Suunto Cobra too conservative

[boulderjohn]

The various settings for fitness (P0, P1, and P2) and altitude (A0, A1, and A2) can make a significant difference. Back when I used my Cobra regularly, I was very frustrated by its conservatism during a dive trip before I realized the fitness setting had somehow been changed. Then I pretty much didn't use it for a couple of years until I did some diving in FLorida this past winter. I was just using it for the air pressure readings, and so that was all I was paying attention to on it. About half way through the dive, I remembered that I had last used it at altitude, and it was on its highest altitude setting. I figured that would be trouble, and it was. Even though I was nowhere near NDLs on the actual dive, the Cobra had me bent like a pretzel because of the incorrect altitude setting, and it went into error mode for 48 hours after the dive. I could have prevented it by hanging around at 10 feet for another 10 minutes, but I decided it wasn't worth it, since in error mode it would still give me gas pressure, and that was all I really needed from it.

Do check your settings.

 

[DEEPLOU]

you can dive nitrox without have knowledge or certification.
if you're certified, you must know that partial pressure 1.4 to 1.6 limits %oxy or/and depth.
more oxy, less depth, and vice-versa.
of course, if you're diving breathing 1.6 PpO2 instead 1.4, you will able to dive deeper, and you will have more deco time, or a shorter "no deco" time.
but breathing air at 70ft gives a PpO2 of 0.6, lower these limits.
check also surface interval.
Suunto computers dislike short intervals

Suunto computers just don't like multiple dives.
Today for example, dove to 110 max with multi levels to about 70ft for total dive (to surface) of 38 min, then after 45 min surface dove to 68 ft max, at about 40 min in to the dive, the Suunto was in the single digits of NDL and my Aires had almost an hour of NDL, not even one bar into the yellow on its bar graph.

---------- Post added May 19th, 2013 at 09:15 PM ----------

Another issue I have encountered is that too many people (I didn't say divers) jump on a dive boat and have no idea how to set their computer or even worse no idea how to read and interpret or utilize the information displayed.

Some don't seem to understand that they need to monitor their computer and air pressure. Not just one or the other.
Had a guy the other day blow off 2 minutes of deco on his computer because he only had about 350 psi. Then he asks if that 2 minutes can be deducted from his NDL on his next dive. Needless to say for him there was no next dive. Although his was a very conservative computer, and he had no symptoms we would not let him go in the water again.

 

[DuboisP]

Had a guy the other day blow off 2 minutes of deco on his computer because he only had about 350 psi.

350 psi at the begin, or end of the deco ?
it if is at the end, why not use these 350 psi ?

 

[BabyDuck]

while i agree some nitrox review is going to be nothing but helpful, your computers are among the most conservative sold. does that make them safest? only you can decide that. if you like the added cushioning they put on every parameter of your dive, then dive them cheerfully & get out of the water when they say (or, similar thing said a different way, plan your dive based on what you know your computers will like). if they are frustrating for you and cause you to become anxious and angry and consider skipping what they're telling you, get different computers that aren't so conservative.

computers are tools to avoid dcs, but they aren't infallible and neither is deco science. there's a lot of 'best guess'-ing involved. you decide what tool you want helping you, and use it as directed by the manual.

 

[altaskier]

I've done 5 nitrox dives a day in the 60-90 foot range on a liveaboard with a Suunto computer and have not had problems with non-decompression limits (one frequent dive buddy has an Aeris computer, and our dives have ended due to gas in our AL80s rather than my NDLs - and my warm water surface air consumption or SAC rate is 0.45 in imperial units which is OK for a guy).

It's my impression that Suuntos penalize you for rapid ascents; I tend to come up pretty slowly now. Could this be involved in what DEEPLOU is reporting?

As others have pointed out, nitrogen loading and non-decompression limits are somewhat different than oxygen loading and PPO2, as discussed in your nitrox course...

 

[designbysue]

I've done 5 nitrox dives a day in the 60-90 foot range on a liveaboard with a Suunto computer and have not had problems with non-decompression limits (one frequent dive buddy has an Aeris computer, and our dives have ended due to gas in our AL80s rather than my NDLs - and my warm water surface air consumption or SAC rate is 0.45 in imperial units which is OK for a guy).

It's my impression that Suuntos penalize you for rapid ascents; I tend to come up pretty slowly now. Could this be involved in what DEEPLOU is reporting?

As others have pointed out, nitrogen loading and non-decompression limits are somewhat different than oxygen loading and PPO2, as discussed in your nitrox course...

The issue is never with nitrox - I can also dive 5 to 6 dives a day when using nitrox. It is only an issue with air, and hence my frustration. I am used to doing repeated dives in a day and can't when I can't get nitrox, as is the case in Cancun. It is never a lack of gas that ends my dives, it is normally the schedule that the dive shop need to keep that ends my dives.

I don't have rapid ascents - I download my logbook using a Mac and DiveLog and it is almost never that I get any warnings showing up in my records. What DeepLou stated is exactly what I was posting about. A Google search confirms that many others find this an issue also

Originally Posted by designbysue
I dive 2 dives, about 45 minutes each to about 70 ft on air and by the end of the 2nd dive I am running into low no deco numbers



Why is that a problem?

Tortuga68 - Because I prefer to dive a full day of full dives.


​

 

[Ste Wart]

I am finding that my Suunto computers (both Cobra and Zoop) are way to conservative - I dive 2 dives, about 45 minutes each to about 70 ft on air and by the end of the 2nd dive I am running into low no deco numbers. Both computers are identical in the numbers. I unusually dive nitrox and don't have any problems but I am in Cancun and there is no nitrox available.

Appreciate any help on this one.

Sue

Sounds like you are using a Suunto.... oh you are!

Normal for Suunto I'm afraid and very little to do to extend your time without finding some nitrox.

Best thing to do is head for 9m when you start to get a little low, all Suuntos basically give you unlimited time at this depth (unless Deco has been incurred). With a mult-level reef dive this is your best option.

 

[designbysue]

Yeah, Ste, when I dive air I try to stay a bit high during the dives to conserve my limits but I was diving in Cancun and the currents there are strong and the reef are small so you can't get very high up. Also when you are jumping from one coral outcropping to another you need to be along the bottom so not to get pulled off the reef.

I have dived Cancun for several years and because of the lack of nitrox have had to keep the dives to only 2 a day. Frustrating but just the way it is.

 

[Ste Wart]

Yeah, Ste, when I dive air I try to stay a bit high during the dives to conserve my limits but I was diving in Cancun and the currents there are strong and the reef are small so you can't get very high up. Also when you are jumping from one coral outcropping to another you need to be along the bottom so not to get pulled off the reef.

I have dived Cancun for several years and because of the lack of nitrox have had to keep the dives to only 2 a day. Frustrating but just the way it is.

You really don't work for the Cancun tourist board!

I'll pass on a trip there. Enjoy what you can.

 

[designbysue]

Didn't mean to be negative to Cancun - I dove with Scorpio Divers and had a great time. The problem is the conservatism of Suunto computers - I know that there are other computers that would not limit the dive times. Please don't avoid Cancun - just go better prepared!