Analysis of a 47m deco proifile.

[Mark Chase]

This profile raised questions comments about how long it was etc etc. I found this odd as I did the ratio in my head for the dive and the ascent time was about the same as the computer was asking for.

So I thought id put up this comparison between what my computer spat out and what DOTF works out (by my understanding).



The actual profile asked for by the computer was as follows:

2 @ 27
2 @ 24
2 @ 21
2 @ 18
4 @ 15
6 @ 12
9 @ 9
28@ 6

Including ascent times total deco running 10/85GF was 62mins


I ran it through Deco on the fly and came up with: 47mins @ 47m

1 @ 36
1 @ 33
1 @ 30
1 @ 27
1 @ 24
5 @ 21
4@ 18
3 @ 15
3 @ 12
10 @ 9
26 @ 6

I make this a total 62min ascent


If you ignore the decent time then it was a 42min bottom time avg depth 47m

1:1 ratio based on 45m so add 5mins = 47mins deco

so

1 @ 36
1 @ 33
1 @ 30
1 @ 27
1 @ 24
5 @ 21
4 @ 18
3 @ 15
3 @ 12
9 @ 9
24 @ 6

Total 59mins deco ascent.

As it was we did an extra 10mins deco to clear the VR3. Now i beleive the reasion for this was Howards VR3 would have been running something like 1.25 fixed set point and would asume Helium in the mix all the way to the surface. My computer was plumbed into the unit so it took my actual PP02 inot account including the Helium free time spent on 100% at 6m

If we look at Vplanner for a 1.25 setpoint profile with He in the mix it comes out at this:


Decompression model: VPM - B

DIVE PLAN
Surface interval = 5 day 0 hr 0 min.
Elevation = 0m
Conservatism = + 2

Dec to 47m (3:08) Diluent 21/50 1.25 SetPoint, 15m/min descent.
Level 47m 43:52 (47:00) Diluent 21/50 1.25 SetPoint, 11m ead, 19m end
Asc to 27m (51:00) Diluent 21/50 1.25 SetPoint, -5m/min ascent.
Stop at 24m 1:00 (52:00) Diluent 21/50 1.25 SetPoint, 0m ead, 10m end
Stop at 21m 1:00 (53:00) Diluent 21/50 1.25 SetPoint, 0m ead, 9m end
Stop at 18m 3:00 (56:00) Diluent 21/50 1.25 SetPoint, 0m ead, 8m end
Stop at 15m 4:30 (60:30) Diluent 21/50 1.25 SetPoint, 0m ead, 7m end
Stop at 12m 5:00 (65:30) Diluent 21/50 1.25 SetPoint, 0m ead, 6m end
Stop at 9m 7:30 (73:00) Diluent 21/50 1.25 SetPoint, 0m ead, 5m end
Stop at 6m 30:30 (103:30) Diluent 21/50 1.25 SetPoint, 0m ead, 4m end
Surface (105:30) Diluent 21/50 -3m/min ascent.



If we asume 100% 02 at the 6m stop it looks like this:

Decompression model: VPM - B

DIVE PLAN
Surface interval = 5 day 0 hr 0 min.
Elevation = 0m
Conservatism = + 2

Dec to 47m (3:08) Diluent 21/50 1.25 SetPoint, 15m/min descent.
Level 47m 43:52 (47:00) Diluent 21/50 1.25 SetPoint, 11m ead, 19m end
Asc to 27m (51:00) Diluent 21/50 1.25 SetPoint, -5m/min ascent.
Stop at 24m 1:00 (52:00) Diluent 21/50 1.25 SetPoint, 0m ead, 10m end
Stop at 21m 1:00 (53:00) Diluent 21/50 1.25 SetPoint, 0m ead, 9m end
Stop at 18m 3:00 (56:00) Diluent 21/50 1.25 SetPoint, 0m ead, 8m end
Stop at 15m 4:00 (60:00) Diluent 21/50 1.25 SetPoint, 0m ead, 7m end
Stop at 12m 5:30 (65:30) Diluent 21/50 1.25 SetPoint, 0m ead, 6m end
Stop at 9m 7:00 (72:30) Diluent 21/50 1.25 SetPoint, 0m ead, 5m end
Stop at 6m 9:30 (82:00) Oxygen 1.60 ppO2, 0m ead
Stop at 3m 15:00 (97:00) Oxygen 1.30 ppO2, 0m ead
Surface (98:00) Oxygen -3m/min ascent.


Whilst the Vplanner profiles are nothing like the VR3 profiles this demontrates how much diference it makes leaving He in the mix. It adds 7mins to the dive. Howards VR3 added 8.

I am interested to see what others make of the actual profile? WOuld you do something diferent with the DOTF? i know that at set point and just above the DPTF 1:1 ratio is very conservitave but do you taylor the deco with this in mind or do yo do the same adjustments on all DOTF profiles?

ATB

Mark Chase

[Clare Gledhill]

Mark - the standard response has to be "don't learn deco on the internet" - but then you know that

Deco on the Fly is not a way of working out deco - it is merely compleing your stops whilst you travel rather than halting the team. Ratio deco is about looking for patterns in decompression profiles which is what you are referring to.

There are some errors in your suggested 'out of the box' Ratio Deco profile - we would certainly not, as standard, do the stops that you have set out as there is simply not enough time at 21 and far too much at 9.

The other problem is that you are using set point 1 ratio deco (worked out for one deco gas) yet your rebreather allows you the equivalent of two (or multiple ) gases. As such, the straight 1:1 profile is not really relevant.

The longer bottom time also skews the relationship slightly. Once we move beyond 40 minutes bottom time the stops have to start shifting.

There is no magic in Ratio Deco - it is just another way of working out profiles. The two or three set points which are often quoted on the internet are just two or three of the ratios that we can look at. As dives get longer we can shift these to take into account different loadings.

I'm definately not going to get in to a 'I'd do less that you' contest. Do what you believe is right for you and for the people you are diving with. The last thing I would ever want is for someone to feel that they have been peer pressured into doing too little deco.

Not what you are looking for I guess, but others will no doubt post that.

[jptaylor9]

deleted

[Bob Cooper]

Originally Posted by Mark Chase

I am interested to see what others make of the actual profile? WOuld you do something diferent with the DOTF? i know that at set point and just above the DPTF 1:1 ratio is very conservitave but do you taylor the deco with this in mind or do yo do the same adjustments on all DOTF profiles?

Mark - this looks like a typical Moldavia profile to me? One that you must have done dozens of times before? Therefore, if it were me, I would just do the same deco as I did last time, and the time before that....etc. assuming that you felt ok after these dives and that your deco wasn't overly protracted (i.e. you hit the surface and find everybody else has been on the boat drinking tea for the past 30mins..!)

I certainly wouldn't get involved in the sort of number crunching you have here. It's not exactly breaking new ground is it?

If it's *about* 47m for *about* 40 mins, I'd probably be on the surface in less than *about* 90mins.

However, it's not a race - just do what you are comfortable with.

Bob

[jptaylor9]

deleted

[Lou]

Originally Posted by Clare Gledhill

I'm definately not going to get in to a 'I'd do less that you' contest. Do what you believe is right for you and for the people you are diving with. The last thing I would ever want is for someone to feel that they have been peer pressured into doing too little deco.
.

But isn't the root of this thread from comments made on the trip report thread....ones along the lines of "I'm glad I wasn't with you for that deco"? As far as I can see Mark has just moved that discussion - opened by you amongst others - to a different thread. I certainly read the direction of the posts directed at Mark over that profile to read as "why on earth did you do so much?". I am sure it wasn't meant so bluntly, but as easy as it is to say "don't learn deco off the 'net" now, folk really should avoid this habit of criticism over excessive length, however light, of profiles that are posted. It does seem to be getting more and more prevalent on YD of late. i don't know why.

Equally Mark should be big enough and bad enough to take it on the chin, trust his own profiles and ignore such comments

[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.

[Lou]

Originally Posted by Clare Gledhill

I read Marks' tale about keeping down bile .

*shudder*


The real way, of course, is not to keep it down

[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

[The Doctor]

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

Mark