Sac Rates

[Diver0001]

What are normal SAC rates to have? I was just looking at my dive profile from the VYTEK and it lists my sac rates but i have no idea what a good rate is.

I think the lowest you should expect it to be is what it normally is when taking a slow walk. Measure it some time when you're watching TV or something and that will give you a rough idea of your own lower limits.

R..

 

[mempilot]

I calculate mine via a different method that is backed up by checking it against my actual dive data.

1. I breathe off a tank at the surface for five minutes, recording beginning and ending pressure. This gives me a 1 ATA 'No Exertion' SAC of .23 cf/m.

2. I then put together a table with incremental depths based on .5 ATA increments, multiplying my SAC by the ATA's to get a 'No Exertion' DCR (depth compensated rate).

3. I then multiply the baseline DCR for a given planned depth by an 'Exertion' constant as follows. 1.0 for No Exertion, 1.5 for Light Exertion, 2.0 for Moderate Exertion, and 2.5 for Heavy Exertion. Exertion factors (EF) in planned workload, current strength, etc...

4. This is the rate that I use for gas planning.

After logging over 100 deep dives using this method and recording 'actuals' vs. 'planned', I graphed the actual dives against the baseline DCR and subsequent EF values. I found that on deep dives, over 80% of my actual DCR's fall in the Moderate Exertion category which matches up with the currents and workloads I face on my dives. I use this column on my chart exclusively for gas planning now on deep dives.

About once a month, I recheck my SAC due to exercise or lack of and adjust the tables accordingly.

 

[ABQdiver]

I calculate mine via a different method that is backed up by checking it against my actual dive data.

1. I breathe off a tank at the surface for five minutes, recording beginning and ending pressure. This gives me a 1 ATA 'No Exertion' SAC of .23 cf/m.

2. I then put together a table with incremental depths based on .5 ATA increments, multiplying my SAC by the ATA's to get a 'No Exertion' DCR (depth compensated rate).

3. I then multiply the baseline DCR for a given planned depth by an 'Exertion' constant as follows. 1.0 for No Exertion, 1.5 for Light Exertion, 2.0 for Moderate Exertion, and 2.5 for Heavy Exertion. Exertion factors (EF) in planned workload, current strength, etc...

4. This is the rate that I use for gas planning.

After logging over 100 deep dives using this method and recording 'actuals' vs. 'planned', I graphed the actual dives against the baseline DCR and subsequent EF values. I found that on deep dives, over 80% of my actual DCR's fall in the Moderate Exertion category which matches up with the currents and workloads I face on my dives. I use this column on my chart exclusively for gas planning now on deep dives.

About once a month, I recheck my SAC due to exercise or lack of and adjust the tables accordingly.

That's an interesting approach! Do you have the table on Exel or something? Would you be willing to share?

 

[mempilot]

That's an interesting approach! Do you have the table on Exel or something? Would you be willing to share?

I built an Excel spreadsheet. I have a bunch of other stuff in the same worksheet, so give me some time to cut it down, and I'll post it in this thread.

 

[Doc Intrepid]

I calculate mine via a different method that is backed up by checking it against my actual dive data...
After logging over 100 deep dives using this method and recording 'actuals' vs. 'planned', I graphed the actual dives against the baseline DCR and subsequent EF values. I found that on deep dives, over 80% of my actual DCR's fall in the Moderate Exertion category which matches up with the currents and workloads I face on my dives. I use this column on my chart exclusively for gas planning now on deep dives.

That's an excellent example of how SAC rates should be tracked and used. Well done. I'll be interested to see your Excel spreadsheet also.

 

[mempilot]

OK guys, how do I attach an Excel spreadsheet to a post?


Otherwise, I'll have to email it out.

 

[Diver0001]

OK guys, how do I attach an Excel spreadsheet to a post?


Otherwise, I'll have to email it out.

You have to zip it first and then click on the button "manage attachments" near the bottom of the reply screen. The rest should be obvious.

R..

 

[mempilot]

This is a copy of my old SAC/DCR spreadsheet with a handful of dives logged in. The current spreadsheet is too large to attach. It contains data for other tanks with deco. It is a little cleaner and a lot more complex, but relies on the same principles. When I paired out my recreational dives to this sheet, most of them fell in the light exertion DCR tables.

Now, this is my disclaimer. I use this spreadsheet based on my understanding of my unprofessional programming ability. I'm providing it so you can look and possibly use the same technique to build your own tables. My tables work for me based on my historical data. Please do not use these tables without first calculating your own SAC and then verifying under different conditions and depths.

Feel free to criticize. I record every dive manually and by computer, and then verify it back to my planning. It works. I'm still tweaking my sheet for decompression diving.

 

[Rick Murchison]

I wasnt trying to see if mine were better than anyone else's

Well, just in case you were...
On one particular dive that involved a pair of real serious bull sharks, I burned through 1900 psi from a LP steel 85 in 16 minutes at an average depth of 50 feet.
Figure that one out.
Bet mine's higher than yours .
No exertion, all adrenaline!
Rick

 

[ABQdiver]

This is a copy of my old SAC/DCR spreadsheet with a handful of dives logged in. The current spreadsheet is too large to attach. It contains data for other tanks with deco. It is a little cleaner and a lot more complex, but relies on the same principles. When I paired out my recreational dives to this sheet, most of them fell in the light exertion DCR tables.

Now, this is my disclaimer. I use this spreadsheet based on my understanding of my unprofessional programming ability. I'm providing it so you can look and possibly use the same technique to build your own tables. My tables work for me based on my historical data. Please do not use these tables without first calculating your own SAC and then verifying under different conditions and depths.

Feel free to criticize. I record every dive manually and by computer, and then verify it back to my planning. It works. I'm still tweaking my sheet for decompression diving.

Thanks Mem, I like your approach! The spread sheet looks good.