Switch to Hogarthian Setup - Air Consumption Woes

[Peter_C]

If you are adding and dumping weight more than in the past you are probably over weighted. Perform a weight check at 500 psi and see how much you can lose.

 

[Cave Diver]

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!

I've seen this several times where people get SAC confused with RMV.

 

[Bob DBF]

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

Sounds like you tried to calculate from a portion of your dive rather than the whole dive. If that is the case any small anomoly will amplify in the result.

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.

Add to that any buoyancy problem ( SAC not breathed ) and you could show a large rate which dosen't actually exist.

I take tank pressures before and after the dive and let the computers (dive and home-divelog) give me an idea whats going on. I've had some bad SAC rates when working and filling lift bags.



Bob
-----------------------
I may be old, but I’m not dead yet.

 

[diverbrian]

I remember when I first switched to a hogarthian rig, my RMV went up. Eventually with more dives, I was more confident in the gear and had to make fewer buoyancy adjustments. That came with time and experience.

My basic advice is to settle down. Become comfortable with your gear and don't think about your RMV (I don't think about SAC that much because I do tend to switch tanks and the sizes of deco bottles that I carry.). You may be suprised at the results when you finish your formal training and don't feel like you have an instructor checking off your minor mistakes.