Sea-monster resistant sailing ship design

Question

The Setting:

The world is over 99% water with only very small bastions of solid land or ice covered land. The humans who live on this world are very capable swimmers and divers who can hold their breath for a very long time. In general, the people are smart however they are held back from an industrial revolution due to their lack of metal, fuels, and simply because their population is limited by the size of the island. Technological progress has stagnated or for a couple hundred years while theoretical work including math, physics, and philosophy have continued to advance. For example, scholars on the island have a firm grasp of calculus and Newtonian physics but have dismissed ideas of making a steam engine as it would be too expensive and impractical (which is true, they simply don't have the metal or the need).

Technology Level:

The people have wood and other agricultural/biological resources such as fibers and cloth for sails. Metallurgically, the people have somewhat advanced techniques but due to the small size of their island, they don't have a lot of metal. Most of the metal they have is bronze however they also have a large amount of meteoric aluminum. At great cost, artisans can create mechanical clocks and devices but these are reserved for the island's elite.

Additionally, the people have quite a good grasp on optics as the nature of their island allows easy glass-manufacturing. Plants with large reflective leaves allow them to make cheap mirrors and reflectors for long range signaling or concentrating sunlight to cook.

The Monsters:

Due to being a water-planet, the land that the humans inhabit has basically no natively-evolved creatures on it and it is very safe. On the other hand, the sea is very dangerous. All varieties of massive fish, giant tentacled beasts, or venomous jellyfish can be found there and occasionally attack ships. The largest creatures are big, think kraken-attacking-pirate-ship big.

The Rationale:

The people, besides needing to travel between their tiny bastions of land, rely on the sea for a large amount of their resources. Fishing is very popular along with trapping (like lobster traps) and diving to harvest underwater plants and resources. Additionally, there is a high cultural drive towards exploration as finding new lands to support the growing human population is seen as important.

The Question:

What features might a sailing ship include which helps the crew fight against frequent monster attacks or make their travels across the dangerous ocean safer?

For example,

• Sharpened wooden spikes lining the outer edge of the ship's hull to combat giant tentacle attacks
• Barrels full of dead fish that the crew can throw overboard to distract any predators
• Listening posts or portholes below the waterline of ships where specially trained crew members can listen or watch for incoming monsters

Answer 1

There are many things that you can do to protect a ship at sea, but they're not all what you might think.

Copper coated hulls

Teredo navalis is a very small sea monster, but utterly destructive of wooden ships in the long term. It's one we have here as well and there's no reason to make it any more dangerous than it already is. Creosote also works.

White paint

Start thinking like a fish, many of them are dark on top and lighter underneath, this is to allow for the different light patterns and gives basic camouflage.

Streamlining

Faster ships are good, but we're still trying to reduce our visibility. A better streamlined hull will be quieter and not attract monsters from such a large area. Any spikes or other heavy defences on the hull will have the opposite effect.

Hydrofoils

Taking this to the cutting edge of what you might be able to pull off with your technology level. Sailing hydrofoils are a thing, if a little fragile, and could potentially allow a small vessel to outrun anything that might cause it trouble.

Sticking to known shallow waters or very deep waters

Octopodes are ambush predators, keep away from waters that provide cover for a large kraken-like creature and keep moving fast. You're mostly vulnerable when passing over underwater crevasses in moderate water depth. If you have access to a gently shelving sea floor there won't be any cover for such a predator.

Very deep waters are basically the deserts of the ocean, there's very little out there.

The most dangerous places are the best fishing grounds. Places where the sea floor shelves up steeply driving deep water currents to the surface. Such locations will have the most food and with that, the most predators.

Kraken-hide ships

With lots of tentacles krakens should be at risk of getting tangled and attached to themselves, but the nature of their skin and tentacles means they don't. Coat/make your ships with kraken skin and they won't be able to attack.

Answer 2

Here's an interesting question I'd like to ask: Why should a ship have to float on the water? What if it floated..... in the sky? Your civilization has the technology for fabrics and textiles-- why not make a hot air balloon? If you can successfully sail high enough in the air (which is probably not that high) you could safely avoid any sort of sea monster!

The drawback here is obviously that you're going to see hugely reduced cargo capacity relative to something like a ship-- but you'll also be significantly safer. You're also more at the whim of the weather-- if you run into a storm, or if you miss-calculate something and fly too high or low, it could end very, very badly for you.

I understand that I may not be fully answering your question, as you probably want to incorporate some of the dangers that would go along with being on a ship in the ocean having to contend with a bunch of cool monsters. That's fair. The hot air balloon might be a scouting vessel, or a last-resort-life-boat type situation for a few crew members to rush to in the event that the boat is destroyed. (I'm assuming that the hot air balloon is tethered to the ship and just floating there at all times, since it would take way too long to inflate the balloon in the event of an emergency)

As for the ship itself-- I think that their best bet is to just avoid being attacked in the first place rather than fend off the attack. The best way to do that is probably to follow in nature's footsteps: Pretend to be something you're not. What's the biggest, baddest, scariest creature that anyone has ever found in the ocean? See if you can make the ship look like that beast. All of the smaller monsters will be scared off by it hopefully. Only the biggest, meanest ones are going to come after the ship. And after all, that's only one type of monster, right crew? There's no way there's an even bigger monster that we haven't seen before that would see that one as a meal! Right???

Another option might be poison. If one of your societies could kill something highly venomous (say, one of those giant jellyfish), ships could coat weapons in that venom. If a predator pursues them, it's now a race to figure out how to poison that creature before it attacks! Maybe you put venom on some of the dead fish that you throw it, as you desperately hope that this monster's insides won't like the venom! Maybe you treat the wood with it? Maybe you take along convicted criminals/enemy soldiers and coat them in the venom, then throw them overboard? The world is your extremely deadly oyster!

Answer 3

Small islands means small trees. Small trees limits the size of your boats, so you will see things much more like islander catamarans and kayaks. People on earth have used these kinds of vessels to travel thousands of miles. That's what you will be limited to. Since we do the best we can with what we have, your best defense will probably speed along with just not being big enough to be worth a really big predators time.

You mention your people being very good with math. This is going to help with the speed aspect. Advanced hull designs and streamlining will have these boats moving along very fast. They will also be able to develop precision instruments and accurate charts. This is extremely important. The best way to deal with a predator is to stay away from where they are. Accurate navigation keeps you in the safe water.

I imagine your people are going to spend a lot of time studying the creatures that are threats. That includes how to kill them. They might try hard to find toxins that discourage the large kraken like creations. An example would be learning about, I dunno, Sea Urchins. Lots of fish might avoid them because of the pointy bits, others because they have irritants. Coat your hulls with the irritants and those predators might stay away, just like skunks drive away their predators with a good dose of spray. Or make a concentrate of the stuff to dump in the water on demand.

In extreme circumstances, you might be able to make explosives. Make those waterproof and you could even create depth charges. These could be made without metal because they rely on pressure waves to kill rather than shrapnel. I know you need charcoal, sulfur, and saltpeter to make black powder. If you island is volcanic you have a good chance of sulfur. Seabirds will provide the saltpeter as guano (on earth we have fought wars over islands covered in seagull crap). The charcoal can come from the unused bits of tree when you build a new boat. I'm not enough of a chemist to know how to make a fuse burn underwater, but that might come from handwavium.

Have some fun with it.