Cartier Tank Anglaise Silver Dial Stainless Steel Automatic Ladies Watch W5310044

US Patent no. 5,608,694 was filed on 25th April 1995 by Omega S.A. on the basis of an invention by Maurice Grimm and Andre Beyer. The name Grimm may not have the same resonance as Breguet as far as tourbillons are concerned, yet the Swiss watchmaker can also lay claim to the first self-winding tourbillon, which was presented by Audemars Piguet in 1986.

Patents can be an incomprehensible technical jungle even for the relatively knowledgeable watch fan like your editor-in-chief. But to get to the gist you just need to skip straight to the "claims". In the case of the Omega patent these mainly cover the central location of the tourbillon, the fact that it is visible on the dial side without any obstruction and the use of a fixed wheel with radial toothing to drive hour and minute discs. Under the protection of this patent, Omega has been producing a limited number of its central tourbillons in a special high-end workshop at the company's headquarters in Bienne, Switzerland for the past 20 years. But as of 25th April this year, any brand can, in theory at least, offer a central tourbillon. So why have only two, Bulgari and Hysek, done so?

The Hysek IO Jumping Hours Tourbillon
Hysek admits that it faced two choices when developing its own version of the central tourbillon: either circumvent the Omega patent by partially covering the tourbillon cage with a decorated bridge or leave the flying tourbillon completely visible (and wait for the Omega patent to expire). It chose the latter, aiming to maximise the visual impact of the central tourbillon and even accentuate it with a whirlwind design for the jumping-hour indication. The result is a concentric reading of the time, starting with the seconds at the very centre of the dial and radiating out to a discreet minute hand (mounted on a peripheral disc) and the jumping hour disc on the outer perimeter.

The use of a central tourbillon poses a number of challenges, however, aside from the obligation of finding a different way of displaying the hours and minutes. The movement components have to be redistributed around the tourbillon and in Hysek's case the centre wheel had to be… decentred. The cannon-pinion is also doubly inversed: it is positioned downwards and the centre arbour is snapped on to the cannon-pinion, rather than the other way round. There is also less space available for the barrel than in a traditional tourbillon. In Hysek's new 100% in-house HW20 skeletonised calibre the barrel meshes directly with the centre arbour and its size remains acceptable, allowing for a 45-hour power reserve that is kept topped up by a micro rotor. Two versions of the Hysek IO Jumping Hours Tourbillon are available as limited editions of 88 pieces in red gold either with or without a gem-set bezel.

Bulgari Papillon Tourbillon Central
By coincidence, the other central tourbillon presented this year also opts for a jumping hour indication and, like the Hysek model, is derived from an existing jumping hour model. Bulgari's patented "papillon" mechanism uses two retractable hands positioned opposite each other on a disc. One hand indicates the minutes around a semi-circular scale on the bottom half of the dial. As it reaches the 55^th minute, the second hand gradually completes a quarter turn to prepare for duty. This allows the brand to use the bottom half of the dial for the minutes indications, leaving the upper half free for the jumping hours, without requiring an actual retrograde mechanism for the minutes. In Bulgari's case, however, the BVL calibre 266 powering the watch is wound manually and offers 60 hours of power reserve. It is available in a platinum or 18-carat red-gold 45mm case and is limited to 10 pieces for the platinum version and 30 for the red-gold version.

Why so few?
In the era of inclined tourbillons, double tourbillon, triple tourbillons, quadruple tourbillons and even a tourbillon of tourbillons, it seems strange that only two brands have taken up the challenge of the central tourbillon. But perhaps it is more a question of identity. Brands like Greubel Forsey are characterised by their multiple tourbillons and their inclinations, others, such as Cartier by their highly complex and highly transparent tourbillon constructions. To use a 20 year-old design could therefore be considered a step backwards. But it is also a question of fitting in with a brand's identity. What may not work for some seems to fit seamlessly into the designs and aesthetics of the Hysek and Bulgari collections.