In the real world, sailing is undoubtedly dangerous, but 90% of that danger comes from either the weather, your mistakes, or other ships. Animals don't really count as a factor, unless you fall overboard into water with sharks in it, or try to go whaling (In which case you deserve everything that comes your way you monster).

If humans were developing their civilization from the mesolithic in a world where all rivers are somewhat wider and deeper, and all large bodies of water (from huge lakes to oceans) contain various dangerous megafauna (from territorial animals that would mistake a boat for a competitor and will try to "chase" it out of their territory to actually predatory creatures some of which would be able and willing to snag some snack right off the top deck of a small boat; basically "what if prehistoric sea reptiles didn't go extinct" scenario).

So "here be dragons" is a phrase with literal meaning now. How would that affect humanity's historical relationship with sailing?

I guess when we'll develop large ships, like galleons, these would be massive enough for the sea creatures to stop being a threat, but will humans even get that far?

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    $\begingroup$ I think you already hit on the answer; every boat will be a whaling (dragoning?) boat. $\endgroup$
    – Matthew
    Commented Nov 23, 2020 at 16:47
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    $\begingroup$ There aren't going to be THAT many large dangerous sea predators. They are strictly limited by the availability of food. Whales can be dangerous to ships other than whaling ships but seldom are because the sea is so large. $\endgroup$
    – Mary
    Commented Nov 23, 2020 at 17:44
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    $\begingroup$ "Your Majesty, next year's budget is mostly devoted to road-and-bridge building, and bridge-protection, just like every budget. Also, like every budget, we make a slight profit from the tolls of all the caravans who don't ship by sea. The army wants to build another dam upstream to dry out Long Lake so they can kill that last family of dragons in the province. And the navy wants to replace the three littoral frigates they lost this year protecting the fishing grounds. And they want to purchase a new poison to impregnate the hulls. Supposedly it doesn't poison the fish." $\endgroup$
    – user535733
    Commented Nov 23, 2020 at 17:56
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    $\begingroup$ so like crocodiles, or hippos, or orca, or sharks, or ... $\endgroup$
    – John
    Commented Nov 23, 2020 at 22:13
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    $\begingroup$ Ships are never going to be so common that a beast of prey will be able to make its regular diet of them. $\endgroup$
    – Mary
    Commented Nov 24, 2020 at 2:22

11 Answers 11


A firey, large bowsprit, among other things

Humans have dealt with predators larger than them before. There are some methods to ward them off. Ships will be more armored from the get-go, but just like with early humans on land, the goal will be to prevent attacks instead of defending against a larger opponent when possible.


The creature would likely be scared of fire, just like it's land counterparts. Ships would likely have a controlled way to create a large fire without taking the rest of the ship with it.

Greek Fire (i.e. fire that stays lit even when water is thrown on it) would be extremely valuable, and likely would have been developed sooner. It would be the best way to make sure the creature was licking its wounds for a while to come after the battle.

Several early sea battles involved setting the other ships on fire, so extra fireproofing would have likely lead to more early sea battles involving boarding the other ship.

Early sailors will have to devise ways to make sure the fire doesn't burn a literal hole in the ship and sink them the old fashioned way.

Making the ship look big

The other trick to avoid large predators is to make yourself look large enough to scare them off. Likely early ships would have added some large pieces of cloth stretched over an out-rigger to make the ship look larger from below.

A larger bowsprit would also help scare off predators, so they'd stop being beautiful girls, and start being large scarecrow-like things.


Small ships will have more fortified bunkers along with pointy spears that can be used to defend against wrapping tentacles. The ship will likely take some damage in a close range scuffle with creatures so the goal will be to prevent this from happening.

They'll still need long-range weaponry for other humans.

Kraken hunting parties

Early tribes will band together to kill large creatures decimating sea trade. The carcasses would be gathered and used for meat and parts when possible. Fighting the large creature would become a rite of passage for the tribe.

As sea fairing grows into big business, ships will be specially designed to hunt and kill these creatures. The Navy will commission special officers with special training in man v Kraken combat.

Big ships faster

We'd get to large, multi-decked ships faster. All ship manufacturing would be large, government subsided businesses. The ships must be large enough and have enough weaponry to defend against the creatures.

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    $\begingroup$ I like the answer, but you might improve it by adding a whole new profession. Big game hunter. You elude Economics, but a new dangerous profession would add to this. Also trade ships are more likely to band together and that might dissuade pirates and much more. The sea trade and thus bulk trade would change completely. $\endgroup$
    – Trioxidane
    Commented Nov 23, 2020 at 21:55
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    $\begingroup$ The section on fire seems much less convincing than the rest of this answer — surely there is a fairly obvious reason why marine creatures, in their home environment, would be much, much less vulnerable to fire than terrestrial animals? Maybe this obvious objection doesn’t really hold up — e.g. if there’s a low-tech way to produce weaponised fire that water wouldn’t extinguish or dissipate — but it at least needs to be addressed! $\endgroup$ Commented Nov 24, 2020 at 1:14
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    $\begingroup$ Fire is generally much more problematic for ships than anything that can dive... So while something to think about I seriously doubt any non-magical fire can be made realistic around wooden sail ships. The only "fire" on such ships is kitchen... and even that kept as small as possible. You just not going to setup campfire on the deck to scare some creature unless you plan to die anyway. $\endgroup$ Commented Nov 24, 2020 at 4:14
  • $\begingroup$ One more thing: Ships in freshwater will be bigger than comfortable (eg. relative to the river size) to further scare off predators. What use is a nice mobile ship if it'll be sunk on its second trading run $\endgroup$
    – Hobbamok
    Commented Nov 24, 2020 at 12:44
  • $\begingroup$ Also, spikes on the hull. And bright color so that local faune eventually knows that these ships are dangerous to mess with $\endgroup$
    – Akita
    Commented Nov 24, 2020 at 12:45

Humans would deal with threats the way they have done throughout history: they would eradicate those animals who threaten their safety and that's the end of it. If any survive, that'll be only because they'll have learned to avoid humans. In continents where megafauna did not co-evolve with humans, all dangerous megafauna (and plenty of other tasty fauna) was eradicated by humans in prehistoric times. Take, for example, the European cave lion:

a busy cat
Source: Heinrich Harder, 1920, via Wikimedia Commons

Humans didn't want to live alongside lions. African lions have co-evolved with humans and learned that despite their fragile bipedal appearance, they could actually pose a danger and should be avoided. European lions were unfamiliar with humans when they first arrived, and were too slow to learn this lesson, so they went extinct.

Humans do not tolerate threats to their life or the life of their children and never will. They don't even tolerate threat to their source of income (such as domesticated animals). Only in the very modern age have they started to tolerate some form of nature, such as indicated by your parenthetical comment in the first paragraph of your question, an attitude for which you would have been in a very small minority 200 years ago, and even this positive attitude only exists on the condition the animals are no threat to humans or to the money humans earn.

So, initially there would be yet another source of danger on the seas, but as soon as humans finish off those animals, it would be just yet another example of ecosystem collapse.

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    $\begingroup$ "dangerous megafauna was eradicated by humans in prehistoric times" - or they learned to fear humans. If you happen across a bear in the forest, the bear will panic and run away (and will only attack if cornered). That's because having a fear of humans is ingrained in them for the many millennia of being hunted. (sadly that started slowly disappearing because of some idiots feeding wild bears and causing them to lose that fear - which then causes the bear to wander into human settlements, and then has to get shot sooner or later) $\endgroup$
    – vsz
    Commented Nov 24, 2020 at 9:13
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    $\begingroup$ @vsz For most large fauna it was too late by the time they learned to fear humans. Mammoths, sabre-toothed cats, cave bears, cave lions, cave hyenas... the ones we are still seeing are only the ones that survived, and the actually dangerous ones are mostly limited to the Arctic (where humans have been mostly absent). $\endgroup$
    – gerrit
    Commented Nov 24, 2020 at 9:36
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    $\begingroup$ Might be harder, though--more like the arctic, humans are mostly absent from large areas of the sea. I guess over time the ones that do attack humans would be weeded out, and the remaining population would be less aggressive towards ships, but if they were opportunistic attackers instead of specifically seeking out ships then it might be more Moby Dick than Jaws... $\endgroup$ Commented Nov 24, 2020 at 14:27
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    $\begingroup$ @gerrit : to accentuate your argument about the attitudes, I remember having read a proposal (I no longer know exactly where) from the 19th century to use the military to drive all big predators (especially lions) to extinction, deliberately, because they use up so much land, and the territory required by just one of them could be used by many humans. They didn't find anything ethically questionable in it, and likely it wasn't done because of the expense, or because of having higher priorities in other areas. $\endgroup$
    – vsz
    Commented Nov 24, 2020 at 14:34
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    $\begingroup$ "European lions were unfamiliar with humans when they first arrived. and were too slow to learn this lesson" Hey Sheila, you look full, did you score some prey? Oh yes. I had one of those stupid smooth skin bipedal creatures, so slow it's funny. WTF. Damn it Sheila. We need to move. Like now. Guys lets pack up, we have an idiot here. Fast people. Relax. What are they going to do! Come at us with torches, spears, and arrows? Hey. What's that over there? $\endgroup$
    – Seallussus
    Commented Nov 24, 2020 at 17:46

Okay firstly, you might want to narrow down what sort of sea beasts there are their commonality, and dangerousness since this will determine how sailing is affected. A world filled with twisty sea serpents that can wrap around your ship looks much different from one where a mosasaurus rips out your rudder. But Im going to throw out some general stuff.

  • Ships will mostly likely feature saw patterned spikes along the keel, and other parts of the ship so its harder to wrap around the ship or bite it
  • If creatures can leap out of the water to get crew on deck then an armored cover would be in order, something like a Korean turtle ship perhaps (add spikes and razor edges on that too)
  • Ports in various parts of the ship to stab spears through would be useful
  • If possible people will defiantly research and utilize various scents and sounds to see if they can drive creatures away or at least irritate them
  • All of this will make sea travel even more dangerous than it already is, however sea travel is still very fast so its likely people will try very hard to use it (assuming people develop large scale boating at all which is very much dependent on what your masters look like and how they behave)

The first thing it would do would be to delay ocean, river and lake travel developmentally.

Humans used rivers as the earliest "roads" pretty much everywhere. With rivers being far more dangerous, they'd either wipe out the megafauna in them (more work than not), harvest them (less work than not), or avoid using the river.

Similar things would happen with seas and near-shore ocean creatures. Either humans wipe out the hostile creatures, harvest them for food and resources, or have to avoid sea/ocean going.

Assuming these hostile creatures aren't a net boon:

People's that didn't require clearing the waterways -- like steppe or plains nomads -- would have an advantage over the settled cities that rely on goods being transported by river, ocean or sea. So I could see "nomad" civilizations getting further ahead than (in our world) the flood-plain, and river/forest/coast civilizations (which started becoming more dominant around 6000 years ago).

Now, in our world, the nomad civilizations still tended to regularly conquer the water-dependent civilizations (often they where pushed by nomads further inland, and found the city dwellers rich and easy to conquer), especially early on in our history (Persia, for example, was a nomad civilization conquering a city-civilization originally).

Maybe this lasts longer.

In our world, eventually the city-civilizations started scaling up more. In the West, Rome, Egypt, Greece and their descendents start getting strong enough that they are able to usually hold their own against "barbarian" waves (at least until the Mongols). All of them, however, relied on water to do this. So I'm not sure how much it would help.

The other side of the coin, where harvesting this megafauna is a net benefit, is you'd see faster expansion of the city civilizations as they develop better ability to harvest it. Much like the mammoth fueled human expansion, the same could happen along the coasts of the world. It is possible that the land-based Nomads would arrive in an area and find it already harvested and fortified by the coastal peoples, slowing down their growth.

Learning deeper sea travel and being able to chase the great beasts of the water deeper would become a huge economic advantage. So naval technology might develop faster than it did in our world.

With most of your calories coming from the sea harvest, your base on land wouldn't need the land around it. Farming becomes less important. Fortifying yourself against raids from the relatively impoverished inland nomads becomes important. So you build your settlements on places like Venice, where a land army is at a serious disadvantage. Farming forests becomes key to producing the great ships needed for your food supply.

Maybe you go "a viking" and raid the land-dwellers for resources hard to find at sea, and force them to provide tribute or be crushed by marines. You battle with farmers, ensuring that large stands of forest you need for your ships stay intact.

Leaving sight of land remains dangerous for non-monster reasons, but you get better at it than ancient non-Polynesian people did in our history, because calories is power, and monsters are calories. Your ships scour the 7 seas for places to hunt the monsters and bring more food home. When you find monsters, you land and do the work to preserve the food, before setting out and heading home. Those places where you land become increasingly fortified, and eventually form permanent settlements, which rule over the local non-sea folk.

Advances in navigation eventually lead to global empires at lower technology levels than today.

Inland dwellers fear the coasts and the oceans, and have fragmented governments. Eventually those inland people develop better road technology, bridge fortifications strong enough not to be destroyed by the raiders. Eventually a the dryland war happens, where a large inland empire fights the largest ocean empire, and loses, but almost wins.

This causes a seismic shift in how the ocean civilizations treat the interior. Some attempt to clean out the rebels, others rule them, others start merging with them.

In this phase of history, perhaps the materials science of the drylanders and the astronomy of the wetlanders join, and they develop true ocean going ships, including coal powered iron clads. Around this time the deep oceans are no longer safe for the monsters of the deep, and an extinction event happens; the huge spike in food production followed by the collapse of the monster fishery leads to the wetlanders now needing dryland resources, and a massive war.

Ideally this war should be fought with airships, clockwork and lots of gears everywhere.


Ships might try to be less detectable.

Counter shading. Light on the bottom and dark on top, so that they blend in with the surface from below. Humans might figure this out earlier (in our world it wasn't really understood as a form of camouflage until the early 1900s).

Garbage and waste would not be casually disposed of overboard. Ships would have to figure out some way to store this, which will be difficult for onboard sanitation. They might store as much as possible then dump it all at once when they can quickly leave the area.

Using tar on ships is not going to work, they will smell you from miles away. Maybe they would use something like teak or birch bark that doesn't need extra preservatives as an outer coating.

Sound reduction. This one is going to be really hard. The actual noise of a ship sailing with the wind is probably not too bad, but there was a lot of yelling and moving heavy objects around involved, so that's going to have to stop (or at least not be transmitted into water--maybe it would be OK to have noise in the air). Hulls might have some kind of noise insulation along the inside. Boots might have soft soles, or something soft on the outside to muffle them.

Maybe coastlines might have things that make extra noise continuously, to drown out any noise that ships make.


The question has a false premise, that large aquatic animals that could be called "sea monsters" are a significant threat to ships.

In reality many possible dangers in the oceans are many, many times more likely to damage or sink ships or kill people aboard them than encounters with large sea creatures, which are a tiny fraction as likely to cause trouble as storms, uncharted rocks and reefs, navigation errors, fires, epidemics, scurvey from lack of proper food, etc. But even today, boats as large as some ships in fantasy settings are occassionally sunk by encounters with sea life.

I recently read about an infestation of jellyfish in Japanese waters. Japanese fishermen took to catching Jellyfish for lack of more valuable prey, and one boat tried to haul up a a netfull of jellyfish so heavy that the boat capsided.

And I read about an American fishing boat which had a similar fate. It hauled up so many fish that it eventually capsized and sank. The fact that one of the fish it hauled up was a ten-ton basking shark probably contributed to the sinking, since it probably did a lot of damage thrashing around.

Many sailboats have been damaged and/or sunk by collisions with large sea life, for example with orcas or with pilot whales, which are certainly smaller than great whales. And those sailboats may seem tiny compared to modern ships, but might be as large as some ships which were used to cross oceans during the age of sail.



The large outrigger canoes used by the Polynesians to colonize widely scattered islands in the Pacific Ocean were also small enough to be easily sunk by encounters with sea life, though of course other dangers would be far more likely.

Procopius claimed that a sea monster (species uncertain) terrorized shipping in the Sea of Mamara, sinking a number of ships for fifty years, and its size as described by Procopius would certainly make it a rather ordinary, medium sized, whale - if it was a whale.

So it is no wonder that some wooden sailing were damaged and/or sank by mostly accidental collisions with large whales - and in a couple of cases allegedly by being struck by the whales' tail or by the whale leaping out of the sea and landing on the ship.

I am uncertain how many ships have been sunk by accidental or deliberate whale actions, but certainly that was a real though unlikely danger in the days of wooden ships and iron men. Different sources on the internet give numbers of whaling ships (as opposed to whaleboats) sunk by Mocha Dick ranging from zero to two dozen, for example.

So possibly your fictional world has far more species of whales, and some of them are far more numerous than in our world. Thus the potential for accidental or deliberate collusions with whales could be higher than in our world.

I note that whales were far more common up to about a couple of million years ago, when many species became extinct. And in those days the giant carniverous shark Megalodon preyed on numerous species of small and medium sized whales, as did the carnivrous whale Livyatan mellvilli.

A world where great whale sized predators similar to Megalodon and Livyatan preyed on whales might also be one where those predators also attack ships for some reason.

Or maybe there is at least one species of whales in that world intelligent enough to have language and government. And perhaps a group of humans somewhere decided to try hunting those whales, and as a result the whale government decreed that any ships detected should be attacked and sunk at once, so now no ship can sail far without a whale attack.

And of course in the age of reptiles there were a number of species of giant sea reptiles which were many times larger than any sea turtles or sea crocodiles of today, in the Megaladon size range. And they might attack ships wondering if they were good to eat.

And possibly your oceans could contain an abundance of large squid, some of them much larger than the largest known in our world.

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    $\begingroup$ It's a nice long answer, but it appears to me that it answers a different question of "what animals could make seas more dangerous?", focusing on whales to boot. In my scenario seas already host numerous species that both can wreck the ship and can have the consistent desire to do so, my question was how would people adapt to these conditions. $\endgroup$ Commented Nov 23, 2020 at 21:18
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    $\begingroup$ Agreed, its a nice answer but, uh, doesn't really answer the question $\endgroup$ Commented Nov 23, 2020 at 23:47
  • $\begingroup$ A consistent desire to wreck ships is immensely implausible. Ships are too rare for any animal to make them a regular diet, especially an animal large enough to pose a danger to one. $\endgroup$
    – Mary
    Commented Nov 24, 2020 at 16:52

If you want to make your seas REALLY hard to navigate, do not waste time on big animals with lots of brute force.

Instead, make seas populated with a SMART animal like dolphins or orcas which use tools and communicate, have culture and cooperate defending their realm.

They might even ACTIVELY HUNT human ships to get metal tools which they cannot manufacture underwater.

Some people even might SELL THEM metal tools in exchange for protection during fishing or something.


ships would form convoys, banding together for protection. these nasty giant octopus might be able to attack and sink one ship, but a dozen who support each other? in history, convoys were formed against pirates or u-boats and have proven to be somewhat effective.

ships would be build to hinder the monsters natural attacks. giant whale capsize ships from beneath? install pointy metal objects on the underside. kraken grappling the ship whole? install spikey stuff all around. ships might adopt the hedgehog-philosophy ...

balistas and similar weapons would be developed sooner and be much more common on ships. some clever mind will find some way to attack the monsters even while underwater. harpoons, for example.

we'd probably see more weapons on board. for the most time it wasn't uncommon for a sailor to be armed, but in your world it would be crazy strange to go unarmed.

if there are any powerful seafaring civilization, they'll want to protect important trade routes, so there might be warships patrolling these routes and the surrounding, hunting these monsters.

humans will study these monsters and find their weaknesses. is a monster largely territorial and marks its territory? find out how to do that and now mark your territory, and maybe deter it. does the monster need deep water to survive? sail through shallow coastal waters as much as possible. learn what habitats the individual monsters prefer, to get an idea whats comming. make maps that mark known populations.

sea trade will be somewhat effected because all this makes it more expensive. we'll probably see a focus towards goods that bring more profit per ton, because everything else is not worth it, economically. sea trade might be less important to your economies. another option would be to travel at land for as much as possible and just cross the smallest sea possible. for example if you want to trade from casablanca to valencia, you'd not sail your goods from c to v, but instead bring them to the strait of gibraltar by land, cross the short distance there by ship and continue to transport by land.

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    $\begingroup$ Exactly. This is how they responded to U-boats in the war, which are just mechanical sea-monsters. The ships formed convoys and were accompanied by battleships to protect them. Special weapons were developed as well - depth charges etc. $\endgroup$
    – RedSonja
    Commented Nov 25, 2020 at 11:42

Well, I would go for a different spin. We can do so much with beasts like this!

Take Dune and make it moist.

If the animal is that large and dangerous, why not spend some effort to bring them to use instead of hunting them down or trying to evade them?

Make your humans live in a symbiotic relationship with your dangerous megafauna, not only using them as prey for food but hunting partners, animals of burden, guard animals, beasts of war and so on.

Nessie is far less likely to try anything funny against your ship if you're being scorted by Krumpy, your pet kraken!

Heck, you may even ditch sails entirely. Why use it, if you can make friends with a dragon turtle to ferry your stuff around? What about a racing boat tugged along by a pair of massive mega sharks? Or what about a group of sea nomads that travel around on the backs of massive manta-rays, "flying" along the coast?

Water beasts used in this manner isn't unheard off in mythology. One of those famed beasts is the Hippocampus, or the Mer-horse, if you will:

enter image description here

I mean - animals that large everywhere already have several issues that you'll have to handwave anyway. Making them smart enough to be tame-able wouldn't be the hardest thing to explain away!

So, my suggestion - instead of using it as a constraint for your worldbuilding, have fun with it and use it to push your narrative in a more fantastic direction. Bring them inside the fold of your civilizations, make them part of it, and I'm sure some amazing stories will end up writing themselves out!


It would create a giant dent in sea-travel. People tend to avoid the unknown and dangerous (besides the most adventurous of us). So most people would merely stop sailing.

Alternatively, people would find safe routes that avoid those undersea monsters hunting grounds. The whole point of a map saying "here there be dragons" is like saying "avoid this area at all costs or be utterly decimated".

Of course, the most adventurous people would find a way to hunt those creatures. They would make ships able to withstand attack from the monsters, sail out, and hunt them down. The ships would most likely have metal plates added to the bottom and perhaps have some way of dropping a form of payload underneath to drop into the gaping mouth of an attacking beast and destroy it from the inside


Sailing may become limited or even non-existant

This may not be an answer you were expecting, but Windhaven by George R. R. Martin and Lisa Tuttle describes a world where, due to storms and large sea creatures ("... or perhaps a scylla's tooth, long as her arm, ..."), ships are neither safe nor reliable, except for local travel. In this scenario, other means of long-distance travel may be the better choice:

For the land-bound, the flyers were the most regular source of contact with the other islands. The seas, daily storm-lashed and infested with scyllas and seacats and other predators, were too dangerous for regular ship travel except among islands within the same local group. The flyers were the links, and the others looked to them for news, gossip, songs, stories, romance.


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