CRAB CLAW SAIL
radically opposed approach to the problem of stability was not the only
difference between Polynesian and
boats. Their rigs were also very different.
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.
books and internet sites have still described it as a romantic form, or even ,
a primitive form of Lateen sail.
drawing show the propulsive forces develops by the Crab Claw sail, compared to
the Bermuda and Lateen sails…Surprising is it not ?
curbs explain the surprising performances of the Proas that had bedazzled
Shouten, Cook and Co…***
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 ».
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.
Crab Claw owns " a double pivoting axis" which can be adjusted
horizontally around the higher boom.
adjustment permits it to position the vertical aerodynamic component Fv upwards (
drawing 2 )
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.
this was not necessary.
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.
Concorde flies with it's wings in the Crab Claw's shape
will understand everything about the mechanics that lets the Crab Claw
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,