In this article in our series on the basics of divers' watches we carry on what is probably the most distinctive part of a dip watch: the rotating bezel.
Its function is actually quite simple: before a diver's descent, the 12 o'clock bezel marker is aligned with the second hand, allowing the elapsed time up to 60 minutes, to be read on the bezel (which is the reason why quite a couple of dive watches come with a particularly prominent second hand). A unidirectional, ratcheting construction ensures that -- if the bezel is accidentally moved -- the time spent underwater would be signaled as more than really spent, giving the diver with a security reserve for his currently more imminent ascent. The bezel/minute hand mix doesn't, however, directly measure how much air remains in the air tank, as still can be read quite often in press releases.
A standard scuba dive (where the diver has a regular air tank) generally lasts 30 to 50 minutes, largely based on the depth reached and also the shape that the diver is in (basically, how physically demanding the dive is). This explains why the first 15 to 20 minutes on the bezel inlay tend to be more highlighted -- the conclusion of this sector theoretically indicates the purpose of recurrence (exception: "countdown" bezels that mark the time of ascent). So as to correctly time decompression stops at the end of a dive, central-minutes chronographs like the Aquastar Benthos or even split-minute chronographs, such as the IWC Aquatimer Chronograph from 2004, offer an interesting complication (if the diver not use a pc).
But, back to the start of a dip: In reality, the bezel is adapting when the diver is geared up and ready to start the dip -- that is, the majority of the time, when he's in the water or onto a boat right before entering the water. It's rarely done in a sterile hotel room, wearing no gloves, even when one can take the watch off to set its bezel. So, despite how much I adore the Omega Ploprof (that comes with a bi-directional external bezel using a locking mechanism) and also the Hublot Oceanographic 4000 (whose unidirectional internal bezel is controlled by means of a screw-down crown which is then placed behind a protective cap), neither are among the easiest watches to be operated single-handedly when worn in the water. And I would strongly advise you never to eliminate a moist luxury watch from your wrist when there's a bottomless pit beneath you.
From a construction point-of-view, there are two Chief methods:
1. External bezel
First employed for a dip watch by Rolex and Blancpain (inspired by earlier pilots' watches) at 1953/54, this is still the easiest and most user-friendly strategy. Disadvantages include wear from sand, debris or salt getting between the case and the bezel, and also the possibility of accidentally moving or damaging the bezel.
As a solution to these issues, Citizen introduced a detachable bezel with the Citizen Promaster 1000 in 2002, and IWC launched the Ocean 2000 in 1984, with a bezel that could only be worked counter-clockwise when pushed down (a notion re-introduced in 1998 using its GST Aquatimer). This concept was similarly implemented earlier by Certina, using its DS-2 500m in 1968, and afterwards in 2003 by TAG Heuer for its Aquagraph 2000 Chronograph (with a two component bezel) and by Oris in 2009 with the Oris Prodiver (whose bezel needed to be lifted). More or less complex bezel locking mechanisms -- as first introduced to the Omega Ploprof in 1970 and again in its contemporary variant in 2009 -- may also be found in the Hublot Subaquaneus, the Squale Tiger, some models from UTS, Germano, and Glycine, also, of course, in elderly Yema models.
Citizen Promaster 1000, before (above) and after (below) setting the bezel and submerging
2. Internal bezel
Most probably introduced by Aquastar in the 1960s. In this construction, the bezel is located inside the watch and can be thus shielded by the crystal, giving the watch a much more elegant appearance. The bezel can only be operated with a (usually additional) crown, quite often in both directions (exceptions include the Audemars Piguet Royal Oak Offshore Diver, Hublot Oceanographic, etc.). Disadvantage: An extra opening in the instance (except maybe for the first Aquastar versions, and the current Maurice Lacroix Pontos S, in which the chronograph pusher also operates the bezel) and frequently a rather modest crown to fumble with. The more secure it is designed (unidirectional, screw-in), the less practical it becomes for diving.
In 2002, Eterna introduced, with its KonTiki Diver, an intriguing first blend of both theories: the inner bezel could be controlled from the exterior, a concept that initially permitted a water resistance of 200 meters and, in 2005 around 1,000 meters together with all the more radical-looking Concept Diver.
In 2014, IWC went all the way and appears today to be supplying, for the first time, the best of both worlds: The present IWC Aquatimer household features a system, known as Safedive, that unites a unidirectional internal bezel which may only be rotated with a ratcheting external bezel (which can be transferred in both directions, but just counter-clockwise for correcting the inner bezel). The IWC video below demonstrates how it works: Find out more information click Raymond Weil watches