Petrel v. Vyper :)

[Slamfire]

Richard's response reflects real life conditions of most rec divers. I admit that reading and understanding Erik Baker's papers on m-values is not a pre-requisite before somebody submerges with scuba tank on their backs. Thousands of people do it around the world and somehow manage to survive.

Lowvizwiz makes points towards what should be better diving practices -- plan your dive, dive your plan -- albeit a lot (most?) of divers do not do it that way. Non-compliance to better diving by a majority should not be an excuse to quit evangelizing about it.

Here's where I see Shearwater's superiority. It will work great with planning divers and non-planning divers alike. But if you want to dig deeper into the plannig and be able to know/predict what your computer will want you to do if x contigency rises, Shearwater is better suited for that. There is a wider variety of desktop and mobile dive planning software that will match Shearwater exactly or almost exactly.

Suunto does not have that strength to this degree. In the interest of getting back to the surface in a healthy state, divers should ideally contemplate a wide variety of potential contingencies and plan accordingly for such. It is a very big disadvantage if it is difficult for a diver to predict what the computer will require of him if he gets delayed x minutes past NDL while at the bottom. How will said diver know if he will have enough gas to get back to the surface without breaking deco ceilings?

---------- Post added August 21st, 2014 at 10:08 AM ----------

Additional Reading: Why dive computers are counter-indicated in technical diving

Notes on the Additional Reading: Steve Lewis wrote the article above several years before the advent of 4th generation dive computers like Shearwater's. In the particular case of this thread, I believe Shearwater addresses some of Steve's concerns much better than Suunto does.

 

[victorzamora]

The way I do reef dives is I set a max depth limit for myself. With my wife, I'm 130ft max unless limited by mix. More than once, the original plan has shifted from something shallow to much deeper or reverse. I don't cut tables for those. I also don't cut tables for repetitive dives. I ride my NDLs all the way up. Wife does the same thing. We go down until the computer says we're close. If it's interesting, and I'm not with my wife, I'll go into light deco and just extend my safety stop. I've done it more than once, and I'm seriously not concerned. If the captain/crew asks, I'll tell them it's something goofy with my safety stops.

If my computer dies (like a Petrel would ever die) on a rec dive, I just throw a big fat thumb upwards (happened once on a rental computer....Suunto, actually). If diving with my wife, I check her NDLs for the next dive and dive more conservatively than her (we normally dive holding hands or practically so). If not, I thumb it for the day and move to tables plus another computer.

If I'm diving with someone who has a 12min shorter NDL than I do, I'll be PISSED if I have to ascend with them. I'm not even diving a conservative computer, but I can hit NDLs on air in an AL80 on typical vacation dives (done so in Roatan and Cancun). A lot of drift dives don't give you the option of separating into groups, so when one computer calls it it calls it for the group. A guy in Mx was diving with us with TWO suunto computers because they'd lock him out if he dove just one. Not two at the same time, he'd do 4 dives a day.....dives 1&3 were on one computer, dives 2&4 were on the other.

As for breaching deco to extend bottom time: We've been talking about this being for strictly rec divers. If you throw deco diving into the mix, I hope it's universally agreed upon that the Petrel is better.

---------- Post added August 21st, 2014 at 01:17 PM ----------

Lowvizwiz makes points towards what should be better diving practices -- plan your dive, dive your plan -- albeit a lot (most?) of divers do not do it that way. Non-compliance to better diving by a majority should not be an excuse to quit evangelizing about it.

I'm very much with you. However, it's not always practicable. Dive plans change at the last second very frequently, especially when on vacation. I've done 100ft dives that started as 30ft dives when I got on the boat, and vice-versa. I fly my computer's NDL curve, keep MinGas, and enjoy the dive. There's no need to get too fancy on every shallow dip.

Here's where I see Shearwater's superiority. It will work great with planning divers and non-planning divers alike. But if you want to dig deeper into the plannig and be able to know/predict what your computer will want you to do if x contigency rises, Shearwater is better suited for that. There is a wider variety of desktop and mobile dive planning software that will match Shearwater exactly or almost exactly.

And for bigger dives, this is crucial. For rec-only diving, it'd be very nice to have but not necessary.

Suunto does not have that strength to this degree. In the interest of getting back to the surface in a healthy state, divers should ideally contemplate a wide variety of potential contingencies and plan accordingly for such. It is a very big disadvantage if it is difficult for a diver to predict what the computer will require of him if he gets delayed x minutes past NDL while at the bottom. How will said diver know if he will have enough gas to get back to the surface without breaking deco ceilings?

THIS is the benefit of a Petrel, in my book. You get the planning software (and a huge array of good ones) that match your computer. You can play with all sorts of contingencies, to get a feel for what happens. The benefit of the Petrel is that it gives you an @+5 value if you'd like......which is what's your total ascent time if you stay here for five more minutes. It won't do the gas calculations for you, but when you see it start getting bigger than your current TTS, you need to make the judgement call to head upwards. The amount of information, if you know how to read it, and the amount of flexibility, if you know how to set it, is the biggest benefit of the Petrel.

My problem with Suunto isn't that it lacks an @+5 or good planning software or a flexible screen layout. My problem is that they penalize weird for multiple dives or sawtooth patterns or all sorts of other stuff most dive computers handle fine. There are MANY better computers on the market in the price range or cheaper than Suuntos, and it's just not worth having that stupid, goofy algorithm to me. Pelagic Z+ (one of the Oceanic ones) is a slightly modified Buhlmann ZHL-16C, which is what the Petrel runs.

 

[Slamfire]

My problem is that they penalize weird for multiple dives or sawtooth patterns or all sorts of other stuff most dive computers handle fine. There are MANY better computers on the market in the price range or cheaper than Suuntos, and it's just not worth having that stupid, goofy algorithm to me...

Exactly. The lack of predictability in a contingency scenario is a big turnoff for me. You may not do extensive planning for easy, shallow dives. But if your dive plan goes to crap because you are helping somebody deeper than your intended dive plan, you know what to expect from a Shearwater. Who knows what a Suunto will want from you in penance for your transgressions...

 

[LowVizWiz]

Richard, thanks for your contributions...

I knew going into this that I'm fighting a loosing battle because at one extreme you can pick the guy diving steel 120s and at the other you can choose the vacation diver doing reef dives in Coz. with an AL80.

I recently finished teaching a Nitrox class to 5 divers who dive together. None of them had ever used the plan feature in their PDCs. 2 Suuntos, 1 Mares, 1 Aeris and a Scubapro. They been diving between 5 and 12 years. I made them plan one of their actual dives to 80' using Air and using EANx 32 to show the difference in BT. Then I made them agree on a bottom time and did the dive on EANx 32. None of them were able to complete the entire dive because they were gas limited.
This is what I see on a regular basis and would say reflect the lion share of rec. divers. It didn't matter what computer they were using, but I can't tell you that after that dive they were thinking hard about their gas supplies.

Is it ok to jump off a boat and have your computer agree with what you do underwater? I guess it's okay in some instances.
Hopefully new divers searching for computers will run into this thread and consider how they are diving.

 

[victorzamora]

None of them were able to complete the entire dive because they were gas limited.

On 32%, on one dive, relatively shallow, and on small tanks they were gas limited and that makes it a rule that you'll always be gas limited? Why carry a computer at all?? I'm sorry, but gas limitations are not the only things in play. Like I said, I've maxed out NDLs in the Caribbean on a single AL80. What I haven't said is that I did so with a liberal setting. I did it with over 1000psi left in the tank. I also did it on one AL80, although I was set up for two. I'm also 6'6", 250#, and have far from the best SAC on the planet.

 

[LowVizWiz]

On 32%, on one dive, relatively shallow, and on small tanks they were gas limited and that makes it a rule that you'll always be gas limited? Why carry a computer at all?? I'm sorry, but gas limitations are not the only things in play. Like I said, I've maxed out NDLs in the Caribbean on a single AL80. What I haven't said is that I did so with a liberal setting. I did it with over 1000psi left in the tank. I also did it on one AL80, although I was set up for two. I'm also 6'6", 250#, and have far from the best SAC on the planet.

Bud, how are you inferring a rule from what I said?

I said, they resemble the average rec. divers and they were gas limited.

My point, using a recent example of what I see on a regular basis, is that liberal NDLs are usually a non factor to the large majority of recreational divers when it comes to dive planning.

Do you consider yourself the typical average recreational diver?
How many dives do you think the average recreational diver does a year?
Do you dive more or less than that number?
What size tanks are most used by the average recreational diver?

I would say that most people on this board do not fit the profile, I could be wrong, it looks like a poll is in order.

 

[djtimmy77]

If you dive conservatively in general, then it is a non issue.

In Bonaire, we do 4-5 dives a day at a leisurely pace. Never NDL limited. 90% of our dives stay shallower than 50' or so though, and the most time is spent 30-40'. Only go deeper if there is something specific we want to see (like the garden eels at the double reefs.) Always slow ascents and generally avoid see saw profiles. All SI's over an hour.

During my ANDP class last month, I planned a conservative deco dive using V-planner set at +3. The Vytec cleared well before my run tables were finished. Of course this isn't the repetitive diving that most complain about.

We dive big tanks here at home, and don't feel shorted by our computers, usually it is boat-limited. haha. We also don't worry about coming back with tons of gas, because we have a good idea of what our dives are going to entail before we get in the water.

That all being said, when I progress to trimix, I will likely get a Petrel.

Also, a few people have mentioned Suuntos being overpriced, I haven't paid over $200 for a zoop/gecko and I got the Vytec used for a ridiculously low price.

 

[victorzamora]

What I meant was you were extrapolating dats from a single dive, a condition few of us believe to be the main failing of Suunto computers. You also padded your point by adding a Nitrox mix and relatively shallow depths into the mix. My problem with Suunto is repetitive dives.

Most rec divers don't dive Nitrox, either. I will say that I have a normal to low amount of recreating dives pet year compared to a typical recreational diver. Much less so than most rec divers buying computers and other gear.

Even if you think that my tech dives make my sac super low, I'll tell you I'm fat from a super low sac diver. I hover in the 0.5 ballpark. I had students with better rates in class on their first dives

 

[scubadada]

What an interesting thread. As my dive time is limited, I guard my dive time on each trip. I dive Oceanic DSAT. My SMRV hovers around 0.35 cu ft/minute so my bottom times are relatively long. I usually dive within NDL limits but dive light deco (<10 minutes) about 5% of the time. Usual diveS At 50-60 FEET are about 1:15.

 

[LowVizWiz]

Most rec divers don't dive Nitrox, either.

The bold comment above is a very good point and you are right, Nitrox does tip the scales in favor of a more conservative computer. I can see the flaw in my test, I'd love to see numbers from other computers planning the first two dives with Air.

What I meant was you were extrapolating dats from a single dive, a condition few of us believe to be the main failing of Suunto computers. You also padded your point by adding a Nitrox mix and relatively shallow depths into the mix. My problem with Suunto is repetitive dives.

Well, not quite. My first sample was using repetitive dives. Yes, there are only two dives, but it was mainly just to illustrate a point which, as you pointed out, is invalid due to me using nitrox. However, I mainly guide tourists on local dive charters and most of those dives end because of gas. My sample size (Close to 100 guided dives in the last year and a half) cannot not represent every situation, but I think it's a fairly good representation of the typical diver on AL80s doing easy dives.

I will say that I have a normal to low amount of recreating dives pet year compared to a typical recreational diver. Much less so than most rec divers buying computers and other gear.

I don't understand either of the above statements.

What's normal to low?
How many dives do most rec. divers who are buying computers and other gear have?

Even if you think that my tech dives make my sac super low, I'll tell you I'm fat from a super low sac diver. I hover in the 0.5 ballpark. I had students with better rates in class on their first dives

As I said, I don't think most SB members including you fit the average rec. diver profile. The average rec. diver does not teach scuba nor does he/she tech. dive.

When I do planned deco dives my SAC is much higher than my normal average which is .54. I'm also 6'5" 250, but what does that have to do with the price of tea in China?

Yes, I've also seen new divers (normally women) who sip gas, but they are usually the exception rather than the rule.
I've always said this is the only sporting activity where I would like to be a tiny little girl rather than 6'5" 250

---------- Post added August 21st, 2014 at 07:39 PM ----------

What an interesting thread. As my dive time is limited, I guard my dive time on each trip. I dive Oceanic DSAT. My SMRV hovers around 0.35 cu ft/minute so my bottom times are relatively long. I usually dive within NDL limits but dive light deco (<10 minutes) about 5% of the time. Usual diveS At 50-60 FEET are about 1:15.

Cool, are you diving air, AL80s?
Can you post some profiles or plan the first two sample dives and post the bottom time allowed?