Getting Lost in Deco Theory

[Garf]

Well, I've done me quite a few deco dives at this point, and I'm starting to read around the subject more and more.

I've been using V-planner to cut tables until I got the VR3, now flying the VR3 with tables as backup.

I'm just curious to know what models people follow. there's an astonishing material around about gradient factors, Buhlmeunn, M Values, RBGM models, VPM and VPM b etc etc etc.

I'm just keen to hear what people actually use to dive with, or cut their custom tables with if they use a VR3.

Cheers folks

PS. Both the VR3 and V Planner get me out of the water feeling 100% better than whatever ZX81 was used to program the suunto models.

[Brian Donaghy]

Originally Posted by Garf

I've been using V-planner to cut tables until I got the VR3, now flying the VR3 with tables as backup.

Okay, I'm curious as well. I've never understood why anyone would do this. I don't understand what benefit the computer provides as a primary deco indicator. Could you explain how you would plan the deco & gas management for a simple one switch stage deco dive? What is the difference between your tables/gas management plan vs what the VR3 says?

Originally Posted by Garf

I'm just curious to know what models people follow.

Usually VPM-B after a fashion, but it depends who I'm diving with.

[Mark Chase]

[quote=Brian Donaghy]

Okay, I'm curious as well. I've never understood why anyone would do this. I don't understand what benefit the computer provides as a primary deco indicator. Could you explain how you would plan the deco & gas management for a simple one switch stage deco dive? What is the difference between your tables/gas management plan vs what the VR3 says?

Basically for OC I plan the dive on Decoplanner using 20/80GF. I will put in planned maximum depth or multilevel if I am definite that I will multilevel the dive and insert the deco gas plan. This will map my dive in terms of maximum bottom time for the available gas and provide data on required deco gas quantities.

Then (prior to having two VR3's) I will slate this with the normal +/- profiles and 100/100gf bail out plan.

The actual dive on the VR3 will almost always have less deco than the planned dive, as the actual dive depths are almost always shallower than the estimated dive depth. As an example here is a dive on the Duke planned for
35mins at 55m



As you can see we were above 55m for most of the dive and then dropped down to 57 to look at the prop.

With two VR3s I don’t use tables at all and I can do any profile I like within gas planning limits. The VR3 will show me time to surface on available gas and from experience I know exactly how much deco I can squeeze out of my two 7ltr stages. When I get to my pre set limit of deco gas time I can choose to go up then. Bottom time and depth are not particularly relevant any more. The TTS figure controls the dive.

I like the freedom this gives me I just do the dive with little or no consideration of depth or time. All I need is a worst-case bail out 100/100gf plan in case both VR3s pack up. I normally commit this to memory before the dive. For the above dive its 35mins with 25@6. That’s all I need to know for this dive. I divide the remaining time over the 9,12,15m stops so it would be 5@9 3@12 2@15


When I was on the VR3 and Andyp was still on tables I would usually beat his tables by 10 or 15mins using the VR3 on this sort of dive. However shaving deco is not the reason why I got it. I got it so I am not restricted to the dive plan.

ATB

Mark Chase

[Brian Donaghy]

Originally Posted by Mark Chase

The actual dive on the VR3 will almost always have less deco than the planned dive, as the actual dive depths are almost always shallower than the estimated dive depth.

Sounds like an estimation/contingency planning issue more than anything else.

Originally Posted by Mark Chase

As an example here is a dive on the Duke planned for
35mins at 55m

Well if I run it on V-Planner (VPM-B, +2 conservatism, 1m/min ascent form 6m - surface) I get a total run time of 105mins for 37mins BT at 57m on 18/45 with 50% & O2 for deco gases (you didn't specify so I assumed you would make good choices ) Much the same as your profile (as far as I can see).
37mins at 53m (more realistic average depth) (with conservatism at +1 given slow ascent to surface) I get 93mins runtime. More than the 10 minute advantage you say the VR3 gives.

In a nutshell, I do not believe it is the lump of Al (for two) on your wrist which provides the perceived advantage.

The flexibility comes from understanding and planning. If I wanted to go a couple of metres deeper to see something I'd okay it with the team and then we'd add a little to the deco as necessary.

[Mark Powell]

I use V-Planner and so VPM to plan my dives.

The main reasons for this is that the deco schedule suits what I like to do, i.e. a gradual ascent in the mid part of the dive. It is also very user friendly and it's a good demo tool for showing a number of points.

I use the VPM-B model as I think the original VPM-A was too aggressive. However I do add in additional time in the shallower stops (9 and 6m) for longer/deeper dives dives. Interestingly Ross has added a feature to the new version which seems to do the same thing. I haven't used it in anger yet so can't comment on the difference it makes.

[Mark Chase]

Originally Posted by Brian Donaghy

Sounds like an estimation/contingency planning issue more than anything else.


Well if I run it on V-Planner (VPM-B, +2 conservatism, 1m/min ascent form 6m - surface) I get a total run time of 105mins for 37mins BT at 57m on 18/45 with 50% & O2 for deco gases (you didn't specify so I assumed you would make good choices ) Much the same as your profile (as far as I can see).
37mins at 53m (more realistic average depth) (with conservatism at +1 given slow ascent to surface) I get 93mins runtime. More than the 10 minute advantage you say the VR3 gives.

In a nutshell, I do not believe it is the lump of Al (for two) on your wrist which provides the perceived advantage.

The flexibility comes from understanding and planning. If I wanted to go a couple of metres deeper to see something I'd okay it with the team and then we'd add a little to the deco as necessary.

This is not a deco race, I am well aware that Vplanner reduces deco time and I look forward to VPMB being available on the VR3 in 2005. This is all about flexibility. Understanding and planning becomes redundant when you’re faced with un-dived wrecks or new sites. When I first dived the Duke I planned for 30 @ 58m as the wreck is in the book at 60m, same for the Illinois 30 @ 68 as the wreck is down as a 70. In fact the dive is more like a 62.

Moving on to CCR diving the VR3 really excels. There are no gas limitations or (if using the correct dill) depth limitations within reason and you can do anything you like. The VR3 lets you dive with a blank sheet.

When in Egypt recently we were on a 20m site called the Huts. We got bored and dropped down to 40 for a look found a drop off and dropped down to 64 then we found a canyon & cave so we had a look at that at around 62m then we started to ascend based on TTS and run time. On the way out we found a chimney at 47m so sod it we just had to stop and do that.

Total dive planning none, total gas planning none required (ignoring bail out) the freedom is amazing.

A friend of mine joined a serious tec diving group called Team Delta. He turned up with his VR3 and got the mick taken out of him. Now 18months later they all have VR3’s

VR3s are not for every one but I dived tables for years before got a VR3 and I know what I prefer.

ATB

Mark Chase

[Brian Donaghy]

Originally Posted by Mark Chase

This is not a deco race,

Agreed.

Originally Posted by Mark Chase

Understanding and planning becomes redundant when you’re faced with un-dived wrecks or new sites.

I'd say they become more important.

Originally Posted by Mark Chase

The VR3 lets you dive with a blank sheet.

I didn’t really want to get into a computers vs <something else> argument. I’m sure it’s all been said before. What I’m curious about is how people plan their stage deco dives if they use a computer but have tables for back up. As I see it either the computer provides no real advantage or the option to use tables instead at any given point in the dive in not necessarily viable. Also, could you switch from a VR3 controlled ascent to VPM tables halfway thorough?

Originally Posted by Mark Chase

Total dive planning none, total gas planning none required (ignoring bail out) the freedom is amazing.

I know zero about CCR’s but I would have though that OC bail out planning would be much the same as for a standard OC dive. I would have also thought that the planning for O2 exposure, runtime (scrubber duration vs gas supply) and max depth (dil MOD vs back gas MOD) would be quite comparable, but like I say I don’t know anything about it.

Originally Posted by Mark Chase

A friend of mine joined a serious tec diving group called Team Delta. He turned up with his VR3 and got the mick taken out of him. Now 18months later they all have VR3’s

One bad apple, eh? I’m imagining a team of three divers with two VR3’s each and all six of them saying “Use Tables” because they all did the same thing on ascent to annoy the computer.

[Mark Chase]

Ill answer the questions but as information only. I stress that its a personal choice thing so if a VR3 is not for you then, fine, no problem.

I'd say they become more important.

Not with a VR3 there is little or no information you need apart from max depth and virtually no pre planning.

I didn’t really want to get into a computers vs <something else> argument. I’m sure it’s all been said before. What I’m curious about is how people plan their stage deco dives if they use a computer but have tables for back up. As I see it either the computer provides no real advantage or the option to use tables instead at any given point in the dive in not necessarily viable. Also, could you switch from a VR3 controlled ascent to VPM tables halfway thorough?

Really the computers V tables argument is a non-starter its just personal preference. If the VR3 did not exist I would use ratio deco rather than go back to the disciplines/restrictions of tables.

Obviously I am slightly different as I use two VR3's so I do not expect both to fail at the same time. However if you compare alpinist CCR diving to lets say alpinist VR3 flying using a single unit... For any dive all you would need is your 100/100GF total deco time and 6m stop time for a range of bottom times for bail out.

I use standard deco gas's. Up to 60m 32% and 80%. I will comfortably get 45mins deco out of a 7ltr of 32% and 60mins of deco out of a 7ltr of 80%

I can do any dive with any profile using just the TTS figure on the VR3. When I hit 100mins deco I am at the limit of my deco gas and I have to go up.

Planning over. Go do the dive.

This is exactly the same with the CCR. If I pre plan OC bail out on the CCR all I would need to know is the max bottom time I could do at an average depth based on 1.2pp02 that would let me deco out OC in under 100mins.

For deeper dives just use bigger tanks for bailout. Thats it.

I know zero about CCR’s but I would have though that OC bail out planning would be much the same as for a standard OC dive. I would have also thought that the planning for O2 exposure, runtime (scrubber duration vs gas supply) and max depth (dil MOD vs back gas MOD) would be quite comparable, but like I say I don’t know anything about it.

Main difference with CCR is semi-closed mode. Using semi closed re-breather mode you can suffer a total electronics failure and run the unit on inboard diluent and (by switching the feed hose) your OC bail out gas. The inboard 3ltrs becomes a 12ltr and your off board 7's become 28ltr tanks. You can do one hell of a lot of deco with two 28ltr and a 12ltr deco tanks and a 12ltr of 02

It can be imposable to carry enough bailout for some CCR dives so semi closed is the only viable option.

The VR3 monitors your 02 exposure so you can introduce air breaks or low PP02 breaks. The VR3 will prompt you to take air breaks when the CNS gets too high.

Gas supply is a non issue with a CCR the on board 3ltr will give 10hours worth of gas. Scrubbers are rated to 3 hours with an SAC of 40 in 10c water but they are often pushed to twice this and more in favourable conditions.

Max depth on the CCR is effectively the depth when your dill hits a PP02 of 1.3 so running 10/50 you could dive any depth from 6m to 120m all on a PP02 of 1.3.

One bad apple, eh? I’m imagining a team of three divers with two VR3’s each and all six of them saying “Use Tables” because they all did the same thing on ascent to annoy the computer.

I have done this several times. If you miss a 1min deep stop and fail to return to depth within 60seconds it will show use tables. Its an easy thing to do on a deep reef or inside a big wreck. It makes no difference to the dive. The VR3 will tell you you violated a stop and recommend tables but will continue to provide best guess deco information. On tables you have nothing. If you violated the profile on the tables the tables don’t give best guess info. Its up to you to guess.

Once you finish the dive the VR3 will show bad deco or deco violation depending on which way round you have the screen but it will not lock out and you can dive again the same day. After a couple of days it clears.

The VR3 will tolerate adding slow ascents and deep Vplanner stops to the profile and reduces the shallow stops crediting you for your efforts. The VR3 also has a variable ceiling deco option built in so you can push the GFs on the dive by visually seeing your position against the high M value. With a little knowledge and a VR3 you can run some very efficient deco profiles.

Fact is look at 90% of the serious non DIR deep diving expeditions around the world and you will see VR3s littered all over the photographs and their praises sung in all the write up’s. Having recently moved on to CCR I can now fully appreciate the power of the computer with variable partial pressure decompression, real time linked through an 02 sensor in my HUD CNS monitoring and with up to 10 bail out gases pre programmed into the unit allowing bail out switching to OC and back to CCR if required. The thought of doing this using tables leaves me cold.

ATB

Mark Chase

[wreckweasel]

Call me a pedant....

Originally Posted by Mark Chase

Really the computers V tables argument is a non-starter its just personal preference. If the VR3 did not exist I would use ratio deco rather than go back to the disciplines/restrictions of tables.

Be wary, ratio deco or curve shaping depends on the gases used. Its not always the same ratios.

Originally Posted by Mark Chase

Main difference with CCR is semi-closed mode. Using semi closed re-breather mode you can suffer a total electronics failure and run the unit on inboard diluent and (by switching the feed hose) your OC bail out gas.

Although of course, this doesnt get you out of a loop failure.... Madmoles site seems to show that 20% of the users who replied to the inspiration survey had suffered this.

Originally Posted by Mark Chase

Max depth on the CCR is effectively the depth when your dill hits a PP02 of 1.3 so running 10/50 you could dive any depth from 6m to 120m all on a PP02 of 1.3.

And a narc level of 52 or 68m (depending on if you think O2 is narcotic). 10/52 has only two advantages, its easy to mix and easy to calculate dil flushes.... although that wont help if your brain is screwed from too much narcs, as you discovered in egypt recently Running a dil at a depth where its a 1.3 also makes for a pretty crappy loop flush/bailout gas from a hyperoxic event.

Originally Posted by Mark Chase

Having recently moved on to CCR I can now fully appreciate the power of the computer with variable partial pressure decompression, real time linked through an 02 sensor in my HUD CNS monitoring and with up to 10 bail out gases pre programmed into the unit allowing bail out switching to OC and back to CCR if required. The thought of doing this using tables leaves me cold.

Bailout tables are a piece of piss actually. I do all my CCR dives using tables/ratio deco. You'll find (depending on which deco/physiology models you subscribe too) that using an appropriate ammount of gases produces a deco curve very similar to CCR. So close in fact, that for most of my stuff down to 70m, I just dive the bailout plan.


Anyway, enough derailing of threads.... sorry folks :P

/Zak