supplies.

That's a big maybe, and the whole question hangs on that.

If there are islands every few 1000 km... 9th Century Polynesians.

Then @James is correct that the Polynesians could do it, but incorrect about how, and I wouldn't call it "stone age tech". Polynesian navigation was extremely advanced.

Over the course of about 1000 years, starting roughly at 900 BC on Fiji, Lapita and later Polynesian culture, crossed all the South Pacific islands finally reaching the very isolated Hawaii and Easter Island in 900 AD.

The longest crossings were to Hawaii and Easter Island. From their likely jumping off point of the Marquesas Islands these are both journeys of nearly 4000 km.

enter image description here

So over a few thousand years you could have an ocean spanning island culture using Polynesian technology.

If there are no islands... 16th Century European + 9th Century Polynesians.

While the Polynesians were very good navigators and could cross thousands of km of open ocean, they had their limits. Their crafts were not self-sufficient. They had to carry water and food with them. While they were very frugal and could supplement their stores with fishing and rain water, this was unreliable and eventually they'd run out of food and water. We know they could go about 4,000 km, but not 50,000 km.

We need a self-sufficient voyage that can navigate 50,000 km of open water and survive on open ocean. Let's take that in parts.

Navigation.

There's two problems of open ocean navigation: latitude and longitude. There's a number of ways to handle navigation, star charts or sun sightings, and that's been known since antiquity. No problem.

Longitude is a problem and wasn't really solved until the 18th century. But plenty of explorers were navigating the Earth's oceans well before then, so maybe we don't need longitude. And if you have magnetic compasses you can get a rough idea of your position from magnetic declination.

Latitude is enough to at least keep you on a straight line.

Stores (and Speed).

How much food, water, spare parts (and maybe fuel) you need to carry depends on how fast you can cross.

The Kon-Tiki expedition recreating a possible Polynesian voyage from the South Pacific to South America took 100 days to cross 7000 km at a rate of just 70 km per day. At that rate they'd need about 700 days to cross your 50,000 km ocean.

Christopher Columbus made his first voyage of about 5500 km from the Canary Islands to San Salvador Island in about 30 days making about 200 km per day. At that rate you'd need to carry 250 days worth of food, water, and spare parts.

What if we combined the two? I've been to the Kon-Tiki museum, the Kon-Tiki was basically a big, but deceptively sophisticated, raft. What if we combined the navigation skills and frugality of the Polynesians with 15th century speed and technology?

The Kon-Tiki was able to sustain 6 people in one ship for 100 days. Columbus was able to sustain 90 people in three ships for 30 days, 5 times more efficient than Kon-Tiki. If Columbus had just 6 people he could have sustained them for 500 days. And if he could sustain 15th century speeds of 180 km per day he could have crossed 50,000 in just 280 days.

But a 15th century European sailing ship can't operate with 2 people per ship, they require a much larger crew to operate than a Polynesian sailing raft. Perhaps there is a happy medium. I can imagine a combination of improved 16th century sailing and provisioning technology with 9th century Polynesian navigation and frugality to produce a ship that can sail at 180 km per day with a crew of 10 to cross 50,000 km in 300 days needing 3000 person-days of stores.

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I"m firmly convinced that the kind of storms and "rogue waves" (google it) that an ocean of that size will generate are the cause of every lost ship. You'd need either a fantastically large, stable ship, or preferably one that can go submarine during storm events, to survive.

Ninja'd by Azrantha.

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I have some logistical concerns about this endeavor.

  • If they don't actually know that there is a continent at a specific location and specific distance, then they need to be prepared to keep sailing and keep sailing until they have effectively circumnavigated the globe. So they can't plan to sail for a 50,000km distance, they have to plan to sail a 120,000 km distance (or at least 120,000km less the width of their native continent).
  • The precise technological development to allow this voyage isn't a precise answer as much as it is "in this era, it will take X years, but in that era, it will take Y months." But that begs the question of... if it is considered highly unlikely that the continent is there, then are they willing to make an X-year journey as opposed to a Y-month journey? It may be that if the journey is believed to be fruitless and suicidal, then they would wait until technological development makes the journey easy, rather than just possible.
  • At some point in technological development, around 20th century, you're going to get aviation and satellite technology that will render the nautical voyage moot. They will be able to launch some sort of airplane or balloon that can confirm the continent's location.
  • Suppose, hypothetically, that there is not just one huge continent 50,000 km away, but many smaller, scattered continents that are a similar distance away. For all this society knows, that could indeed be the case. That means that if you do set sail on a particular circumnavigating course, you are not guaranteed to hit one big continent, but could instead sail right through the middle of two smaller continents and not see either one. Imagine a ship sailing from Antarctica to Alaska on a particularly unlucky course that does not bump into mainland North America or Hawaii on its way. This possibility means that a single voyage as described in the original post could both fail to confirm and fail to refute the theory that there are other continents out there. How many voyages of this type must you go on before you are reasonably sure that you are right? In a smaller planet with more land mass, you won't have to go on too many. But on a humongous planet that is mostly ocean, you might actually have to go on hundreds of such voyages just to rule out that there are any very large continents (and even that would not be enough to rule out the existence of smaller land masses). My point is, if this society could go on a single 10-month journey to confirm or refute their theory, then they might undertake it. But if they have to go on hundreds of such journeys, and each individual journey is likely to be a waste of time and akin to throwing your life away, then they might delay exploration attempts until they reach a 20th century level of development.
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Early Space Race Era

I agree it can be doable (with a lot of luck) at steam power era but will need a massive effort akin to put the man on moon, maybe even requiring a international task force. Below I will list some challenges were are not pointed in previous answers.

Why not in the age of sail?

Because we never got an age of sail for start. At sec XV we unified some kingdoms and they started a tech race akin to the space race to finally develop oceanic navigation. At sec XVI we founded colonies in the new world and it pushed the navigation development and with the growth of the colonies culminated in the "Age of Sail". Without those elements OP super earth most likely skiped it entirely.

A Fearsome Sea

The size of this Ocean will bring a lot of weather and climate challenges. You can expect winds, tides and currents to be way bigger. Also expects typhoons to be cataclysmic. The tides per se will be a good challenge for the building of ports. The tsunami size weaves can make even fishing impossible in large coastal areas. The sea conditions will be nasty, even in good weather and impossible in bad weather. Navigation will be a really dangerous business. Also the sea conditions will make coastal erosion a thing. I ever wonder if most of coastal will be of massive cliffs. All those factos summed make me wonder coastal cities will be almost entrenched in big natural harbours and important sea trade routes will be exclusively between cities in bays (the only place where is possible to build a big port anyway) and where the route travels along a, most time, very peacefull chunk of the ocean.

Lots of Trains & Planes but no Fleet

The size of the continet this points out railroads will be in demand early ans planes too but navigation will be very limited in all aspects, speacially in tech. This leads to a strange scenario where we will hit industrial age and even space age skipping sail age.

The Dark Side

The Moon is a great target for mankind aspiration, from dawn of time we can see it but we cannot reach it. We dreamed to land here a million times. But what if for millenia we do know Super-Terra has a dark side out of reach? Once scientist proves we can launch a object in orbit and retrieve it the first thing to be flung out will be a camera to take pictures of the uncharted lands. Once the first pictures are retrieved be sure it will trigger a space/exploration/colonization race.

Age of New World

The reason the new continent will spring a sort of space race is to gather data from the land, not only a coastal line but weather a major biomes, moutains ranges, rivers. Everything necessary for future settlers. Also a new tech race on navigation will sprung. Visionaries will dream of under-water-boats, starting the project of the (probably first) submarine. Long-range-any-weather-transocenic ships will gain the status today we grant to a mission to Mars. It will bring a new age.

What if there already people here? They are probably in another phase in tech development, even using a different "tech tree" but fact we reached them first. Also yes its unlikey but possible small grups can end strained here but OP can wave a complex geologial/ice age to explain it. Maybe thermals isles of heat making a sort of ring of fire connecting boths continents in immemorial times. What in that case the answer instead can be Ice Age

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Check out : generation ship. You're suggesting a ship that can sustain any amount of travel time so it should be assumed they could even sustain death (via reproduction aboard the ship). If previous attempts have been tried and have failed, the next venture would have to assume any possible distance, and proceed accordingly.

Alternatively, if they are confident their Earth is round and they can advance scientifically/technologically without definitive proof of its roundness (eg circumnavigation), they could eventually launch satellites that orbit their Earth that could inform them of the vastness of their ocean, any potential land bridges or straits, the general layout of this other continent (like if it appears inhabited, etc) and even potentially provide a means of communication with the other continent without making the trip.

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    $\begingroup$ This answers how they could do it, but not "What era or tech level in earth's history has the ability to cross a super-earth's ocean 50000km wide?" $\endgroup$ – Raditz_35 May 3 '18 at 9:16
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    $\begingroup$ No need for generation ship, we are talking of what current ship sail in a couple of months $\endgroup$ – Gianluca May 3 '18 at 9:16
  • $\begingroup$ But they don't know the length of the trip or the necessary conditions to consider before leaving. If they just sail blindly with a current battleship, they could still run out of gas, food, or sail right into a patch of icebergs. There's no definite era that's guaranteed to make the trip blindly, but there are certainly ways to prepare for the unexpected. $\endgroup$ – Anthony May 3 '18 at 9:19
  • $\begingroup$ A current ship still has plenty of problems with an inexperienced captain and crew when sailing around the Southern capes. If the objective is to to be successful with little knowledge of what to expect, no modern ship would be equipped. Not without the instruments and crew experience that came from previous re world failure. $\endgroup$ – Anthony May 3 '18 at 9:23
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    $\begingroup$ Fair, but then why do they continue to try and fail to make the journey? $\endgroup$ – Anthony May 3 '18 at 9:49
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Christopher Columbus found the Americas in the 1400s, realistically what you are asking would FIRST be capable in very late 1700s or early 1800s, i know this will probably annoy some people but bear with me

Columbus set out expecting to find land, however he stopped at several islands and had enough water for the comparatively short trip,

Food really isn't the problem for this trip, water is, clean drinking water is expensive, it is widely believed that in 1791 Thomas Jefferson invented the first stages of desalinization, once a ship could be built to house a desalinization plant, then in theory water no longer becomes a problem,then its a matter of building ships, humans have been good at this for hundreds of years, and many much larger than the Santa Maria, the flagship Columbus took, along with two smaller ships, but the journey would be perilous and have little chance to being easily repeatable until the 1900s

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  • $\begingroup$ Desalination requires power. Where is that coming from? As far as I'm aware, we still don't have a sustainable desalination process from land. Not saying it can't be done, just that it requires an active energy source (and lots of it) to achieve. Unless the ship has nuclear power or ready access to coal, this seems unmanageable as a long term solution (especially if the ship itself was competiting for that energy source, eg not a sail ship). $\endgroup$ – Anthony May 3 '18 at 10:43
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    $\begingroup$ Columbus's crew were plotting a mutiny by the end of the trip, and were probably debating on when it would be okay to start eating each other. They basically got lucky that they reached the Bahamas while surviving off the last slivers of food and water they had left. It blows my mind that if land had been another week away, Europeans would very likely have written off Columbus's quest as an inevitable failure and if would have been 50–100 more years before anything similar would have been considered. $\endgroup$ – Anthony May 3 '18 at 10:47
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    $\begingroup$ @Anthony Check out this low tech, solar desalinization. An old timer from the US Navy WWII told me about this. They had them in life rafts back then. $\endgroup$ – axsvl77 May 3 '18 at 13:11
  • $\begingroup$ @Anthony You could write a couple good books with that premise: maybe the Vikings resettled and took over New England, or maybe the Central and South American civilizations developed long bows or cannon, and destroyed the next couple waves of European explorers (better yet, took their ships and sailed over to conquer Europe) $\endgroup$ – Carl Witthoft May 3 '18 at 14:47
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    $\begingroup$ @Anthony, European countries were looking west across the Atlantic for new lands even prior to Columbus; Denmark mounted one expedition in 1473-1474 and may or may not have reached Newfoundland. Iceland was known, and the Norse colony in Greenland was in regular contact with Europe as late as 1420. It's unlikely in the extreme no one would have bothered poking their noses further west (and thus landing in North America) until the late 1500s. $\endgroup$ – Keith Morrison May 4 '18 at 14:55
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Circumference of Earth is approx 40k, continents in question is apart 50k. Hence i can safely assume till 19th century, it was never possible with the sailing technology at the time.

Now, later ships got the capability, but still such voyages are not possible to make as people are not certain on the distance to cover. You cant plan the things without estimating the distance. Though, Many explorers attempted before, only lucky return to tell the tale of emptiness or missed out in the sea. So First step is the distance gauge, such a long voyage can only be possible after knowing the distance to cover.

WW1 era ships with expert sailors can do the job,

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  • $\begingroup$ The OP specifically stated that the Circumference of this super earth is about 120K $\endgroup$ – Gianluca May 3 '18 at 14:51
  • $\begingroup$ Yeah, but position of the island or existence of the island is never known to the people. They only see very rare shipwrecks from the other side $\endgroup$ – Vignesh May 3 '18 at 14:56
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Biology of intelligent species is very important too, if they can survive long time with no water source, food, hibernate, swim in water long distance, can reduce resource they need for travel and lower technology. If very robust life form, they can use ocean current and get there by accident.

They probably travel for explore their planet, and challenge, like travel to north and South Pole. First they explore near areas and then farther areas while mapping where they travel, building maps of their world. They travel for finish their map. Species need strong curiosity.

Evidence for other continent: volcanic ash/dust when no known volcano erupt (or ash have different composition), unknown species dead trees in sea, flying life forms leave and return after months, years (flying life form also show way to other land).

Very small probability have two intelligent species evolve at same time. Continents separate at least 10s or 100s million years, evolution very different in each place.

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  • $\begingroup$ Welcome to WorldBuilding.SE! This has ended up in the low-quality queue, presumably because you seem to be getting sidetracked by how evolution could have happened differently in OP's world and haven't mentioned technology at all. OP has specifically states that the seafaring characters are humans, so with what tech level could they cross this sea? You should edit your answer to address the question better, otherwise it will get deleted. $\endgroup$ – F1Krazy May 8 '18 at 14:58

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