The Shearwater Perdix
If you follow any scuba forums or diving groups on Facebook, you have no doubt noticed that the same questions keep being asked and answered.
Backplate or wing vs. jacket style BCD, longhose or not, for or against snorkels and so on.
With similar regularity divers will be asking about which dive computer they should purchase next, and almost instantly someone will chime in with a suggestion for a Shearwater Perdix.
It’s so prevalent in fact that memes have started appearing about it in diver’s groups.
Where to Buy:
Shearwater Dive Computer Front!
Jokes aside, it is undeniable that there is a vocal group of very loyal, happy customers, and I think the popularity of these particular computers warrants a closer look.
So today, we will take a closer look at whether the hype is justified and review and explore the Shearwater computers and their features. To briefly outline my perspective, I am a technical diving instructor and teach many courses where my students, as well as myself, use Shearwater computers.
Personally, I use a Shearwater Perdix for all my non-deco diving as well, and I use a Shearwater NERD2 on my rebreather.
In the last few years, I have gained extensive experience with Shearwater computers, but I have used maybe half a dozen other computers over the years.
Aside from the near-eye display on the Shearwater NERD computers, presently Shearwater offers two technical diving computers. There’s the older Petrel and the newer Perdix.
The Perdix came out in 2015 and got a lot of people excited due to the somewhat more pleasing aesthetics and the much lower profile than the Petrel. Aside from design changes, there were a few minor differences, too in performance and specifications.
The petrel, built like a tank, is rated waterproof to 300m, while the Perdix “only” offers a depth rating of 200m. For mere mortals and 99,9% of technical divers, it goes without saying that these depth limits are fairly irrelevant.
More important perhaps is the fact that the Perdix has an extra o-ring in the battery compartment (both the petrel and the Perdix use standard AA batteries changeable by the user). The Perdix has two o-rings, instead of only one and should theoretically be more resistant to flooding. To be fair, I don’t know anyone who has flooded their Petrels, but I appreciate the extra security.
Also changed, is the screen, which uses a different LED technology on the Perdix, and is slightly less bright. This can seem like a step backward, but the display is entirely readable in bright sunlight I find, so it’s not something that impacts performance - especially not underwater, where many actually opt to reduce the screen brightness. (The new LEDs, however, means that the computer goes up to 33% longer on each battery Shearwater claims)
Aside from that, the operation of the computers is identical. With a two button interface, and the workings and layout of the screen are almost 100% identical.
The shearwater Petrel and Perdix are obviously not dive computers that can double as wristwatch lifestyle watches. If that’s your fancy, Shearwater has recently launched the Teric, a wristwatch style computer which works in the usual shearwater fashion and has the same functionality. It is a very heavy contender against the upper range Suuntos and the Garmin Descent. This is not a head to head to comparison of these computers though - so suffice to say, that being very large dive computer with huge screens, you have got to want to have a very large display on your arm to enjoy a Perdix or Petrel.
Personally, having dived a number of small screen watch-style computers for the first many years as a diver, I love the difference! You do not need to squint and look at your computer to get info, you can just glance. You do not need to hit a light button or hold a torch at just the right angle to read it in overhead environments or on night dives, the screen just glows all the time.
In all seriousness, for serious dives, once you go big screen, you don’t go back.
Also, the screen is readable at a very wide angle, and you can read the display even if you extend your arm to hold onto another diver, have it on your scooter arm or at an odd angle for whatever reason.
The computer is operated with a two button menu system. The buttons are piezo-electric and react well to taps as well as soft pushes.
There is a bit of a learning curve, as one button will basically be a move to next option (or change this setting), and the other button the select button. There is no dedicated go back button.
When I teach the Shearwater computer to new students, most of whom are used to Suuntos computers or other computers with up/down/select setups, they are comfortably within half an hour or so of going through all functions and settings.
If you sit down with it and play around yourself, you will get it quickly enough. Very helpful I think, is that next to each button, displayed on the actual screen, are hints which will show at any step what will happen if you push left and what will happen if you push right.
If you take it slow and follow the actual on-screen instructions, you will get it.
That you will generally have to tap buttons on each side for anything to actually change, helps ward against accidental activation by other instruments pushing buttons if you have a busy wrist with other instruments on it too.
The user interface may seem a bit difficult, but once you know the layout, you will start appreciating that you can pull up other info or do gas switches very fast indeed with a few quick taps. A somewhat overlooked benefit of the buttons, is that no actual mechanical buttons are moving.
No o-rings, washers, gaskets, springs or anything. This is a constant failure point on other computers where buttons risk becoming stuck, hard to push or even outright fall off!
Having worked in the service department of a large European distributor of various dive gear, I can vouch that this happens with frustrating regularity!
You can reverse the orientation of the screen, so if you prefer to have the buttons on top, rather than on the bottom, which is the default orientation, you can do so.
So who does the Shearwater appeal to? Well, aside from the cost being high and maybe somewhat of a hindrance, I would think it appeals to any diver who wants a large, very bright and clear display, large buttons, an easy interface and who wants a computer on which you can change the AA battery yourself in less than a minute.
The Perdix has various modes, (gauge, CC tec with OC bailout, OC tec and recreational), On the recreational mode, most of the additional info on the tec display is not shown, so it is very similar to most recreational dive computers. (setting it to recreational mode, also auto-modifies the gradient factors for 40/85, which should give it dive no-stop times similar to most main-stream dive computers. If this doesn’t make any sense to you, don’t sweat it. It’ll dive pretty much like your old Mares, Oceanic or Suunto, except with a large easy to read display and so on.)
So basics covered, let’s look at some of the benefits of the Shearwater in no particular order.
Firstly customer service is outstanding.
You hope never to have to use it, but when you need to, you need to. I have never personally had any issues with any of my rental or personal computers (I use three all the time, two hardwired ones on my rebreather, and another one for redundancy on CCR plus open circuit,) but that’s just me of course. Having worked in scuba gear retail and also have had a friend who had a screen issue with his Perdix, I have nothing but approval for the Shearwater service. In the case of my friend who had a weird screen glitch, Shearwater arranged for replacements immediately. As we were diving in the Philippines, where at the time no diveshops retailed Shearwater, the company sent him a new Perdix by currier mail! He was sorted with a new computer within a week! Also, the things are built like bricks, and Shearwater knows that they get handled roughly when crawling through restrictions in a cave or wreck.
No questions asked. As a tec diver I appreciate that!
On the note of treating it roughly, you can get very cheap stick-on screen protectors. If I am not mistaken, a Perdix comes with one on when you buy it!
It may be the only one you ever needs if you are a careful open water diver, but if you squeeze through restrictions, and otherwise treat it to a rough time, it’s good to know that a few dollars will get you a fresh screen protector.
While all the ruggedness is appreciated, it’s what actually goes on inside the dive computer that matters.
Both the Petrel and the Perdix comes with ZHL16C out of the box as the algorithm determining your no stop times in recreational diving and your deco stops (depth and length) when tec diving.
Years ago what’s known as bubble models were all the rage, and in fact, should you wish to it’s still possible to purchase VPM, a well-known bubble model, on the Shearwater website, as an additional “upgrade”) Considering the NEDU study, which Dr Simon Michell explains the implications of in this excellent video I expect this to be something only very few people would pay for today.
If you use your Perdix for recreational dives, it won’t matter, but if you do technical dives, there is no support behind the claim that a bubble model will do a better job. In fact, there is every support that a dissolved gas model, rending the same deco length - like the one that comes out of the box with a Shearwater - is the better and safer choice.
The bottom line is that if you are presently a technical diver or intend to become one one day, it would be prudent to eliminate some dive computer contenders based on which algorithm they run. In my humble opinion, Suunto computers running RGBM, a bubble model, should not be a serious choice.
You will want something that runs ZHL16C, (Aside from the Shearwaters, some comparatively sized and featured technical computers I would personally consider would be OSTC, or Ratio.) If you are shopping for alternatives, you can read tec instructor Andy Davis’ brief run down of “serious” technical divecomputers.
Another great feature is that shearwaters have massive user configurability. Both behind the scenes and in what you are presented with on the screen.
Things like colors and brightness can be adjusted, but also you can choose which items you want to be shown on the main display, (and can then pull up additional info during a dive by cycling through other screens.) Personally, I’ve pulled a timer to the front screen. As a scuba instructor, I often have to time students performing various skills on different courses, and having a handy timer with easy start/stop/reset is great.
If you use your shearwater as your compass too instead of having a separate analog compass, you can pull it to the front screen too.
Two favorite functions that I think deserve special mention is the GF99 and @+5 functions. Behind the cryptic names are very useful features for tec divers.
The GF99 is basically a percentage number that shows you your present tissue supersaturation. Say, for example, that at the end of a tec diving holiday, you have chosen a very conservative ascent profile with long stops for your last dive. Then during the dive, at the start of the ascent, you encounter a stinging jellyfish in the most unpleasant way imaginable. All of a sudden, you would like to get out of the water and get some medical treatment as soon as possible. Even if cutting your deco short.
But how much can you cut it short, and still ascend in a relatively safe fashion?
The GF99 can give you a qualified answer to that, as it gives you realtime calculations on your current tissue supersaturation. Using this, you could ascend from a dive expediently keeping your supersaturation percentage at a set number, like 90% for example, higher than what you were otherwise planning on using your set gradient factors.
Another way to use this, if you have plenty of gas and want to do a bit of sightseeing on a leisurely ascent on a sloping reef for example, is to look at this number and make sure it actually read a percentage, indicating that you are off-gassing.
The @+5 feature is supremely useful, and shearwater gives fair credit to Dan Wible for inventing it for his CCR2000 computer.
It is basically your usual TTS or TAT with a twist (time to surface or total ascend time) meaning how long, from this point in the dive, it will take you to reach the surface if you honor all required stops and keep a sensible ascend rate.
The twist is that the @+5 gives you this TTS/TAT if you decided to stay at your current depth for another five minutes.
This is really useful.
Suppose you are doing a deco dive on a wreck, and at some point when you are just ready to ascend, you notice that you have dropped your GoPro or something. How would it impact you, if you had to stay at the present depth for five more minutes searching?
By comparing your TTS to your @+5 you can see that difference in minutes.
Or suppose that on your ascend, doing a stop at 18 meters, you see a circling manta ray. Looking at your @+5 you can see that it’s almost the same as the TTS, so you are essentially off-gassing well, and can stay a little longer looking at your new dive buddy.
Lastly, while I myself don’t presently use the feature, the Perdix also comes in an AI version. (That’s not artificial intelligence, but air-integration) Where you can hook a wireless transmitter up to your computer and thus read your pressure on the computer display.
You can purchase transmitters labeled as made by Shearwater, but if you already own a transmitter, there’s a fair chance you can reuse it.
Oceanic, (discontinued Aeris), (discontinued Hollis), Aqua Lung, Sherwood, (discontinued Tusa), and Shearwater transmitters are all the same transmitter, manufactured by Pelagic Pressure Systems (now owned by Aqua Lung), and marked on the end battery cap with FCC ID MH8A.
Suunto, Scubapro (and Uwatec, before they were bought up by Scubapro), Mares, Ratio/Seac, (discontinued Liquivison), and Heinrichs Weikamp transmitters are proprietary and will only work within the brand.
The benefits of using a transmitter are that you can have real-time info on your air consumption rate, which you would otherwise have to calculate after the dive.
Some divers are however very vary of air integration, believing it to be inherently more unsafe than an old-fashioned SPG on a high pressure hose. Without getting into details, I think the truth is more nuanced. For a discussion on this, this article is worth a read.
To wrap up my impressions after having used Shearwater computers for about five years, is that they are rock solid, excellent computers and just keeps performing. I have not regretted the purchases for a second. There are other tec computers on the market that I consider reasonable too, but I would not swap my Shearwaters with any of them.
What we like:
- Massive, massive user configurability. You can choose which elements are the most important to you. You can essentially make it the most useful computer, no matter if you dive a rebreather, dive open circuit technical diving, or just a recreational diver who perhaps dives nitrox now and then, but never aspire to dive into the tec side of diving.
- Bright display and ruggedness
- Innovative features and stellar customer service
What we don't like:
- Communicating with shearwater computers via Bluetooth (to download logs or update the welcome screen to a custom "Reward Given If Found - Call Joe Diver 1234-1234-1234") can occasionally pose issues on Mac, with multiple attempts needed.
- Cost (yes, you knew this one was coming)
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