Do you use your SAC for anything? POLL

[Garrobo]

Don't even know what it means.

 

[BDSC]

No, I see no value to it for rec diving, other than amusement between dives.

I'm right there with ya. Other than when I first got certified long ago, I don't think I have ever calculated mine. I have no idea what it is and don't see a need to know for my type of diving.

 

[MarineResearch]

I'm not aquaregia, so forgive the intrusion. When you plan for deco dives it is common to use 2 different SAC rates:

1. Working SAC rate -- for the non-deco portion of the dive when you might be swimming or moving around with a regular degree of physical activity

2. Deco SAC rate -- for the deco portion when you are not supposed to be doing a lot of physical activity. You are supposed to stay mostly idle while offgasing.

Logically, your working sac rate will be greater than the deco sac rate.

To answer your question directly: Yes.

Your working SAC rate or RMV, is calculated during a hard swim over a 10 minute period and corrected for depth. I have only exceeded my working RMV on one occasion when untangling a large anchor and chain from a shipwreck.

I use a fairly conservative Deco RMV since not all Deco situations are as easy as they should be. A cave Deco, where you can lay on the bottom or wedge yourself between some rocks, is a lot different than Deco in rough ocean waters.

 

[BoltSnap]

I keep track of my SAC rate for each dive in my logbook. The only time I use it is when I am doing "deeper" dives (below (130 ft) to enable me to do a "guesstimate" of the air time for these deeper dives and to make sure I have enough gas for the intended dive profile.

For most of my diving where I am doing a more relaxed recreational dive, I plan my dive time based on expected depth/exertion level of that specific dive using on the starting gas pressure and tank gas capacity. I set different milestones for my gas consumption U/W including "turn around" and "terminate the dive" pressures.

MY SAC rate varies between my dives as I look back in my logbook and I usually use the highest SAC rate for dive planning to be on the more conservative side especially for the dives that I consider "higher risk" dives. I don't take into consideration if I have a buddy or not, I plan everything as if am I diving solo. I don't expect or plan my dives assuming anyone will help me U/W for an added measure of conservatism.

 

[farsidefan1]

Bragging rights

 

[aquaregia]

Just out of interest aquaregia what do you mean by "working SAC"? Is that your SAC while swimming or something more strenuous than that?

Sorry, I did use that in a somewhat unconventional way.

When I'm puttering around looking at little fishies, my SAC rate is a little higher than my friends. When I'm recording data, screwing around with lift bags or 'supervising' newer divers, my SAC rate is much, much higher. I imagine my emergency SAC rate would be even higher than my working SAC. Having never been in an emergency below the surface, I can't really be sure, but I'm paranoid that it's not going to end well for me.

 

[LakeCountyDiver]

Ok well let me ask this. How do you properly calculate your SAC on a multilevel dive?

 

[TSandM]

There are two ways, one of them more accurate than the other. The first is to note the time and pressure at two points while you are at roughly the same depth during the dive, and do the calculations from there. The second is to use the average depth of the dive and the total gas consumption and dive time.

One would think, for heavily multileveled profiles, that the latter would be rather inaccurate, but I have to say that I have calculated my consumption for square profile dives and multileveled dives, and it comes out pretty much the same (within the variation it has from dive to dive, anyway).

 

[LakeCountyDiver]

There are two ways, one of them more accurate than the other. The first is to note the time and pressure at two points while you are at roughly the same depth during the dive, and do the calculations from there. The second is to use the average depth of the dive and the total gas consumption and dive time.

One would think, for heavily multileveled profiles, that the latter would be rather inaccurate, but I have to say that I have calculated my consumption for square profile dives and multileveled dives, and it comes out pretty much the same (within the variation it has from dive to dive, anyway).

Thank you I just learned something. I mainly do multilevel dives so I have never kept track of my SAC and now I think I will start noting it.

 

[Charlie99]

There are two ways, one of them more accurate than the other. The first is to note the time and pressure at two points while you are at roughly the same depth during the dive, and do the calculations from there. The second is to use the average depth of the dive and the total gas consumption and dive time.

One would think, for heavily multileveled profiles, that the latter would be rather inaccurate,.......

Using the average depth is the proper calculation, not just an approximation, so you shouldn't have any reservations about calculating over the entire dive, using the average depth, whether square profile or multilevel. Since measuring the presssure difference over just a 10 or 20 minute period is likely to have errors, I actually prefer measuring over an entire dive.

The errors, if any, would only come from extraneous factors such as tank cooling the beginning of the dive, or freeflows during a surf exit.