Anything is allowed to think about - sciences however did ban thinking about some ´impossibilities´. For example, when ever term ´Perpetuum Mobile´ appears, self-imposed blockade perfectly works.

With this script I want to point out, it´s well possible to ´earn´ more useful energy than originally given, for example more-fold of energy of winds.

At script Why Sails do not pull I mentioned, why surfers are able to drive much faster than wind blows. That surplus of energy, I deduced as effect of suction: wind is only triggering power, faster than wind one can sail only by normal atmospheric pressure resp. pressure-differences based on partly protection at lee side of sail.

Now one reader argued, higher speed results of fact, whole ´surf-machine´ practically would work like transmission-gear. That´s good idea to check this problem once more.

Surf sail is assumed some 300 cm height and 133 cm width, so shows surface of some 2 sq.m or 20.000 sq.cm. Mass of air pushes onto this surface by wind´s speed.

Surf board is assumed as rectangular body of some 300 cm length, 50 cm width and 10 cm height, so shows maximum lift power of 150 liter resp. 150 kg. If whole surf-machine inclusive surfer weights e.g. 100 kg, body of board would dive into water some 6.6 cm, so frontside below water line is 330 sq.cm.

Surf boards are not rectangular but show most smooth shape. Nevertheless, when board moves within water, water in front of board must be transported behind board. This is done as frontside water mass is pushed aside and this water-hill flows back behind board, some after board has passed this point. So at backside vertical surface of board is no water, so no pressure corresponding to frontside pressure.

Water at frontside must be lifted over (theoretically assumed plane) water surface, by sideward push, no matter how that´s done, at any case exists pressure-resistance at frontside surface of previous 330 sq.cm. Smooth shape of bow only gives more time for this pushing-aside-movement, otherwise much higher wave resp. water masses must be pushed aside.

Density of water is some 1000 higher than density of air. Surface of 330 sq.cm within water thus would correspond to surface of 330.000 sq.cm within air. So it´s not astonishing, these few 20.000 sq.cm sail-surface transports surfer into direction of wind only by parts of wind´s speed (e.g. 1.2 m/sec drive-speed by 5.0 m/sec wind-speed). That course (sail cross to wind´s direction) thus is named ´dead before the wind´. So not at all, surf-machine is able to work like transmission-gear, transforming wind-speed into higher drive-speed.

If surfers would drive only by energy of winds, speeds at all other courses would be slower once more. If surfers obviously move faster than wind blows - and above this resistance rises by square of speed - much more drive energy is demanded, must be available of other source and it must be possible to use. Source of this surplus power is gravity resp. weight of air resp. partly and intermediate protection of atmospheric pressure.

Onto each of these 20.000 sq.cm sail-surface weights normal atmospheric pressure, at both sides of sail each 1 kg each sq.cm, these are each two tons, so much stronger forces than wind produces. So it´s demanded only some minimum of pressure-reduction at lee side of sail to overcome resistance of water at these 330 sq.cm of frontside surface of board.

At previous chapter (and many times at this website in details) I described, how this effect is achieved by suction. While resistance rises by square of speed, effectiveness of suction effect rises by speed. In addition, most faster ´seaming-wind´ affects at sails, which is ´true-wind´ enforced by ´drive-wind´. Acceleration is only limited by fact, vector of resulting power-surplus more and more shows cross to direction ahead.

So it´s proven, at sails wind-energy functions only as trigger, lastly however gravity is causing source of power surplus used. As any system is open concerning gravity, this (additional) power is usable in principle within any analogue ´perpetuum mobile´.

So it will make sense to search for best usage of this source of power, like at chapter Small Wind-Engine one technical design is described as an example.

Evert/1999