Switch to Hogarthian Setup - Air Consumption Woes

[falloutzwei]

I recently switched to Hogarthian gear during my NAUI Intro to Tech class and my SAC rate doubled to 1.34 cu. ft/min. I expected some increase due to learning new gear, but this seems excessive.

This SAC rate was obtained by measuring air consumption during a constant depth non-strenuous swim at 20 FFW.

I am trying to figure out why, because the obvious reasons don't seem to apply.

1.) Fitness

I'd say my fitness is better than it was when I started diving. I've developed into a pretty strong swimmer and my cardiovascular health is much better. Also, at no point in the swim did I feel short of breath.

2.) Comfort level.

I was slightly nervous but I didn't feel like I was extremely stressed. There may have been some performance anxiety on going.

3.) Gear streamlining.

I felt like I had less drag than normal. I was diving in a t-shirt and short, which may have contributed to drag. I felt everything was in an efficient, non-dangling position. The harness was somewhat loose at first, despite having tightened it.

4.) Lung capacity. I have huge lungs. When I first started diving I struggled with buoyancy, due to the fact if I took a deep breath, I became extremely positively buoyant. As a consequence, I started exhaling very rapidly in my early days of diving. I think this may be the culprit, as I was nervous about repeating the past, so I was exhaling too fast to maintain buoyancy, when it wasn't necessary due to the buoyancy characteristics of my back plate and wing.

Any other thoughts on what could be causing my elevated air consumption?

 

[Peter_C]

Welcome to Scubaboard

Quit worrying about how much air you are using, breathe all you want, relax and enjoy the dive. Often times when you forget to focus on breathing it will settle down. Oh and get a bigger tank :tongue:

Work on buoyancy instead, which is more important than how much you breathe.

Do you get headaches?

 

[DevonDiver]

New kit, new skills, plus 'pressure' of being on a training course. It's not unusual for your SAC to spike. It'll settle back down once you get familiar with the new kit and procedures.

 

[ajduplessis]

Relax and dive, your SAC will drop down to previous levels after training. You are stressed and your SAC fixation is not helping either.

Chill:cool2:

 

[Bossman]

Welcome to Scubaboard

Work on buoyancy instead, which is more important than how much you breathe.

I encountered the same thing, until I got my buoyancy and trim dialed in. Don't focus on how much you breathe, dive as much as you can and take a peak performance buoyancy class.

The other thing that spikes my SAC is cold water, was the water colder than you're used to?

 

[DA Aquamaster]

There can be trade offs at times.

For example lung volume can involve a 4-5 pound buoyancy swing so if you are trying to maintain precision buoyancy you need to know exactly where the neutral "average" is at, otherwise you'll interrupt an efficient
breathing pattern to maintain precise buoyancy.

Also if you are following a cave or wreck profile you'll need to decide whether it is more efficient to accommodate a temporary change in depth with gas added/dumped from the wing or with a modification in lung volume. You'll get better at that over time and that combined with greater comfort and the lack of class induced performance anxiety will bring your SAC back to normal.

In any event, stop worrying about your SAC as doing that will just increase your anxiety and task loading and will take your focus off wha you really need to be attending to.

 

[Doppler]

Did the size of your cylinder(s) change?

I had a trimix student who swopped cylinders with a buddy halfway through a course and his RMV went from around 14 l/p/m to more than 24!

Remember, although the buoyant effect changes the weight of your gear, its mass is unchanged and inertia is inertia.

 

[falloutzwei]

To answer questions:

No, I don't get headaches. I used to but that hasn't been a problem for the last 10 dives or so.

The water temperature was 85 deg F at depth, 94 on the surface, so definitely not cold.

No cylinder size change, I was diving a standard aluminum 80.

Thinking back on it all this morning, I was maintaining my buoyancy, but it was definitely more effort to do so. I noticed myself having to add/dump air from the wing more frequently than I did with my previous kit. In the past I had to add little to no air to maintain neutral buoyancy. I thinking more water time with this kit will do wonders for it all. I know several people who have been diving Hogarthian gear for some time, so I may ask them to observe my trim in the pool. That is one of those things that is hard to judge for yourself.

Thanks for the advice.

 

[a22shady]

depending how often you had to keep adding Air/dumping air if were doing it alot that will also contribute to your SAC rate showing higher.

 

[Slamfire]

I recently got a set of LP108 doubles. Just before testing them for the first time a did a deco dive in my usual Al80's doubles while slinging another Al80 and a Al40. Usually, when I sling bottles my SAC rate jumps a bit. That dive it ended up being .55 cu ft/min for the entire dive. Ten days later I tried the LP108 doubles with no slinging of bottles and trying to keep everything simple. My SAC rate went to .637 cu ft/min. I also found that my backfinning is not nearly as effective as when I carry my usual rig (even if I'm carrying two slung bottles). Conclusion, I have to put in a lot more dives to tame these puppies.

Other things to do with the new doubles: Change the angle of the isolating post, it's just a tad harder to reach that the one in my usual rig. I also want to change all handles to soft rubber and get rid of the hard plastic knobs currently on.

I think band position and overall position on my back is good, because I have no problem getting in good trim.