Recreational Pony Bottles, completely unnecessary? Why or why not?

[Gareth J]

Pffff.... we are trained to stop our breath for at least 15 minutes while rescuing our buddies using only one hand and taking pictures of the surrounding environment for documentation purposes!

 

[ginti]

@tursiops, see @Ayisha's next post, that's the correct answer. [post edited because I misread what you wrote when I first answered ]

Hi @boulderjohn, I didn't really get what you mean here:

or do you plan for one diver to ascend using that procedure, knowing that if ****happens, using your brain will tell you that you still have oodles of gas--much more than is necessary solve that emergency with a direct ascent?

In general, I plan my dive with gas enough for two divers to reach the next source of breathable gas (it can be the deco-bottle in tec dives or the surface in rec dives). Bear in mind that some procedures (especially for rec-diving) are not fresh anymore, so I might be making some mistakes here. I know I should have a look again at my fundies material, but I don't find the time now

P.S. a direct ascent, for you, is just an ascent at a constant speed to the surface, without stops, right?

 

[Ayisha]

Remember the 10 ft/min ascent rate is only for calculating MINGAS, not actually for ascending, which is 30 ft/min up to some depth, then and only then slowing.

The 10 ft/min ascent rate is actually used for ascending from half max depth (for a 100 foot or less dive), not just for calculating MG. In practice, it's a slow and smooth slide from stop to stop.

I think what gets conflated here is that a MG calculation works for many emergency situations, but it by no means covers all scenarios. If we reserved enough gas for every potential issue, there would be little or no bottom time.

Using a MG calculation and practicing the corresponding ascent rates just gives the team a healthy amount of gas to work with and the skills to slow the ascent down in an emergency, if they are able to. If gas reserves are depleting and/or the victim is overwhelmed/panicking, you do what you have to do.

IOW, a MG calculation and an appropriate ascent profile is practiced to help achieve the best outcomes in an emergency, but not every potential emergency situation will be covered - by design.

 

[boulderjohn]

@tursiops, see @Ayisha's next post, that's the correct answer. [post edited because I misread what you wrote when I first answered ]

Hi @boulderjohn, I didn't really get what you mean here:


In general, I plan my dive with gas enough for two divers to reach the next source of breathable gas (it can be the deco-bottle in tec dives or the surface in rec dives). Bear in mind that some procedures (especially for rec-diving) are not fresh anymore, so I might be making some mistakes here. I know I should have a look again at my fundies material, but I don't find the time now

P.S. a direct ascent, for you, is just an ascent at a constant speed to the surface, without stops, right?

This thread was specifically about recreational diving, and the hallmark of recreational diving is that you can make a direct ascent to the surface. The time required to get to your next deco gas is not relevant.

A direct ascent to the surface means ascending at a safe speed with no stops. In NDL diving, that should always be possible; it is, in fact, the true definition of NDL diving. A safety stop should be exactly what the name implies--a brief stop in the 15 foot region just to be sure you have not ascended too fast.

Some people using newer computers are using a different approach to safety stops; that is, watching their SurfGF factor until it drops to a number low enough that they feel safe surfacing. For those people, it would be common to wait until it drops to 70-80. I just did two weeks of diving in Roatan. On those dives, I never surfaced with a Surf GF higher than the mid 40s. On one dive, it never got above 19 at any point in the dive. All the other divers in the groups dutifully did their safety stops, even though those SurfGF numbers indicated that they were completely unnecessary. We could have gone to the surface safely at any time.

 

[tursiops]

The 10 ft/min ascent rate is actually used for ascending from half max depth (for a 100 foot or less dive), not just for calculating MG. In practice, it's a slow and smooth slide from stop to stop.

I think what gets conflated here is that a MG calculation works for many emergency situations, but it by no means covers all scenarios. If we reserved enough gas for every potential issue, there would be little or no bottom time.

Using a MG calculation and practicing the corresponding ascent rates just gives the team a healthy amount of gas to work with and the skills to slow the ascent down in an emergency, if they are able to. If gas reserves are depleting and/or the victim is overwhelmed/panicking, you do what you have to do.

IOW, a MG calculation and an appropriate ascent profile is practiced to help achieve the best outcomes in an emergency, but not every potential emergency situation will be covered - by design.

The point is not the actual GUE ascent procedure. It is the silliness of calculating MinGas at 10 ft/min, over the entire depth? What is the point of doing that if it is never used. In fact specifically disregarded, in the lower half of the dive?

 

[ginti]

The point is not the actual GUE ascent procedure. It is the silliness of calculating MinGas at 10 ft/min, over the entire depth? What is the point of doing that if it is never used. In fact specifically disregarded, in the lower half of the dive?

I do not use the speed of 10ft/min over the entire depth. As you said, it wouldn't make sense. I use the actual speed I need (30ft/min for the first half and 10ft/min for the second half). If I want to increase safety, I can use an increased gas consumption to calculate the minimum gas (the gas consumption must be the one of the weaker diver, appropriately augmented to take into account the stress). This procedure affects the calculation less than using a 10ft/min speed for the entire depth.

Using a 10ft/min speed for the entire depth doubles the time needed - and, therefore the minimum gas!

This thread was specifically about recreational diving, and the hallmark of recreational diving is that you can make a direct ascent to the surface. The time required to get to your next deco gas is not relevant.

You're right; I mentioned the deco bottle to explain the reasoning behind it, but I agree it is better to stick to the topic.

A direct ascent to the surface means ascending at a safe speed with no stops. In NDL diving, that should always be possible; it is, in fact, the true definition of NDL diving. A safety stop should be exactly what the name implies--a brief stop in the 15 foot region just to be sure you have not ascended too fast.

Ok, got it; then yes, I calculate minimum gas in a way such that a direct ascent for two divers sharing gas is safe and possible.

 

[Ayisha]

The point is not the actual GUE ascent procedure. It is the silliness of calculating MinGas at 10 ft/min, over the entire depth? What is the point of doing that if it is never used. In fact specifically disregarded, in the lower half of the dive?

That is NOT how MG is calculated. It's 30 ft/m to half of a max 100 ft depth, THEN 10 ft/m to the surface.

Not sure what you mean about never using it or disregarding the 10 ft/m. I suspect the confusion about how to calculate MG in its entirety as well as the associated ascent rate creates these misconceptions.

 

[tursiops]

That is NOT how MG is calculated. It's 30 ft/m to half of a max 100 ft depth, THEN 10 ft/m to the surface.

You mean the OP does not calculate MG correctly?

 

[Ayisha]

You mean the OP does not calculate MG correctly?

The OP posted screenshots from the new "Fundamentals of Better Diving", I believe, to show where the new calculations are from. Most of the GUE divers on this thread have never heard of the new formula, and we've never been taught it. I believe it might be part of Pragmatic Minimum Deco.

I sat in on a GUE Fundamentals course this past summer, and they were using the typical CAT formula. The ascent rate was the typical 1 minute to solve the problem, and then 30 ft/min to half depth, then 10 ft/min to the surface. So this new calculation that the OP showed had not trickled down to Fundies classes yet.

Most GUE divers would be familiar with a 6 minute ascent from 80 feet. Who knows when the 9 minute ascent that the OP is talking about will trickle down. If we haven't been trained in it, it's unlikely too many GUE old-timers will be using it - just like CAT likely isn't being used by many GUE divers trained before 2015/16.

I guess I'll see what's being taught if I sit in on any new Fundies courses...

 

[Wibble]

9m/30ft per min then 3m/10ft per min was certainly around in the 2015 Fundies notes: