RMV math…

[Wibble]

When you use your SAC to calculate how much gas you expect to use on a dive how do put a fluctuating value into your calculator? if as you assert SAC is not a diver specific constant.

It’s not like SAC calculation is difficult.

You need a note of your start and end pressures. Pick some square profile dives and work out the averages.

The easiest way is a spreadsheet of depth in metres for each minute of the dive then divide by 10 and add 1. E.g. 30m / 10 = 3 + 1 = 4ATA.
Work out the volume of gas consumed = (start pressure minus end pressure) x cylinder wet volume.
Then divide the volume of gas by the total pressure minutes.

Do the same for your decompression gasses.

Then you’ve a baseline.

With that baseline you can work out you higher workload (x1.5 to x2) and extreme workload (x3)

It’s those higher consumption figures you use for working out minimum gas and having sufficient for contingency, maybe even gas sharing

 

[60plus]

Several pages back, you made a statement that pretty much confirmed you have no idea what SAC even is.

It is not a constant like you stated. It varies based on the activity level of the dive. It can also change based on your health. However, it can still be useful. If I’m hunting, I know it’s going to be higher than a leisurely dive. But if I know what I’m going to be doing on the dive, I can figure out how long my gas should last. That doesn’t mean I ignore monitoring pressure during the dive.

A higher than expected SAC might warrant some investigation if the reason is not clear. I don’t think that anyone other than you claimed that SAC is a constant and never varies.

The way people on this forum claim to use SAC for calculations mean that in effect it is a diver specific constant. If a diver has a variable (not constant) SAC then its pretty pointless or impossible to do a worthwhile calculation.
You sate "It varies based on the activity level of the dive." Your SAC does not vary based on the activity level of the dive, it is your actual underwater air consumption that varies. Your SAC is what you measured it at on the surface.

 

[Wibble]

People have different SAC amounts. Some seem to sip gas, others are gas hogs. Add stress and workload and you’ll have an appreciation of the amount of gas they should take

 

[60plus]

Do the same for your decompression gasses.

This topic stated in basic scuba so allowing for decompression time was not an issue.

 

[60plus]

From what I have seen posted I suspect some posters are mixing up (not intending to insult anyone here) SAC and RMV. RMV varies with depth, SAC does not. Surface RMV is the same as SAC.

 

[Wibble]

They’re the same thing
SAC = surface air consumption; number of litres of gas at 1 bar consumed in one minute

 

[lermontov]

Then you’ve a baseline.

With that baseline you can work out you higher workload (x1.5 to x2) and extreme workload (x3)

It’s those higher consumption figures you use for working out minimum gas and having sufficient for contingency, maybe even gas sharing

The way people on this forum claim to use SAC for calculations mean that in effect it is a diver specific constant. If a diver has a variable (not constant) SAC then its pretty pointless or impossible to do a worthwhile calculation.
You sate "It varies based on the activity level of the dive." Your SAC does not vary based on the activity level of the dive, it is your actual underwater air consumption that varies. Your SAC is what you measured it at on the surface.

i think your saying the same thing-what is the argument about

 

[tursiops]

This topic stated in basic scuba so allowing for decompression time was not an issue.

It is no longer in Basic. So you can now say whatever nonsense you want and we are free to tell you it is nonsense.

 

[Belzelbub]

The way people on this forum claim to use SAC for calculations mean that in effect it is a diver specific constant.

No one was claiming that. Oh wait, there was one who claimed that. See below.

You sate "It varies based on the activity level of the dive." Your SAC does not vary based on the activity level of the dive, it is your actual underwater air consumption that varies. Your SAC is what you measured it at on the surface.

Your SAC will absolutely vary based on the activity level of the dive. As your consumption goes up, so too does your SAC. SAC takes your consumption and corrects for what it would be at the surface. This is so you can apply that SAC to plan future dives regardless of the depth. It’s really not as hard as you are making it out to be.


Oh, yeah. The one who claimed SAC was a diver specific constant was you. Here’s what you said in case you need a reminder.

That statement is incorrect, SAC is regarded as a diver specific constant It does not vary with what is going on with the dive..

 

[L13]

From what I have seen posted I suspect some posters are mixing up (not intending to insult anyone here) SAC and RMV. RMV varies with depth, SAC does not. Surface RMV is the same as SAC.

RMV does not vary with depth. It is a scientific term (not a diving term) and is the volume change of the lungs in a minute and has nothing to do with depth (volume per breath X number of breaths per minute).

SAC is defined in two ways in the diving community.

• Cylinder pressure change/time
  • cylinder must be specified
  • normalized to 1 atmosphere
• Volume/time
  • Same as RMV
  • normalized to 1 atmosphere

• A few strange souls try and define one or the other not normalized to 1 atmosphere, but by doing so they demonstrate their ignorance of how the terms are used by knowledgeable individuals.

You should not be commenting on this subject. You do not appear to understand the definitions of the terms, or the concepts they deal with. As such, your opinion on their usefulness is suspect.