SAC Rates??

[Greg G.]

In the context of tech/deco diving, then yes, I guess it would be important. My humble apologies for assuming we were discussing sacs and rec. diving. Most divers I know (including myself) dive exclusively non-deco (rec) diving using standard 80cu. ft tanks, with maybe an occasional 100. In planning these types of dives, I don't know of anybody who calculates their sac. Most divers I know (including myself) pretty much know how to manage their air supply from prior experience and apply common sense, e.g. if you know you're an air hog, you probably won't want to go to 90ft+ depths, or if you do, start your ascent early while you still have half a tank. At least that's what I do, the rule of thirds on deep (90-120fsw) dives just doesn't work for me. Dives are mostly planned around the location and conditions, e.g. depth and currents present.

More power to youse guys who enjoy the deco stuff and all it entails. For me, in my humblest of preferences, all those precise calculations of deco stops and air mixes takes all the fun out of it. Basic nitrox is as far as I care to go.

Originally posted by roakey

It's *extremely* important for planning gas consumption on decompression dives.

It has little use in the recreational arena.

Roak

 

[roakey]

Originally posted by Greg G.
In the context of tech/deco diving, then yes, I guess it would be important. My humble apologies for assuming we were discussing sacs and rec. diving.

Actually Greg I took your response as a response aimed at rec diving, I just wanted to make clear that there are some reasons for knowing it for technical diving.

You're right, there really is no reason in rec diving to know your SAC. In rec diving your plan, if limited by gas, is "OK at X psi" we'll turn the dive." Or "At X psi we'll surface." SAC is a non-issue.

Even when doing weenie cave diving you don't have to know your SAC: "OK, we'll go in until the first person hits thirds and then turn the dive." No SAC necessary.

SAC comes into play when, for example in caving, you want to go such-and-such a place in the cave. Knowing the depth, distance, your swimming rate and your SAC will let you determine the amount of gas you need to carry to accomplish that objective. For rec diving, if you want to go to a certain location, you pilot the boat there; you don't start two thousand feet away from it just for grins.

The need to know your SAC is most important in deco diving. If you try and do a cave dive to a location and you don't have enough gas, you simply turn the dive early. No problem. But if you’re in deco you better have enough gas or you may end up bent. So you figure out your SAC for your bottom gas and your deco gas and make sure you have plenty. Maybe even more than plenty.

Note that also most technical divers have two SACs computed, one for under load and one for resting (used to compute deco gas requirements). My under load SAC was computed at 60 feet while swimming at a very good clip, well over my normal “moseying around” rate but not at a panic rate. It was a long-term sustainable rate (but I was huffing a bit at the end! ). My other SAC was done while hanging out on a line at about 20 feet doing absolutely nothing. This tells me at what rate I’ll consume my deco gas.

I can use those two numbers to compute what kind of gas requirements I have for a particular dive, but only when necessary. When I’m rec diving or doing my weenie cave dives, gas management is much, much simpler and my SAC doesn’t even enter into the picture.

For most rec divers, SAC is the equivalent of “Mine’s bigger than yours!” but in this case, smaller is better.

Roak