Shearwater for a newbie ?

[rongoodman]

Thank you all for these great answers.

One more thing, I've seen many CCR computers without any cable interface for CCR devices. How exactly is it used in CCR mode ? Isn't the computer meant to keep an eye on the pO2 (among other things) ?

When used as a back-up, you set the stand-alone computer to the same set-point you have on the rebreather. It won't be able to track the actual pO2 on the unit, but should be close enough to calculate your decompression obligation in case you have to depend on it to get you to the surface.

 

[Peter69_56]

I'd be curious what might be the capabilities of a PDC in 5-10 years..... Look at the changes in the last 5 years regarding the SW line.....
Predator -> Petrel -> Petrel2 -> Pedrix -> PedrixAI -> ?????

How many folks have bought and then "had" to upgrade?

It is as silly as the SmartPhone "must have" chasers....

I have 2 petrels, first computer was an Oceonic Proplus2 which still works fine after 11 years, still use it when I dive a BCD and recreational gear. Just bought a breather and it has a Predator on it. All my shearwaters work fine and other than that the battery in the Predator sucks because its not like the Petrel, however they are all still fine to use. The service/warrenty if you have an issue is second to non. They are easy to read and can be read from about 1 metre so you can ready your buddies PC if they have one too.

A shearwater would do you fine for a number of years, and still be a great computer while diving recreational. My recommendation is if you are seriously considering tech in the near future, shearwater is a very worthy selection.

To get both algorythims ZHL-16C and VPM-B you have to buy the unlock code $75 AUD for VPM-B which I chose to do as I do swap between them depending on my diving.

If you can afford it you can buy the Petrel with fishker connection for breather, as a recreational computer the connector is covered and PC selected for OC or recreational. In tech mode open circuit it can be OC, with a breather it can be CCR if cable connected to the breather via the Fishker or OC if a backup and no connection. I wish I had the fisker connector as now I have a breather and could use it instead of the Predator and then have 2 Petrels one connected, and one not connected and backup. But will use the Predator connected and Petrel as backup not connected.

 

[rongoodman]

I don't think so. the hardware differences are nice but the real meat of the DC is the deco algorithms, and as far as i know they are the same algorithms on all models. IE If ZHL-16C in on one model it is on all models. they dont quit updating the older units like predator and continue on the perdex.

The real advantage of the Shearwaters, in addition to the superb customer support, is the underlying philosophy. No lock outs, no annoying alarms, no proprietary software. The computer presents the information, the diver uses it. If and when better algorithms appear in the future, implementing them can be done with firmware updates.

 

[Peter69_56]

The real advantage of the Shearwaters, in addition to the superb customer support, is the underlying philosophy. No lock outs, no annoying alarms, no proprietary software. The computer presents the information, the diver uses it. If and when better algorithms appear in the future, implementing them can be done with firmware updates.

Totally agree, the no lockout is very valuable IF used wisely, you miss a stop due to an issue, it keeps calculating on best deco based on new depth. A wise diver might add some more time at 6m to increase the safety margin but the PC does not go off its nut and lock you out, it keeps trying to give you best information with the changed dive conditions, but again dont be lasy and think missing a deco stop is no big deal, the function it provides is a backup if the poo has hit the proverbial fan.

If it alarms and then if you accept it, doesnt alarm again unless you breach a rule again, no spesky noises, but again use it wisely and dont just accept the flashing, understand what it says and understand the risks at your peril if you ignore it. Also the shearwater PC dive log is very good as well for saving dives.

 

[dmaziuk]

The real advantage of the Shearwaters, ... (is) ... no proprietary software.

I don't think "proprietary" when applied to software means what you think it means.

Totally agree, the no lockout is very valuable IF used wisely, you miss a stop due to an issue, it keeps calculating on best deco based on new depth.

So what does it do when it calculates you're bent into a pretzel? Every subroutine has a range of input values it can operate on, once you're out of range, it'll crash and burn or worse: give you very bad outputs. The typical answer for DC is, when you're out of range it locks you out until your gas loading is reset to "clean slate" which now is believed to be 24 hours. What do shearwaters do instead? Calculate you a year of deco on top of Mt. Kea?

 

[tbone1004]

@dmaziuk

Shearwater uses open versions of VPM and Buhlmann ZHL. Unadulterated, open source, you can model exactly what that computer will do with any software out there.

Suunto has a proprietary algorithm. No one outside of them knows what it does or how it does it
Oceanic/Hollis et al have a proprietary algorithm. Same as above
I believe Atomic uses a proprietary algorithm as well.
These are less than ideal because they have unpredictable behavior. Suunto's are notorious for penalizing for sawtooth profiles, short SIT's, reverse profiles, etc. but you have literally no way of predicting what it is going to do. From a dive planning standpoint, that is annoying, and potentially dangerous.

From a lockout standpoint. The Shearwater computers track your theoretical tissue loading and make recommendations on deco stops. No computer knows that you are bent or not. The Shearwaters will continue to track your tissue loadings until such time that you shut it off. This is very important because you may be in a scenario where you are forced to blow decompression stops to save your life or that of someone else. You blow 30 mins of your 20ft deco stop to get someone to the surface so they live, then go straight back down. You have bubbles forming, and another computer will lock you out. You have no method of tracking your tissue loading. The Shearwater however will flash a bunch of red signs at you telling you that you are an idiot. You get the guy to the surface, then go back down to somewhere below your last cleared stop. It just keeps tracking your tissue loading until you decide that you want to go up.
Less severe scenario. You are a conservative diver and normally dive with a gf-Hi of 70. You are sitting on your final deco stop and go "oh sh!t" because something catastrophic happens, or for whatever reason you need to get out of the water quick. You go in, adjust your GF-Hi to whatever, 90-95-99, doesn't matter, and then get out when it's cleared.

From an instructor standpoint, that is a safety thing and I refuse to dive any computer that can lock me out when I'm teaching. That goes from open water, all the way up. From a recreational diver standpoint, it may not be the biggest thing in the world, but does locking you out really make the best sense? If you do something stupid and you know it, you should beach yourself, not the computer.

 

[Peter69_56]

I

I don't think "proprietary" when applied to software means what you think it means.



So what does it do when it calculates you're bent into a pretzel? Every subroutine has a range of input values it can operate on, once you're out of range, it'll crash and burn or worse: give you very bad outputs. The typical answer for DC is, when you're out of range it locks you out until your gas loading is reset to "clean slate" which now is believed to be 24 hours. What do shearwaters do instead? Calculate you a year of deco on top of Mt. Kea?

If you stupidly miss many stops yes I expect it will give a years deco, trying to help, if you don't have the gas, either way you are bent or dead

I am talking about missing a stop or two, it will try and help by recalculating. There is an assumption though that due to your training you ar not totally stupid, if you are your stupidity will get you in trouble.

If you follow the modified deco plan and don't get bent, a wise diver would change the algorithm to a less aggressive one on subsequent dives as well as long SI ornot dive at all that day.

It doesn't make it a bad computer, but one requiring better understanding if in tech mode. If you only want a computer to dumly dumbly follow because you are lazy or a poor diver then I agree, get an ultra safe one that locks you out if you stuff up. They are safe but restrictive and designed for minimal skills and more simple pleasure. That doesn't make my proplus2 a bad pc either, it's just a tool designed for certain usage, same with the shearwaters. They are less restrictive if in tech mode but along with that an expected minimum skill base and elevated risk. If you don't want the risk then use it in recreational mode and it's a dumb recreational computer (I think).

 

[_Ralph]

One of the most respected (non instructor) tech divers I know still uses his original Sunto Zoop (in gauge mode) and a digital stop watch for all of his diving, including RB (yes, a Petrel is flying the machine for him ... but that's about all he uses it for).

Personally, I still have my Veo, and a Petrel 2 (that I acquired used). And still use them both regularly (Veo is a backup in gauge mode, Petrel is a sanity check).

You won't go wrong with a NITROX puck style computer and upgrade/augment later to a "Latest and Greatest" "tech" computer...

_R

 

[Peter69_56]

I


If you stupidly miss many stops yes I expect it will give a years deco, trying to help, if you don't have the gas, either way you are bent or dead

I am talking about missing a stop or two, it will try and help by recalculating. There is an assumption though that due to your training you ar not totally stupid, if you are your stupidity will get you in trouble.

If you follow the modified deco plan and don't get bent, a wise diver would change the algorithm to a less aggressive one on subsequent dives as well as long SI ornot dive at all that day.

It doesn't make it a bad computer, but one requiring better understanding if in tech mode. If you only want a computer to dumly dumbly follow because you are lazy or a poor diver then I agree, get an ultra safe one that locks you out if you stuff up. They are safe but restrictive and designed for minimal skills and more simple pleasure. That doesn't make my proplus2 a bad pc either, it's just a tool designed for certain usage, same with the shearwaters. They are less restrictive if in tech mode but along with that an expected minimum skill base and elevated risk. If you don't want the risk then use it in recreational mode and it's a dumb recreational computer (I think).

I think the previous post is better written and a better explanation of the shearwater and I totally agree with it. My response above is more simplistic and not necessarily technically accurate and written in general terms only

 

[Peter69_56]

Sorry I meant tbone1004 post. Someone slipped a post in between and I can't edit on my phone