Calculating Average Depth

[coldsmoke]

You guys seem to be some of the most knowledgable on this site not to mention very willing to help.

I have a pretty simple question - what is the best method for determining your average depth. I have a computer but it doesn't display average depth. The way I was taught, which might not be the best, is to document your depth every 5 minutes or so and then average. Is there a better way?

I have searched around and haven't found much. Most seem to use computers.

As an aside - Bob (aka NWGratefulDiver) I wish I had taken my AOW with you! After reading what you seem to teach from either your posts or other divers giving you credit - my AOW sucked in comparison.

Maybe I can get out and do something with you this summer. How would I go about that?

Thanks.

 

[do it easy]

Maybe I can get out and do something with you this summer. How would I go about that?

Just wait at Cove 2 on any random afternoon! Tell him you're a brand new diver and learned how to dive last weekend, but your instructor was drunk, so you just wanted to practice a few things that he might have missed.

 

[Charlie99]

http://www.5thdx.com/xducation/pdf/ratiodeco.pdf discusses, starting around page 5, how to calculate "average depth" based upon depth samples every 5 minutes. I put quotes around "average depth", because the average depth discussed is weighted in such a way as to be useful for estimating decompression obligation. It isn't the true average depth that would be used for gas consumption calculation purposes.

 

[coldsmoke]

Charlie99

Thanks for the link. I will bookmark it, however, I am asking about average depth in the context of gas consumption.

 

[TASea]

Charlie99

Thanks for the link. I will bookmark it, however, I am asking about average depth in the context of gas consumption.

Without being able to get average depth from your computer, it will be difficult to make a good estimate (unless you just drop to the bottom and sit there). Five minute samples probably won't be very accurate. As an example, if I set my computer for a 15 second sampling rate it gives a much more accurate average depth than if it's set for a 30 second sampling rate.

I suggest doing some dives with someone else who can give you that info from their computer. Heck, come on out, I'll dive with you.

 

[Charlie99]

If you are trying to measure your air consumption, you don't need to know the average depth for the entire dive. If you are diving for a while in a relatively constant depth area, just looking at time, pressure and depth at one point and then again 15 or 20 minutes later will be precise enough for SAC calculation purposes.

 

[coldsmoke]

Thanks, I will take you up on that. I have been trying to get that way for some time, but work keeps getting in the way. My wife has a good friend in Seattle. I am sure we'll get there at least once this summer.

 

[Cold_H2O]

Easiest way to dive with Bob? ~ Just let us know you are heading our way.
Its usually not hard to get Bob to come diving.
Heck he even dives willingly {I don't have to pay him} with ME.

Stay with your wife's good friend and save $$ on hotel bills.
That will allow you more dive $$.
Sounds like a trip to Seattle is in your future.

The diving here is Great ~ Cove #2 is always a treat.
There are so many shore sites to dive and all of them have something fabulous to offer.

 

[H2Andy]

If you are trying to measure your air consumption, you don't need to know the average depth for the entire dive. If you are diving for a while in a relatively constant depth area, just looking at time, pressure and depth at one point and then again 15 or 20 minutes later will be precise enough for SAC calculation purposes.

yeah ... the longer the sample time, the better your results

one good way is to plan a dive to a specific depth and stay there as long as possible while doing normal "diving" stuff ... if you just sit there, you'll get an abnormally low SAC rate

 

[coldsmoke]

If you are trying to measure your air consumption, you don't need to know the average depth for the entire dive. If you are diving for a while in a relatively constant depth area, just looking at time, pressure and depth at one point and then again 15 or 20 minutes later will be precise enough for SAC calculation purposes.

I understand what you are saying, but will that give me a realistic average? I understand that all things being equal the math will be the same, but all things aren't usually equal and I would think that the most accurate result comes from the widest range of data. The accuracy is rather moot in my current profiles, however, I hope to continually advance my skills and I feel proper gas management to be an important skill.

I guess my question is - is a 15-20 minute snapshot at a fixed depth averaged over several dives more accurate than 5 minute interval recording over the course of several dives?

Thanks.