Recreational Trimix

[Blackwood]

Contrast this to a regular no deco ascent of 3mins to 15ft, then a 5min hang. Total ascent time is about the same, but the mindeco ascent is a bit smoother from 50ft.

When comparing models, I think it's appropriate to consider the assumed ascent rates. Most NDL tables I'm aware of use 60fpm, and don't include a safety stop. People may be diving them at 30fpm and hanging out at 15', but that's a personal touch.

 

[Wookie]

30fpm to 1/2 depth, 10fpm thereon. So 'min deco' from a 100 foot NDL dive, for example, is almost 7 minutes.

Consider me educated. I think it might be more useful if it were called "max ascent rate", or "The Warhammer Maneuver", but if you want to call it "minimum deco", have at it. You might want to let us folks certified by other agencies know when you are in secret handshake mode. Or keep the secret handshakes in the secret handshake forum, to which I don't belong.

 

[Wookie]

Make sense? When diving 30/30, this slower, more controlled ascent (from 50ft) gives the Helium the time to come out of solution in a controlled manner.

Yes, that makes complete sense. My education was sorely lacking. It's what the rest of us do, we just don't have a nifty name for it.

 

[PfcAJ]

I think my NAUI tables had a 30fpm rate, I could be mistaken, though.

Regardless, a 60fpm rate only serves to make my point even more. Its a quick rush to the shallows, followed by a 3-5min hang time (the PADI RDP specifies the need for a safety stop on dives past a certain depth, too, I think...). If we assume a 60fpm ascent rate on that above example, its now a 6.5min ascent from 100ft (including a 5min stop).

Any way you look at it, its not great.

 

[LiteHedded]

Consider me educated. I think it might be more useful if it were called "max ascent rate", or "The Warhammer Maneuver", but if you want to call it "minimum deco", have at it. You might want to let us folks certified by other agencies know when you are in secret handshake mode. Or keep the secret handshakes in the secret handshake forum, to which I don't belong.

30/30 is a gue standard gas. gue responses are to be expected IMO

 

[Blackwood]

Consider me educated. I think it might be more useful if it were called "max ascent rate", or "The Warhammer Maneuver", but if you want to call it "minimum deco", have at it. You might want to let us folks certified by other agencies know when you are in secret handshake mode. Or keep the secret handshakes in the secret handshake forum, to which I don't belong.

It's just a different [-]paradigm[/-] approach. Many agencies teach that "all dives are decompression dives," but GUE (and now UTD) go one step further to remove the misnomer NDL. Instead, they teach that there is a minimum amount of deco to do from each and every dive (which as I'm discussing below is true of NDL tables, more appropriately called no-stop tables, but they aren't always presented that way), and to go along with that they call the limits "MIN deco limits", beyond which more than that minimum is required.

I think my NAUI tables had a 30fpm rate, I could be mistaken, though.

Table annotations (instructions) may be 30, but I think the NAUI's is a modified USN table, i.e. 60fpm in the math (which is the true "minimum" associated with the NDL).

Either way, I agree, it makes the point stronger.

 

[DaleC]

How do you get trimix in your tank without understanding the deco obligation it requires?

 

[LiteHedded]

How do you get trimix in your tank without understanding the deco obligation it requires?

around here you pretty much just ask for it

 

[MXGratefulDiver]

I did a recreational double dip on the Spiegel Grove today. Decided to use my doubles which were already loaded up with 30/30. Figured displacing all that evil nitrogen with heavenly helium would give me nice, long no decompression limits. Did that ever turn out to be a stupid move!

As it turns out, 30% NITROX would have yielded a NDL of 26 minutes at 100' vs. 14 minutes on the relatively pricy trimix. My "stoke" buddies got a 28 minute NDL on their 32% Nitrox and I ended up doing a lot of deco time on my fancy back gas.

I'm fully aware that the primary benefit of increased helium percentages is reduced narcosis as opposed to increased NDL bottom time. However, I was shocked to discover that more helium actually dramatically reduced NDL limits all other things being held constant.

Can someone please explain this to me?

Back when I did my first (IANTD) recreational trimix class I got this same effect with the Nitek He computer I was using. Odd that ... a computer designed for trimix that doesn't like helium. I bent the damn thing on almost every dive (but never bent myself in the process), until I figured out it penalizes you right up to your 30-foot stop, no matter how slowly you come up.

I got rid of the thing and got a computer that recognizes the benefit of slow ascents and deep stops ...

... Bob (Grateful Diver)

 

[DaleC]

around here you pretty much just ask for it

and I thought I was the risk taker