Petrel v. Vyper :)

[scubadada]

First dive NDLs are easy to find and compare for most computers and algorithms. It's repetitive dive information that is difficult to find. Some years ago, Scuba Diving Magazine published some repetitive dive comparisons that I found very informative. Unfortunately, this type of testing and reporting did not catch on. This type of information would be very useful in a discussion such as this.

Recreational NDLs (min), on air, 1st dive, most liberal setting:
	Oceanic	Shearwater Petrel	Suunto
Depth (ft)	DSAT	PZ+	45/95	RGBM P0
50	81	65	76	69
60	57	48	51	50
70	40	35	35	36
80	30	26	25	28
90	24	19	19	21
100	19	16	15	17
110	16	12	12	12
120	13	10	9	10
130	11	8	8	8

 

[LowVizWiz]

I'm one of the people speaking poorly of Suunto computers. Your data backs me up, actually. I'm not saying that the first dive is too conservative. I'm saying that repetitive dives get goofy on the Suunto algorithm.

Ok, I'll play along.

Dive one: Tables 25 BT, Vyper 25 minutes BT before deco (51 total BT) , Petrel 23 minutes (51 Total BT)
Dive two: Tables 60' after SI. BT 29 minutes, Vyper BT before deco 56 minutes, Petrel BT before deco 90+ minutes.

During the second dive let's say the average rec. diver has a SAC rate of .60 after 50 minutes at an average depth of 45' they would have consumed ~72 cubic feet of gas. Is the dive Time limited or Gas limited? Of course assuming the typical AL80 tank size.

Not only do they get far more conservative within NDLs, repetitive deco dives get HARSHLY penalized. Unrealistically so, on some profiles.

Yes, I had back to back deco dives on the Suunto. Is the typical rec. diver doing those? Maybe, if that's where they are at then sure move on. But that's not what I see out there most of the time.

The other point against Suuntos I have is that their proprietary algorithm makes them nearly impossible to match to anything else,

Maybe this is what I'm missing... I have yet to find a dive buddy tell me I'm holding up his dive 'cause I don't have enough bottom time..

and the ones with the stupid heart rate monitor are even worse because they're trying to account for stuff that no decompression studies have ever found correlation between....and they apply it seemingly randomly.

I think you're talking a different brand here... No comment!

As for AI and audible alarms: There are too many reasons to not have them. I can understand why people like them in theory, but in reality they just suck. Also, if that's the only thing keeping you from getting a Petrel, your priorities are WAY out of whack. Shearwaters are arguably the most reliable computers on the market, supported by arguably the best company on the market, with arguably the best screen on the market, and they can go above and beyond what nearly any diver could ever dream of doing.

Again, I'm not trying to diminish the virtues of Sharewater computers. I own one. I love it! Rather, I'm trying to understand what seems to me an irrational aversion for a particular computer based on mostly anecdotal info or hearsay.

 

[Agility]

I have posted this link before but I cannot find it on scubaboard
A sense of algorithm - Divernet
A comparison of the algorithms used in different divecomputers

It shows that the conservative setting in RGBM can increase deco significantly (as it of course should)

 

[victorzamora]

You're right, it was Scubapro for the heartrate thing.

As for your "repetitive dives".....I really don't count 2 in a day repetitive. I'm talking about 3-5 dives per day for a week. I was on a dive trip where a guy on a Suunto (on all the dives with me) had like 20min less NDL than I did. BIG TIME NDL limited on that one. He surfaced with like 2000psi.

Your example has the suunto showing 56min and the Petrel showing over 90minutes. THAT dive might be gas limited, sure. Deeper dives may not be. The third or fourth dive in a day surely won't be gas-limited, especially on the Suunto.

 

[Lorenzoid]

It's been said here in previous threads that since we don't see divers who use liberal computers getting bent any more often than divers who use Suuntos, then there is no objective reason to believe Suunto keeps one safer than any other computer. But isn't it true that the correlation between DCS and repetitive dives, especially over a span of several days, hasn't been as thoroughly studied as for single dives or a simple set of two consecutive dives? If that's true, it seems reasonable that Suunto's conservativeness for repetitive dives/days and short surface intervals might provide a buffer or margin against that less-studied territory. I think of my Suunto as a vacation diver's computer. If a vacation diver is well educated enough to keep himself safe by determining and adhering to his own safety margins, a Suunto may not be of value. But maybe it does have some value for lazy vacation-type divers?

 

[Dr. Lecter]

My only point in comparing the two was that one is well liked and with plenty of reason, while the other seems to be a whipping dog because of some perceived limitation. Yet, on the first dive both computers gave similar bottom times and on the second dive the Suunto also provided plenty of bottom time on a typical recreational dive which is the intended target for the computer. And it's my experience that this also holds true over multiple days of diving.

It seems irrational IMO or I'm really missing something! I have more issues with the lack of support and really poor desktop software than the computer itself.

First off, I agree with you on that last bit: I know tons of instructors and DMs who dive Suuntos, so the things work as DCs (even if they spend a significant amount of time in "deco" on NDL dives sometimes). My main beef with Suunto is quality, U/I design, support, and price-value gap.

But you're assuming 30/85 is the "right" setting for comparing the two, and I don't agree. Your own data also shows Suuntos don't handle even a single repetitive dive very well. If you want to pay a significant amount of money for generic performance, Suuntos are workable DCs. The Petrel is a ing perfect DC - it's not a perfect SPG, and it won't audibly yell at you if you do something it doesn't like...it won't even force you to choose between following it and not having any help at all. Which is a big part of why it's the perfect DC The other reasons are a workable size, brilliant screen and U/I, universal battery compatibility, and service/support that are best compared to the likes of Atomic and Light Monkey.

 

[LowVizWiz]

But you're assuming 30/85 is the "right" setting for comparing the two, and I don't agree.

I try not to assume much as you probably know what they say.
30/85 is the default setting. I have not played with the Rec. Nitrox setting at all, but I wonder what that is set to.
Maybe I'll do the same test diving the Petrel in Rec. Nitrox mode and see what comes up.

---------- Post added August 20th, 2014 at 04:52 PM ----------

But maybe it does have some value for lazy vacation-type divers?

Is that what they call a back-handed compliment?

 

[bap]

Maybe this is what I'm missing... I have yet to find a dive buddy tell me I'm holding up his dive 'cause I don't have enough bottom time..

:vintagediver:

 

[LowVizWiz]

:vintagediver:

LOL, you spoiled RB divers don't count and we were due back in the boat in an hour anyway

 

[Dr. Lecter]

LOL, you spoiled RB divers don't count and we were due back in the boat in an hour anyway

Hey, don't confuse us with those weird vintage diver guys!