UWATEC "Smart" users: how useful is the RBT model?

[two.crows]

You're asking for a rather huge number of variables to be plugged into a computer. How is it supposed to account for solo vs. buddy dives, high SAC vs. low SAC?

If you mean variables I can plan beforehand: by adjusting the target pressure at the end of dive to the circumstances. If you mean variables that come up unexpectedly: if they affect my consumption, I understand the computer factors them into the equation.

Yes?

 

[victor]

The danger of using this tool is relying on it without understanding how it works and what its limitations are.

Changing air consumption is an example of a variable that could, and I emphasize could, get you into trouble.
e.g. A drift dive down to the end of the reef.
It’s a leisurely drift dive in 1 to 1.5 knots of current descending from 40ft at the start of the dive to 100ft.
Air consumption on the first 3/4 of the dive is negligible.

Now you have to stay at the end of the reef while swimming against the current.
As soon as you try and hold position at the end of the reef your air consumption trebles.
Once the sample rate of the computer catches up and recognizes the change it warns you that you have insufficient air to reach the surface.
Air consumption punching into a 1.5 knot current while trying to do a free ascent, is worse.
Probable result a rapid ascent and an OOA during the safety stop with the diver drifting down current.

If you know the profile and understand the software you can just dive ignoring RBT for this dive.

 

[two.crows]

(Apart from the fact that that profile is an OOA waiting to happen in the first place.) So what you are really saying is that the predictive model is not good enough? Because it can't know that your trebled SAC at the end of the dive is not a momentary anomaly? Makes sense. I gues this means we need to have tools for improved modelling - e.g. that allow to download a complex plan (the implicit "plan" that appears to be currently implemented would be one with a rectangular profile/constant SAC ) and having the computer keep track of the deviations:idea3: .

 

[TPete61]

As far as what the computer is calculating being Solo or not has no effect on RBT neither does High or Low SAC. The computer is making a constantly updated assumption it would change if your SAC rate changed or a buddy started using you air.

 

[bperrybap]

Interesting, thank you. Has anyone experienced a situation where it actually would have been a poor decision to follow the computer's RBT advice?

I don't have a UWATEC AI computer, I have a different
vendors AI computer, but the same will apply.

I've been in situations on a nice reef wall dive where the current
starts out small to none and at some point it changes to the
direction you were going. This means that your SAC will be higher
on the way back because you will be swimming against the
current. So if you waited until your RBT started to approach
your bottom time as a signal to turn around, you might not
have enough air to make it back.

You may be able to return at a shallower depth to reduce
air consumption on the way back but if the current
really picked up or you were at a shallow depth already,
the added resistence of the current may use more air than is
saved by reducing your depth.

I like seeing RBT. I think it is a valuable tool but you do
have do add some common sense in as well.

--- bill

 

[Puffer Fish]

Interesting, thank you. Has anyone experienced a situation where it actually would have been a poor decision to follow the computer's RBT advice?

I think viewing that information as "advice" might be a mistake. I have one and view the information from it as anything from interesting to really important. Depends. As the dive profile and conditions are far more important, it would be a mistake to take the historical information (which is what a RBT is based on) and assume it is valid for the rest of the dive.

One of the somewhat important pieces of information one can get, is that of how you compare with your dive buddy...that, by itself is really valuable, as it lets both of you know who will run out first. All things being equal, this is easy to know if you both start with the same size tank and the same pressure, but that, for me, is normally not the case. With the RBT calculation, you get the information very early on in the dive. It changes how much time we spend looking at each other's pressure and how we should be managing our dive.