Question: I just downloaded V-Planner to start learning about deco dive planning. For the fun of it, I looked at a US Navy Dive Table for 21%. The NDL for rec diving is 100 ft for 25 mins. I entered 100 ft for 24 mins into V-Planner just to see what it would do, and this is what I got...WHY? V-Planner is showing deco stops as so...but in normal rec diving, all that anyone would do for a NDL dive like this IS a safety stop of 3 mins at 15 ft. Whats up?
-Planner 3.10 by R. Hemingway, VPM code by Erik C. Baker.
Decompression model: VPM-B
DIVE PLAN
Surface interval = 0 day 2 hr 0 min.
Altitude = 0ft
Conservatism = + 2
Dec to 100ft (2) on Air, 50ft/min descent.
Level 100ft 22:00 (24) on Air, 0.83 ppO2, 100ft END
Asc to 40ft (26) on Air, -30ft/min ascent.
Stop at 30ft 3:00 (29) on Air, 0.40 ppO2, 30ft END
Stop at 20ft 4:00 (33) on Air, 0.33 ppO2, 20ft END
Stop at 10ft 9:00 (42) on Air, 0.27 ppO2, 10ft END
Asc to sfc. (42) on Air, -30ft/min ascent.
Off gassing starts at 70.8 ft
OTU's this dive: 17
CNS Total: 5.7%
83.1 cu ft Air
83.1 cu ft TOTAL
JeffG
April 4th, 2003, 05:45 PM
Hmmmmm Good Question...
Maybe you should not to too quick to sell your Dive Rite Scuba Ni Tek Computer
ScoobieDooo
April 4th, 2003, 05:49 PM
Naa,
Thanks, but I find the Bottom Timers easier to use and besides, I'm headed in a DIR direction...computers will rot your brain! Ask Uncle Pug!
O-ring
April 4th, 2003, 05:55 PM
I don't use V-planner too often, but for one thing you have the conservatism on +2 so that will make your stops longer. Another thing is that you are comparing apples to oranges...the rec NDLs are based on a dissolved gas model and this is a bubble model that takes into account dissolved gas and bubble formation.
ScoobieDooo
April 4th, 2003, 05:57 PM
O-Ring, so what should the conservatism be on?
O-ring
April 4th, 2003, 05:59 PM
ScoobieDooo once bubbled...
O-Ring, so what should the conservatism be on?
IMHO, that's a personal decision. Point this thread out to WreckWriter...I know he uses VPM and knows a lot more about it than I do. Actually Ross is on the board now too, so maybe he will answer your question.
ScoobieDooo
April 4th, 2003, 06:01 PM
WreckWriter?
?????????
MechDiver
April 4th, 2003, 06:05 PM
One other possible thing is having a SI set to only 2 hours. That would signify you still had loading from a previous dive. Not sure what values V-P would use in that case, but it tracks exposure for up to 2 days I believe.
MD
Uncle Pug
April 4th, 2003, 06:05 PM
oh... O-ring already said that...
What should the conservatism be on? What are you trying to accomplish?
Rick Murchison
April 4th, 2003, 06:08 PM
Not an exact science, is it?
Note that the Navy table with doppler limits applied has a max NDL of 20 vice 25 minutes, and while V-planner will still give you a few minutes more stop time, they're getting closer.
Now, if you really want to have some fun, look at a series of 15 minute dives to 100' with an hour surface interval.
With V-planner (VPM-b, nominal) you can do these indefinitely with a 3 minute stop, while the Navy tables require no stop on the first dive, a 3 minute stop on the second dive, 2 @ 20 and 24 @ 10 on the third dive and on the fourth dive you're up to 9 @ 20 and 28 @ 10, where it finally goes constant.
When you take your decompression course you'll be better equipped to make an informed decision on what to use for your specific dives.
Rick
ScoobieDooo
April 4th, 2003, 06:08 PM
Only trying to see how this program works in relation to US Navy dive tables and stuff. I'm just a recreational diver right now, but interested in how these programs calculate, etc. and how combined with a bottom timer might be useful vs using a computer to calculate it all for me...
ScoobieDooo
April 4th, 2003, 06:10 PM
Rick,
Ahhh, ok, thanks...I'm seeing that I know nothing about tech or deco diving to date...
WreckWriter
April 4th, 2003, 06:22 PM
ScoobieDooo once bubbled...
WreckWriter?
?????????
Wassa matter, you don't like me or something?
First thing, VPM-B is a modern deco model, Navy tales (Haldanian model) are a very old model. A LOT of folks got/get bent running the NDLs to the stops on Navy tables, a big percentage in the 90'-100' range.
Like Rick said, its not an exact science, more art than science maybe. This table will get you on the boat, unbent, pretty much every time. Its simply more conservative.
Leave your conservatism set at 2 unless you're a Navy Seal or a trialthete.
One more bit of advice: don't dive air at 100'
WW
ScoobieDooo
April 4th, 2003, 06:27 PM
WreckWriter,
Play nice-a, nice-a...
I just punched 21% in for fun, because lets face it, people DO dive 21% to 120 ft - or thats the MAX DEPTH all the PADI or US NAVY tables recommend.
MikeFerrara
April 4th, 2003, 06:46 PM
ScoobieDooo once bubbled...
O-Ring, so what should the conservatism be on?
Feel lucky?
Yes what they said!
Pick up 5 different table and you get 5 different answers. Use more than one software and you get more than one answer.
The worst part is that with different settings in the same software you will generate very different schedules.
This is one of my favorite subjects and like most I don't know crap. Except, I have increased the depth and length of my dives a little at a time. You read all the theory untill your certain you understand everything and then you realize that what counts is how you feel. If it works it's good.
Even though some guys seem to have it nailed as far as what works the scientists don't seem to be able to really explain it.
Also since there isn't any money in it it isn't likely anyone is going to do any serious research either.
WreckWriter
April 4th, 2003, 07:02 PM
ScoobieDooo once bubbled...
WreckWriter,
Play nice-a, nice-a...
I just punched 21% in for fun, because lets face it, people DO dive 21% to 120 ft - or thats the MAX DEPTH all the PADI or US NAVY tables recommend.
Have I said anything less than nice to you?
Actually the U.S. Navy air tables go to 300', people dive it too, but that doesn't make it a good idea.
WW
rossh
April 5th, 2003, 12:34 PM
V-Planner is calibrated to recreational NDL's. The Navy tables are not recreational tables - they are for the navy, and have a significant risk of DCS.
The standard recreational NDL for a 100ft dive is 16 minutes. If you set the conservatism to nominal, then you will find the results your looking for.
Regards
--
Ross Hemingway
padiscubapro
April 5th, 2003, 01:28 PM
rossh once bubbled...
V-Planner is calibrated to recreational NDL's. The Navy tables are not recreational tables - they are for the navy, and have a significant risk of DCS.
The standard recreational NDL for a 100ft dive is 16 minutes. If you set the conservatism to nominal, then you will find the results your looking for.
Regards
--
Ross Hemingway
I wouldn't go that far.. PADI (The largest RECREATIONAL agency says its 20 mins!)
I would agree most current dive computers come up with 16 or 17 mins..
No deco tables are usually based on surfacing values which are a bit more liberal than decompression oriented tables.
There are other factors also when looking at the NDL limits each table has its own rules and definition of what bottom time is.. I'll give an example I use frequently
Padi uses 100 for 20 ANDI uses 100 for 23, they look quite different don't they.. but actually they pretty close..
PAdi says BT starts on the decent and ends upon Beginning the ascent..
ANDI says bottom time starts after passing 2 meters/ 5 feet and ends upon reachine the 30 ft stop (I'm not going into the entire ANDI ascent/descent procedure)
But if you take into account a normal ascent rate the bottom times are pretty much the same.. (2 plus minutes of ascent rounded to 3 minutes), so the diver must leave the bottom at 20 minutes..
An instructor giving a class on decompression theory should cover information like this..
ScoobieDooo
April 5th, 2003, 04:12 PM
According to Table Tutor dive tables, a dive to 100 ft is more than 16 mins, I believe I am seeing 25 mins. Quite a differance in times, 9 mins to be exact.
Rick Murchison
April 5th, 2003, 07:32 PM
rossh once bubbled...
The Navy tables ... have a significant risk of DCS.
That sorta depends on how you dive 'em. For example, in my previous post, where I proposed a series of repetitive dives of 15 minutes bottom time to 100' with one hour surface intervals, the Navy tables actually dictate a far more conservative profile over time (after the first dive - and if a safety stop is used the first dive's allowed direct ascent becomes a moot point) than does V-planner - so if the Navy tables have "significant risk" where does that place V-planner?
Indeed, for air dives at typical recreational depths and times, strict adherence to the Navy tables on repetitive dives will result in shorter allowable bottom times and/or longer surface intervals required than V-planner (or any dive computer, for that matter) just about every time.
Another example: Using the Navy tables, even if we consider the three minute safety stop as a decompression stop, doing a series of 40 minute dives to 60' will require a minimum surface interval of 1:16 between dives one and two, and 2:39 between all subsequent dives. (Using the Navy tables in "no decompression" mode would require surface intervals of 2:59 between dives 1 & 2 and 4:03 for subsequent dives - and using the Navy Tables with doppler limits applied (the SSI modification) would require surface intervals of a whopping 4:26 between dives 1 & 2 and 8:00 (!) between subsequent dives) Using V-planner (VPM-b, nominal), for no-stop dives to 60' for 40 minutes, a surface interval of only 30 minutes is required between dives 1 & 2, and 40 minutes for subsequent dives. So, again, as a practical matter, the Navy table is far more conservative and has a significantly lower risk of DCS than VPM.
It is "common knowledge" that the Navy tables are for young, fit Navy divers and carry a "significant risk of DCS"... but common knowledge, when the actual numbers are crunched, just doesn't hold water. The Navy tables - in recreational no-stop diving, and especially when used for repetitive diving - are in fact very conservative.
Rick
WreckWriter
April 5th, 2003, 08:27 PM
ScoobieDooo once bubbled...
According to Table Tutor dive tables, a dive to 100 ft is more than 16 mins, I believe I am seeing 25 mins. Quite a differance in times, 9 mins to be exact.
What exactly are "table tutor" tables? Is that what you're actually diving?
If it gives you 25 at 100 its obviously Navy tables in a different wrapper.
Bottom line is that you can dive Navy tables and have more perceived time available or you can dive a modern algorythm (VPM, RGBM, modified Buhlmann) and be safer and feel better after your dives.
Those of us that have been diving for more than a few years all dove Navy tables in the past, most of us managed ok. What Rick says is true, for repetitive dives the Navy tables get pretty conservative. Based on what I've seen though (no clue if stats would bear this out) I've always felt that there might be a problem in the 80-1-- foot area as most of the divers I've seen get bent have gotten bent in this range. Coincidence? Maybe.
WW
padiscubapro
April 5th, 2003, 10:22 PM
WreckWriter once bubbled...
What exactly are "table tutor" tables? Is that what you're actually diving?
If it gives you 25 at 100 its obviously Navy tables in a different wrapper.
Bottom line is that you can dive Navy tables and have more perceived time available or you can dive a modern algorythm (VPM, RGBM, modified Buhlmann) and be safer and feel better after your dives.
Those of us that have been diving for more than a few years all dove Navy tables in the past, most of us managed ok. What Rick says is true, for repetitive dives the Navy tables get pretty conservative. Based on what I've seen though (no clue if stats would bear this out) I've always felt that there might be a problem in the 80-1-- foot area as most of the divers I've seen get bent have gotten bent in this range. Coincidence? Maybe.
WW
It also depends on the schedule.. Some NAVY schedules are know to have some serious risks.. the 150ft table comes to mind.. doing repetetive 150ft dives has a known dsc risks.. I have seen various numbers published (depends on wht they are calling a hit) anywhere from 6% on the low side to as much as 14% on high estimates.
The navy tables were basically designed as deco tables and If I remember correctly the surface halftime used is the 120 min compartment, while many other tables use the 60 min compartment.. This is definately a necessity if you are deco diving on air because you are still on gassing in the slower tissues.. The navy doesn't do gas switches like tech divers do.. decoing on 50% or 100% besides helping the offgassing, stops the slow tissues from ongassing..
on 50%@20 you are at an EAD of .5feet, shallower than this, you are at the equivalent of altitude..
on 50% @ 30 feet you are at an EAD of less than 7 feet..
SO all your long stops are shallower than even the 10ft stop..
padiscubapro
April 5th, 2003, 10:25 PM
ScoobieDooo once bubbled...
According to Table Tutor dive tables, a dive to 100 ft is more than 16 mins, I believe I am seeing 25 mins. Quite a differance in times, 9 mins to be exact.
There SHOULD be a difference like I stated earlier, no deco tables and decompression oriented schedules use a different limit for the surfacing gradient.. Tables based on Navy limits also use different limits on what is good/ bad.. the 2 things you must consider is (1) that to the navy getting bent isn't a problem they have chambers and you are replaceable..(2) most other tables have been modified to limit when bubble have been detected.
Even my old us divers monitor 2 which uses a Spencer model only allows 17 mins NDL@100
ScoobieDooo
April 5th, 2003, 10:26 PM
Table Tutor is a free scuba dive table shareware program...
