Busting dive watch myths: a deep dive into deep (and shallow) diving

Buffy Acacia

Dive watches have now been the most popular form of sports watches for a while. Everyone knows that only a tiny fraction of dive watch owners actually go diving, and even then, how many are really aware of the science behind those watches? There are tonnes of myths being perpetrated about dive watches in regards to their water resistance, their legibility and their hardiness – and it doesn’t help when brands contribute to the mythologising of dive watch trends. If you plan to wear your watch below the waves no matter how deep, here’s what you need to know.

Water resistance

Water resistance may not be deeply understood, but that’s nobody’s fault. It’s a complicated topic with a lot of asterisks, but it’s generally accepted that 200 metres is the minimum rating for any amount of serious diving. Still, there are some things to keep in mind. A water resistance rating is never permanent, and regular servicing is important to ensure that all of the watch’s rubber seals are in good condition to prevent water ingress. All it takes is one dry spot to crack from too many years of neglect, and then it’s game over for the rest of the movement.

Another common misconception is that a screw-down crown increases a watch’s water resistance. While screw-down crowns or canteen crowns were used on some of the oldest “waterproof” watches, metal threads actually don’t do a great job of keeping out water with any significant pressure. It was only when gaskets made of cork or rubber started being used that serious results were achieved, replacing the earliest attempts with waxed cotton or string. The gasket is what does all the work, and in theory, you can still dive with your watch crown unscrewed, but locking it down prevents you from moving the crown into an open position and letting water past the seal.

Circling back slightly to the topic of depth ratings: the reason most often proffered for needing a 200-metre rating for diving is usually attributed to how depth does not equal pressure. For example, the pressure at a depth of 50 metres may equate to 5 bar when perfectly still, but currents and arm movements can cause that pressure to increase, simulating greater depths… Well, it turns out that’s a bit dramatic. Back in 2011, WatchUSeek user lysanderxiii went to the effort of calculating exactly how fast you’d need to move your hand to increase the pressure by just one bar, and the answer is 32mph. The top speed achieved by Michael Phelps in a race against a great white shark was 8.8mph, so you needn’t worry about swimming too quickly. As long as you’re not shooting a power washer into an open crown, even a 100-metre-rated watch will do just fine for most dives.

Dial colour

This is perhaps the most contentious topic when it comes to dive watches, as personal anecdotes, scientific research, and aesthetics all seem to conflict with each other. It’s often said that orange is the most visible colour underwater, and it seems much of that reputation is linked to testing that Doxa undertook in the murky waters of Lake Geneva in the ‘60s, leading to its popular orange Professional and yellow Divingstar colourways. However, looking into the science of light penetration paints a very different picture. The further down you go, the narrower our spectrum of visible light gets. Red is the first colour to disappear below 50 metres, followed by orange, yellow and purple below 100 metres, before all that’s left is a variety of blue and green hues.

That kind of guide is what inspired some of those rainbow decompression dials from the ‘60s, as the fading colours would inform you of your depth below the waves. But then why is the archetypal dive watch just black and white? Really, what matters most is contrast. As long as you can discern the hands and markers from the rest of the dial, the colour is slightly irrelevant. In most low-light diving scenarios, many divers will have torches that they can shine onto their wrists anyway, lighting up whatever colours are present. Another issue is that not all bodies of water are the same, and different levels of cleanliness and clarity will affect how colours interact.

All that said, an extensive study was performed in 2011 by Mustang Survival for colour visibility underwater, mainly for safety and life-preserving purposes. Yellow takes third place for most visible colour, with orange in a strong second place, but by far the most visible colour underwater is actually bright fluro green. “Wear green and be seen” is a common phrase for ocean safety, but it’s a pretty unsightly colour for watch dials.

A dive watch’s utility

Aside from sheer water resistance, what’s the only thing that makes a dive watch different from any other watch? The answer is the dive time bezel. It’s an essential factor for a dive watch and is even mandated in the ISO 6425 specifications to have individual minute markers for the first 15 minutes. The purpose of this bezel is to help you keep track of how long you’ve been underwater, and thus how much air you’ve got left in your tank. Right? That may be true if you know your exact air consumption rate, how much air you start with, and how to do that calculation on the fly in your head. Or, you could just check your pressure gauge. All the bezel does is allow you to check how much time has elapsed underwater, and that has much more real-world utility when tracking parking meters and cooking times.

I do hope this doesn’t come across as overly cynical, because all divers are aware that a dive computer is much more useful than an analogue watch. The fact that the timing bezel is better for day-to-day use than actual diving may be the reason why it has become the definitive kind of sports watch, even being worn with business attire in offices all around the world. They definitely deserve their place in the spotlight and have rightfully captured the imaginations of non-divers, but that has allowed plenty of misinformation to spread. As long as you’re aware of your watch’s limitations, you’ll be able to enjoy its strengths more fully.