Analysis of a 47m deco proifile.

[Digger]

If bailout is pushing deco harder than you would normally like to do, then why not carry more bailout? I had a discussion with a mate on Friday that largely revolved around don't make a dive plan fit the gear you have, make the gear you have fit the dive plan. This was for a dive with a set bottom time and set depth. That for me would include bailout (or obviously in this case cutting bottom time or depth). I'm not very comfortable with the idea of bailing out and knowing I was about to run an agressive profile when I did it.

The numbers don't look all that bad to me. I'd probably tweak here and there, but it's not more than a few minutes from one stop and onto another. But then you and I don't have to worry about adding in a few extra minutes anywhere really, the units save that hassle.

I run the plan using setpoint then run O2 RB as a safety factor. Makes a lot of sense. In this case I'd be in the water an extra 8 minutes, which is fine by me. Or I could go for the Juz standard do whatever plan you were going to do, then add 10 minutes at 6. Works for him, works for me. Unless I really need a wee.

Digs.

[ibbo]

with the vr3 if you set it on to a mix, then alter the set point to 1.5 at 5m does it still plan on a % of helium in the mix? or have i missed the plot as usual? i tend to run at 1.25 for the bottom and ascent, then flush as much as poss when up at 6m

[Janos]

For 47mins at 47m I'd be looking at a total run time of 110 minutes. The Shearwater would probably give me a few minutes more than this as I'm happy to let the ppO2 drop as I ascend which obviously extends the deco.

Worst case bailout (on 18/45 and 50%) would be 100 minutes but I'd be asking to be put on O2 as soon as I hit the surface.

Janos

[Mark Chase]

Originally Posted by Clare Gledhill

Actually Lou - I read Marks' tale about keeping down bile and the problems that they faced on the surface getting back on the boat...on this occasion. But your point is fairly made.

Hey you have two sausage & egg Mc muffins on the trip out and you have to pay the price . Indigestion is something I live with on a lot of dives so it wasent a biggy just going head down is a no no.

I would of folowed the Shearwater out 10mins earlier. I am perfictly happy running 10/85. However for the reasions i have explained already we had to wait for the VR3 to clear. When i ran two VR3s one plumbed in and one on a fixed set point, it was a problem i had all the time.

ATB

Mark Chase

[Mark Chase]

Originally Posted by ibbo

with the vr3 if you set it on to a mix, then alter the set point to 1.5 at 5m does it still plan on a % of helium in the mix? or have i missed the plot as usual? i tend to run at 1.25 for the bottom and ascent, then flush as much as poss when up at 6m

No it should work, but I dont know many people who bother to change the set point on the VR3.

I generaly found the VR3 to be arround a 20/80GF profile + a couple of pyle stops. The main diference therefor between howards profile and my profile was that at 6m I was on 1.6 02 and he was on 1.25 trimix 77/7/16.

ATB

Mark Chase

[Paul Oliver]

Just be glad you were not sticking with me on my Vytec

[Garf]

I'd be looking at at about 55 mins of deco with this profile. However, the curve I would run would be nothing like you planned Mark. I would do my first deep stop at 33 metres, not 36. I would also maybe do 30 second stops through the deeper stops rather than one minute and maybe do a 1 minute stop at 24 just to get the ascent slowed down before the gas switch. This would be at about 65% of the ATAS anyway so I'd be happy. I'd do linear stops through the intermediate part of the ascent, and would certainly not do all that time at 9. I wouldn't make the last 5 mins part of the deco, but would complete the final stop at 6m and then do a 5 minute ascent. Off the top of my head I'd probably end up with about 55 mins.

[And]

Originally Posted by Mark Chase

Bob Clare et all,

The point I am genuinly interested from a point of view of OC bailout. Bailout is by nature sometimes pushing deco harder than i would normaly like to do.

The above ratio profiles are what I would do. The 50% of deco at 6 then spit the remainder between the 21-9m stops. Rather than the new KISS idea of 5,5,5,5,5 I still prefer to extend the shalow section by nicking time off the 18-12m stops. Hesce my mucking arround with the times.

I am interested to see how you would manipulate these numbers to make it more agresive in an emergancy. I was wondering is there a formula or is it just a case of shaving.

No ruck desired. I wouldent use it unless i had to I am too unfit.

ATB

Mark Chase

Hi

From looking at it, the runtime I worked out was 96 mins with RD and then checked on HLplanner and got 97 mins , but I see it as 40 mins at 47, not 47 mins, as it took at least 5 mins for you to get to that depth, and I don't usually count that time. There are 2 spare minutes, so I guess another couple of mins at 6 polishes it all off at 100 mins.

The issue of having to cut short the deco is to cut the shallow stops rather than the deep stops, so I would stick to the deco as long as I possibly could, and then cut short the 6 mtr stop for example. To be perfectly honest, it really depends on the emergency and whether this emergency means I need to get out of the water, or whether I am able to go back down and continue the deco after sorting out whatever needed sorting out.

As an aside, doing 45 mins (40 mins BT at 48mtrs so 45 mins deco) on the 50% bottle is really maxing out the available gas, and this is where I would start thinking about taking along an AL40 of o2, which would take off another 10 mins and bring my time down to 90 mins.

So in answer to your question about being aggressive, you could forget the descent time and then do the deep stops, cutting short the 6 mtr stop if you have to. In terms of your runtime, I wouldn't be so bothered about doing more deco, although staring at Bob for an extra 20 mins might require a stiff drink when I get back on the boat.

Andy

[Mark Chase]

Originally Posted by Garf

I'd be looking at at about 55 mins of deco with this profile. However, the curve I would run would be nothing like you planned Mark. I would do my first deep stop at 33 metres, not 36. I would also maybe do 30 second stops through the deeper stops rather than one minute and maybe do a 1 minute stop at 24 just to get the ascent slowed down before the gas switch. This would be at about 65% of the ATAS anyway so I'd be happy. I'd do linear stops through the intermediate part of the ascent, and would certainly not do all that time at 9. I wouldn't make the last 5 mins part of the deco, but would complete the final stop at 6m and then do a 5 minute ascent. Off the top of my head I'd probably end up with about 55 mins.

OK I can see what your doing but:

75% of 47m is 35.25 I rounded up to 36 by adding 0,75m you rounded down to 33 by taking away 2.25m

The 1min stops from 33 to 21 are not stops as you know they are 3m/min ascent rate with a pause. The run time remains the same I didnt add any run time for the ascent between these stops as they are not real stops.

Linnea stops = what i said

5 @ 21
5 @ 18
5 @ 15
5 @ 12
5 @ 9

I beleive this idea was brought in to avoid having to memorize the six standard intermediate profiles. I also beleive the use of linnea stops in no way improves the performance of the deco schedual, It makes it worse, doesent it?


These were the old stile intermediate stops for 5 -30mins

1,1,1,1,1
3,3,1,1,2
5,5,1,1,3
5,5,3,3,4
7,7,3,3,5
7,7,5,5,6

So apart from doing away with a 1min 36m stop your total run time should be the same as my profile. Spending the 5 ascending to the surface doesn't alter the in water time and I think most of us are doing this if the conditions allow. Howard and I ascended and cleared at 3 then went straight up because it was a big swell on the day and anything else just wasn't practical.

However with the intermediate stops I prefer the old school deco where they paused at 21 to Open the "02 window" (sorry Howard) then skipped through the 15 and 12m stops quickly to then push the off gassing gradient right up on the 9m stop.

The official GUE profile for 25mins of stops is/was

7 @ 21
7 @ 18 These two stops on a high PP02
3 @ 15
3 @ 12
5 @ 9 Extended 9m stop to max the off gassing gradient


Again I have looked at deco from several angles and one thing remains constant. Getting shallow fast speeds up deco. There is a irony to this concept that is missed by some divers, in that by running over 100GF they are getting shallow faster by getting out of the water and off gassing back on the boat at ambient rather than in the water at 0.6atm. And they are decoing on air

So if i wanted to make my deco faster, would i not redistribute the stop time to the 9m stop to maximize this off gassing effect?

It seems logical but not in line with thinking on ratio deco


So it seems as an outsider looking in that the main areas for reducing the deco on a standard ratio deco profile are:

• Ignore the decent time
  
• err on the shallow side of average depth
  
• Round up the deep stop to the stop above never the stop below.

I am assuming then that after this its just up to the individual diver to shave off deco where they think its appropriate and use this experimentation to form schedules for the future?

This is a perfectly valid approach in my mind but the question is, does the alteration of the profile remain a constant? IE i always reduce the 6m stop by 10% 10mins what ever or does it vary across the depth run time range on an ad hock basis?

Personally i tend to run 10/85 GFs or 20/80 GFs for everything. Doesn't matter the run time or the depth. I am starting to consider changing that concept.

ATB

Mark Chase

[Garf]

Mark, don't get too tied up in "official GUE line", becuase the only "official" line I have hjeard is "do the right deco for you". The standrad gases are only recommendations and may get changed for a specific project. The "standard" deco is only a starting position, not the official line on whjat you mudt do, hence my comments are for what I would do, noty anyone else.

With regards to 33 or 36 metres, why are you rounding deeper. We round shallower becuase there's little point rounding down so you are still ongassing. We round up to the nearest number divisble by 3 with the intention of being shallower than 80% of the ATAS.

You are talking about 1 minute stops (3 metres per minute). This is not what I said. I would do 30 second stops up to 65% of the ATAS - 6 metres per miniute ascent rate. Then slow it down to 3 metres per minute at 24 metres.

As For linear, non linear, in the intermediate stops, I haven't really noticed any difference, I think you could get away with murder in the tech1 ratio deco level. If anything I would padd the 21 sop a couple of minutes, but I wouldn't extend the 9 necessarily.