Shearwater V65 Update

[michael-fisch]

Thanks Lynn, that was a fast answer and one that I can live with.

Michael

 

[Shearwater]

VERY roughly speaking, if your current depth is lower than your average depth, you are offgassing. So, staying at depth can and will result in a lower TTS at the end. Think of it as deco at a less than optimal depth...

The question is, how much are you offgassing? Sometimes it matters. For example one of my favorite wrecks is the Duane. It's very upright, with the crow's nest at half the depth of the deck. So, if I've spent 20 minutes on the bottom and make my way up to the crow's nest, I still have really cool things to see and do. But I'm either near deco or maybe even in it. Will exploring the crow's nest cause me to need to stay longer on deco, or less?

Delta+5 or @+5 tells me. Not only does it tell me whether I'm offgassing or not, it tells me how *well* I'm offgassing.

So, using the example given above: I'm currently at the crow's nest at 20 meters. My current Time to Surface is 15 minutes if I leave *right* *now*. That's the *fastest* I can get there under ideal circumstances. But I've got plenty of gas, and want to keep looking at the crow's nest. If I stay an extra 5 minutes here, what does it do to my TTS?

Delta+5 = -3 minutes. That means that after 5 minutes at my current depth, my Time to Surface will be three minutes less than it is now. That means that at my current depth, I'm offgassing 60% as fast as if I moved directly toward the surface (following any stops, etc.). Nice! That means it will only cost me *two* minutes to spend *five* minutes at my current depth. Seeing as I have the gas, I'll exchange 2 minutes of deco for 5 minutes of fun dive time.

The *only* difference between Delta+5 and @+5 is how those numbers are shown to the diver. Delta+5 shows only the CHANGE in TTS if I stay where I am for five minutes. If I'm currently below the average depth of my dive, that number will be positive: I'm on-gassing, and I'll take more time to get to the surface and the number will be positive. If I'm currently *above* the average depth, I'm off-gassing, and the number will be negative.

For some people, that's confusing. They'd rather simply know what the absolute TTS will be in 5 minutes. That's what @+5 is. It's a prediction of what the TTS will be five minutes from now if you don't change depth. And like was said, it's simply Current TTS + Delta+5. Same number, different presentation.

By the way, my use of average depth is certainly not correct. It's merely a rough approximation. Of course, the computer is doing a lot more careful calculations based on a large collection of tissue compartments with different parameters. There's m values and tissue speeds and gradient factors, and I'm sure a whole lot more. But it gives you the general concept!

@tmassey thank you very much for doing a much better job than I did at explaining these.

 

[BoatingDave]

VERY roughly speaking, if your current depth is lower than your average depth, you are offgassing.

Would it actually be better to say if your current depth is SHALLOWER than your average depth you are offgassing? (Rather than "lower" which could be confused with "deeper"?

 

[tmassey]

Would it actually be better to say if your current depth is SHALLOWER than your average depth you are offgassing? (Rather than "lower" which could be confused with "deeper"?

You are exactly correct. I often use "lower" for "shallower", which makes absolutely no sense. The depth number is 'smaller', but that doesn't really make it 'lower'...

I'm glad everyone was able to figure out what I meant!