Riding Blind with your DSMB reel

[boulderjohn]

BTW, one of them did a very high altitude deco dive a few years after that. He and his buddy, also from our group, were still in the "no computer" mode of diving, but I don't know how they calculated their deco. Perhaps they did make an adjustment because of that higher altitude. Circumstances were such that they never completed their deco, so we won't know the effect their profile would have had if they had completed it. (His buddy is still a no computer--ratio deco only advocate, if that is a clue.)

His body was never found, and it was quite a few months before his buddy could walk again.

 

[PfcAJ]

They ignored altitude because they were taught to ignore altitude when using RD. They were 8 feet deeper than they thought they were.

Well 8ft deeper is the way to go if you have to make a goof.

Can't help you with the altitude thing, you already know what I think about that.

Going back to Remy's question about UTD's ratio deco class, my recommendation is to keep your wallet in your pocket and run as fast as possible in the opposite direction.

 

[KevinNM]

The GUE tech 1 presentation I have has multiple slides on the sane version, but I would assume it's a fairly long class in the actual 6 day tech 1 class.

 

[boulderjohn]

Well 8ft deeper is the way to go if you have to make a goof.

I don't think we are communicating effectively. They thought their average depth was 150 feet, and they planned their deco accordingly. It was actually 158 feet, so they should have done 7 more minutes than they actually did. That does not count the other mental errors they made, including a much too slow ascent to their first stop, meaning that they really had more bottom time than they had planned, and a miscalculation on their total stops time, meaning that they actually did less deco than they thought they had done.

 

[PfcAJ]

I don't think we are communicating effectively. They thought their average depth was 150 feet, and they planned their deco accordingly. It was actually 158 feet, so they should have done 7 more minutes than they actually did. That does not count the other mental errors they made, including a much too slow ascent to their first stop, meaning that they really had more bottom time than they had planned, and a miscalculation on their total stops time, meaning that they actually did less deco than they thought they had done.

Gotcha.

The entire thing sounds like they were totally unprepared for the dive. Following tables would have resulted in the same result if the didn't know their depth, didn't ascent at the correct rate, and ignored altitude.

Just as a computer doesn't help you if you input the wrong info (done that before, myself) any deco plan will be wrong if you don't stick to the parameters it was based on.

 

[PfcAJ]

Seems based on this conversation that whatever UTD is teaching for calculating the deco time is fundamentally different than what GUE is teaching.

You sort out the deco schedule before hitting the water and if there's a variation from what's planned (say you're 10ft deeper than your planned avg), you either adjust the deco time a bit longer or cut your bottom time in order to end up with the same planned deco.

Alternatively, if your bottom time ends up being cut short, you shorten the planned deco time.

It's not like you hop in the water and figure all this stuff out on the bottom, which kinda sorta seems to be what John's describing?

 

[boulderjohn]

Seems based on this conversation that whatever UTD is teaching for calculating the deco time is fundamentally different than what GUE is teaching.

You sort out the deco schedule before hitting the water and if there's a variation from what's planned (say you're 10ft deeper than your planned avg), you either adjust the deco time a bit longer or cut your bottom time in order to end up with the same planned deco.

Alternatively, if your bottom time ends up being cut short, you shorten the planned deco time.

It's not like you hop in the water and figure all this stuff out on the bottom, which kinda sorta seems to be what John's describing?

Oh, all of that was preplanned, but they just did not execute the dive as expected. You can't adjust your deco plan to meet the unplanned changes in the dive if you did not realize you made those unplanned changes. They planned to have an average depth of 150 feet, and they thought they had accomplished that.

But, BTW, the UTD instructor I had really did do the planning as you go route on some of his dives. He didn't teach it that way, though.

 

[The Chairman]

Another dozen posts and still no benefits presented for using RD over a PDC.

 

[PfcAJ]

Another dozen posts and still no benefits presented for using RD over a PDC.

Wellllllll

For one with RD you're not reliant on a computer. I like that a lot. If my bag of computer(S) gets lost, damaged, stolen, ran over by a truck, I can grab a watch and a depth gauge and carry on without issue.

Two you can willingly make adjustments to your plan and know the result before a computer will be able to tell you. I recall a neat dive where we did just that: we were on one wreck for a while the decided to scooter a hundred yards or so to another wreck that was shallower so we could get more bottom time. We all knew how the shallower depth would impact our allowable bottom time and the resultant deco time.

I'm not aware of a computer that allows you to say "ok now I wanna go up to 130', how does that impact my dive?" At best you'll get info once you get to 130'.

RD let's you know whats going to happen, a computer let's you know what's happening.

Additionally, having a working knowledge of ratio deco lets you easily converse on the surface about the dive plan without needing to run plans either with a laptop or with your computer's dive planning feature. If the boat goes to another wreck that's shallower or deeper it's nothing to quickly rework the timeline.

 

[The Chairman]

Wellllllll

That's it? It's only usefulness is if you can't do a little "what ifs" in your head during a dive? Pfffft. So, there are no real benefits then. It's indeed a solution in search of a problem. I'll stick to redundant PDCs.