Deco gas quantity

[Pierre Farrugia]

<font color='#0000FF'>Hello all,

As before I asked for cylinders size, then start wondering if gas planning tought by TDI (eg) differ from that of DIR methods or GUE. I was tought that if I need eg 1000l of gas at surface then I will need double so 2000l (for buddy) and then divide by 185bar (if you fill to 200bar) so 15 bar is for emergency and you get cylinder size 11 liter. Do DIR recommends the same? or you use rule os thirds and have a stage bottle hanged? Or you will have bail out on travel and back gas? Can you please explaine what methods you use and why if possible?

Regards

Pierre Farrugia

[Mark Chase]

Hi M8

As you know I am not DIR but I just wanted to ask how your buddy could use the deco gas? My ones only have one reg on so the best i could do is give it to the buddy when I was finished with it. I dont realy think buddy breathing a stage is such a good idea but I supose its possable. &nbsp;Generaly I would have a lost travel gas profile and the buddy (or I ) would follow that to the 9 /6m stop on back gas and switch to deco gas and send for the drop tank if required.

Deco planner will accept diferent SAC's for travel and deco gas so I can instantly see if my standard 7ltr tanks are adiquate for the dive. I have a 50 bar reserve for deco gas set but I prefer 100 bar extra deco gas just in case.

It takes a prety seriuous dive to push a 7ltr deco stage to its limits. On my SAC I can get 87mins put of a 7ltr @ 200 bar on a 6m stop. Or at planned levels 65mins with a 50 bar reserve.
Thats a prety big dive if it requires 60mins at the 6m stop. A plan for 40m at 65m only gives 45mins on 100% at 6m. The travel gas is the problem especialy if your taking lift bags. The 40 @65 profile uses 200bar in a 7 without a lift bag so you would need a minimum 250bar fill or do what I did and go for a 10ltr.

If I was starting out kit wise again I would get two 10ltr stages. The extra weight is not worth worrying about and they can cover prety much every dive I would ever do.

atb

Mark Chase

[Tibbs]

On Tech 1 we were taught to have a 50% 'Goober Factor'. It covers against having to 'feather' the valve if the first stage fails, or giving a backup to hand off to your buddy.

Basically since the advice is to keep the runtimes of an ocean dive to 90 mintes or less, on a 21/35 dive with a 50% deco bottle, if one of the team loses his 50% bottle, it is possible to deco out on Backgas - using some of your buddy's if necessary. If you want more time on the wreck, do two dives!

On a two deco bottle dive, the idea is to be able to have enough to hand one of your bottles over when you've finished with it, so your buddy has enough deco gas to do his. This was only skated over on Tech 1, as multiple deco bottle diving is really a Tech 2 skill.

Chris

[Mark Chase]

Originally Posted by [b

Quote[/b] (Tibbs @ Sep. 22 2003,16:47)]

Originally Posted by [b

Quote[/b] ]On Tech 1 we were taught to have a 50% 'Goober Factor'. It covers against having to 'feather' the valve if the first stage fails, or giving a backup to hand off to your buddy.

Thats OK if your buddy can wait for you to finish deco before you hand him your gas. Also you would have to seporate on the deco because the profile on back gas compaired to the profile on deco gas would be totaly diferent. So to ensure the buddy found you he would have to clip off on you or you would both have to be on the shot. All in all it sounds a slopy plan at best. &nbsp;

Originally Posted by [b

Quote[/b] ]Basically since the advice is to keep the runtimes of an ocean dive to 90 mintes or less, on a 21/35 dive with a 50% deco bottle, if one of the team loses his 50% bottle, it is possible to deco out on Backgas - using some of your buddy's if necessary. If you want more time on the wreck, do two dives!

I didnt know this guideline and I asume it is a Tech 1 limitation because 90mins is nothing in deep diving. 21/35 deco on back gas on a planned 90min profile is rubbish.

As an example a 57m dive using 21/35 and 50 and 100% for deco planned dive time 90mins would have 55mins deco on deco mix. Total loss of deco mix would require 353bar of back gas on twin 12's. and 245mins deco. Using 50% for deco it would require a 200bar fill to do it on a 7 but it could be done. If you went 32/30 for travel you would require 358bar in a 7 to get away with it.

Originally Posted by [b

Quote[/b] ]If you want more time on the wreck, do two dives!

Tides and the other divers on the boat might not make this an option. In the reel world you spend £100 on the dive you travel 2.5 hours out to the dive site and you max the dive. The you go home. Going out all that way, spending all that money and doing a 20min botom time is lunacy to me but then I am a dive muppit so waht the hell do I know

ATB

Mark Chase

[Andy Phillips]

Originally Posted by [b

Quote[/b] ]If you want more time on the wreck, do two dives!

Two dives, where did that idea come from. What you going to do, bob around the channel for 5 hours waiting for the next slack, what about gas, take two twin sets, not got them, so whats the option, nip back to port and get a quick trimix top off, I don't think so.

Tis true, to push your gas is a risk, but then going to 65M in the first place is a risk. Arguing with my partner in the kitchen with all those sharp knives about is also a risk.

Two dives, that is just a silly idea.

Andrew

[Tibbs]

Originally Posted by [b

Quote[/b] (AndyP @ Sep. 22 2003,20:29)]

Two dives, where did that idea come from. What you going to do, bob around the channel for 5 hours waiting for the next slack, what about gas, take two twin sets, not got them, so whats the option, nip back to port and get a quick trimix top off, I don't think so.

Tis true, to push your gas is a risk, but then going to 65M in the first place is a risk. Arguing with my partner in the kitchen with all those sharp knives about is also a risk.

Two dives, that is just a silly idea.

Andrew

No, do it the next day or next week. No hurry when it comes to diving - the wrecks will still be there!

As for the 'diving to 65m is a risk' it's that acceptance of the risk that causes problems. Personally I want to eliminate as much risk as possible. If it means doing a max of 90 minutes in the water and going again next week, I'll do it. I want to still be doing this diving in 30 years and I fully intend on doing so. The wrecks will still be there then, so I can afford to be patient.

And as for the 90 minute max time - nope, it's advisory for all ocean dives. You get 25 minutes on a 70 metre dive, which is plenty. As ever, you want more, go again!

Obviously for extreme depths the timings go out of the window - you wouldn't get much bottom time on the Britannic at 120m!

[Tibbs]

Originally Posted by [b

Quote[/b] (Mark Chase @ Sep. 22 2003,19:46)]Tides and the other divers on the boat might not make this an option. In the reel world you spend £100 on the dive you travel 2.5 hours out to the dive site and you max the dive. The you go home. Going out all that way, spending all that money and doing a 20min botom time is lunacy to me but then I am a dive muppit so waht the hell do I know

ATB

Mark Chase

If you can not blow off a dive without a thought for the money, you shouldn't be doing the dive. If you get mad at your buddy because he thumbs the dive at the bottom of the shot at 70m, costing you a twinset of gas and a shedload of deco, because 'he didn't feel right' you shouldn't be doing the dive.

Of course if you want to cover more wreck in less time and do less deco, buy a scooter!

Diving is expensive, get used to it.

Chris

[Rob Evans]

Originally Posted by [b

Quote[/b] ]Obviously for extreme depths the timings go out of the window - you wouldn't get much bottom time on the Britannic at 120m!

Recent quote from the Inspiration list&gt;&gt;

Just a quick note to say we have returned from a very successful Expedition
 to HMHS Britannic in the Aegean.
 
 As you may be aware, Britannic has been off limits to recreational divers
 since '99, however our team has been working on a documentary for National
 Geographic US and Carlton and got special dispensation for the Expedition as a media
 project and forensic analysis.
 
 We had a lot of bullshit to deal with within the various Greek Ministries
 which cost us a few days diving, but overall the Expedition was a raging success
 as we achieved most of our mission objectives. I cannot go into specifics at
 this stage as we are under contract with National Geographic and Carlton TV,
 but I can say we have achieved results that we were told were not possible, all
 of the divers did a great job
 
 All divers were on closed circuit, mostly Inspirations (2no. Megs) and all of
 the units performed brilliantly.
 
 The wreck itself is visually stunning, in ambient light and everything is so
 easily recognisable making navigation and scootering along and into the wreck
 real easy, it's the ultimate for freeswimming divers. We were pulling between
 30-48 minute bottom times on the Inspirations for no more than 6½ hour total
 run times. All decompressing was on VR3 with additional Deep Stops with no real
 problems.
 
 There's still tons to do on the wreck, I think you could spend years on it
 and still not be satisfied, but I'm really proud of what the guys achieved in
 the time available.
 
 There will be 2 versions of the Expedition/Documentary, One on Channel 5
 which will be the history of Britannic with a little of the Expedition and another
 on National Geographic which will be all about the dive and the logistics
 involved. Should be on around Christmas time.


Sorry, couldn't help that one guys  

[Diving Dude]

Originally Posted by [b

Quote[/b] (Rob Evans @ Sep. 22 2003,22:49)]  mostly Inspirations (2no. Megs)

Rob.

What's 2 no megs?

[Rob Evans]

Dunno. Nasty new technology I think. Won't have any truck with it m'self.

Dammit, wrong forum again