Age-old sailors almost were able to, e.g. wikings with their square sails. However, fast like wind wasn´t allowed. Pushing hull through water results resistance, so some part of wind´s energy is used to overcome.

Modern sailors still are able to. Sailing frontal of wind, spinnaker is raised in order to catch most volume of wind´s power. Ship runs soft, nearby as fast as wind blows. Nevertheless, zooming off only starts by sailing close to the wind, where ´seeming´ wind roars at rigging and ship runs faster than ´true´ wind blows.

Faster than Wind - no Problem for Surfers and Sailors

That´s theoretical problem of general and grave importance: ´dead before the wind´, ship and wind runs same speed, so kinetic energy of wind is totally transferred into drive (minus inevitable resistance of hull below waterline). Sailing close to the wind, ship runs faster than wind, so without any doubt additional power is demanded. However, where from could surplus of energy come?

Sailing-instructor explained: Sail affects like wing. Upside, way is longer than downside. So speed of wind upside is faster than downside.

Sailing-student lapsed into dreaming to be airy guy: keeping hands of airy girl, flying towards wing, being separated, she downside, he upside - nice girl got lost, however: Why should I hurry up, only to meet this old girlfriend behind wing? Flying normal speed, I´ll sure meet another girl, might be even younger and nicer one.

Sailing student hears sailing instructor telling: upside-ahead of wing thus comes up local area of less pressure, by which lifting-power results, showing upward-ahead.

Again, sailing student daydreams, crashing onto wing´s nose, being pushed hard upwards, ramming others towards stars above - questioning how thus I could lift airplane into heaven?

Sailing instructor interrupts: Analogue affects sail. On the one side exist pushing force by wind´s pressure, on the other hand exist pulling forces - of double intensity - by suction, thus ship is dragged ahead. Is that clear? Next subject, mooring.

Inattentive student again broods about: Sail´s backside is practically of same length than sail´s frontside. So I´ll stick on old girl-friend anyway.

All students agreed. None of got it. Like at Einstein´s theory.

Some Pressure and Lots of Suction

When ship is running into direction of wind, sail is put cross to wind. Wind power affects onto maximum surface of sail. If however ship runs cross to wind or even some against direction of wind, sail is put by small angles towards wind. Effective surface of sail for wind´s pressure thus becomes smaller, large part of pressure affects as cross-drifting power, only small component affects as power for driving-ahead. In addition, ship inclines, so effective surface once more is reduced and resistance of water at hull is increased. So wind´s pressure at courses cross to wind is used less effective than at courses into direction of wind.

At the other side, suction exists. By bended sail, air before (at luff side) is redirected backwards, so behind sail (at lee side) less air is available. So there comes up local area of less air-pressure, so of relative less density, so area of suction. Now, nobody had ever seen ´rubber band´ of gravity and like this, nobody can imagine how suction should be able to pull at sail´s surface.

However well known and easy to see is ´Braun´s molecular movement´ and one well can imagine, molecules in general are moving on and on. Molecules of air for example are moving by some 1.5 of soundspeed, chaotically into all directions of space.

Suction structures Molecular Movements

Air molecules are moving also at lee-side of sail. Purely by chance, molecules are pushed into direction of that area with less density - and fly into this relative ´empty´ space relative long distances without colliding. So at their starting area of relative high density, they now are no more available as potential colliding-partners. So following molecules (by pure chance hit into that direction) can also fall behind rather long distances. So many molecules can fly into same direction, relative near together, by structured flow, with relative few collisions among each other, or by colliding only in similar directions ahead, relative to previous chaotic movements.

So this flow not at all is limited to local area of suction. Molecules from steady longer distances are integrated within this flow, from far ahead of sail (or wing´s nose). This flow is not depending at wind-speed, but molecules fall into this area by their normal speed - above sound-speed. Naturally this area of less pressure will be filled up. However, the faster wind blows and / or the faster ship runs, the faster this suction-area wanders backward off ship, so new suction-area is build up resp. this area of less density is replaced ahead on and on.

At lee side of sail (and analogue at upper side of wing) so higher speed exists indeed - cause there to normal speed of wind is added as essential component enormous speed of normal molecular movement. So an area of suction results relative well structured flow with relative high speed.

Speed-Difference results Pressure-Difference

If molecules at lee side of sail fly alongside e.g. by double speed than molecules move at luff side, they have purely and simply and maximum half chance to ´crash´ onto sail by cross-collisions. So there exists only relative weak (static) pressure onto lee side of sail.

Opposite, at luff side weights wind pressure. In addition there weights normal air pressure, i.e. pressure based at collisions of normal chaotic movement of molecules. Already few ´bar-difference-percents´ makes surfer and sailors move faster than original wind blows.

Injured Law of Energy-Constance

Original wind here only acts as trigger. Sail here acts ´only´ for transforming normal chaotic movements of molecules into ordered flux, where immense molecular speed partly is integrated into wind´s movement. High kinetic pressure of this flux, here is merely used, but only its reduced static (sideward) pressure. Nevertheless, every sail injures common laws - is nothing else than perpetuum mobile, making available more usable energy than originally available.

This example of lift by sails makes obvious, how to use unlimited available kinetic energy of totally normal molecular movements within fluids - by some smart ´tricks´. Lift and drive is no question of power-input, but question of senseful organisation of ordered flows.

Fluid-Technology