How Do Shearwater Work Out SAC Rates?

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@sebastienschaer8111
#askmark would it be possible to explain how the SAC rate is calculated in the shearwater? It seems different that the SAC rate calculation that you can find in internet. I also know that everybody is different and the condition also affect this consumption , but what value would be a average SAC rate vs a good SAC rate?
@leemiller358
#askmark - 4 dives on my Perdix 2 and loving the AI and the easy to read screen and functionality. Here's another question on SAC rate. Perdix is telling me my average SAC is 20.4 psi/min. My introductory understanding is if I want to convert to cubic feet/min (RMV - using DAN's definition) I would need to factor in tank volume and working pressure. Does Perdix allow for this? I have two tanks I routinely use that are slightly different. I don't see where I can enter "Tank 1- 100 cu ft, 3445 psi" and Tank 2- 100 cu ft, 3144 psi" in the computer. Shearwater associates the AI serial number to the tank to support up to 4 transmitters. How about managing multiple tanks with one transmitter.
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[@rey_nevan]

Hi Mark, lovely episode. My favorite so far. Keep up the good work!

[@douglasljdunn]

Useful preso. I track my RMV manually, simple calc to do.

[@charlemagne8764]

My Garmin (MK2i) gives me a SAC rate in L/min as well as RMV in L/min. I understand the SAC rate is the consumption adjusted for depth, ie at the surface and RMV is the actual consumption. Do you know if my understanding is correct?

[@leborde]

Isn't the internal volume of a 12l cylinder something like 11.1l?

[@ScubaDiverMagazine]

An Ali 80 has an internal volume of 11.1L. Steel 12L is the most common size cylinder here in the UK

[@KitoriSin]

Awesome episode! May i know what is the blue bracelet that you are wearing called? and where can i purchase it from?

[@ScubaDiverMagazine]

That is from a company called Bracenet. They make a range of items from collected ghost gear. All of their bracelets are named for different seas and oceans, the blue one is named Arctic Ocean.

[@KitoriSin]

@@ScubaDiverMagazine Thank you! 😊

[@stevenwood1468]

#ASKMARK My predix ai does a calculation for GTR (gas time remaining) , do you know how that calculation works ?

[@ScubaDiverMagazine]

Shearwater are clever with this one also: They take the known tank pressure and subtract enough gas to ascend to the surface at a safe rate and also subtract enough gas for a reserve. This remaining gas is then divided by the ambient pressure and your SAC rate to work out how many minutes it would take for you to breath down that gas and still be able to ascend to the surface with some reserve. But. It won't take deco or safety stops into the calculations so, don't go right up to the limit or you may need to go into your reserve

[@EnergiZeScuba]

Hi Mark, (Hi Shearwater, if any of you are reading this), I use the Perdix 2ti and every now and then (in 22 dives 2x) I have the problem that the SAC rate was very high (45bar/min or higher). I can't explain why this error occurred. Do you have any idea? My normaly SAC Rate is about 1,6bar/min

[@Yggdrasil42]

I would send that dive log to Shearwater support. Definitely interesting.

[@a.karley4672]

Hmmm. How *smooth* is the value from your *electronic* cylinder pressure gauge? If this is (erroneously) dropping to zero (or a low value), then you'd see that effect. I've seen this in (in house) lab equipment from loose wires in the analytical machinery. But we could go to manual calculation and get round the problem. Next break in operations, out with the soldering iron and solder the pressure cell's connections. Bug report filed to the technician who built it. The last time I calculated "SAC" rates was for cave diving, to work out if I'd be able to make a particular air bell before reaching 'thirds'. But always, the answer to such questions is "bigger tanks". Skip-breathing isn't really an option. I'm trying to remember what 1cu.ft/minute is in L/min. (28.4 L/cu.ft - I had to work it out.

[@ozDomaNET]

3 suggestions: flooded/damaged transmitter or make sure your octo. is not free-flowing during your dive or if it is not happening during DSMB deployment. Shearwater is probably not as good and reliable as it used to be. My Perdix2Ti pressure sensor failed just after 6months/280 dives (soaked in fresh water every day) Another guys Teric pressure sensor also failed (within Waranty period).

[@linyasen5]

Hi Mark. What kind of watch you are wearing? Is it a dive watch? If it is, what brand is that? I'm in the market for a dive watch/computer right now. Thank you!!! :)

[@comebackdk]

it look like a TERIC

[@ScubaDiverMagazine]

Yeah, that's my Shearwater Teric. It felt right to wear it when Shearwater were sponsoring the video. It comes in a few colours now and there's also the Shearwater Tern if you're interested.

[@JulieVenhaus]

#askmark Hi! Not Shearwater or dive computer related (although my husband and I have both ordered the Peregrine TX!). Would love to know your thoughts on XS Scuba’s Highland Backplate and wing products. Our local dive center carries them (and their regulators) and we cannot find any videos, good or bad. Thanks!

[@ScubaDiverMagazine]

I've used a few of their bits and they're decent quality. It's hard to go far-wrong with BP/W hardware... They're not a particularly _flashy_ brand so you won't find a lot online about them but, the quality and materials are fine. Have fun with the Peregrines, they're a top tier computer

[@JulieVenhaus]

@@ScubaDiverMagazinethanks!

[@sparksi2519]

Wait.... Shouldn't sac rate be in liters/min, rather? Surely the size of your tank doesn't affect your sac rate 😅