How do I eliminate air craft usage in my story?

I think that the majority of my suggestion could still apply. The world can be split into three parts, Land, Sea & Sky.

Land is primarily made up of large island to continental sized landmasses, and produces a stable magical field around itself. This magical field stabilises the local environment, and is the main basis through which the landmasses don't run into each other, though any landmass as small or smaller than Ireland is likely to get run over by a continent it can't get away from quickly enough, though some continents do still run into each other anyway. As you have said that magical energy is not accessible for use, just treat the magical fields as if they are natural landmass-wide electromagnetic fields. They're there, and you can observe them, but you can't really affect them in any way to benefit yourself.

Sea & Sky is where things are different. Both do have magical energy like the land, but it's not keeping things stable like it is for the land, instead it makes things more chaotic. Due to that, if one goes outside of the stable magical field produced by the land, if one goes too high, they're likely to be ripped apart by the winds that only get more and more ferocious as you go higher. Alternatively, if someone tried to make a submarine and go beneath the waves, they'll discover than the ocean depths similarly become more environmentally chaotic and destructive the deeper you go, easily tearing apart any submarine that attempts to delve it.

Then why do ships work? Well, because ships travel the surface of the ocean, the midpoint between Sea and Sky. While there isn't the inherent protection that the land's magical energy produces, the chaotic energies in the Sea and the Sky mostly neutralise each other when they come into contact. As such, there's a comparatively safe zone, the surface of the sea, that can be utilised for travel. It's not perfect, in area's where the ocean's energies are overwhelming you get devastating storms (because the water's getting into the air), while in area's where the sky's energies are overwhelming you get tornado's and whirlpools (because air's getting into the water).

While, yes, this does prevent you from creating underwater civilisations, from what you have presented so far, I'm assuming that you don't want your characters to be able to dive into the water anymore than you would want them to be able to fly everywhere.

 

Ahhh I see. The first part of suggestion, (the "electromagnetic"/magical fields) is quite interesting. Partly because I think it's very versatile, and fits with some other ideas given in the thread. Someone before had suggested that the landmasses naturally repel each other to a certain degree (so they don't get too close), so they create turbulent weather conditions at sea and I'm thinking it'd be interesting to see how this sort of "balance" would be disrupted by smaller landmasses like Ireland for ex. I can foresee some dramatic storylines with this. But also a lot of versatility, which I want.

As for the Sky, I think that just about makes sense. The general idea I was going to be developing would be that the atmosphere is simply too chaotic from natural conditions (combined with technological limits but ofc those are not always a guarantee) to fly or travel. The tornadoes and devastating storms also sounds very appealing. The only part would be the underwater, since I did want to expand on underwater stuff way before this thread. Also a couple of other plot points in my story kinda deal with under water.

I think I can make a lot of this work though, most of what I want is the same, it's just about now forming a solid reason. Which I think I'm basically almost at. Just a few more days of organizing my notes maybe.. Also thank you so much for the ideas, this story is something I've been mulling over on for quite some time and it's amazing to get some help from unsuspecting strangers. I was in a stump a few days ago about this

 

I'm not sure about the other posters, but this type of thing (coming up with mechanics behind how some fictional world design choice I decided upon works) is the type of thing I do to entertain myself. So my two posts can be considered me going "Shiny thing! Play with shiny thing! Oh, here's your shiny thing back, thanks for letting me play with it!"

 

Fragile materials and gravity(the bigger a world is the higher the gravity), the electromagnetic waves mess up the GPS, air resistance, groups of animals, the aircraft can't be big enough to carry enough fuel and if there is then they waste a lot of fuel, unstable and unpredictable weather, weird air pressure, etc.

 

IRL the magnetosphere protects the world from cosmic radiation, just make a magic version
e.g. there is magical radiation or turbulence in the air, either it comes from the sun or from space, it makes magic violent and unpredictable, but the landmasses generate a magical/magnetic barrier that prevents the radiation/turbulence from getting too low
its possible to go up, but the higher people goes their bodies and machines erode faster, its not enough to kill a person on the short term, but machines' components get messed up more easily
At sea there is no turbulence/radiation, because the sea floor provides magnetism too

 

Here is a new proposition:

It was mentioned that the landmasses teleport randomly around. If this isn't physical movement and actual spatial teleportation, it can be a reasonable setting that every teleportation causes spatial turbulence extending into the atmosphere. Imagine if you had some liquid of high viscosity, kind of like pudding in a bowl. If you scoop some of it out, the surroundings will slowly smoothen the gap caused by the displacement of pudding. When you put the pudding back into the bowl at a different place, it will also slowly assimilate back into the rest of the pudding. If the world is like the bowl of pudding and the landmasses and their teleportation is like the scoop, then it would be reasonable to think that aircrafts cannot travel.