Using just one fantastical element (a rock that under certain conditions produces a strong buoyant force) how would sail ships in the air be designed? It doesn't need to look like a traditional naval ship, but what would be the best way to harness the winds under these conditions?

Some of my thoughts:

  • The center of buoyancy would still need to be well above the center of gravity for the vessel to be stable
  • The vessel wouldn't need to be airtight like a naval ship would be
  • Without the friction of water, the vessel would be at the mercy of the wind a lot more than a naval vessel. Would a keel even help in this circumstance or would a large tail to add some drag be appropriate? (Or maybe both?)
  • Maybe I'm wrong but I feel like a big old keel would still be effective, but it would need to be significantly larger than the keel of a naval ship.
  • $\begingroup$ Sounds like an airship, a.k.a. zepplin? $\endgroup$
    – IronEagle
    Commented Dec 18, 2020 at 17:43
  • 2
    $\begingroup$ Ships and sails take advantage of the boundary between air and water. They are often flowing in different directions and at different rates, and you can use that difference to generate power to for steering and propulsion. Without a boundary to exploit, you're just drifting wherever the wind takes you unless you use an external power source (like a motor) to propel yourself through the air (powered flight). Using sails without a boundary generates no power because you are already drifting with the wind. $\endgroup$
    – user535733
    Commented Dec 18, 2020 at 18:09
  • $\begingroup$ Jules Verne had a clever idea in his Five Weeks in a Balloon (1863, first English translation 1869). Freely available at Project Gutenberg. $\endgroup$
    – AlexP
    Commented Dec 18, 2020 at 18:48

5 Answers 5



A purely wind-driven floating ship would be utterly at the mercy of the wind it is in, no form of tacking or flying against the wind would be possible because unlike a seagoing vessel, it cannot push against the water in a different direction that the wind is blowing. This is an inevitable consequence of relying on the wind at the ship only.

So, allow the ship to use the wind in different locations! Kites, of the flying wing type and having a (relatively) stationary anchor point, can tack against the wind. Or at least pull significantly off from true downwind. All that is needed is for the wind at the kite to be moving at a different speed than its anchor point is moving.
By flying a kite at a significant distance from the ship, in an airstream moving at a different speed, you can use this difference in wind speeds to generate a pull. Because of the flight characteristic of the flying wing kite, this pull need not be directly in line with the wind direction at the kite!

By using two or more kites on opposite side of the ship, you should be able to generate quite a bit more pulling force and thus speed than the wind itself, and use the differential pull between the kites to facilitate steering too.

You won't be able to go against the wind, but tacking at an angle many degrees off downwind should be quite doable.


Control by controlling the sail area

Unlike sea ships, air vessels are completely at the mercy of the winds. While watercraft have their hulls sitting the water (which is much more stable than air), airships have no choice but to move with the surrounding air.

However, careful positioning of aerial surfaces can make the flight much more controlled. Airships still have significant mass, and their sail area would dictate how fast the ship would be responding to the winds. The sails of the ship should be able to quickly fold, unfold and reposition to catch the wind in the favorable direction and do their best to ignore the unfavorable ones.

  • $\begingroup$ Jules Verne had a clever (and possibly better) idea in his Five Weeks in a Balloon (1863, first English translation 1869). Freely available at Project Gutenberg. $\endgroup$
    – AlexP
    Commented Dec 18, 2020 at 18:48

If you can control the buoyancy - possibilities abound.

So if you have a magical element that generates lift, perhaps you can control its effective output. If so you can control your altitude.

What this means is you can use a technique that balloonists use - navigating by different air currents at different altitudes. Contrary to belief, air often flows in different directions depending on altitude.

Therefore I would imagine your society would keep copious observations in maps of air currents at different times of year, different times of day and night.

The other factor to use would be your ratio of potential to kinetic energy. You don't have a keel, unlike a boat, but you do have a rudder. So warships I would imagine would want to be at the highest altitudes possible, with long rudder-like surfaces, such that they have the best manoeuvre advantage when engaging an enemy. By converting potential to kinetic energy, they can get tremendously fast, and as such on a downward trajectory even travel 'into the wind'. I know yacht racing captains that use this technique to squeeze as much speed to round a mark without tacking by 'diving' into the wind.

So, features of your air ship would be:

  • long linear hull, still like a fish, for those instances where diving for manoeuvre into the wind makes sense
  • large rudder surfaces to control direction on downward trajectory without losing speed
  • I agree with PcMan - kites would be useful for cruising into the wind
  • Ability to control your magic element
  • Chartroom with many charts and observations over many years to assist navigation (this would actually be much more complex than 2D charts in old naval vessels)
  • because you would want to be as high altitude as possible in a conflict situation, air might be quite thin, so you may need to consider breathing apparatus.

You face one large problem with a wind powered aircraft: no resistance to offset the wind direction.

Sailing ships can tack against the wind, because their hull is in the water, which provides resistance to the direction the wind wants to push the ship. That, combined with angling the sails, allows a ship to sail in a direction different from which the wind is blowing.

In the air, there is nothing to anchor your ship to, so you're going to go in the direction of the wind.

And that's exactly what hot air balloons do: they go wherever the wind takes them. It's a fascinating journey, but zero directional control, other than being able to rise or fall.

One possibility: let's say you have two elements that produce buoyancy when brought near each other. You could build a sailplane that could produce lift on demand. No tow plane needed, and no hunting for thermals.

By angling the wings up as you rise, or down as you fall, wind pushing on the angled wings gets it going forward. But, you'd need direct control over buoyancy to do that.

So your wind ship could be long and narrow, with long, graceful wings stretching out.

Or perhaps you could domesticate a dragon to tow the ship (brave soul!).


You don't need a fantastical element. Physics will do. A vehicle CAN theoretically sail (not drift the wind) in air and generate power, thrust, and whatever else you need.

All you need is two sails in two control volumes, that have different properties. Very roughly put - if you have one wing in ground effect, and another in the stratosphere, you can transfer energy between the two, and siphon part of the transfered energy into your vehicle.

Bouyancy - you can make your wings smaller and minimal speed lower by making your vehicle more bouyant. Without fantasy, on earth - you're stuck with a zeppelin, which usually means lots of drag and whatnot, but a zeppelin can be used as one of the sails. The second sail can be a kite attached to the zeppelin, which extends into a different portion of the atmosphere, with (for example) a different air current velocity.

The greater the difference between the two control volume properties, the better the effect.

I distictcly remember a scientific publication that proved that a sailing airship can be built for Mars exploration, but can't find it anymore.

Edit: There might be a significant gap between theory and practicle implementation, i.e. you might need super long and light wings, which can't be built with known materials, or a tether between the two wings, which might be too heavy without new materials.


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