V Planner Deco Conservatism

[nereas]

Ain't that the truth.

Doing air dives with no deco gas just is just stupid so I don't really see they point in trying to validate which profile is "correct". They all are and at the same time none of them are!

Even though I completely agree with you, any minute now a slew of vintage pro's is going to chime in and tell you why you are dead wrong on this, and why USN are the best tables since sliced bread.

 

[sea2summit]

Remember you can play with your gradient factors as well and that may have an affect on the tables it gives you to dive. 15/85-30/85 your probably in the right area depends on where you want to spend your time.

 

[rjack321]

Remember you can play with your gradient factors as well and that may have an affect on the tables it gives you to dive. 15/85-30/85 your probably in the right area depends on where you want to spend your time.

Neo-Haldanean Buhlmann models use gradient factors. V-planner does not.

 

[Rhone Man]

One other thing that my TDI manual points out - USN tables are calculated on the basis that bottom time includes descent time - most deco planning softwares are not. To compare like with like, you need to deduct your descent time from the bottom time that you enter in the planning software.

 

[Sabado]

I appreciate all the discussion. While I would not perform this dive as I have planned (Bring Deco gas - 99, use EANx 28, etc), I was trying to illustrate the conservatism I was seeing with V Planner and seeing if I wasn't the only one and if there was an explanation. Even with Deco gas at 20', you cut that stop in half...you still have quite a bit of deco.
Cheers

 

[Blackwood]

One other thing that my TDI manual points out - USN tables are calculated on the basis that bottom time includes descent time - most deco planning softwares are not.

VPlanner counts descent towards BT.

 

[nereas]

I appreciate all the discussion. While I would not perform this dive as I have planned (Bring Deco gas - 99, use EANx 28, etc), I was trying to illustrate the conservatism I was seeing with V Planner and seeing if I wasn't the only one and if there was an explanation. Even with Deco gas at 20', you cut that stop in half...you still have quite a bit of deco.
Cheers

Exactly, with 100%O2 you cut deco time in half or more.

I have noticed that when diving to 110 fsw with EAN32 and going into deco, my DiveRite NiTek HE gives a certain amount of required deco time with EAN32, a very good gas, and then when I switch onto my O2 bottle and switch gasses on the Nitek, the deco obligation now goes to 1/2 of whatever is left at 20 fsw.

My personal view is that the VPlanner is probably quite correct about the extended deco times required when diving and deco-ing on air. But as was pointed out before by RJACK, there is no reason to test it, since I would never dive with air deeper than 50 fsw anyway, or else only in places like parts of Mexico where I cannot get nitrox anyway. And in the latter case, I certainly would not rely on the USN deco tables, but rather on the Nitek with air data, and VPlanner as a backup for the slate.

Therefore USN air tables give me pause, anytime I look at their charts, which I seldom do anymore, relying instead on NAUI or SSI reductions of USN to determine NDL, and with VPlanner to determine deco. With modern software and dive computers, USN tables have become pretty much unnecessary.

When planning a deco dive, I always use VPlanner and write up a slate with various depths and times. Then I execute the dive with the Nitek HE, and it normally comes quite close to what VPlanner has given me. I tack the extra time onto the end of the 20 fsw stop on O2, if any. Plus that way, if the Nitek fails or malfunctions, I still have the slate and the bottom timer as a backup to measure deco with.

But it all boils down to field testing in gradual steps for yourself, ramping up before anything deep and long.

I am still waiting for some old salt to chime in and say USN tables were good enough for his grandaddy and they are good enough for his grandkids and himself as well. But not yet apparently???

 

[battles2a5]

There is a reason people call the Navy tables "bend and mend". Those tables were never intended to be used by sport divers. They were meant to be used by Navy divers, in Navy operations, with Navy surface support and a pot on stand-by. Not to mention that the average Navy diver is in better shape than the average sport diver and the acceptable rate of DCI occurrence is probably a lot higher when you have a chamber 10 steps away.

Even if you run Buhlmann with the GFs set to 100/100 you get 13 minutes of deco. So just riding the critical m-value of the controlling compartment on Buhlmann with GFs that assume no free phase gas you still gives you a lot more deco. This shows how aggressive the Navy tables are. Truthfully, nominal conservatism on V-planner is still rather aggresive. Most people will start on +2 and +3 and work their way down from there as they gain experience with the model and as their body permits.

 

[nereas]

...Truthfully, nominal conservatism on V-planner is still rather aggresive. Most people will start on +2 and +3 and work their way down from there as they gain experience with the model and as their body permits.

Exactly! I use +3 on VPlanner, and have even found this at times to be cutting it close, in terms of comfort afterwards.

And by tacking the extra VPlanner time onto the 20 fsw O2 stop, I effectively am enabled to convert the Nitek HE into VPlanner output.

 

[Blackwood]

Exactly, with 100%O2 you cut deco time in half or more.

I have noticed that when diving to 110 fsw with EAN32 and going into deco, my DiveRite NiTek HE gives a certain amount of required deco time with EAN32, a very good gas, and then when I switch onto my O2 bottle and switch gasses on the Nitek, the deco obligation now goes to 1/2 of whatever is left at 20 fsw.

You'll see the same thing if you read up on the ratio deco methodology.

Each bottle cuts that segment time in half.