Windwagons and Sandyachting

Windwagons and Sandyachting

With the advent of stronger ultra-light materials and frictionless bearings, sand yachts became fairly practical over many different terrains in Araxes.

The physics is pretty much the same as for ocean going vessels.

The Araxes Desert Caravel is between 12 and 20 meters long, massing between 34 and 160 tons. The average being about 15 meters massing about 63.75 tons.

The Desert Caravel has three masts with six sails, and about 170 square meters of sail to capture the wind.

The force against the sails is the windspeed in meter/second squared time the area of the sails in square meters. Thus, with a minimal breeze of 4m/s and 170 square meters of sail, we have about 63.75 tons of propulsive force. Not a lot, but it’s free for the taking.

The minimum wind speed is rarely as low as 1 meters per hours, and averages on a relatively calm day of 4 m/s. Gusts of nearly 60 m/s are not uncommon. Anyone who has spent any time in the open desert of Araxes should not be surprised by this.

Structurally, desert caravels can survive such an onslaught, but sails are usually cut for anything over 20 m/s.

An unladen desert caravel also masses 63.75 tons, not a coincidence. Thus, unladen, it easily travels a relatively brisk 4 m/s with average winds. It doesn’t sounds fast, but it feels fast when you are standing on the bow. I strongly recommend covering your mouth and wearing goggles.

The maximum loading of the Caravel is about 150 tons, with such a load, it moves about a 30% of its unladen velocity.

Power to Weight Ratios are a bit tricky to calculate, but with some math and careful about units, 1 HP per pound is about 17.5 pounds lift per pound. A simple propeller driven hovercraft can easily (and relatively quietly) manage 0.5 horsepower/pound, which works out to about 8.75 Pounds per Pound.

A 60 tonnage (~2000 cubic meter) caravel carrying about 150 tons of cargo including about a twenty-five ton of engine for the hover ability. Some very advanced engines are only 12 tons, but one can find twenty-five ton engines off the shelf, you don't have to special order. This effectively makes all of the thrust from the winds in the sails going into propulsion with almost no resistance from friction.

The 64 tons of propulsive force from the 4m/s winds will translate to a modest 2.5 miles per hour velocity under a full cargo load, 9 mph unladen.

2.5 mph does not sound like a lot, but it is quiet and stealthy and carrying nearly 125 tons of passengers and cargo, twice that with only 25 mass tons of cargo and passengers. It is not as quiet as over salt flats and other solid surfaces when using wheels, but it does have the distinct advantage that it can be used over soft dunelike sands. The hovercraft engine can be a backup for when the wind wagon has to go over dunes.

Wind Wagons and Sand Yachts can also travel, with some very challenging steering, on paved roads, but are usually used on open rock, salt flats, and other open desert terrains where the more improvisational steering is less problematic.

Ultra-light racing yachts which can easily travel at up to twice the speed of the prevailing winds and can handle much higher wind velocities, but it is a very dangerous hobby.