Deco Software

[boulderjohn]

Anyway I think this kind of fiddling is far from unified team approach.
And personally I don't really understand the reasoning behind using several algoritms to guide a single dive.
Carrying a Suunto naturally means you must obey it to prevent error mode.

I have no idea why you would want to use different algorithms in a dive. You are the one who brought it up; you even said it was common.

I also have no idea why anyone would use a Suunto computer on a technical dive.

 

[boulderjohn]

It is common practice to alter gradient factors on ascent. Using multiple deco models during a dive would melt my brain.

Wow! What an interesting thread. I am learning all sorts of stuff about what is common in technical diving.

I have never met anyone who does this. Why on Earth would anyone do this?

 

[Parklander]

Alter gradient factors or the active deco model during a dive? I didn’t understand which you meant.

 

[RainPilot]

On my Perdix, I have the ability to change my GF during the dive, the only reason I would do so is if some emergency made it inadvisable for me to continue with my originally planned conservatism (buddy going unconscious, flooded drysuit etc)

This is something you should be taught and have in your toolbox on any dive but it is FAR from being a common thing to ACTUALLY do.

If someone is regularly changing their GF during a dive to alter their "conservatism" then they may need to reconsider how they are choosing their original GF in the first place.

Swapping BETWEEN dives, depending on the conditions (repetitive or single, cold or warm, dehydrated or not etc) is a different issue.

 

[taimen]

I have no idea why you would want to use different algorithms in a dive. You are the one who brought it up; you even said it was common.

I also have no idea why anyone would use a Suunto computer on a technical dive.

I agree with you 100%
Except that I have to live with buddies using Suunto computers on technical dives. I actually think that Suunto computers with their insane "error mode" and sometimes unpredictable algorithm promote bad team diving practices.

(you gave me good advice on how to adapt to this situation, I was following that line of thought. I didn't mean to argument against you. There was another poster above who also told he uses two algorithms in a dive. I should be more careful with quotes.)

 

[Parklander]

Ok, I totally agree with that. I think I expressed myself incorrectly. Common meaning that it is taught and is not a fire walled action. But yes, not common if you interpret that as something you would intend to do every dive or often.

 

[Parklander]

Also, as an intersting side-note, the Teric does not currently allow the changing of high GF while in the water. They are going to add to a firmware update in the near future. All other Shearwater consoles allow for this change on the fly. No low GF changes once in the water. I’m not certain if that is at surface or after descending beyond 10 feet. But the only reason I can think one might want to change low GF would be if it was not correctly set on board. And that’s another discussion entirely.

 

[boulderjohn]

I do know people who in effect alter their GFs during the dive, although they don't physically change it on the computer. They plan and execute the dive using a GF they feel sure will lead them to the surface safely. That enables them to plan their gases--they know they should finish the dive with a safe reserve of deco gas. Even if something goes wrong, they should have enough gas to reach the surface safely.

So, when they complete their final planned stop with nothing having gone wrong, they have plenty of reserve gas they didn't need. They then figure, "What the heck?" and extend that stop, effectively turning (say) a 50/80 into something along the lines of a 50/70.

 

[taimen]

the Teric does not currently allow the changing of high GF while in the water.

Teric has a "surface GF" display that actually tells you everything you need if you have to do an accelerated emergency ascent but still want to stay in some limits, say GFhigh 100%.

So, when they complete their final planned stop with nothing having gone wrong, they have plenty of reserve gas they didn't need. They then figure, "What the heck?" and extend that stop, effectively turning (say) a 50/80 into something along the lines of a 50/70.

I have been taught to do exactly this when conditions and gas reserve allow. The surface GF display would be nice feature for this too.

 

[KenGordon]

I ask out of curiosity and honestly not trying to argue.
What is the advantage you gain by using several algorithms during one dive? Other than being able to use another computer you happen to own as a backup?
How do you discuss, communicate and agree this as a team? Do you decide beforehand which one is the primary and which on is an emergency plan. Do all of your team members have the same set of algorithms in their computers or are all others adapting to your method?
Is there some theoretical or experimental support for the idea that a shorter ascent with a deep stop profile is safer than cutting the final longer stop in an emergency situation?

Computers and algorithms, they are not so different as SB likes to think. Personally I will use the Suunto as primary as I have more experience of it on deepish dives. Compared with 50/80 it adds a few minutes at the end, but is much faster than 30/70.

Everyone else has whatever computer they happen to have. Some have two Suuntos, some a Petrel and BT, some an OSTC, even the divecomputer.eu thing.

OC I will use Nitrox if I can, if my buddy is cheap, or a student not allowed it I will dive two Suuntos, one set to whatever I am breathing and one set to whatever they are breathing. That helps avoid the embarrassing situation of finding your buddy has 10 minutes of stops when you have none.

These days I usually use a rebreather, so have two SW computers (set differently though), but my buddy might have anything, or be a GUEy using a 1.2 setpoint and 30/80, for sure we will need to take account of there being differences. The protocol is the same as any ascent, signal up to next stop, maybe indicate the expected stop depth, ascend to the stop and signal how long. Resignal as appropriate or if you are bored and have nothing else to do, wait until every one is clear at that depth and move up.

The general case is that divers have different deco, not the same. We deal with that. There are other reasons for mismatch. Has everyone got the same dive history today? The same gas?

Now I am talking about dives up to maybe an hour and a half, maybe if the ascent is going to be two or three hours you might care more, so do what it takes to have a plan you are happy with.

The original question is about backup computers. There are different reasons to have a backup computer. One reason is to be able to do an ascent in the face of failure, another is to be able to continue diving following a failure, if not the same dive at least subsequent dives. In the first case you don’t care if you bend one in an emergency, in the second you don’t expect an emergency, it is just to cover the computer failing.

When I have two SW computers one is for a bailout ascent. That will be rare so I can set it to be aggressive without unduely increasing my average risk.