Stop Times and Run Times??

[Alastair]

OK I would agree that in the past those statements get bandied about. To take your example the "forget the 3m stop" comment is still applicable, usual practise is to pull all the 3m time at 6m (on 02) and then have a slow ascent to the surface. This is trying to make the oxygen do its good at a higher PP02; you just need to offset the tox risk by using sensible back gas breaks.

If I take your dive example of 45mins at 70m, it’s slightly unusual as I would do a shorter dive in the ocean so this isn't something I’ve done. I'd have to assume I have my scooter so I can take lots of stages and not have to worry about swimming.

In terms of the deep stops I'm slightly lazier than Graham and go for 75% of depth for the first stop which means I'd start to slow my ascent at 51m. Doesn't make a huge difference and the maths is easier.

In terms of how long I'd be in the water I would most likely do less time than you Mark, but that's what works for me. I know you make your deco conservative and wouldn't disagree with that.

Cheers
Al

[Mark Chase]

Quote: (Originally Posted by graham_hk)

Mark - 80% ATA is 0.8x8 = 6.4 = 54m. It would take 2 min to get to 54m and then 1 min per 3m to 42m (.65% ATA) so 5min. 10 min to 24m then 3 min there. I would do 50min between 21 and 6 and 3 x 12min on O2 (2 x 6 off) and 5 up

total dive time 165-170min

Quite right sorry thats why i dont do ratio deco :D I of course ment 53 not 63.


ATB

Mark

[Mark Chase]

Quote: (Originally Posted by Alastair)

OK I would agree that in the past those statements get bandied about. To take your example the "forget the 3m stop" comment is still applicable, usual practise is to pull all the 3m time at 6m (on 02) and then have a slow ascent to the surface. This is trying to make the oxygen do its good at a higher PP02; you just need to offset the tox risk by using sensible back gas breaks.

If I take your dive example of 45mins at 70m, it’s slightly unusual as I would do a shorter dive in the ocean so this isn't something I’ve done. I'd have to assume I have my scooter so I can take lots of stages and not have to worry about swimming.

In terms of the deep stops I'm slightly lazier than Graham and go for 75% of depth for the first stop which means I'd start to slow my ascent at 51m. Doesn't make a huge difference and the maths is easier.

In terms of how long I'd be in the water I would most likely do less time than you Mark, but that's what works for me. I know you make your deco conservative and wouldn't disagree with that.

Cheers
Al

I don't care how much or how little time people do for deco as long as they feel ok after. I have in emergencies pulled some fairly drastic deco. I once cut 45mins off my planned deco due to feeling unwell and i didn't get bent.

This didn't encourage me to shave 45mins of every dive thereafter i just felt lucky to have got away with it on the day.

On monster dives i shave deco. Were planning a 130m dive in Aug and I have shaved the deco down from 5 3/4 hours down to 4 1/2 with some creative gas planning and pushing the limits of narcosis and my faith in Helium off gassing as far as i can go. I could kid you that the risks of being in the water for just under six hours justify the efforts to reduce the deco but in truth I am just horrified at the thought of a 5 hour hang time.

This is a one off dive, a big risk in every sense. I openly admit I am pushing it hard.

For "normal" dives (Less than 180min run time) I really cant see the point in doing aggressive profiles. You save 20mins? so what?

What I try and do is provide balance when someone posts things about deco in a way which i find misleading. Intentionally, through ignorance or unintentionally doesn't matter, its still misleading.

Lots of deep stops and short shallow deco is not a soft profile. It should not be promoted as such and certainly should not be promoted as better than or more beneficial than, conventionally accepted decompression.

By conventionally accepted decompression I mean:

A: Buhlman: Get shallow fast and this shortens the overall decompression but its aggressive.

Or

B: GF deco: Do deep stops to reduce body stress and compensate for this by extending the shallow deco

For every GUE deco diver thats pulled off a deep stop + short shallow deco profile and not getting bent, I can offer 1000 BSAC divers diving 88's with the same result. For every monster dive pulled off using GUEs system I can offer a monster dive pulled off using just a VR3??? Go figure who's right and who's wrong. I sure as hell don't know.

Following "conventional" wisdom extending time deep extends time shallow. GUE have in the past said this was wrong but this research doesn't back up their belief, it backs conventional beliefs.

Don't let this stop you doing what your doing, if it works for you it works. But my uncle is dead from cancer age 64 and he didn't smoke. My aunt died of cancer aged 59 and she never touched a cigarette in her life. My mum (their sister) is 72 and she has smoked 60 a day for forty years. Shes fit as a fiddle but i don't hold her up as proof smoking is not bad for your health.

ATB

Mark

[Mark Chase]

Quote: (Originally Posted by Alastair)

OK I would agree that in the past those statements get bandied about. To take your example the "forget the 3m stop" comment is still applicable, usual practise is to pull all the 3m time at 6m (on 02) and then have a slow ascent to the surface.

Al

GI3 wrote:
do your calculation and then discard the ten foot stop completely from the figures - throw it and its time out completely - that is total bullshit. Then ask yourself how much time do I need at 20. The answer is, enough to make it work if I did the deeper steps correctly.


Your explination ist how i read GI3's

ATB

Mark

[GLOC]

Quote: (Originally Posted by Mark Chase)

GI3 wrote:
do your calculation and then discard the ten foot stop completely from the figures - throw it and its time out completely - that is total bullshit. Then ask yourself how much time do I need at 20. The answer is, enough to make it work if I did the deeper steps correctly.


Your explination ist how i read GI3's

ATB

Mark

What we were taught on T1 was to, in effect, swap the 6m and 3m stop times. Do your 3m stop time at 6m and then spend the 6m time ascending from 6m to the surface. For T1 limits this is in the region of 5mins.

This is what Al was alluding to.

[Janos]

Quote: (Originally Posted by Alastair)

Mark the point of the presentation was too educate people on the latest research on deep stops however that does not mean we don't do them! From what I understand from your use of GF on your shearwater you are following GF model which is a mechanism to introduce deep stops - you are therefore subscribing to the same ideas that we do.

I think the model that Mark and I subscribe to is that deep stops are good, but when you do a deep stop, although you are off-gassing fast tissues, you are still on-gassing the slow tissues, and so increasing your shallow water time.

I set my computer for 30/85, but stop deeper. I know this will extend my shallow water stops. I am happy with this and I exit the water with 85% of my (theoretical) saturation limit. I know people who run 10/125, as they want to have the same total deco time, but shaped differently.

Janos

[Alastair]

Deco is a fascinating topic partly because everyone is to a certain extent guessing what is correct. One of the other lectures at the GUE conference was one by Simon Mitchell who explained how tables and profiles are only part of the picture when it comes to decompression. A divers physiology is at much a factor as the table they chose.

His example was a guy who was horribly bent for a relatively conservative no-stop dive contrasted to a fisherman who did ludicrous dives with no deco whatsoever thousands of times and yet only once had sustained a very mild bend.

One of the studies he talked about showed that were substantially reducing your risk of DCS if you enagaged in 40mins of cardio exercise within a 20 hours period pre-dive. (Plenty of info on this if you google).

You may find the best way of lowering your DCS risk before your big dive is to get some good exercise the day before you dive and focus less on whether a GF of 30/85 or 10/90 is better. There are lots of factors which are believed to contribute to DCS such as smoking, de-hydration, obesity, age, fitness level which are actually worth thinking about if planning some serious deco. To a certain extent what works, works and that is probably an excellent explanation for the deco that GI3 has talked about and done.

Cheers
Al

[lamont]

Quote: (Originally Posted by Mark Chase)

Following "conventional" wisdom extending time deep extends time shallow. GUE have in the past said this was wrong but this research doesn't back up their belief, it backs conventional beliefs.

No, this research does not invalidate the GUE (and BRW/RGBM) perspective on deep stops.

Both conventional beliefs and GUE/BRW/RGBM beliefs suggest that for long stops you will ongas in dissolved form and need to offgas later/shallower.

For short, deep stops the argument is that the ongassing in the dissolved phase is offset by the benefits of keeping the free phase bubbles small and offgassing in the free phase. At some point on a deep stop you hit a point where the cost to the dissolved phase outweighs the benefit to the free phase and at that point the deep stop is no longer doing you any good, so you need to move up.

This is backed up empirically and quantitatively by the analysis which BRW posted to TDS of the NEDU profiles which confirmed that bubble models accurately predict the increased rate of bubbling and DCS that NEDU observed.

You cannot test the efficacy of the first minute of a deep stop by doing an additional 9 minutes at that level, which is what the NEDU study is implicitly claiming. All they're proving is that if you massively go over a stop time that you need to add more time. It doesn't suggest anything about the utility of the first minute of the deep stop, however, unless you assume a linear extrapolation -- and the whole point of the GUE/BRW/RGBM approach is that the tradeoff between the free phase and dissolved phase strategies is not linear. They'd need to prove it was linear first.

Also, when it comes to Tech1, the GUE slides suggest that you use 20/85 GF with manually entered deco stops (with the algorithm calculating the ongassing at the deep stops). There's no throwing away of the 10 foot stop, no inserting deep stops without accounting for ongassing and the 20/85 GF profile is more conservative than straight bulhmann. GUE != GI3.

[Leigh u]

Can someone tell me a profile that a GUE trained diver routinely dives that is stopping too long deep, and has too short of shallow deco ?

I don't know anyone around here that shaves off the shallow stops, wether running Deco Planner or other software. I don't mean a mystical internet gleaned profile..or an extreme profile..but an average 200 foot OC dive for say 30 or 40 minutes.

We are all told that shaping things correctly, we could leave the water earlier in an emergency with much less danger...but who shaves the stops from 21m up just for the hell of it. Does nyone really go straight to 6m and hang there for 3 hours ?

[Mark Chase]

Quote: (Originally Posted by Leigh u)

Can someone tell me a profile that a GUE trained diver routinely dives that is stopping too long deep, and has too short of shallow deco ?

I don't know anyone around here that shaves off the shallow stops, wether running Deco Planner or other software. I don't mean a mystical internet gleaned profile..or an extreme profile..but an average 200 foot OC dive for say 30 or 40 minutes.

We are all told that shaping things correctly, we could leave the water earlier in an emergency with much less danger...but who shaves the stops from 21m up just for the hell of it. Does nyone really go straight to 6m and hang there for 3 hours ?

I could easily facilitate this but i dont have permision to post the profiles I have been sent.

Sufice as to say i tried to mimic the profiles using deco planner and they came out at 10/130 if I remember corectly.

It was a 65m dive and they spent about twice the time below 21m that I did but about half the time at 6.

The simple way to do this is for you to post a profile for 40mins at 200ft (65m) using DOTF and Ill post the Deco id do.


This is one I have to hand; 65m for 45mins



I beleive I had to run it like this to match the DOTF time but please check the DOTF time as i havent: