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My New Shearwater Pursuit July 1, 2009

Posted by Chris Sullivan in Equipment, Technical Diving.
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Consider this part one of at least a four part product review. This describes my out-of-the-box impressions of the Shearwater Pursuit. Part 2 will describe diving the unit within the no-decompression limit. Part 3 will cover decompression diving, and hopefully part 4 will be about the logging functions. Later on I might add deep diving and some day trimix diving.

It will be a few days before I dive it, but I’m now the proud owner of a Shearwater Pursuit SPOT. The SPOT is an open circuit only model, which is fine as I’m an open circuit only diver, with Trimix capability. I haven’t certified on Trimix yet, but will do so before too long, I’m sure, and I wanted my computer to be ready for it.

The computer is fairly large and fairly heavy. I find it a bit odd that the dimensions and weight are not found in the manual or on the Shearwater web site, maybe they don’t want to scare people off. Now that I have one I can tell you that it’s 3 1/4″ wide, 3 1/8″ long, and 1 1/4″ thick. The clear covering (acrylic, I suppose made of Lexan) over the screen is 1/4″ thick. As for weight I’d say about a pound, but I’m not a very good judge of weight. I calculate it displaces about 7 oz of water so it is probably quite negatively buoyant.

Pursuit

The manual doesn’t come with the unit but must be downloaded from the web site (I personally like this trend – always up to date, but more importantly you can read the manual before buying the product, which was a major influence on my purchase). It is very clear upon reading it that it has a bias towards closed circuit diving, as you have to pick out the bits that are applicable to open circuit divers. I think there probably should be a section catering to each, as an open circuit diver with no knowledge of CCR diving might have trouble figuring it out. It took me a while.

Operation of the unit (on the surface at least) is pretty easy. I really like the way the status displays can be cycled by pressing the right hand button without resorting to modes, sub-menus, and other contrivances to get the information you want. Definitely the thing for the narced-out deep air diver. Similarly, setup is pretty easy, with the left button getting involved to select the function you want. These have 1 level of sub menu as you cycle through the main menus with the left button and use the right one to select the one you want, then go back to the left button to cycle through the sub menu.

The Pursuit lets you do just about anything. It doesn’t lock you out no matter how far from the profile you have strayed, it lets you run all the setup menus (except shutting it off or changing the time of day) while submerged, including setting up gases. This means in addition to being able to control which of 5 gases you are calculating your decompression with, you can also change any of those gases while under water. It would be a pretty unusual situation for you to want to do this, but the Pursuit will let you do it if you want.

As I’ve mentioned before, one of  the things I like the most is the decompression algorithm is based on published literature (Buhlmann  ZHL16C with Erik Baker’s Gradient Factors) with no proprietary “secret sauce”. While some of these proprietary algorithms are no doubt valid and built with good intentions and real-world testing, unless they’re generally available to the scientific and diving communities I’d rather pass on them. I don’t want a black box telling me how to deco (the Pursuit does of course strongly resemble a black box but that’s not what I meant).

One other thing not mentioned in the manual is installing the cap on the Fischer connector on the left hand side, which presumably I need to install before I go diving! I know it seems obvious but you’d think the manual would at least give it a mention. Should I lubricate its little o-ring? I guess so.

The buttons on the unit are very flat, a striking contrast to the  VRx with its thin, half inch throw stiffly sprung buttons. The Pursuit’s buttons don’t move when you press them, and so don’t have a positive feel to them. Still, I have become used to their operation very quickly. I like the fact that the only function that isn’t a simple push of either the left or the right is that to turn the computer on you need to press both at once. The VRx has short push, long push, left, right and both for all sorts of functions that seems way too complicated. The VRx also has very disturbing delays after a button push, often a different length of time even for the same function. As one friend put it, it kind of resembles MS-Windows for responsiveness. In contrast, the Pursuit has sub-second response to anything I thrown at it so far (remembering I haven’t taken it underwater  yet), which is sufficient feedback to know that your button press has been effective.

The Pursuit is more like MS-DOS than Windows. If you like fancy graphics, colour, games, books and other nifty features this isn’t the computer for you. On a dive, with the open circuit model the main display shows Depth, Time, Stop Depth, Stop Time, Gas mix, No decompression limit and Time to surface, plus rudimentary graphics for battery life and ascent rate. In open circuit mode you can modify the last 3 numbers to give you the maximum depth, CNS%, and current PPO2 with a push of the right button. Push it again and you get the current gradient factors, and again gives you the temperature and the battery voltage. That’s it. There’s nothing else to display. Pushing the left button lets you do configuration in or out of the water.

The computer uses a 3.6 volt Lithium AA size battery. I don’t know how hard these things are to obtain locally, but they’re all over the Internet. If the Home Depot doesn’t have them then I’m sure the local photo store will. The two wrist straps are attached to the computer by a metal flange (shaped like a miniature backplate. They are made of stretch material and use squeeze clips like you find on a backplate harness.

The weaknesses I’ve seen so far? I can’t really tell from the manual what the computer will do at altitude. As I dive only in the sea or in Ontario lakes and rivers this isn’t a big concern for me, but the documentation should at least mention it. The Buhlmann algorithm was designed to work at altitude but I’m not convinced that the Time To Surface display would be accurate if the surface was well above sea level. There’s also no fresh water setting, although I hear it’s coming. This would give direct reading and logging of actual depth rather than reading slightly shallower than actual, but it has no meaningful affect on decompression.

The logging program is also a problem. Apparently the current one is so bad it is being withdrawn. It was only $25 but is an extra cost item. The computer interface comes with the unit. The logging program is being replaced by a new one which apparently will be $40, although the 5 people who bought this computer at our local shop are apparently getting a complimentary version. Shearwater Research also threw in a complimentary T-Shirt for the 5 of us.

So far there are no unpleasant surprises. The computer appears to be just what I expected, and I’m looking forward to using it underwater.

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Comments»

1. deepstop - July 2, 2009

Regarding the cap for the Fischer connector I got the following answer from the Rebreather World Forum.

Re: OC with SPOT & the Fischer Connector
Quote: (Originally Posted by [Deepstop]) View Original Post
I just got my new Pursuit SPOT and want to make absolutely sure I’m doing the right thing before taking it in the water. The computer came with a little cap for the Fischer connector which is attached to a wire, and the bag also contains a lug connector and a tiny piece of crimp tubing.

It seems fairly obvious that I should install the cap in the connector on the computer, but I was surprised it doesn’t screw in or lock somehow. With a little wire attached couldn’t it be pulled out really easily, especially before submerging?

Also the other end seems to want to be trimmed short and attached to the lug connector, and I suppose then screwed in under the closest screw of the ones holding the metal plate on the back of the computer. Do I crush the end of the lug connector to the wire with a pair of pliers? Then what do I do with the little piece of crimp tubing?

While the computer is exactly want I want for diving, the manual is very CCR oriented and as all my experience is with OC, I’m probably lacking in knowledge that’s assumed by the author.

Thanks.
———————————————–
You can either loop the wire round a strap slot and use the crimp tubing to permanently secure, or, crimp the wire in the lug and secure the lug under the nearest screw.

Even if the cap comes off, the computer will not flood. The cap is to prevent saltwater getting in and corroding the pins. If the cap comes off, or is forgotten, simply rinse with fresh water thoroughly and all will be well.

Brent

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2. Terry Killeen - July 2, 2009

Great write-up on the Shearwater. The SPOT is what I’m looking at right now, as I’m an OC trimix diver and no real plans to make the leap to a CC rebreather. I was a bit alarmed about the Fisher connection cap and the flooding issue, but thankfully you cleared it that up with your follow-up post! I think I need to bit the bullet and just buy one today so I can start diving it next weekend!

BTW – Keep sharing your experiences!

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deepstop - July 2, 2009

I’ll do that! Let me know how you make out with yours, too.

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3. deepstop - October 15, 2009

Update (see later posts in this blog)…

Shearwater now has beta desktop software available that works pretty well. I’ve had some good results with it.

A software upgrade is available now to handle altitiude diving.

It still works great.

I’ve now seen the earlier, larger model. While the current Pursuit isn’t exactly compact, it’s no behemoth either.

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4. Terry Killeen - October 15, 2009

I have only managed to dive my pursuit on a few wreck dives off of NC, and a weekend cave diving trip. The Gradient Factor settings had me fairly confused, despite reading the suggested articles until I read “Gradient Factors for Dummies”: http://www.rebreatherworld.com/general-and-new-to-rebreather-articles/5037-gradient-factors-for-dummies.html

I compared it to my Cochran Commander (two mix nitrox), and it gave the same overall deco time with the factor set GF – though the stops started deeper. I have changed them slightly since then.

I have been extremely happy with the simplicity of use, though I have yet to do a trimix dive with it – they have all been canceled for one reason or another. However, I have no doubt it will perform very well!

Safe Diving!

Terry

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5. deepstop - October 16, 2009

That article is quite well written. Actually there’s a lot of good stuff on rebreather world and Bruce from Shearwater regularly answers questions directly and has arranged upgrades for his customers there as well.

I haven’t tried trimix either. I’m not certified for it yet but hope to do so before too long, which probably means sometime next summer.

Thanks for the pointer, and I’m glad the computer is working out for you.

Chris

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6. Shearwater Predator – I want one! « Chronicle of an older diver - November 5, 2009

[…] Pursuit, Technical Diving trackback The Shearwater Predator, an upgrade to the already wonderful Shearwater Pursuit is on my Christmas list. Right after I get back from my upcoming trip to Florida I’m going to […]

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7. Recreational Diving with a Shearwater Predator « Chronicle of an older diver - March 7, 2011

[…] Predator is a great dive computer. Mine used to be a Shearwater Pursuit and was upgraded once the Predator was introduced. The main differences between the two are the […]

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8. Chris Sullivan - November 18, 2016

7 years later my Shearwater Predator, upgraded from the Pursuit, is still going strong. I also finally did a trimix dive a little while ago, although it was just a weak leftover mix and I’m still not certified. I’m now certified for CCR (AP Inspiration) and will continue on to CCR Trimix once I have sufficient hours, which will have to wait for next summer. The Fischer connect isn’t useful for the AP unit but it is still useful in constant PO2 mode as a backup for the AP’s built in computer.

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