not a shearwater fan ?

[scubadada]

The trouble with the SurfGF/GF99 numbers shown by dive computers is they are a very narrow view. It comes from just the leading compartment. Other compartments are hidden, thus the first dive of the first day on x/95 and the last dive of the day a week later will have different risks for the same Indicated GF. This is the same mechanism that has been used to show excessive deep stop profiles are bad. The extra loading on slow tissues becomes an issue with repetitive dives too, but the one leading tissue is used to generate the single number which is supposed to represent risk.

I am absolutely not saying tables and silly rules are better than a live computer. I am saying that using an indication like SurfGF instead of safety stops is a mistake.

And what is wrong by designating the leading compartment?

 

[KenGordon]

And what is wrong by designating the leading compartment?

It ignores the others, they might be mostly empty, like a bounce dive, they might be mostly full, like at the end of a day of deco dives.

 

[scubadada]

It ignores the others, they might be mostly empty, like a bounce dive, they might be mostly full, like at the end of a day of deco dives.

I'm sorry, I don't understand your concern about the non-leading compartments. What is the risk?

 

[Lostdiver71]

I will switch to Shearwater when they support 3-4 transmitters instead of 2, that is my only complaint about their computers.

 

[dmaziuk]

Ps of course, not forgetting that the dissolved gas models like ZHL16C ignore a lot of things, so even if the measure was over more compartments it is still terribly simplistic.

KISS principle: the simplest stupidest one that gets you out of the water not bent (or, more accurately, bent every one in exactly the same X number of dives), is the best.

 

[KenGordon]

I'm sorry, I don't understand your concern about the non-leading compartments. What is the risk?

You know the little bar chart of saturation per compartment, or the heat maps in Subsurface? If they are all filled up with N2 it is riskier than if they are not all filled up with N2. When you surface your faster tissues will soon drop off, leaving the previously non leading slow tissues as the controlling tissue. Those elevated ‘GF per tissue’ last longer for the deeper/longer/repetitive/excessive GF low dives and so increase risk. This is the mechanism that accounts for the 2011 NEDU deep stops conclusions.

 

[dmaziuk]

I'm sorry, I don't understand your concern about the non-leading compartments. What is the risk?

The first stop on a dive is controlled by the fastest compartment, therefore on a no-stop dive we only really track the fastest compartment. Which is why you're clear as driven snow after 6 hours SI by DSAT (but don't try to fly), and why DAN studies conclude that "undeserved hits" happen "in the slower compartments".

Anything that happens in the "non-leading" compartments is not our problem.