Want better RMV/SAC?

[Altamira]

This thread is not news to most SB members, but it may help new divers. Despite fully understanding the what to do/not to do to answer the question, I always find it interesting to compare my underwater movements and their effects on my RMV/SAC. I download all my dives from my AI computer, and evaluate my actual RMV/SAC numbers vs what I was doing and feeling underwater. An excellent comparison for me is to look at my volunteer dives at Spring Lake, San Marcos, vs a slow, easy, shallow Caribbean Reef dive. Although the water is colder at Spring Lake, I am equally warm and mentally relaxed in both dive environments. The main difference is how much I am just moving my hands. At Spring Lake, I am almost constantly moving my hands while removing invasive vegetation, or fanning the sand away from the spring's hundreds of water outlets, while on the Caribbean reef, I sometimes think I could fall asleep just watching the reef critters. Being in the .5 -.59 cu/ft/min in @scubadada's air use survey, I certainly am not a gas sipper like many on this board, but when relaxed and barely moving on a pretty reef, my RMV is usually .49 -.53, whereas when moving around a lot at Spring Lake, my RMV has been as high as .69. While I am never surprised at the difference, it is always a good reminder for me to go slow, easy, and stop fidgeting with my stuff. Busy hands waste gas.

 

[Belzelbub]

Totally agree. Ironically, my volunteer dives at an aquarium are when I’m more relaxed. Those dives are often in the low 0.5s, or even lower depending on the job I’m doing.

My other dives, I’m usually hunting, so lots of swimming and definitely some work. Those are often a bit higher.

One of these days, I’ll probably do an actual relaxing dive.

This is also one of the reasons I like AI computers. The chart in Subsurface (others as well) can show points in the dive where consumption is higher or lower than the rest of the dive, and you may be able to associate those peaks with something that happened during that portion of the dive.

 

[Sebs]

I've been logging my air consumption for quite a while now and sat pretty comfortably at around 15-16L/min. Then on my recent red sea trip everyone was coming back up to the boat with 100bar tanks while I had 50 bar left. I very easily get splitting headaches from improper breathing (skip breathing or even just holding my breath on the top of the inhale for a second or two) so I would literally continuously breathe, never pausing between exhale and inhale.

So I then paid attention to how I naturally breathe on the surface and I often pause for 2-5 seconds between breaths.

Back underwater, turns out pausing on the inhale for 1-2 seconds worked wonders and my RMV wen't from 15 to around 12.5L/min. No headaches either. I think the lowest I got last week in the red sea was around 11.5L/min on an unguided "find some interesting fish" reef dive.

So my tip would be to just try to breathe more naturally when underwater. It sounds simple but even after 100+ dives turns out I was not breathing right.

 

[Klopo]

I've been logging my air consumption for quite a while now and sat pretty comfortably at around 15-16L/min. Then on my recent red sea trip everyone was coming back up to the boat with 100bar tanks while I had 50 bar left. I very easily get splitting headaches from improper breathing (skip breathing or even just holding my breath on the top of the inhale for a second or two) so I would literally continuously breathe, never pausing between exhale and inhale.

So I then paid attention to how I naturally breathe on the surface and I often pause for 2-5 seconds between breaths.

Back underwater, turns out pausing on the inhale for 1-2 seconds worked wonders and my RMV wen't from 15 to around 12.5L/min. No headaches either. I think the lowest I got last week in the red sea was around 11.5L/min on an unguided "find some interesting fish" reef dive.

So my tip would be to just try to breathe more naturally when underwater. It sounds simple but even after 100+ dives turns out I was not breathing right.

Hi Sebs

Do you also dive in the Dry Suit in the lakes of Switzerland ?
When I dive here in the Walensee or Zürichsee in winter when it is really cold, then I usually have 17.5 - 18.5. Now in summer where it is also a little warmer here, 16.5-17.5.
That but when I just dive, as soon as gas change comes to it, then goes mostly for this time a little up. For example for deco stops mostly around 14.5 as there is not much movement anymore.

 

[happy-diver]

for relaxation I ingratiate myself with tank fillers have them put a bit more air and think no further than that

 

[splitti]

Hi Sebs

Do you also dive in the Dry Suit in the lakes of Switzerland ?
When I dive here in the Walensee or Zürichsee in winter when it is really cold, then I usually have 17.5 - 18.5. Now in summer where it is also a little warmer here, 16.5-17.5.
That but when I just dive, as soon as gas change comes to it, then goes mostly for this time a little up. For example for deco stops mostly around 14.5 as there is not much movement anymore.

I do. I found that a variety of things influences my air consumption.

When I get cold, I breathe more. So taking warmer undergarments or heating helps.

When I dive with buddies that I do have to look after more and pay more attention to than certain others, I use more air as well as I can't relax as much.

When visibility is shite and there's navigation involved I focus more and thus don't relax just as much.

When I started with tec diving, it helped to take a minute to mentally go through the planned dive, that helped me be more relaxed and thus my SAC went down.

 

[Klopo]

I do. I found that a variety of things influences my air consumption.

When I get cold, I breathe more. So taking warmer undergarments or heating helps.

When I dive with buddies that I do have to look after more and pay more attention to than certain others, I use more air as well as I can't relax as much.

When visibility is shite and there's navigation involved I focus more and thus don't relax just as much.

When I started with tec diving, it helped to take a minute to mentally go through the planned dive, that helped me be more relaxed and thus my SAC went down.

I understand what you mean about going through it in your head. This also helps me amazingly well.
The visibility has with me especially an influence if I do not know the dive site well. But for example at the Walensee where I know the dive sites well this has no influence. As soon as I can tell where I am even in poor visibility, I am relaxed. Do you dive a lot in Lake Zurich ?

 

[splitti]

I understand what you mean about going through it in your head. This also helps me amazingly well.
The visibility has with me especially an influence if I do not know the dive site well. But for example at the Walensee where I know the dive sites well this has no influence. As soon as I can tell where I am even in poor visibility, I am relaxed. Do you dive a lot in Lake Zurich ?

Zürichsee, VWSS, Zugersee most of the time, yea

 

[Sebs]

Hi Sebs

Do you also dive in the Dry Suit in the lakes of Switzerland ?
When I dive here in the Walensee or Zürichsee in winter when it is really cold, then I usually have 17.5 - 18.5. Now in summer where it is also a little warmer here, 16.5-17.5.
That but when I just dive, as soon as gas change comes to it, then goes mostly for this time a little up. For example for deco stops mostly around 14.5 as there is not much movement anymore.

Hey. Yeah I've only been in the lakes here like 8 or so times. My RMV was around 18 for those dives with the bad breathing technique. The rest I'm attributing to still being new to drysuit diving and messing around with the inflation too much.

 

[Klopo]

Hey. Yeah I've only been in the lakes here like 8 or so times. My RMV was around 18 for those dives with the bad breathing technique. The rest I'm attributing to still being new to drysuit diving and messing around with the inflation too much.

With me it is so, that I had made only 4 dives in warm water. Otherwise, I always go in our beautiful but cold lakes.
I had certainly needed 30 dives to master the dry suit without that I have to think about it. When I had that out with the dry suit is my AVM again 1 - 1.5l sank.