[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