Does Venturi and breathing adjustment all the way on during a dive have any impact on the bottom time ?

[WOB0.01J]

A tip you may already now, but for playing in currents. If you plaster your self against the bottom the current is not nearly as strong. Depending on what you are trying to do...
even just 5ft off the bottom the current tends to be stronger than just skimming bottom....

Umm. that's interesting, i honestly have never thought about that myself. However, I tend to stay 3-5 feet above the bottom because don't want to damage the reef plus it gives me much better field of view for navigation purposes. I only go skimming bottom if I see something cool

 

[WOB0.01J]

TBH, I don't recall if I have ever seen any tests on WOB with venturi on or off, but IIRC, venturi's sole purpose is air flow to prevent or at least mitigate free flow

It would be cool if they have done a WOB with different venturi settings

 

[SlugLife]

Awesome break down of the issue. I wasn't CLOSELY monitoring breathing rate. Finning hard plus out of breath might be the issue here. I guess it has very little to do with the reg setting

Even "moderate" breathing can cause me to burn through my scuba-tank in about 66% of the time, compared to my slow pace.

The other day, I had a tank with 1250 PSI remaining and no place to be. I did a 32 minute dive, 15 feet deep, and used 600 psi on an AL80. I was mostly just very-casually looking for treasure and at random crap dropped below a couple boat docks.

Umm. that's interesting, i honestly have never thought about that myself. However, I tend to stay 3-5 feet above the bottom because don't want to damage the reef plus it gives me much better field of view for navigation purposes. I only go skimming bottom if I see something cool

You can also go downstream from obstacles, which will help a little.

Ideal trim is horizontal. However, if I really want to avoid kicking things while inches away from the bottom, I'll make myself barely positively-buoyant, and trim about 5-to-10 degrees down.

 

[johndiver999]

Your air consumption is primarily dependent on exertion level.
Next factor in importance is probably thermal stress - getting cold requires more air
Then you comfort level, mental relaxation etc.
Then maybe way down on the scale is a regulator performance - unless it is free flowing or super hard to get air.

 

[WOB0.01J]

Your air consumption is primarily dependent on exertion level.
Next factor in importance is probably thermal stress - getting cold requires more air
Then you comfort level, mental relaxation etc.
Then maybe way down on the scale is a regulator performance - unless it is free flowing or super hard to get air.

I completely agree. Next time I will be checking closely to the exertion level. During that dive my exertion level was really high

 

[Belzelbub]

The only difference that I can recall between those two dives were my reg venturi was on the whole time yesterday, but the venturi was turned off for 10 mins or so on the last week dive. Does venturi and breathing adjustment have that big of an impact on air usage? I do like my venturi and breathing adjustment all the way out which makes it as easy as possible to get air : )

I can't see how this could make a real big difference. In fact, I would imagine that if the venturi were off (I'm assuming this means in the pre-dive position) it might lead to an increase in consumption as it will make it a bit harder to breathe.

But, I don't think you really gave us enough to confirm that your consumption actually did go up. Did you use a computer on those dives? If so, are you able to download the dives to an electronic log? Many will calculate RMV or SAC if you enter your start and end pressure and tank information. Most dives are not flat. It could be that the big difference was that your average depth may have been different between those two dives.

TBH, I don't recall if I have ever seen any tests on WOB with venturi on or off, but IIRC, venturi's sole purpose is air flow to prevent or at least mitigate free flow

I haven't seen anything either. I sort of disagree on the sole purpose of the venturi. The main purpose is to reduce the work of breathing. The flow of air around the venturi vane helps to keep the valve open. That should mean reduced WOB. The problem this brings is that it can lead to freeflow, which is why most regulators with venturi assist have a switch where you can turn this effect off, thereby reducing the chance of freeflow.

 

[admikar]

I haven't seen anything either. I sort of disagree on the sole purpose of the venturi. The main purpose is to reduce the work of breathing. The flow of air around the venturi vane helps to keep the valve open. That should mean reduced WOB. The problem this brings is that it can lead to freeflow, which is why most regulators with venturi assist have a switch where you can turn this effect off, thereby reducing the chance of freeflow.

Yeah, that might be its main purpose, but I wasn't able to discern any difference between breathing venturi on and off. Me tuning my regs to the edge of freeflow might have something to do with that too.

 

[Gone for diving]

My dive rite reg shoots the air at the diagram in pre dive. And down the mouthpiece in dive....

Usually I just forget about it... either way I tend to get use to it....

In heavy currents I just tighten up the spring knob...