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

[two.crows]

I think the concept of integrating pressure, depth and consumption into one parameter - RBT - is really quite, ahem, smart. At least in theory. Because that's exactly what I would be doing in my head anyway. But how good/useful is it in practice? What's your experience? Do you look at your RBT when you dive? Do you act based on it? Or do you find that you are usually ignoring the recommendation and work it out in your head? (Not that I'd mind, I was raised on tables all the way.) Or (!) do you find that the RBT actually takes you closer to coming up low on gas then you normally would have been?

Thanks for sharing your experience.

 

[rookers]

I ignore RBT when I have it in computer mode. I actually use my smartcom in gauge mode a lot on deco dives just as an SPG/backup time and depth tracker.

 

[xiSkiGuy]

As long as you understand the assumptions that it is making, it can be a useful tool: Sort of an added reassurance to the plans and calculations in your head. Just remember that any given reading assumes that you will continue to consume gas at the same rate, stay at the same depth, and will ascend at the max rate it (the computer) allows to get to the surface with a reserve of whatever psi you select. It cannot predict having to share air with another diver and should not replace rock bottom calculations or proper gas management.

I do look at it when I dive, but I never dive until it tells me to ascend and hope everything will be alright. I treat the NDL number on the computer the same way. I get into the water with a plan cut by V-planner and do not rely on the deco info it (the SmartTec) gives me. Time, Depth, and max depth are by far the most important.

 

[MichaelBaranows]

I use the RBT all the time. You have to realize the computer is always recalculating your RBT. I am still diving non-deco dives so I feel perfect fine diving relying on the computer. I don't see a reason for buying one of Smart computers if you are just going to do dive in in gauge mode. If I am just going to dive in gauge mode I might aswell buy a set of gauges cause it will be cheaper.

 

[two.crows]

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

 

[soldave]

Can't answer this second question, but I have a Smartcom and I look at the RBT quite a lot. It gives you a good idea of how your current breathing rate, combined with the depth you're at and remaining tank pressure, will affect the length of your dive. Quite a nice tool to have IMO.

 

[caveseeker7]

I still have my old Uwatek Air Console, the grey brick, which calculates RBT also.
I found gas integration a good tool, RBT as well as excertion warnings during the dive,
the ability to analyze the downloaded data afterwards. It was quite intresting to see
at what times during a dive my gas consumption was high and allowed me to work
on that specifically. A good tool for learning I believe.

I consider RBT as good a tool as TTS (Time To Surface) on non-integrated computers,
and indeed used it as a tool to plan the next dive, as well as adjust the dive plan as needed.

 

[CompuDude]

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

Haven't experienced one, but I can give an example: If your RBT is under 10 minutes and your OOA buddy needs an air share, your air needs just shot up DRAMATICALLY (well over double, considering stressed SAC rates), and you probably won't have enough gas to do a proper ascent and safety stop. Sure, it'll recalculate in short order and tell you that you don't have enough gas, but the added screaming from the computer isn't going to help you at that point.

I use mine as a general cross check to what I had in mind anyway from my dive plan. It's nice to see when the numbers mesh up, and should they ever differ dramatically it's food for thought and good to consider why they might. Generally it's pretty close on easy dives, but I wouldn't want to ever depend on it blindly. You have to bear in mind what it is doing and how, so you can see where it falls short and know how much to compensate.

 

[two.crows]

... because the OOA situation should be accounted for by the reserve pressure you tell the system to target for, when you surface, not part of the regular plan. In the situation you are describing, the dive is over, regardles of the RBT. Of course - but that should go entirely without saying - you have to adjust the target surface pressure to the plan, i.e. have enough for your own as well as your buddy's ascent.

The question I really have is: how should a plan be different from the RBT model? And if it should be, can't we just write different (more conservative?) RBT models? And if it doesn't have to be, then where do the reservations come from? After all, if you view it operationally, isn't RBT exactly the same thing as the mental calculation we actually do perform, then distill into a single decision: stay or ascend?

So, can a tool like RBT actually lead to sloppy gas management, because it does not account for contingencies that we do account for in our head?

 

[CompuDude]

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?

I think there is a limit to what can be expected of a computer. And what works well for you wouldn't work well for anyone. Perhaps it would be best if they just left the feature out... but that wouldn't help sell computers, and an awful lot of people seem to like the feature...