Deco times

[Manta]

When I was doing my Adv. Nitrox & Deco procedures course we went through a couple of Deco Programs with the instructor. Now I've started looking at various on my own and I've run through V-Planner (+2 conservatism) the following plan.

40m 20min 28%
30m 10min 28%
20m 10min 28%
Deco gas used 40%

and came up with the following results.

Depth Time Run-Time Mix
0-40m 2 2 28%
40m 18 20 28%
30m 10 31 28%
20m 10 42 28%
9m Deco 1 44 40%
6m Deco 17 61 40%

What do you think about the outcome, do you agree, I'm I doing something wrong with the configuration? Unfortunately for the time I can't get anythink richer than 40%.

Thanks for your input.

[RichW]

I'd probably do a few minutes between 15 and 9, but other than that, it doesn't appear outlandish.

What were you expecting?

Rich

[Gareth Burrows]

Much as I hate to disagree with the bloke that teaches me, but...

I get a similar runtime and stops for just the first segment of the dive, 40M for 20 mins. If you add in the 30M section, where you will still be ongassing, the deco racks up even more. for the same plan I get a runtime of about 85 mins using gradient factors, compared to your 61 minutes.

You are putting a long stop in at 30m where you will still be ongassing

You are staying on your backgas until you get to 9 metres, which means you need about 6000 litres of backgas given a sac of 25, so youd need twin 18s assuming you are keeping a third in reserve.

Using only 40% as a decogas you are not getting a real gradient from your backgas, try running the figured with 50% as a deco gas and all of a sudden the numbers completely change becuase you can get on it for the 10 minutes at 20M

i think the runtimes and stops you give are for the 40M for 20 mins segment only. If you use 50% instead of 40% then your figures make sense fo the entire dive.

Of course it could be friday and I might have just planned the most conservative dive ever by mistake

[RichW]

Originally Posted by Garf

Much as I hate to disagree with the bloke that teaches me, but...

LOL.

OK, I don't have decoplanner on my desk here, so here's how I looked at it.

The first phase 40m for 20 will probably rack up in the region of 20mins of deco on a 50% deco gas, so not a huge difference from the 40%. The switch depth would be a factor for me here.

Moving to 30m is moving up to 80% of the depth in ATA's of the first portion. This is generally where we begin our deep stops, as this is roughly where we start to switch from on-gassing to off-gassing. In this dive, this will cause the faster tissues to essentially do nothing, and the slower tissues will continue to ongas. You'd probably get similar N2 loading to a longer (20+10min) dive to 30m, in fact. So this phase to me can be decompressed similarly to a 30m, 30min dive. i.e. not a lot needed.

The 20m phase is all off-gassing, barring the very slow tissues, so I didn't consider it for the deco.

This left me with the deco from the first bit of the dive, which was of the order of 20mins. Add in some deeper stuff from 15m, and we're done.

Usual disclaimers apply.

Rich

[Manta]

Originally Posted by RichW

I'd probably do a few minutes between 15 and 9, but other than that, it doesn't appear outlandish.

What were you expecting?

Rich

As you said few minutes around 12m, maybe 1-2 min. longer at 9m or slightly longer at 6m.

[nickb]

V-Planner gives me 41 minutes at 6m using +2 conservatism, 86 minutes run-time.

Just doing the 40m for 20 minutes gives this:

Dec to 40m (2) Nitrox 28 15m/min descent.
Level 40m 17:12 (20) Nitrox 28 1.39 ppO2, 36m ead
Asc to 30m (21) Nitrox 28 -9m/min ascent.
Stop at 30m 1:53 (23) Nitrox 40 1.59 ppO2, 20m ead
Stop at 12m 1:20 (26) Nitrox 40 0.88 ppO2, 7m ead
Stop at 9m 3:00 (29) Nitrox 40 0.76 ppO2, 4m ead
Stop at 6m 27:00 (56) Nitrox 40 0.64 ppO2, 2m ead
Surface (58) Nitrox 40 -3m/min ascent.

Switching to 50% gives this:

Dec to 40m (2) Nitrox 28 15m/min descent.
Level 40m 17:12 (20) Nitrox 28 1.39 ppO2, 36m ead
Asc to 21m (22) Nitrox 28 -9m/min ascent.
Stop at 21m 1:53 (24) Nitrox 50 1.54 ppO2, 10m ead
Stop at 9m 2:00 (27) Nitrox 50 0.95 ppO2, 2m ead
Stop at 6m 20:00 (47) Nitrox 50 0.80 ppO2, 0m ead
Surface (49) Nitrox 50 -3m/min ascent.

Sorry, ignore all this bollocks, I had the elevation set to 1800m to show a workmate what a difference it makes

Here's the real data for your dive:

Dec to 40m (2) Nitrox 28 15m/min descent.
Level 40m 17:20 (20) Nitrox 28 1.39 ppO2, 36m ead
Asc to 30m (21) Nitrox 28 -9m/min ascent.
Level 30m 10:00 (31) Nitrox 28 1.11 ppO2, 26m ead
Asc to 20m (32) Nitrox 28 -9m/min ascent.
Level 20m 10:00 (42) Nitrox 28 0.84 ppO2, 17m ead
Asc to 9m (43) Nitrox 40 -9m/min ascent.
Stop at 9m 0:33 (44) Nitrox 40 0.76 ppO2, 4m ead
Stop at 6m 17:00 (61) Nitrox 40 0.64 ppO2, 2m ead
Surface (63) Nitrox 40 -3m/min ascent.

and switching to 50%:

Dec to 40m (2) Nitrox 28 15m/min descent.
Level 40m 17:20 (20) Nitrox 28 1.39 ppO2, 36m ead
Asc to 30m (21) Nitrox 28 -9m/min ascent.
Level 30m 10:00 (31) Nitrox 28 1.11 ppO2, 26m ead
Asc to 20m (32) Nitrox 28 -9m/min ascent.
Level 20m 10:00 (42) Nitrox 28 0.84 ppO2, 17m ead
Asc to 9m (43) Nitrox 50 -9m/min ascent.
Stop at 9m 0:33 (44) Nitrox 50 0.95 ppO2, 2m ead
Stop at 6m 14:00 (58) Nitrox 50 0.80 ppO2, 0m ead
Surface (60) Nitrox 50 -3m/min ascent.

[Manta]

Originally Posted by Garf

Of course it could be friday and I might have just planned the most conservative dive ever by mistake

Garf,

Since it's friday afternoon and world cup is starting in a few minutes I think you have made a small mistake. You've put in the plan 40m for 30 mins instead of 20mins.

[Gareth Burrows]

shit. works out at 62 mins. Arse. If Mark Powell sees this I'll never hear the end of it

Have a nice day

[RichW]

Originally Posted by Manta

As you said few minutes around 12m, maybe 1-2 min. longer at 9m or slightly longer at 6m.

I think a slightly longer 6m stop on this dive is the place to add conservatism. There are other ways, but if you can only get 40%, then these aren't really viable for you.

Bottom line is, if you're not happy with the profile, don't dive it.

Rich

[Manta]

Originally Posted by nickb

[color="Red"]Here's the real data for your dive:


Dec to 40m (2) Nitrox 28 15m/min descent.
Level 40m 17:20 (20) Nitrox 28 1.39 ppO2, 36m ead
Asc to 30m (21) Nitrox 28 -9m/min ascent.
Level 30m 10:00 (31) Nitrox 28 1.11 ppO2, 26m ead
Asc to 20m (32) Nitrox 28 -9m/min ascent.
Level 20m 10:00 (42) Nitrox 28 0.84 ppO2, 17m ead
Asc to 9m (43) Nitrox 40 -9m/min ascent.
Stop at 9m 0:33 (44) Nitrox 40 0.76 ppO2, 4m ead
Stop at 6m 17:00 (61) Nitrox 40 0.64 ppO2, 2m ead
Surface (63) Nitrox 40 -3m/min ascent.

and switching to 50%:

Dec to 40m (2) Nitrox 28 15m/min descent.
Level 40m 17:20 (20) Nitrox 28 1.39 ppO2, 36m ead
Asc to 30m (21) Nitrox 28 -9m/min ascent.
Level 30m 10:00 (31) Nitrox 28 1.11 ppO2, 26m ead
Asc to 20m (32) Nitrox 28 -9m/min ascent.
Level 20m 10:00 (42) Nitrox 28 0.84 ppO2, 17m ead
Asc to 9m (43) Nitrox 50 -9m/min ascent.
Stop at 9m 0:33 (44) Nitrox 50 0.95 ppO2, 2m ead
Stop at 6m 14:00 (58) Nitrox 50 0.80 ppO2, 0m ead
Surface (60) Nitrox 50 -3m/min ascent.

Nick,
How do I have to input the data in order to make a switch to 40% while I'm at 20M?
20,10,40?