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

[Ayisha]

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.

Exactly. That was the point.

 

[stuartv]

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.

I'm not exactly sure what you are trying to say by calling some things ad hoc.

What I am saying is that it is not abnormal to have a plan (or maybe just desire) to go to a site with a hard bottom of 135' and then end up at a site that is 45-ish, because of conditions at the time. Or, in other places, it could be the reverse.

Before ever going out, you know what the various possibilities are and plan accordingly. If all the potential dive sites are in the depth range covered by one row of the GUE Standard Gas chart, then goodie. But, if they aren't, then you have a good chance of diving a mix that is far less preferred for the depth you're at than if you use the Best Mix approach to selecting the gas you take.

If you got to a site that is 135' to the bottom and you have 32% and limit your depth, then you are still limited by your gas choice - whether you say you didn't really want to go deeper anyway or not.

 

[eelnoraa]

If I brought 32%, and for whatever reason I ended up at a site with 135' bottom and nothing but lifeless blue water at 100ft, if I knew this before splash, I would probably not even go in. If everyone made a mistake, thinking the site was at 100ft, I would go in. When I descent to 100' and still can't see the bottom, I will call the dive and go back to the boat to figure out what just happened.

The same question to you. You bring best mix for 135' thinking you will go to max 135'. Then ops brings you to a site with 150' bottom. Will you dive to 150'? Or in Ayisha's example, you were told the site is 80' and you brought best mix for 80'. The site is 100', will you go to 100'?

The way I see it is whatever gas you bring standard or best, if you get to a wrong site, you have a chance of not diving.

 

[TrimixToo]

But, you can't take 4 cylinders on the boat. Only 2. Not enough room for people to be bringing extra cylinders. You're going out for 2 dives and you don't know what sites you're going to, basically until you get there. I mean, they can tell you where they are going to TRY to go. But, it's not unusual at all to divert after the boat is already well offshore.



That looks like the same list and source I found. I think the copyright on it was 2001, so I figured it was outdated.

Generally speaking, if I can't bring at least six tanks aboard (two sets of doubles, two deco tanks), I'm on the wrong boat. This has never been an issue in the Northeast, or even on the boats I've used in NC. For CCR divers, two AL80 bailouts seem to be the norm.

Also, captains get that people are not necessarily prepared to go deeper than planned, because of things like gas requirements, level of training and experience, and thermal protection. I have never once been on a boat where the captain did not ask everyone whether they could divert to deeper water before going there. Usually, someone or ones can't, and the boat goes somewhere shallower. While I'd have brought different gas in some cases when that happened, it was certainly safe to dive what I brought, every time.

 

[Diving Dubai]

What I am saying is that it is not abnormal to have a plan (or maybe just desire) to go to a site with a hard bottom of 135' and then end up at a site that is 45-ish, because of conditions at the time. Or, in other places, it could be the reverse.

I have to agree with you (shocking I know )

We do it all the time, because our sites are totally subject to wind (for the dhow) predicted current, actual water flow and sunlight (time of day) which means some sites will be divable some won't be, and the plan will change during the day (I forgot to mention pirate activity and gunfire too). When you jump in the water the vis might be abysmal below 25m or vis versa

So we all in my group run 27% which gives us the option of upto 41m or 49 at 1.6 as contingency We also all carry bailouts of 21% and deco of 40 or 50%. This weekend we all (14 divers)took 9 cylinders each of backgas plus our bailouts and spares, carting additional "optimum" mixes isn't practicable as it was we had 180 cylinders on our boat.

If we're on a shallow dive it doesn't matter if we hit deco then we'll take deco (we know our stops based on our gas) and at least we have contingency to be able to drop in on the deeper ones as required without being constrained by MOD of a rich mix

 

[eelnoraa]

Also, captains get that people are not necessarily prepared to go deeper than planned, because of things like gas requirements, level of training and experience, and thermal protection. I have never once been on a boat where the captain did not ask everyone whether they could divert to deeper water before going there. Usually, someone or ones can't, and the boat goes somewhere shallower. While I'd have brought different gas in some cases when that happened, it was certainly safe to dive what I brought, every time.

That is my experience as well, and that is what I expect from a responsible captain. I have never had any caption s brought us to deeper site than planned without first getting consensus from everyone.

But let me also ask Stuartv, if you are allowed 2 cynlinders only and planned for 2 dives, this is for sure a rec charter. What are you doing at 135' diving single tank? What is your mix? And what is your NDL?

 

[stuartv]

That is my experience as well, and that is what I expect from a responsible captain. I have never had any caption s brought us to deeper site than planned without first getting consensus from everyone.

But let me also ask Stuartv, if you are allowed 2 cynlinders only and planned for 2 dives, this is for sure a rec charter. What are you doing at 135' diving single tank? What is your mix? And what is your NDL?

I'm not sure if you are trying to change my point on purpose or not.

But, back to front, yes, this whole conversation was predicated on an assumption that we're talking about a recreational boat. The rec limit (for must US-based agencies) is 130'/40m and people dive the Spiegel Grove as recreational dives all the time. I am not EVEN trying to complicate things by getting into what gases tech divers would take on a tech charter. It's about what a diver who has taken GUE Fundies, but nothing more advanced, would take on the boat, if he or she is strictly following GUE training.

Further, I never said anything about being taken to a site that you had no idea you might go there.

I was asking about a situation where you know in advance that you might go to a site that has a hard bottom at 135', or you might go to one with a bottom that is 70'. Or a variety of choices in between. The only thing you don't know (at the time you're loading your tanks onto the boat) is which one of the possible sites you will actually end up on.

And, actually, I specifically asked about diving out of Morehead City or Beaufort, NC, where the max depth would be 125. The 135 only came up as an example to illustrate that NC diving is not "abnormal". Other places have the same issues (of widely varying depths as possibilities and you don't know what you're going to get until you're already out on the boat). As @Diving Dubai has now chimed in and affirmed (thanks! ).

 

[TrimixToo]

I'm not sure if you are trying to change my point on purpose or not.

But, back to front, yes, this whole conversation was predicated on an assumption that we're talking about a recreational boat. The rec limit (for must US-based agencies) is 130'/40m and people dive the Spiegel Grove as recreational dives all the time. I am not EVEN trying to complicate things by getting into what gases tech divers would take on a tech charter. It's about what a diver who has taken GUE Fundies, but nothing more advanced, would take on the boat, if he or she is strictly following GUE training.

Further, I never said anything about being taken to a site that you had no idea you might go there.

I was asking about a situation where you know in advance that you might go to a site that has a hard bottom at 135', or you might go to one with a bottom that is 70'. Or a variety of choices in between. The only thing you don't know (at the time you're loading your tanks onto the boat) is which one of the possible sites you will actually end up on.

And, actually, I specifically asked about diving out of Morehead City or Beaufort, NC, where the max depth would be 125. The 135 only came up as an example to illustrate that NC diving is not "abnormal". Other places have the same issues (of widely varying depths as possibilities and you don't know what you're going to get until you're already out on the boat). As @Diving Dubai has now chimed in and affirmed (thanks! ).

The light is starting to dawn. I didn't pick up from this split-off thread that the context was recreational diving. That's a horse collar of a different color altogether. GUE and standard mixes are, to me, far more associated with tech than with rec.

 

[eelnoraa]

I am not trying to change anything, certain not your opinion. I just want to understand and possibly explain why your concern doesn't apply as in a general cases.

The issue I see is exactly as your describe:

Before loading the boat but after you pay the booking, the captain tells all divers that two sites are possible with this charter, one is 70", the other is 135'. For that matter, even 125'. We don't know which site we will go until we are on the way.

I can tell you no one in Monterey book will this charter. And thus, this kind of rec charter setup doesn't exist in my area. In fact, I have never heard one.

We do have charter that goes to 130-150 or even deeper site. But again, I don't remember ever be on a charter where the depth is undecided before loading and can vary 60ft.

Back to your question, if the site has max depth of 125', and I plan to spend a meaningful amount of time there, I will plan it as a 125' dive.

My question still stays. For your charter with max depth of 125', what is your best mix in your single tank, what is the NDL? And I'd you see an anker at 135', will you go there?

 

[seeker242]

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...

Not really all that normal. I dive Key Largo all the time as it's less than a 2 hr drive from here. The boat knows where they are going before they leave the dock. the boat knows where they are going a week ahead of time, sometimes more. If the Spiegel is blown out due to a ripping current or something, then yea they may do a shallow reef instead, but that's not normal. If you sign up to dive the Spiegel, you normally dive the Spiegel.

And if you are rec diving the Spiegel, following strict GUE standard, you take 32% and it doesn't matter if you go to 45' instead because you would be diving 32% at 45' anyway.