Riding GF99 instead of mandatory/safety stops

[BlueTrin]

Because it's decreasing more or less monotonously. E.g. your fist stop is controlled by the fastest TC that also has the highest M-value, the next controlling compartment will have a lower one -- but not "abruptly" lower.

The computer has to extrapolate of course: you can't go up until all TCs have off-gassed enough, so when the leading TC changes (at a stop or during ascent), that has to be factored in before you tell the user how long and how deep their next stop is going to be.

Ah ok I think I get it now.

It’s a funny one actually.

 

[inquis]

Ah ok I get it, you mean that the first derivative is changing?

The GF99 is continuous across TC changes, and the first derivative is discontinuous across them.

(Yes, "continuous" is a little bit of a stretch given discrete-time computations by the computer, but that's effectively how it works. The instant the controlling tissue GF99 drops below the next-highest GF99, it ceases to be controlling. In that instant, the two GF99s are darn close to each other.)

 

[dmaziuk]

I'm still thinking in the context of OP's question (sorry, I have an attention span, its a curse).

Continuously "riding" GF99 as computed by Shearwater is probably a bad idea if it's computed relative to 100/100 because most people seem to believe 100/100 is too aggressive.

Continuously "riding" the M-value line as defined by your Hi/Lo conservatism settings should be OK (practical difficulties aside) but will get "bumpy" when the leading tissue compartment changes: the TC you're switching to can be
- at its M-value, in which case you'll have to stop, or
- below its M-value but with slower off-gassing rate (half time), so you'll have to slow down. Or, rather, up.

In staged decompression those bumps will be folded into deco stops.

 

[inquis]

Continuously "riding" the M-value line as defined by your Hi/Lo conservatism settings should be OK (practical difficulties aside) but will get "bumpy" when the leading tissue compartment changes

The equivalent to riding GF99 along the GF Line in this manner is to follow the ceiling up. The only bump when the controlling TC changes is to the ascent speed.

 

[dmaziuk]

The equivalent to riding GF99 along the GF Line in this manner is to follow the ceiling up. The only bump when the controlling TC changes is to the ascent speed.

Yes. To slower speed and in the degenerate case: to 0. (By numbers: I've no idea if 0 could actually happen IRL.)

 

[BlueTrin]

Yes. To slower speed and in the degenerate case: to 0. (By numbers: I've no idea if 0 could actually happen IRL.)

I don’t think 0 is possible: as a hunch if you had 0 it means that one tissue is holding you but is not offf-gassing at the depth it is holding you at (unless you run GF = 0? )

 

[inquis]

LOL, 4 inches per minute is close enough to 0 for me (e.g., a 30 minute stop).

 

[dmaziuk]

I don’t think 0 is possible: as a hunch if you had 0 it means that one tissue is holding you but is not offf-gassing at the depth it is holding you at (unless you run GF = 0? )

Yeah, you're right: you keep switching to ever-slower ascent rates. It may have to be 4 inches per minute, but you'll never completely stop.