Best Mix VS Standard Gasses (split from a GUE fundies course report)

[stuartv]

The other thing is nobody says you have to go with one of the bigger charters. When my friends and I go to NC we charter out a six pack and plan on extended run times on most of the sites. So if I was diving OC I’d use 30/30 and bring some O2 to deco with. Same thing goes with Helium, if it’s not readily available, nobody says you can’t arrange ahead of time for it.

Now that I’ve switched to mainly diving a rebreather, I really found the benefit to standard gasses. Each stage/bailout bottle has one standard gas for a given range. Same with my onboard bottles. Just grab a bottle and go, no worrying about remixing gasses to provide the “optimum” blend to save 2 minutes of deco.

I dunno, maybe it’s me, but I never found standard gasses to be restrictive.

*disclaimer: not GUE certified but see the benefit to a lot of their methods

Yeah, diving CCR is a whole different ballgame.

I'm keeping my dil cylinders filled with TX20/40. 1 BO bottle (for recreational NDL dives) is EAN28. 1 BO set is TX20/40 and TX50/20. I can also just grab bottles and go. Which BO bottles just depending on the dive plans.

I don't see where Standard Gases would have any particular advantage for any of that.

For NC diving on OC, I just use the EAN30 they bank, for NDL diving. For tech dives, I'll use whatever back gas I determine is appropriate, but I pretty much always use EAN80 for my last deco gas. I like to be able to get on it at 30' and stay down there, out of the surface surge. Some days there is not really any surface surge, but you can never know that in advance, so I choose my deco gas on the basis that it will be rough near the surface and hope for a pleasant surprise.

 

[PfcAJ]

Yeah, diving CCR is a whole different ballgame.

I'm keeping my dil cylinders filled with TX20/40. 1 BO bottle (for recreational NDL dives) is EAN28. 1 BO set is TX20/40 and TX50/20. I can also just grab bottles and go. Which BO bottles just depending on the dive plans.

I don't see where Standard Gases would have any particular advantage for any of that.

For NC diving on OC, I just use the EAN30 they bank, for NDL diving. For tech dives, I'll use whatever back gas I determine is appropriate, but I pretty much always use EAN80 for my last deco gas. I like to be able to get on it at 30' and stay down there, out of the surface surge. Some days there is not really any surface surge, but you can never know that in advance, so I choose my deco gas on the basis that it will be rough near the surface and hope for a pleasant surprise.

Sounds like you’re well on your way to using standard gases, there just different than what GUE uses.

 

[stuartv]

Sounds like you’re well on your way to using standard gases, there just different than what GUE uses.

Sure. For CCR, where it blends on my back, on the fly, I see no reason not to just keep the same gas in my dil at all times. For BO, where the plan is to never use it, same deal. May as well just be setup for my max depth and let them sit. Doing a bit of extra deco if I ever have to bail is fine. I'm certainly not going to drain and re-fill full BO cylinders every time I go diving, just to have them filled with the best mix for the planned depth. If I were using them every dive and getting them filled again, then I would.

My point was simply that I see no advantage to specifically choosing those gases from the Standard Gas list.

 

[RayfromTX]

This thread is a split off discussion of differing opinions on best mix and standard gasses approaches to choosing mixes for different depths and conditions. It became far too involved in off topic discussion and since it is potentially valuable we have split off the discussion to continue here.

 

[stuartv]

Yes, it's not exactly normal to not know what depth you will be diving to. And if you are diving below 100' without he, then you are already outside the standard.

Knowing within a range of 70 - 120 or so is normal for diving out of the places I have been in NC.

I have also been on boats out of Key Largo where the dive site was not determined until the boat was already underway - and the depth range of possibilities was anything from 45-ish feet, on Molasses Reef, to 135, on the Spiegel Grove.

Seems normal to me...

 

[eelnoraa]

Normal or not, if a rec boat takes divers to a 135ft site out of adhoc, then it doesn't sounds like a responsible ops to me.

The issue is not necessary the depth variation, but where the variation is. A 60-100ft range is very different than 100-140ft range.

 

[stuartv]

Normal or not, if a rec boat takes divers to a 135ft site out of adhoc, then it doesn't sounds like a responsible ops to me.

The issue is not necessary the depth variation, but where the variation is. A 60-100ft range is very different than 100-140ft range.

The Spiegel is very tall. Just because I go swim around on the sand at 135' doesn't mean that anyone else has to descend past the main deck.

As you say, where the variation is matters. When the variation is all within one row of the GUE Standard Gas chart (as many GUE divers seem to like to choose when giving examples of why SGs are good), it's all very convenient. But, when the variation crosses over into 2 different rows, then SGs start to not look so good. With Best Mix, you can always choose your mix to be, well, the best mix for whatever range you are contemplating. You are not forced to choose from either a gas that will limit your depth (if you end up at the deep end of the range) or a gas that is way leaner than what you'd really want (if you end up at the shallow end of the range).

You don't end up using TX30/30 on a 130 foot dive and you don't end up using TX21/35 on a 90 foot dive.

 

[Ayisha]

Normal or not, if a rec boat takes divers to a 135ft site out of adhoc, then it doesn't sounds like a responsible ops to me.

The issue is not necessary the depth variation, but where the variation is. A 60-100ft range is very different than 100-140ft range.

It happens in various areas. We've been booked on the Crystal and Tradewinds for a max depth of 130 feet in Lake Erie, for example, and been blown out (many times), with the nearby choices being the Tiller at 100 feet, Sherkston quarry or the Niagara river at 30 feet or less.

One time, almost all of us had 32% for a dive on the Wexford at 80 feet with a contingency plan of the Tiller at 100 feet. One instructor had decided to bring a "best mix" of 36% for 80 feet. We got blown out and that instructor went home without any dives.

Some shipwrecks are extra beautiful but are in bodies of water that can be extra rough and need perfect conditions to get out there. Everyone knows in advance what the contingency plan is if there are sheltered dive sites available.

 

[eelnoraa]

The Spiegel is very tall. Just because I go swim around on the sand at 135' doesn't mean that anyone else has to descend past the main deck.

As you say, where the variation is matters. When the variation is all within one row of the GUE Standard Gas chart (as many GUE divers seem to like to choose when giving examples of why SGs are good), it's all very convenient. But, when the variation crosses over into 2 different rows, then SGs start to not look so good. With Best Mix, you can always choose your mix to be, well, the best mix for whatever range you are contemplating. You are not forced to choose from either a gas that will limit your depth (if you end up at the deep end of the range) or a gas that is way leaner than what you'd really want (if you end up at the shallow end of the range).

You don't end up using TX30/30 on a 130 foot dive and you don't end up using TX21/35 on a 90 foot dive.

You didn't get the context of my messages. In your example, the plan isn't adhoc. Everyone knows the dive site, which is a 90ft site but if you swim further out, you have access to 135ft. This kind of site is common. But going to 135ft is your own choice, not site dictates. What I am saying is if I plan to visit down to 90ft of this site, I will bring 32% and allow myself to go to 100ft max. Now because I know the site profile, and if know I will go to 135ft, I will plan the dive entirely differently. The key here is neither the site or the depth is adhoc decision.

If site and depth is adhoc, the any gas, standard or not, has equal chance of not diving. If you bring the optimal gas for 135ft, if the ops brings you to a150ft site, will you go or will you not go to 150ft? This has nothing to do with standard gas or not. It is a discipline question.

 

[eelnoraa]

It happens in various areas. We've been booked on the Crystal and Tradewinds for a max depth of 130 feet in Lake Erie, for example, and been blown out (many times), with the nearby choices being the Tiller at 100 feet, Sherkston quarry or the Niagara river at 30 feet or less.

One time, almost all of us had 32% for a dive on the Wexford at 80 feet with a contingency plan of the Tiller at 100 feet. One instructor had decided to bring a "best mix" of 36% for 80 feet. We got blown out and that instructor went home without any dives.

Some shipwrecks are extra beautiful but are in bodies of water that can be extra rough and need perfect conditions to get out there. Everyone knows in advance what the contingency plan is if there are sheltered dive sites available.

This example just prove with an adhoc site and depth, optimal gas mix has equal chance of not diving. In fact in this specific case, the optimal is not diving, the standard gas is diving. But there could be example of other way around.