Do you use your SAC for anything? POLL
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fire_diver
Contributor
I think it's very sad that so many divers see absolutely no need to understand thier breathing rate when diving. How in the hell can you PLAN a dive if you don't know how long your tank will last. "Oh I'll just jump in and come up when I reach 700psi" is not dive planning.
You should know your 3 SAC rates. resting (aka deco), normal, and stress.
Resting would be very little movement such when doing a drift dive.
Normal would be your typical swimming around dive.
Stress is swimming very hard.
Before your dive you should be planning what depths you are going to, how long you can SAFELY stay at that depth, and how much work would be involved in this dive. What happens if your buddies 1st stage dies? Will you have enough air to share (in a now emergency situation) without running out before reaching the surface? Or do you just make every dive praying nothing goes wrong?
Every diver should constantly strive to improve thier diving. Knowledge about yourself and your equipment the priority in improving.
As for "air hogs", different people breath differently. It doesn't mean they are a "bad" diver. If you do use more air than others, you can hang a little higher in the water during the dive to help offset the difference.
You should know your 3 SAC rates. resting (aka deco), normal, and stress.
Resting would be very little movement such when doing a drift dive.
Normal would be your typical swimming around dive.
Stress is swimming very hard.
Before your dive you should be planning what depths you are going to, how long you can SAFELY stay at that depth, and how much work would be involved in this dive. What happens if your buddies 1st stage dies? Will you have enough air to share (in a now emergency situation) without running out before reaching the surface? Or do you just make every dive praying nothing goes wrong?
Every diver should constantly strive to improve thier diving. Knowledge about yourself and your equipment the priority in improving.
As for "air hogs", different people breath differently. It doesn't mean they are a "bad" diver. If you do use more air than others, you can hang a little higher in the water during the dive to help offset the difference.
You may be able to get high pressure tanks but in my experience they are of little use as you tend to get the same fills anyway! We have tanks and valves with a working pressure of 240bar but we have not found a shop that fills to that level. We get 200 to 220 bar fills like people who have lower pressure tanks:doh:
I think some diveboat operators "take advantage" of people who go through more air to control the length of the dive. We have certainly had occasions where our fills were consistently a lot less when the operator worked out that we don't go through a lot of air!
I understand they may need to have a set time for dives in order to operate a cost effective business and be back for the next load of divers. I just think they should be honest and let you know the dive time when you book!
When we dive with someone outside our normal buddies we will ask them to indicate when they get to 100bar. We can then get a general idea of their consumption and make some decisions about turn around and safety margins based on our knowledge of the site.
Sure the person should be responsible for their own dive plan but if they don't know the site that can be hard. I have to say I wouldn't blindly trust someone when they told me about SAC or any other dive skill. Not everyone is capable of honest self analysis. Many dive shops will look at certificates and dive logs but limit the first dive till they determine the real skill level in the water which I think is a great approach.
Having a standard turn around at 100 bar no matter what dive you are doing is just plain lazy and dangerous IMHO! The old method of going out for a third, turn and use a third to get back and have a third in reserve is just as easy to say and is an awful lot safer!
RMV? not sure I know what that stands for
SAC can be worked out no matter what cylinder you are using. We have two sized Cylinders and work out SAC each dive depending on the cylinder. We have a pretty clear idea of what we can do on each cylinder for a given dive, depth and fill pressure.
RMV? not sure I know what that stands for
We have a pretty clear idea of what we can do on each cylinder for a given dive, depth and fill pressure.
In Oz RMV (Respiratory Minute Volume) is a medical term & almost never used in diving. If it is, it is interchangeable with the term SAC (Surface Air Consumption). They are both expressed in terms of volume/minute at 1 bar.
In the US they also measure surface consumption rates in terms of pressure/minute.
Because of the variations in the ways tanks are marked for US imperial & international metric, the variation in the use of SAC, RMV, & SCR, some confusion can arise.
In my training here in the states, learned that SAC is calculated for a particular tank and expressed in PSI/minute.
Found a thread discussing calculating RMV
Found a thread discussing calculating RMV
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