Question SAC rates change by dive

[Blackcrusader]

I’ll let the depth point to bed. Same max depth and bottom times. Not a big spread, like 15% reduction over the course of the day. I’m extremely comfortable in the water, and never have pre dive jitters. I have honed in my kit over the last 30+ dives and feel comfortable in it. I agree that it’s likely extortion, latent anxiety and probably the first temperature exposure.

When I haven't dived for awhile I always use my first dive to settle in back to my "zone" So I expect a little higher RMV than on later dives. Other factors like strong currents of course can affect gas consumption.
Yes I find it normal on first dive of a vacation to use more gas but it's not a concern it's just me adjusting to being back in the water again.

 

[stepfen]

I would suggest to the OP to stop overanalyze gas consumption as it is a slippery road that leads nowhere else than wasting time, effort, pleasure and eventually to increased gas consumption (!).

Your focus should be on improving your general diving skills (comfort underwater, buoyancy, fining/turning techniques, familiarity with your gear, situational awareness etc). Low gas consumption is NOT a diving skill that can be learnt. "Low" consumption (whatever low is for each of us) is the result of all these and not the other way around.

To clarify I'm not suggesting you forget SAC calculations altogether. On the contrary . You should record and be familiar with your SAC, but on a long term basis. Knowing your normal gas consumption is a key factor for safe diving.

What you should NOT do though, is wasting time to analyze why your sac rate was X% lower in that dive vs the other one and try to lower it on a dive by dive basis. To me, your "theory" that first dives have higher SAC rates than later ones falls within this realm. Even if this theory was true, you can't/won't lower your SAC by actively trying to "fight" it.

Keep diving, keep improving your basic skills and your SAC WILL improve over time (as in years, not days not weeks not even months) reaching your "normal" rate at some point in the future.

Yes first dive of the day/trip might have slightly higher SAC rate but so what? Should you skip it and dive directly on the second one ?

All the best...

 

[tbone1004]

I’ll let the depth point to bed. Same max depth and bottom times. Not a big spread, like 15% reduction over the course of the day. I’m extremely comfortable in the water, and never have pre dive jitters. I have honed in my kit over the last 30+ dives and feel comfortable in it. I agree that it’s likely extortion, latent anxiety and probably the first temperature exposure.

what are the exact SAC values? 15% is a fairly wide spread IMO if we are talking about otherwise identical dive profiles. I am almost always calculating mine manually and they are usually within 5% which I consider within normal deviations given relatively vague pressure gauge readings. That said, mine can EASILY swing up 25% if workload/stress increases, which one of my AI's loves to pick on me for when we are teaching together because he will passively keep an eye on my SPG and loves to laugh at me whenever we get up to the surface when my SAC rate goes up because he knows I've either been chasing students up and down or yelling at them thru my regulator

 

[inquis]

When I was taking various OC tech classes my SAC would increase to around 0.7 cuft/min at the beginning of each one. Once it fell back to normal (0.5ish) toward the end of a class, it was a nice indication that I was no longer stressed.

 

[boqurant]

Yeah, I’ve noticed this too, but put it down to simple reasons of prior travel, potential lack of sleep, “coming down” from work stresses etc. Also simply readjusting to being in the water, and being particularly mindful to spot any issues with equipment etc.

 

[happy-diver]

I maintain all my gear and never ever for decades did I concern myself with hypothetical gear issues
until on here I struck a wall of gear hypochondriacism

and I still have had zero issues, but alas I am only one

So my post shows nothing
or something

 

[tursiops]

I maintain all my gear and never ever for decades did I concern myself with hypothetical gear issues
until on here I struck a wall of gear hypochondriacism

and I still have had zero issues, but alas I am only one

So my post shows nothing
or something

Indeed.

 

[happy-diver]

Indeed ha ha ha ha ha ha ha, but which indeed that is the question, ha ha ha ha ha ha ha!

 

[scubaozy]

My sac increases marginally during a holiday. My explanation to this is that I get tired over days of multi dives and my concentration is less than beginning of the holiday.

 

[MB NZ]

My sac increases marginally during a holiday. My explanation to this is that I get tired over days of multi dives and my concentration is less than beginning of the holiday.

Mine does the reverse

I remember a time when putting on SCUBA gear and jumping in to the ocean was a natural as getting in to a car or taking a shower. Those were the days of a really low SAC.