Nitrox course. What's the point?

[ToneNQ]

I hate the cold . And I get on my 5.5 mm wetsuit in less than 10 seconds. Taking it off ( especially the feet) is the real hassle . My comment about drysuit was not the point. It was just a piece in a stupid argument. All I want is to learn and get advices from more experienced divers without being disrespected. Your post is why I am on SB.

Might feel like it, but no chance. 10s per sleeve maybe, unless you have the skinniest wrist ever. Regardless, whatever makes you happy. Exposure protection can be one suit fits all, if you aren't sensitive to changes in the environment. What works at your current age won't work for you forever, everything changes with age and experience. The more you dive, the more you will see other people using different gear. If you take a moment to observe, maybe ask a few questions, you'll see other perspectives. You'll try things, like things, hate things, you'll find your happy place and then you'll find the limits of that happy place.

The real joy of a drysuit is diving in cold water in hot weather. Also diving on a site with a thermocline, a 4°C change in water temp is sharp in a wetsuit. You can have the suspenders on, and in the last minute before gearing up, throw the top bit on, zip yourself in and get into your gear. Last trip I was on was choppy, a lot of spray in the boat. Sucks being cold and wet a full hour before the dive, but I wasn't, mmmwahahahaha.

 

[Belzelbub]

I never dive on the fly, I plan all my dives. I always know what I intend to do. Force of habit.

That’s good, but doesn’t change the fact that your computer doesn’t know the exact ascent profile until you actually make the ascent, so can’t use that in calculating the NDL.

The ascent will be for offgasing (though some slower compartments may still be ongassing for a bit). Two dives done to NDL to the same depth (one on air, one on EAN) and following the exact same ascent profile should end with the EAN diver with less residual nitrogen due to breathing less nitrogen on the decompression (ascent) phase of the dive. Might be minor difference. Otherwise there would be no benefit to using high O2 (low N2) mixes as deco gas.

 

[Celt]

Two dives done to NDL to the same depth (one on air, one on EAN) and following the exact same ascent profile should end with the EAN diver with less residual nitrogen due to breathing less nitrogen on the decompression (ascent) phase of the dive. Might be minor difference. Otherwise there would be no benefit to using high O2 (low N2) mixes as deco gas.

If nitrox is used the computer calculates the assent is also on nitrox, if air is used it calculates the assent is on air. It allows extra bottom time on the assumption that nitrox will be used for the entire dive including the assent. If you were to do the bottom time on nitrox and switch to air for the assent you’d run the risk of getting bent. O2 on deco only accelerates the deco and shortens the time at the stops if you complete the stops on air the same nitrogen is removed.
P.S. I don’t use a computer in the water.

 

[Belzelbub]

If nitrox is used the computer calculates the assent is also on nitrox, if air is used it calculates the assent is on air. It allows extra bottom time on the assumption that nitrox will be used for the entire dive including the assent. If you were to do the bottom time on nitrox and switch to air for the assent you’d run the risk of getting bent. O2 on deco only accelerates the deco and shortens the time at the stops if you complete the stops on air the same nitrogen is removed.
P.S. I don’t use a computer in the water.

The computer calculates the ascent with the gas selected at the completion of that ascent. It does not know what the ascent will be, so doesn’t factor that in to NDL. At the most, some computers give a TTS as an estimate only. It wouldn’t make sense for them to assume an ascent profile that may not be followed.

Agreed that if you dive to NDL using EAN, and switch to air without telling the computer, you run an increased risk of DCS as the partial pressure of nitrogen is higher than the computer thinks. Not sure how great of a risk, though. Probably small with a direct ascent with safety stop. Higher if the ascent is more gradual, like following the shoreline.

However, if you switch to air in reality and on the computer, the computer will make any adjustments necessary to reduce that risk. All will depend on which compartment is the leading compartment.

P.S. By computer, I’m referring to a dive computer that is taken on the dive. A PC running a dive planning software may operate differently.

 

[Storker]

I said that it was half a joke, come on. Dry suit was not even the topic. Can't a newbie make joke without being hammered out for that?

It didn't read like a "joke" to me. Rather, it read as a statement.

I love deadpan humor myself (it's a Nordic specialty), but if you choose deadpan, be prepared that people don't get your joke. Or "joke".

I'm a little tired of someone saying something really stupid or seriously objectionable and then saying it was a joke. I'm probably overly sensitive to this, living in the US.

You're not the only one, and it's not a phenomenon exclusive to the US.

 

[Celt]

However, if you switch to air in reality and on the computer, the computer will make any adjustments necessary to reduce that risk. All will depend on which compartment is the leading compartment.

You can switch gases and tell the computer in the water in real time that you have switched, that is fantastic. Can you also tell the computer that you have switched to a higher O2 mix on your assent. Do you mind me asking what computer is able to do this as I’ve been looking at some thank you.

 

[Belzelbub]

You can switch gases and tell the computer in the water in real time that you have switched, that is fantastic. Can you also tell the computer that you have switched to a higher O2 mix on your assent. Do you mind me asking what computer is able to do this as I’ve been looking at some thank you.

Sure. In my case, it’s a Shearwater Perdix AI. But there are many others that enable gas switching as well. My previous computer was an Oceanic, and many in the Oceanic line allows this as well. I think you’ll find that many computers offer this capability. The real question is how does the UI enable this. Some are much easier than others. From ease of use the Shearwater UI is worth looking into it, and all their line, even the rec oriented Peregrine offer gas switching.

In the case of the Peregrine, you are limited to 3 different gasses. The Perdix allows up to 5 gases.

Edit. Oh, one more thing. You can absolutely use this function to switch to a higher O2 gas for ascent or deco. Key thing is that the different gasses should be turned off unless they go on the dive with you, to avoid selecting the wrong one. If I only take one gas with me, I leave in simple Nitrox mode which only allows one gas. If I take a pony with me, I’ll turn that one on as well, though likely never switch to it.

 

[Gareth J]

You can switch gases and tell the computer in the water in real time that you have switched, that is fantastic. Can you also tell the computer that you have switched to a higher O2 mix on your assent. Do you mind me asking what computer is able to do this as I’ve been looking at some thank you.

There are a number both in the technical computer market and the top end recreational. (i.e Trimix or Nitrox).

Shearwater
OSTC
Suunto

and others

Even the old version of the Suunto Vytec (2000 era) had gas switching (still miss the one I had).

Shearwater are very popular here on Scubaboard.

I've got an OSTC, bottom end of the market version that doesn't do CCR or Trimix, but will do multiple mixes and on the fly switching. It's a backup to the CCR computer.

 

[Divin'Papaw]

You can switch gases and tell the computer in the water in real time that you have switched, that is fantastic. Can you also tell the computer that you have switched to a higher O2 mix on your assent. Do you mind me asking what computer is able to do this as I’ve been looking at some thank you.

Yup. Most "modern" computers support multiple gases. All except the base entry level computers I believe. The more technical computers support more gases including helium mixes and CCR modes. But most nitrox computers today typically support at least 2-3 different nitrox mixes. You are able to set the mix you are actually using and change the computer setting when you've done a gas switch if appropriate. In the TDI training world I'm familiar with that is what is covered in the Advanced Nitrox (use of up to 100% nitrox) and Deco Procedures courses. The use of higher oxygen content mixes along with staged decompression to accelerate decompression. Different agencies break their training down differently.

 

[Storker]

Most "modern" tech computers support multiple gases.

FTFY.

I may be out of date, but IME typical rec computers don't allow for switching gas during the dive. One tank (or twinset), one mix is the rule I know of.