100m dive

[legal.diver]

All,

Seeking advice for my first dive to 100m - I'm using iDeco Pro and am planning on using the following gas mixes:

1. Back gas (24L) - (12/52)
2. Deco gas and travel gas (11.1L) - (EAN32)
3. Deco gas (11.1L) - (EAN72)
4. Deco gas (11.1L) - (100% O2)

Grateful for any thoughts / comments on the above gas mixes.

 

[PfcAJ]

END is high. 12/70 would be much better, giving you an END around 25m. Less WOB, lighter gas weight, clearer head to handle and problems when youre in a spot where problems are exceedingly bad.

Add helium to the deep deco gas (35/25). 36m to 12m is a long way. 50% gets you on a new bottle down at 21m. and thats also where your stops are likely to start to lengthen a bit and 32% wont be very efficient. Depending on you consumption rate and gradient factors you might be able to get away with an al40 of 35/25 instead of dragging an 11l because of the deeper gas switch to 50% vs 72%

Yes to oxygen.

 

[legal.diver]

Many thanks PfcAJ.

So revised gas mixes:

1. Back gas (24L of Tx 12/70).
2. Deco gas and travel gas (11.1L of Tx 35/25) - first gas switch at 33m.
3. Deco gas (11.1L of EAN50) - second gas switch at 21m.
4. Deco gas (11.1L of 100% O2) - third gas switch at 6m.

Any further thoughts / advice from anyone?

 

[PfcAJ]

What will be your total bottom gas volume? Bottom time?

 

[J-Vo]

I would look at 21/35 for travel gas. It increases your deco time, but leaves you closer to your next gas from the bottom segment in case of gas loss. It also conserves your bottom gas.

 

[legal.diver]

Bottom gas volume is 3200 litres and bottom time is 12 minutes.

jvogt - thanks for the suggestion, that seems to work and I like the conservatism aspect of preserving bottom gas.

Revised plan (with a bottom time of 13 minutes and runtime of 103 minutes):

1. Back gas (24L of Tx 12/70) using 2900 litres.
2. Deco gas and travel gas (11.1L of Tx 21/35) - first gas switch at 45m and using 860 litres.
3. Deco gas (11.1L of EAN50) - second gas switch at 21m and using 940 litres.
4. Deco gas (11.1L of 100% O2) - third gas switch at 6m and using 920 litres.

 

[PfcAJ]

With that plan do you have enough bottom gas to survive a loss of that 21/35 bottle?

 

[kensuf]

Definitely have helium in the deco gas below 30m. I got very powerfully narc'ed to the point I had to grab a wall when I made a switch from 12/65 to 32% at 36m a couple of years back.

I would also second using 21/35 instead of 32% and make that first switch at 58m, it'll give you a deco gas you can switch to deeper.

Also, how long is the dive plan? I personally don't like doing anything in the open ocean that's more than 3 hours in length -- conditions can change too quickly.

 

[legal.diver]

PfcAJ - yes, I've run the plan and still have enough bottom gas / deco gas if I lost the Tx 21/35.

Kensuf - out of interest why would you switch at 58m? The reason I chose to switch at 45m is because that's my first deco stop - if possible, i've always preferred to switch at a designated deco stop as opposed to on the fly.

Runtime is 103 minutes and the above plan is for an inland dive but completely agree re long dives in the open ocean.

 

[Superlyte27]

END is high. 12/70 would be much better, giving you an END around 25m. Less WOB, lighter gas weight, clearer head to handle and problems when youre in a spot where problems are exceedingly bad.

Add helium to the deep deco gas (35/25). 36m to 12m is a long way. 50% gets you on a new bottle down at 21m. and thats also where your stops are likely to start to lengthen a bit and 32% wont be very efficient. Depending on you consumption rate and gradient factors you might be able to get away with an al40 of 35/25 instead of dragging an 11l because of the deeper gas switch to 50% vs 72%

Yes to oxygen.

What he said. You need more helium