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I'm creating a human civilization which exists on a largely arid planet, with a great deal of Tatooine / Arrakis-like terrain.

These humans have no idea they are not native to the planet outside of religion and myth (many believe the stars rejected them for being childish, which isn't far from the truth.)

This is a civilization which has not developed wheels / tires which can effectively travel through sand dunes- they are at roughly a European Renaissance level of technology with combustion engines just being discovered within the past few years (Dieselpunk, you might call it?) Wood and metal wheels exist, perhaps leather tires, but nothing that wouldn't just sink right into deep sand and struggle to gain traction.

The story is to focus on a very large vehicle to act as the desert equivalent of a sailing ship. The issue is that I want to avoid a tracked vehicle for the sake of not feeling like a copy of the Sandcrawlers in Star Wars. What might stop the development of such a simple solution, if anything?

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I suppose the answer "camels" is not helpful here? – Lostinfrance Mar 14 at 10:07
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I am not exactly sure how you are going to construct a civilisation that has combustion engines but no wheels. Wheel and axle is one of the six components of the classical "Simple Machine", which will show up long before you can start thinking about something as enormously advanced (in comparison) as an internal combustion engine. I guess you will need to worry less about imitation and more about plausibility here because you will end up with some pretty contrived logic if you try to do away with wheels and tracks. – Michael Karnerfors Mar 14 at 11:11
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@MichaelKarnerfors The OP didn't say the humans hadn't invented the wheel, merely that they hadn't developed tires and suspension capable of gaining any appreciable traction in desert driving conditions (which we're still struggling with on Earth). – type_outcast Mar 14 at 12:36
    
Ah, good point. – Michael Karnerfors Mar 14 at 12:38
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The question doesn't make sense. "Wood and metal wheels exist, perhaps leather tires, but nothing that wouldn't just sink right into deep". Why not? There are razor-thin rubber tires that would sink right in, and there are ones wide enough to float on sand. The trick is to make it wider, not to make it out of rubber. – Agent_L Mar 14 at 15:48
up vote 19 down vote accepted

I would suggest that such a society would develop a primitive Screw-propelled vehicle. Such a vehicle is ideally suited to moving through ground that is easy to sink into with wheels or tracks, and can be simply constructed from a log with the correct carved grooves in it.

Such things are used in real life in niche applications where even tracks will have trouble such as operation is swamps or deep snow. There have been experiments using such things dating from earlier than world war 2 and indeed have been used to traverse Siberia.

I cannot find any reference to such a vehicle being used in the desert, but it is not such a stretch to imagine such a thing working.

Example of how such a craft works: A counter-rotating screw drive vehicle

I thought I would mention the other pros and cons of such a vehicle as well, to help with story ideas.

Pros:

Such a vehicle, suitably designed, is relatively easy to make amphibious. The screws propel almost as well through water as they do on land, and if the craft is constructed from suitable materials, it can float rather easily.

Cons:

Such a vehicle would have trouble going over very rough terrain, because a reliable suspension system has not yet been discovered (to my knowledge). It would also be very inefficient compared to many of our current methods of propulsion, and would lose a lot of energy to friction when moving over a solid surface compared to wheels.

Source(s)

http://patentpending.blogs.com/patent_pending_blog/2008/03/1907-screw-driv.html

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Screws are terribly inefficient. It would require way more powerful engine to drive it forward instead of simply rolling it to the side. – Agent_L Mar 14 at 15:52
    
I mentioned in the body of the question that this is the case. However, there are few other simple propulsion methods that are not very lossy due to friction. However, a screw drive is as I have shown links to, the most efficient in several different scenarios which shifting sands would come under. – Rugnir Mar 14 at 16:06
    
Kinda reminds me of those sidewinder snakes. – DaaaahWhoosh Mar 14 at 19:56
    
It's not much of a stretch to imagine this wearing out in a hurry, from spending so much time sliding across natural sandpaper. – Mark Mar 14 at 21:11
    
If this ran into a larger dune would it get stuck trying to push through it can it tilt upwards to climb a dune, does it have enough house power to climb a dune? – sdrawkcabdear Mar 15 at 0:20

If you eliminate wheels, that leaves you with either skids, legs or hovering.

Skids

This option would include actual flat-bottomed boat hulls, catamaran like double or triple hulls and very wide and flat ski-like skids. The advantage of course is that it's very cool and like your desired sailing ship idea.

The major problems would be rocky/rough terrain and the very high friction, meaning you would need storm-like winds or unobtainium-plated friction-less surfaces to even get moving. I'd suggest using the skin of the enormous worms that live in the deep sands, but that's already been done...

Legs

Not just a few legs, but dozens and dozens of legs. Enough to make the crystal spider creatures green with envy. With the weight of the "ship" distributed over many broad feet, none of them would sink into the sand too much.

The major advantage is that the legs would work even on rocky and uneven terrain, where the skids would fail miserably. The disadvantages would be the maintenance on all those legs and relatively slow speed.

Here is some inspiration: windpowered beach walkers.

Hovering

With Diesel Power(tm) at your disposal, a hovercraft may be possible, though it is unlikely that early generation diesel engines could produce enough power without becoming too heavy to lift. These would be very fast on flat and smooth surfaces like salt seas, but unable to handle inclines or rough terrain that the skirt would snag on.

The Best of Two Worlds

My recommendation would be a combination of legs and skids. The legs would have wide shields/skids along their length. On rough terrain it would walk centipede-like on all legs. On smooth sands most legs would fold into a horizontal position, putting the skids on the sand. The remaining vertical legs would push the "ship" forward in low-wind conditions (assuming some diesel power) or when going uphill. When wind conditions are favorable, the upright legs are only required for steering (by creating drag on either side) as the "ship" goes into full sailing mode.

Why no Wheels?

For wheels, the short answer is: No rubber.

Leather (inflatable or not) wheels exist but they are unsuitable for large vehicles, since they're not strong enough to carry a heavy load and very vulnerable to sharp rocks and ridges hidden in the sand.

Wood is better and barrel-shaped wooden wheels with ridges or even paddles is probably the closest you'd get to desert driving. But without the flexibility of rubber, you'd have to "drive" very slowly or risk shattering wheels on impact with hard terrain features.

A tracked wheeled vehicle might do better, but there may not be enough metal available for solid metal tracks. Tracks with metal core links and bolt-on wooden components are likely to wear out and break at an unworkable rate, especially with sand getting in the links. Replacing a single skid or leg in the middle of the desert would be much quicker than trying to restore a broken track somewhere under the bottom of the vehicle.

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Thank you for taking the time to come up with a solution. I think people sometimes forget the difference between something making sense from a practical standpoint and making sense for the purpose of suspension of disbelief- no offense to the other answers, of course. – user15170 Mar 14 at 11:22
    
Also, just want to mention that most of your ideas were things I had halfway come up with, I just needed to tie them together properly. – user15170 Mar 14 at 11:33
    
The biggest problem with skids is not rocky terrain, but sandy one, with the skids sinking in the sand. – SJuan76 Mar 14 at 13:26
    
Hence very wide ones with upward curving tips and fictional frictionless surface. Being frictionless, they would sink into the sand more easily when at rest, I suppose. – Cyrus Mar 14 at 13:36
    
@user15170 You did forget to tell us that was what you were looking for. :) – Graham Mar 16 at 12:22

This is a civilization which has not developed wheels / tires which can effectively travel through sand dunes

To which I can only reply: "Why not?" Being entirely serious, you're going to have to do some very serious thinking to work that one out.

Any engineer able to work with wheels should know that the narrower the wheel, the more it sinks in. So the softer the sand, the wider the wheels need to be. This pretty naturally leads to two wheels with 20-foot planks between them. And tracks become an obvious next step.

You've also got a major anachronism problem with combining Renaissance technology levels with internal combustion engines. The internal combustion engine needs levels of machining accuracy which Renaissance engineers couldn't even measure to, never mind achieve. It also needs incredible control over your quality of steel. The external combustion (steam) engine needs less accuracy, but the smaller and higher-power you make it, the better your machining and steel have to be, otherwise your boiler becomes a street-clearing IED. It took roughly 150 years of continous development to go from the Newcomen beam engine to early internal combustion engine prototypes. You don't get that kind of R&D in a vacuum, so for an internally-consistent world you're going to need all your other technologies to have had the same kind of advances. That means your entire civilisation MUST be at a late-Victorian technology level. Anything less will not support an internal combustion engine.

You can also completely forget about large vehicles if you want the science to work. The larger the item, the more mass of item needs to go into holding the item together, and the general rule is that this increases by the cube of the size. Double the size of your vehicle, it becomes 8x heavier. Make it 10x larger, it becomes 1000x heavier. You'll have problems keeping this above the deep sand; hell, you'll have problems getting it to move at all with primitive engines.

Of course, much of this assumes deep sand is a major impediment. If you look at sandy deserts on Earth, you'll find that much of it is not deep sand, and areas which are, no-one much goes there. Trade traditionally happened along areas where travel is possible without needing special vehicles. If you want to head out into the deep sand, you'd need a compelling reason to do it.

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+1 This. Exactly what wen through my head while reading the question. – fgysin Mar 15 at 7:36

If they have wheels, then it would seem fairly straight forward that they would have figured out long ago that you need a lot of surface area in order to prevent the cart/chariot/wagon etc from sinking into the sand.

On a more practical level, while a planet might be arid, it isn't going to be 100% sand dunes. Mars is a great real life example, although it is more of an arctic desert, it has hard pan, sand dunes, chaotic terrain, mountains. polar ice caps and even the seabed of the Vastitas Borealis basin. Jerry Pournelle once mocked the idea of a planetary uniclimate with the immortal phrase "It was raining on the planet Mongo that morning". http://www.strangehorizons.com/2002/20020225/planets.shtml

So your people are not going to be living or venturing into the sand dunes much, unless there is something very valuable in there. Far more likely they will be living along the equivalent of the Nile river, or around other small, fertile spots, and their primary vehicles will be adapted to moving over hardpan and perhaps farm vehicles for tilling the soil. If there is an urge to go exploring in the desert, then adapting farm vehicles with wider tires and lower ground pressure would be a good starting point.

If we assume that there is no powered farm machinery to provide a starting point, the other way to look at things is to see how the British adapted existing vehicles to operate in the desert in their explorations in the 1930's and later during the Desert Campaign in WWII. In this case, adaptations included traction mats (large plates that could be pushed under tires to help unstick you from deep sand, see the perforated plates strapped to the side of the truck in the picture), special radiators and overflow systems to prevent the loss of water as engines overheated and water boiled out, and devices like "sun compasses" to allow drivers to navigate. The introduction of lightweight vehicles with higher power to weight ratios (Jeeps) helped immensely as well

LRDG truck

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I 100% understand that a planet won't be entirely sahara-style desert. There are a few seas on the planet, it's just that desert-like terrain is more common because less than 50% of the planet's surface is water. Most of the people on the planet live in much more reasonable climates around the few major seas that exist. I have created good motivation for traveling through those dunes, but like you said, it's generally quite impractical, so it's never been done before for the purpose of the story. – user15170 Mar 14 at 11:30
    
On this note, I would really expect any kind of desert nomads to have a caravan of small vehicles, rather than one giant vehicle, especially given the very low technology. It's far cheaper, safer, and more practical to occasionally leave a truck behind after spreading its cargo and crew to a dozen other trucks, than to get stuck in the middle of nowhere because deserts hate technology. Even the screw-type vehicle in the accepted answer is simply not going to work at anything resembling sandcrawler scales without space magic. – MichaelS Mar 15 at 3:25

I really like this old idea: https://en.wikipedia.org/wiki/Vacuum_airship . Some recent developments are in the works, trying to fabricate materials to contain the vacuum with modern tech, but you could make up some material that exists naturally on your planet.

Are airships an option? a low flying hot air balloon is fairly low tech and makes getting over those curving dunes a walk in the, um, desert.

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Rather than coming up with an entirely new way to provide traction, why not just make exceptionally wide wooden wheels? A double set of spokes, an extra large diameter, and 6-12 inch wide rims (maybe wider), maybe with slates glued across lengthwise to further increase surface area, and you've got a wooden wheel that can handle loose sand. The details might vary, but a wooden wheel doesn't have to be narrow, and a wide wood wheel will still look different enough to be novel, while not requiring variation from the current level of tech.

If you want a sand-sailing ship, you need to pay attention to prevailing winds. You risk becoming stranded in the desert if the wind dies down, and if the prevailing wind blows east, and you want to travel west, you will be lucky if it only takes you twice as long to travel against the wind. For a real life example, read about sailing through the Drake Passage, at the southern tip of South America. It could take ships weeks to get through it even though it is relatively short because the weather is unpredictable and usually rough.

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The wheel from Pirates of Caribbean: Dead Man's Chest is wonderful example. Just take 4 of them and off one goes! – Agent_L Mar 14 at 15:46

Sidewinder snakes use a very specific kind of body motion, with different parts of the snake's body in contact with the ground, or in motion at different times. It's not impossible to imagine machines using flexible tubing or similar mechanism to enable locomotion.

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