THE CRAB CLAW SAIL

The radically opposed approach to the problem of stability was not the only difference between Polynesian and European boats. Their rigs were also very different.

If   we had finally adopted the idea of navigating on two or three hulls with no ballast, it’s not the same story with the Crab Claw’s rig.

Different books and internet sites have still described it as a romantic form, or even , a  primitive form of  Lateen sail.  

The drawing show the propulsive forces develops by the Crab Claw sail, compared to the Bermuda and Lateen sails…Surprising is it not ?

The curbs explain the surprising performances of the Proas that had bedazzled Shouten, Cook and Co…***

The fastest, the Flying Proas, navigate at 17 to 18 knots, with the a maximum of 24 knots. The price to pay for  attaining theses speeds consisted of any complication of tacking and veering : the « Pacific » Proa makes picturesque manœuvre called the «Cavu » after which the « Bow » becomes the « Stern ».

Obviously, a manœuvre like that can compromise it’s chances in short regattas on the Olympic triangle, but in an Ocean race…
Besides all of this, the Crab Claw is a lot easier to handles. For example, a simple increase in the slack of he sail brings an immediate and spectacular fall of the aerodynamic forces, equivalent to the setting of it’s area.

The Crab Claw owns " a double pivoting axis"  which can be adjusted horizontally around the higher boom.

This adjustment permits it to position the vertical aerodynamic component Fv upwards ( drawing 2 )

1.      2.     3. 

At a 45° angle it is equal to the force of the list. From this angle, the Fv force takes over. The sail starts to work like a kite, all the while keeping its propulsive function, the position of the sail on a vertical level, can stay unchanged. To be verified...
May be this is the reason why the polynesians have never used a divided rigs. They colonized innumerable Pacific Islands using only one sail,sometimes over than 300m2, without any reefing system.  

Obviously this was not necessary.

Ignored by the yachting world, the amazing  Crab Claw sail has at last found it’s place in our modern times. With a new name DELTA WINGS » it made an incredible career in aviation, equipping most supersonic planes and even the Space Shuttle. The Delta Wings, elaborated with the help of the most powerful computers, give way to exactly the same aerodynamic phenomena as the sail invented a thousand years earlier by the «savages » from Oceania,  who knew how to profit from lessons given by Mother Nature.

Yes, Concorde flies with it's wings in the  Crab Claw's shape ...

***You will understand everything about the mechanics that lets the Crab Claw develop such incredible forces, after the reading of «  SAIL PERFORMANCE «  by C.A Marchaj, from which the drawings of this page.

If you are interested in the Crab Claw Sail performances, look also V&V Test 

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