# Forum > Gaming > Homebrew Design > World-Building >  How Do Ships Sail Off Of The World?

## brian 333

In most space-fantasy, rocket ships or some such blast off to outer space. Spelljammer had naval vessels sail into the sky. The visual imagery of such ideas left me a little underwhelmed.

One day someone on this forum posted something that sparked my imagination, and I envisioned space as a vast ocean with currents, tides, and prevailing winds. Worlds were flotsam in this galactic ocean, creating gyres in three dimensions, all caught in stellar gyres, which were caught in galactic gyres.

At the smallest, asteroids and other debris have such minute gravitational potential that they do not generate gyres of their own. They simply flow with the currents and the winds.

Small moons with slight rotation are not much better; however, a small moon or dwarf planet with a high rotation can create gyres. This will typically be in the form of a North and a South Pole, centered along the axis of the world's rotation. Wobbly rotation creates weaker or sporadic gyres, while tighter rotation creates more powerful and steady gyres.
In the center of these whirlpools are tornado-like funnels which draw down, (N,) or spit out, (S,) the astral vapors of the galactic ocean. Entering these whirlpools, even on small worlds, tends to grind material into its constituent components. However, its outer surface is much like the surface of an ocean, twisted around the tornado-like stalk of the vortex. A ship can ride these outer surfaces up into space or down to the world by getting beneath the gyre in space and sailing its outer surface. Sailors say this is like riding out a ferocious storm. Counterintuitively, larger vortices provide smoother rides.

The complex mathematics that predict the size of vortices keep the learned up late into their nights. Generally, mass and spin of the world are predictive of the size of the vortices. 1/2r=h, and πh=Dv, or the height of the gyre above a world tends to be half the radius of the world and the diameter of the gyre tends to be 3 times its height above the world. Of course, faster spin can increase the diameter of the gyre and decrease its height, and other gyres and currents in the local area can similarly affect these dimensions.
For example, a tidal locked moon may have no gyres of its own, but may 'borrow' one from its primary. If its rotation around its primary is fast enough, relatively weak gyres may form on its axis.
Furthermore, on a large enough world, Sympathetic or Induced Gyres may form, such gyres being responses to the counter-rotation of the North and South Poles. Typically an Earth-sized world will also have an East and West Pole, whose bases move around the world's equator. Sometimes an Earth-sized world can have sporadic vortices form due to other factors, but such events are difficult to predict. Mars-sized worlds rarely have more than two permanent vortices, while Jovian worlds can have sixteen or more at a time.

Navigators must learn to locate and predict such gyres, to predict and map the stellar and interstellar winds, and to understand the currents of the galactic gyre itself. Captains must learn when their intuition should over-ride the calculations. Common sailors must learn to pray that their trust in their officers is not misplaced.

The galactic ocean is a beautiful, dangerous, mysterious place filled with treasures and terrors. Only those brave enough, and knowledgeable enough, should venture there. But for those who set their sails to ride the East Pole into the sky, the galaxy awaits.

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## Quizatzhaderac

As the aether flows through the cosmos, it is inevitably pulled down towards planets. However, where the other four elements get caught on each other and stick to the planet, the aether does not. What goes down, must come up; as much aether as falls to Earth at the equator must shoot off into space at the poles.

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## brian 333

> As the aether flows through the cosmos, it is inevitably pulled down towards planets. However, where the other four elements get caught on each other and stick to the planet, the aether does not. What goes down, must come up; as much aether as falls to Earth at the equator must shoot off into space at the poles.


Exactly!

I envision it as, two pole minimum, and aside from odd situations, poles come in pairs. Jove has sixteen, Mercury two. Moon only has two, but wouldn't have any if she was not being dragged around Earth's primary N-S pair, strengthening and weakening Earth's secondary E-W pair as she distorts them in passing. (Both are strongest when she is above one, and weakest when 90° from both.)

I also envision dust columns in the lower part of the Moon's and Mars' gyres but ships which fly in space can navigate them to soft landings in their respective dust seas.

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## Catullus64

Interesting stuff. For my _Kingdom Under the Sun_ setting, to which you offered some interesting contributions, I thought a while about how I wanted to handle the planet-to-orbit part of travel, before the fantastical explanation of cosmic rivers and firmaments can take over to explain how interplanetary travel is possible. I ultimately decided on explanations grounded in ancient physics: the cosmos has absolute directions of up and down, through which all matter is endlessly falling. Earth alone is fixed in place, and it holds the spheres of the other planets in place as well. Water, originating in the infinite firmament which surrounds the cosmos, flows down from the northern hemisphere, where it enters the atmosphere via cosmic rainfall, to the south pole, where it drips out into the void. Earth's oceans are thus a big spherical pond in the course of one of the great firmament rivers. Thus, ocean-going ships, by sailing far enough south, can simply fall out of the world and into the currents which will carry them to other planets. 

Of course, not every planet has the same consistent and navigable flow from top to bottom as Earth. Three other planets' peoples have independently developed interplanetary travel: the Mercurians, the Empire of Mars, and the various barbarian peoples of Uranus. 

Mercurians have the fantastical substance, named after their god and planet. Mercury, when treated on its home planet by the proper alchemy, can be made to move on command. Large quantities of the stuff can be made to levitate. Thus, a Mercurian ship, with a complex Mercury circulation system in its hull, can be levitated just long enough to break orbit and reach the firmament waters. 

Martians, gifted in ancient sorceries from their god, have historically relied upon a complex system of portals to pass between worlds. The ecological damage wrought by this portal network has damaged Mars' ecosystem severely, and the Martians have been forced to adopt foreign spacecraft in order to reduce their dependence upon these portals.

Uranians are lucky to inhabit a planet which is the natural nesting-grounds of the great celestial rocs, with whom they have built up a long-standing alliance. The rocs, in exchange for royal treatment and veneration, consent to be harnessed to what are essentially big space chariots. The roc provides the initial flight out of orbit, before depositing its chariot in the river that will carry it to its destination; they lack the strength to pull the chariot through space over longer distances, but they will generally fly alongside it, so it can help it return home.

How these different planets and methods of navigation accommodate one another to form an effective cosmic trade network is something I'm still figuring.

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## brian 333

So, instead of the old metaphorical 'energy runs downhill' you literally have 'everything runs downhill' as the basis of your world's physics!

It has a poetic symmetry. Now we need a Water-bearer deity to pour an endless amphora over the heavens.

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