Question about Suunto Vyper and Deco Theory

[scubahiro]

Hi All,

I have a Suunto Vyper, which I really like. Being conservative by nature, I tend to set the personal mode not at the default (P0/A0) but at (P1/A0), even though I have none of the factors mentioned. In short, according to the manual I should be at the default setting, but I err on the side of caution.

In practical terms, this means that on a 100 ft dive the NDL is 14 mins instead of 17 mins. And on a 70 ft dive the NDL is 29 instead of 36 (both NDLs are based on Air).

This is all fine and dandy from my perspective as I normally dive Nitrox and get nowhere near the NDL, even on the conservative profile. However, when I dive in Cozumel, I normally do the first dive on Air, as it is a wall dive and to avoid the potential OxTox problem.

The dive operators I use all use computers, and I presume set their computers to default. So, this means that if I follow the DM exactly, I still have to come up a little to make a multilevel dive within the NDL. With this said, here is my question:

I surmise it is a problem to "ride" your NDL up when doing multilevel diving. Even with my conservative setting, I tend not to ride the NDL, but come close to the conservative NDL setting, within 5 mins, especially on deep dives. In short, there is the problem of riding my conservative NDL if I follow the DM.

Generally, I rationalize this by thinking, while I would like to keep at least 5 mins, and pref. 8-10 mins away from my NDL, with the conservative setting, I am in fact doing that. For instance, on a 100 ft dive, when my conservative NDL is at 1 min, the default would be at 4. On a 70 ft dive, when my NDL is at 1 min, the default would be at 8.

Is this a theoretically reasonable rationalization? I should note that the Suunto NDLs are more conservative than the tables, on square profiles.

Thanks for the thoughts,

scubahiro

 

[scubahiro]

I also wanted to add: Does anyone know any details regarding the sensibility of switching between air and nitrox on the same day?

Thanks,

scubahiro

 

[svidlano]

I surmise it is a problem to "ride" your NDL up when doing multilevel diving. Even with my conservative setting, I tend not to ride the NDL, but come close to the conservative NDL setting, within 5 mins, especially on deep dives. In short, there is the problem of riding my conservative NDL if I follow the DM.

Generally, I rationalize this by thinking, while I would like to keep at least 5 mins, and pref. 8-10 mins away from my NDL, with the conservative setting, I am in fact doing that. For instance, on a 100 ft dive, when my conservative NDL is at 1 min, the default would be at 4. On a 70 ft dive, when my NDL is at 1 min, the default would be at 8.

Don't forget one thing. You are not staying away from YOUR NDL, you are staying away from your computer's NDL!!!

So what's the difference between following a divemaster and following a computer? Both ways you're following somebody else's NDL.

 

[svidlano]

I also wanted to add: Does anyone know any details regarding the sensibility of switching between air and nitrox on the same day?

Thanks,

scubahiro

Isn't air just EAN21?

 

[svidlano]

BTW, what is a NDL? Just a name for a deco dive during which you can swim directly to the surface without getting bent (with xx.xx% probability and only if you obey max ascent speed).

 

[DepartureDiver]

A lot depends upon performing safety stops. Think of the no-stop times as a percentage and not minutes. Notice the conservatism level has been cut back by about 20% on the setting you chose. So staying within 5 minutes on a deep dive is nice, but 5 minutes doing a multi-leve or on a shallow dive doesn't add that much. Also, while a 20% cut back is a good one, you still have significant gas loading ... which is where a good staged safety stop starting with a nice brief deep stop helps. This is one of the best things you can do for yourself. To try to make this make a little more sense., if you cut your no-stop times back by 50%, you have only reduced your gas load by about 25% based upon the rapid ingassing that occurs and continues throughout the dive. So it sounds like you are thinking and planning your dive just fine and a good safety stop (for some nice off-gassing) should accomplish what you are looking for. Lastly, there is no reason you can't switch from nitrox to air and vice-versa ... but why would you want to? Keep the benefit of the nitrox. This can also be a little more padding when you're diving with the DM so you stay within the conservatism level you like. BTW, good job thinking for yourself and not just blindly following the DM.

 

[rjchandler]

Hi All,


Generally, I rationalize this by thinking, while I would like to keep at least 5 mins, and pref. 8-10 mins away from my NDL, with the conservative setting, I am in fact doing that. For instance, on a 100 ft dive, when my conservative NDL is at 1 min, the default would be at 4. On a 70 ft dive, when my NDL is at 1 min, the default would be at 8.

Is this a theoretically reasonable rationalization? I should note that the Suunto NDLs are more conservative than the tables, on square profiles.

Thanks for the thoughts,

scubahiro

This is called "lying to your computer" similar to " I'll use nitrox and tell my computer I am using air". You are saying that you will dive with an eye to the default NDL but tell your computer that you are really using the conservative setting. If you exceed your NDL, what is your computer going to say to you and what are you going to say to it?

If you have chosen the conservative settings to generate your NDLs for the dive, then you measure "riding the NDLs" by how close you get to those NDLs not the defaults.

You don't have to follow the DM,s profile do you?

 

[pipedope]

That will add a substantial conservation factor to the DM's profile.

Remember, whatever level of safety factor you put in there is always 'some' risk of DCI if you dive. If you are alert to the signs and get prompt treatment in the event of suspected DCI it can be a minor annoyance rather than a disaster.

DCI is rare but if it happens to you, prompt treatment makes all the difference.