Bailout Gases for long 60 metre dives

lbihler

Hi all,

I m going on a Deep Virgin Wreck diving livaboard south thailand next week. I just can t figure out which gases I would take for bailout. I m quite a beginner on deep wreck dives and wanted your opinion before doing a fatal mistake.
Profile is usually 60 metres for 40 minutes, 2 dives a day. Onboard I use 100% (98) and 14/44 trimix, 1.0 ppO2 bottom 1.4 ppO2 ascent for that mix.

Knowing that they have O2 at will at 6 metres under the boat and that I can not really count on other divers as I will probably be the only CCR diver and as everybody tends to go solo.
Last time I took 12litres Air and 12 litres 36% as bailout, which is enough for me to complete all my deco on OC. Thing is I ran out of O2 during the dive (stupid me, don t ask) with a fully functionning unit and had to ascent in semi closed, which took me ages to deco.

Question is, what would you guys use, knowing that available gases are any mix below 40% O2 including air and trimix, and 100% O2 ?

I was thinking about taking a 12litres Air at 200 bars
and a 12litres 02 at about 100 bars (no booster on the boat) so that even if I work a bit at the bottom I have enough O2 to finish in fully closed and I can
fly the unit manually and spare my back gas for emergencies.
I ll be a bit short on OC ascent if the problem occurs at the end of the dive and I do not find the deco bars (not a probable case, brilliant viz and no current). But again, in semi closed mode, I can even loose the down line and finish my deco without problem.

What are you guys thinking about it ? Any risk I forgot to consider ?

jhaaja

I would not want to bail to air at 60m.

I would consider two or three bail-out gases. Three if diving solo, TX20/35, EAN40 or EAN50 and O2. Two if with a team/buddy, TX20/35 and EAN40 or O2. The buddy could then carry the other deco gas.

Mikel-Deko

As people that used the Ouroboros for long long dives, i will take a 3-5 litres O2 tank to use in case of on-board O2 lost and to use in -6 mtrs stop if bailout. It does not distrub at all.

Two other stages with Tx20/45 and EAN60.

Regards

Mikel-Deko.

gathan

I do dives with similar profiles on a fairly regular basis, most of them solo. I personally like to take three bailout gases with me - they are 18/45, 35/25, and EAN70. I usually carry them in 80cft cylinders if diving solo. I was using heliox 10/90 as a dil for a while, but have gone back to using mostly 10/50 now. The main reason for the change was the physical amount of bailout gas that I could carry while solo.

Andre

6Gill

I prefer three gasses as well, Tmix for bottom gas (if I have to bail at depth, it's not a good time to get slammed) and then consider SAC rate and the amount of gas to make a comfortable ascent to the next switch. I like 40cuft stages where possible, so I try to plan the next switch for 70' (EAN 50) and a final switch at 20' (O2). Try looking at the amount of gas you will consume between switchs and the differences in deco time (usually not great) and it will help point you to the best mix. For deeper dives the bottom stage needs to be 80cuft unless your doing team bailout.

Mark Chase

10 ltr 18/45 and a 10ltr of 50% is optional. One asumes its likley you can go pure 02 CCR even if its broke and that there is 02 drop tanks on the boat but even so 40min's at 60m is do-able on a 10ltr of 50%.

ATB

Mark CHase

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db8us

I would also go for a Trimix, and a 50% for deco and a good dive buddy.

Niels Doorduijn

[quote=lbihler;69681]

You wrote that you are a beginner on deep wreck dives. I would consider two times 40 minutes at 60 meter a day to be too much to start with.

Rgs,
Niels

lbihler

For the 40 minutes 60 metres done already, and as a beginner on CCR deep wreck dives I do not penetrate the wrecks, simple as that, which is also the reason for the air bailout.
If I penetrate, I ll definitely need a trimix bailout instead of air, but ascending to the first deep stop from 55 will be no pb on air in a non overhead environment, and because it will reduce my ascent time of 10-15 minutes.
(NB: bottom is 60 on the sand but the main part of the dive is 50-55).

Thanks for everybody advices, next time I ll definitely go on a 3 gases bailout (80cf tx 20/45 or Air depending on the difficulty of the dive, 80cf EAN40 (to be able to use the continuous flow blending system), and O2 in whatever tank I can get, at least 5litres, probably 7litres)
adding a small O2 tank is definitely a better option than replacing a bailout gas with an O2 Tank.

Now another question, when you carry a very small tank of O2 (3-5l) how do you mount it, on the right on the harness, pretty much like an argon tank you would mount gue style on the left hand side, or do you don it like any other 3rd deco cylinder ?

Janos

You need to also factor in that one of the reasons for you bailing out could be a CO2 hit, and CO2 is about a billion [1] times more narcotic than air. I would not want to bail off a CO2 laden loop, with CO2 in your lungs and bloostream, onto air.

Janos

[1] - Ok I'm exaggerating here, but you get the idea. I think it's several hundred times more narcotic.

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