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How Rolex Tests Their Dive Watches

May 8, 2019

BY Andy Callan


In theory, every Rolex watch outside of the Cellini range can be used for diving. Or, more accurately I suppose, anything with an Oyster case is more than capable of surviving recreational scuba depths, whether or not it is actually considered to be one of their dive watches like the Rolex Submariner or Sea-Dweller

The absolute limits for no-decompression diving, i.e. those that don’t require safety stops on the way back up to let the body metabolize some of the nitrogen that has seeped into the bloodstream is between 30m-40m, depending on which training agency you go with. The modern incarnation of the water-tight case that Rolex founded in the 1920s – which has formed the backbone of the vast majority of their output ever since – ensures water-tightness down to 100m. That also happens to be the official depth requirement set out by the ISO 6425 guidelines for what models must be able to reach before they can actually be called a dive watches.

Of course, it would be a brave soul who took their Day-Date with them to explore a coral reef, or timed their next underwater excursion with a Sky-Dweller. Fortunately, we don’t have to do this, as Rolex makes some of the most capable, popular, and downright iconic dive-ready timepieces in the industry, designed from the outset for those very jobs.

65 Years of Getting it Right

There is a long list of other prerequisites that timepieces must have in order to be classed as dive watches, according to the International Organization of Standardization. Interestingly, vintage examples of the Submariner, without a doubt the most famous diver of them all, don’t meet all the modern conditions.

ISO 6425 which, in fairness, didn’t come into force until 1996, states that a mechanical model must have a unidirectional bezel to measure elapsed time. But the Blancpain Fifty Fathoms, the piece that beat the first Submariner to the punch by a matter of months in the 1950s as the first ‘modern era’ dive watch, held the patent on that particular innovation until 1983. An important safety feature, having a surround that only rotates one way means that if it gets knocked, it will only ever display an overestimation of immersion time. So, the various Submariner references made up until the early 80s, along with the initial Sea-Dwellers, technically fail to qualify by modern ISO standards.

Dive Watches

However, if that is one small black mark against two of the most illustrious names in all of horology, Rolex has since made up for it. Their trio of dive watches, with the mammoth Deepsea making up the third, suffer incredible tortures at the hands of the brand’s engineers, all devised to guarantee that they remain at the forefront of what is possible – even though the chances of any of them ever getting to set foot on a dive boat are slim to none.

These days, pretty much none of Rolex’s tool watch collection is used for their original intended purposes. Yet, just as very few Ferrari drivers will ever top out their machines in the real world, it’s nice to know that they can always get you out of trouble if they need to.

Dive Watches

Rolex Testing: Dive Watches

The history of Rolex as a company is inextricably linked to the sea. Whether above the waves or below, the challenges presented by the world’s oceans have forced the company to develop new technologies and pioneer groundbreaking materials. It is an ongoing mission, and what keeps the brand on top is its willingness to push its creations further than any other manufacturer. To that end, the tests that Rolex dreams up for its dive watches are unsurpassed.

Each and every Oyster model, from the Air-King to the Yacht-Master, is subjected to pressure testing to ensure water resistance. For all but the divers, that assessment is carried out through a series of multiple tests that ensure the watch is water-resistant to a depth of at least 100 meters.

Dive Watches

With the dive trio, rated waterproof from between 300m and an incredible 3,900m (pretty much two-and-a-half miles under the surface), pressure tests need to be performed slightly differently. Rolex uses a pair of enormous hyperbaric chambers; one for the Sub and the Sea-Dweller, and another very special one for the Deepsea. The second was provided for them by longtime compatriots COMEX, the French saturation diving specialists, and the two companies have enjoyed a long and fruitful relationship ever since they collaborated while Rolex worked to refine the design of its Sea-Dweller.

To comply with the official ISO regulations for dive watches, each watch has to be able to withstand 125% of its stated depth rating, although it is rumored that Rolex goes far beyond even that. In the case of the Deepsea, just sticking to the bare minimum equates to 4,875m, meaning it has to withstand a colossal pressure of about 7070psi. (Just for reference, the current world record for the deepest scuba dive is around 332m.)

Dive Watches

Once the watches are finished with their water baths, they are removed and inspected for any leaks. That is done by heating each one on a metal plate to 100°F before placing a cold rod onto its sapphire crystal. Some condensation is unavoidable due to the moisture in the air, but if it hasn’t dissipated within one minute, the watch is deemed to have failed the condensation test.

The actual numbers are not publicly available (because this is Rolex); however it is said that fewer than one in every 1,000 watches actually make it to this late stage of production and fail this test at the Rolex factory. Any identified with a leak are given a run through a vacuum chamber to see where the faults are.

Dive Watches

The Other Tests

It is worth noting that for ISO certification, every single watch that Rolex makes, not just a sample from each batch, has to be tested, and the grueling trials above are only one part of an especially malicious sequence. As well as being proved water resistant, the accuracy of the movements is also checked after a series of artificially created scenarios meant to represent what the watch could be subjected to on a dive excursion.

Dive Watches

That process includes a series of shock resistance tests, ensuring each model is strong enough to survive the sort of battering which is part and parcel of life aboard a dive boat. The most challenging involves the front and left side of the case receiving a blow from a 3kg hammer that has an impact velocity of 4.43m/s.

And to simulate a dive in tropical conditions, where the air temperature can be many degrees warmer than the water at depth, a thermal shock assessment sees the watch submerged up to 30cm and heated to 40°C, cooled down to 5°C, then taken back up to 40°C for five minutes at a time, with each transition taking no longer than one minute. To pass these tests, the movement must retain timekeeping accuracy to within +/- 60 seconds a day.

Dive Watches

Going Beyond

The Sea-Dweller and the Deepsea are both intended for use in the world of professional saturation diving. Here, crews are required to work at incredible depths for long periods of time – something that they can only do by breathing a carefully controlled mixture of different gases. Specifically, helium is used to negate the toxic effects of oxygen and the narcotic effects of nitrogen when they are put under extreme pressure.

COMEX was the leaders of this type of work in the 1960s, and the problem which soon became apparent (and the reason for the Sea-Dweller’s existence) was the tiny helium molecules seeping inside the cases of their diver’s watches. Upon ascent back to the surface, those bubbles would expand too quickly, forcing the crystals to pop out of the cases of their watches.

Dive Watches

Rolex and COMEX co-developed the HEV, or Helium Escape Valve – a small, one-way regulator set in the side of the case which allowed the gas to leak out safely and preserve the integrity of the watch. Consequently, these valves also have to be thoroughly tested before certification can be given.

The watches are kept in a helium-rich gas mixture, again at 125% capacity, for 15 days before being brought back to ambient pressure in just three minutes – an extraordinarily demanding trial, and one no actual diver could ever survive. Any piece that can survive this is more than capable of even the most severe real life challenges.

Dive Watches

It has been a good few years since mechanical dive watches have been standard issue equipment for those who make their living working underwater. At most, and particularly those made by a luxury manufacturer like Rolex, they are now more likely to be just a backup to a backup computer. The Submariner has long been more a status symbol than a tool, and with this year’s release of the first Rolesor Sea-Dweller (and don’t get me started on that), the middle child is headed down the same path.

But whether or not these legendary names will ever taste the life aquatic, they remain some of the most rigorously inspected and highly accomplished examples of dive watches in the entire industry.

Dive Watches



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