Zenith

Even if the Christophe Colomb Hurricane watch abounds of horological delicacies I find pleasure and satisfaction in the fact that all of these propose solutions to eminent problems in timekeeping.  More concretely, the following challenges are addressed:

- influence for gravity

- isochronism

- precision

To be honest I would not except anything else from Zenith. While I admit that there are certainly simpler solutions to each of these problems, particularly in view of modern materials and production technologies, I should note that this timepiece is an eminently traditional piece with a reference to the past. Thus, I have little problem in accepting those elaborate solutions.

In view of the above I chose to structure this part of my report according to the specific challenges addressed. 

1.) Gravity: gyroscopic suspension of the escapement:

It is well known that gravity has particularly disturbing influences on a watch's accuracy, particularly in a wristwatch. Several approaches have been devised to address the problem, the most well-known certainly being the tourbillon.

Zenith went a totally different way. Instead of correcting the influence after the fact the company opted to prevent gravity's influence by ensuring that the escapement always resides in a horizontal position. This has two main advantages: (i), a position is chosen where gravity has the least influence; (ii) regulation is streamlined as the watch basically has only a single position which needs to be controlled.

Zenith's idea was to mount the entire escapement in a gimbal-like gyroscopic system which they call the gravity control module. What reads simple and logical has a quite complex practical implementation:

Gimbals consisting of three concentric rings allowing a supported compass or gyroscope to rotate freely have first been described by the Italian Renaissance mathematician, physician, astrologer and gambler Hieronymus Cardanus (24 September 1501 – 21 September 1576):

By the way, one of Cardanus' gimbal-supended watches can be admired in the Patek Philippe museum.

Since then, gimbals have been proven essential for marine instruments such as compasses, marine chronometers or tonearms (image credit: Wikipedia and vinylengine)

Zenith itself used a gyroscopic system for its famous marine chronometer. Here the entire watch is suspended within the gimbal:

Under the guidance of former CEO Thierry Nataf the development of a gimbal system for a wristwatch begun. It was clear from the beginning that in this case the gimbal needs to be incorporated into the movement:

This has the major consequence that the power of the mainspring needs to be transported to the escapement through the gimbal, without limiting the free suspension of the gimbal on the one and without disturbing the escapement's beat rate.

The adaptation of this mechanism for a watch movement is simply mind-blowing and absolutely unprecedented - just compare it to a simple compass gimbal (image credit (left image): Wikipedia). Altogether 173 parts compose this part.

It is amazing how well the gyroscopic effect works. Regardless how you position the watch - the balance wheel and the rest of the escapement always remain in a horizontal position: 

The mainspring is coiled around a stationary axle (arbor), inside a cylindrical box, the barrel. The force of the spring turns the barrel. In a fusee clock, the barrel turns the fusee by pulling on the chain, and the fusee turns the clock's gears.

When the mainspring is wound up (Fig. 1), all the chain is wrapped around the fusee from bottom to top, and the end going to the barrel comes off the narrow top end of the fusee. So the strong pull of the wound up mainspring is applied to the small end of the fusee, and the torque on the fusee is reduced by the small lever arm of the fusee radius. As the clock runs, the chain is unwound from the fusee from top to bottom and wound on the barrel.

As the mainspring runs down (Fig. 2), more of the chain is wrapped on the barrel, and the chain going to the barrel comes off the wide bottom grooves of the fusee. Now the weaker pull of the mainspring is applied to the larger radius of the bottom of the fusee. The greater turning moment provided by the larger radius at the fusee compensates for the weaker force of the spring, keeping the drive torque constant.

Winding the movement up again, the fusee is turned and the chain unwinds off the barrel and back onto the fusee, thereby winding the mainspring. 

The presence of the fusee means that the force required to wind up the mainspring is constant; it does not increase as the mainspring tightens.

The Grand Voyage is not the first Academy with a fusee: Earlier this year the manufacture presented the the technically identical Hurricane model which features an additional fusee-and-chain transmission system. In the image below you can very well see the path of the chain between fusee (left) and the mainspring barrel (right). 

It would be surprising if Zenith would not incorpoarate its signature 36.000 bph high-beat escapement in this top-range watch. Indeed they did, and they implanted even their silicon escapement technology which I tried to illustrate in the following picture (note the purple escapement wheel at about 7 o'clock?):

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