Deco gas quantity

[Tibbs]

Originally Posted by [b

Quote[/b] (diving dude @ Sep. 22 2003,22:56)]

Rob.

What's 2 no megs?

It's probably this rebreather:

Megalodon Rebreather

Chris

[Mark Chase]

Originally Posted by [b

Quote[/b] (Tibbs @ Sep. 22 2003,22:17)]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.

Diving is expensive, get used to it.

Chris

Very noble sentiments but total bull in realiaty. If my buddy called the dive at the bottom of the shot or any where else on the dive except the surface or 6m bubble stop, I would call the dive no question. To actualy plan to do a short bottom time is the bit I dont get. If it is warm enough to do the hang time I will do it to my personal max.

25mins at 70M? I dont think so.  Using your back gas and 32/30 and 100% for deco you would be in the water for over 100mins running a 30/85 profile. To get down to 90mins you would have to run a 30/100 profile. So on one hand you add safety by shortening the bottom time and on the other you take a big risk running agresive deco profiles ?? I dont get it.  

We just take diferent risks. I would do the bottom times planning a minimum of 30mins on a dive up to 70m and aiming for 40+ if I can manage the gas and do the deco. No rule of thirds, but additional bail out on travel gas and drop tanks on the boat. Then I would plan a nice safe 20/80 profile to get me out of the water feeing good.

You aparently plan short bottom times, have loads of gas in reserve that you have to blow off after the dive and then run agresive deco profiles to stay within a set run time.

A trimix dive costs £100 or more each trip. I get maby two deep dives booked a month if I am lucky and then the weather can blow out half of them in a bad year. So forgive me but once I actualy get to site I will try to max the dive.

Your comments on 'diving is expensive get used to it or dont dive' are insulting. Diving is not just for the rich. There are a lot of divers out there who can just about afford to do it. To tell them you shouldent do it unless you have shead loads of mony to burn like me are inflamatory but i have tried not to rise to the bait.

ATB

Mark Chase

[Tibbs]

Originally Posted by [b

Quote[/b] (Mark Chase @ Sep. 23 2003,08:47)]Your comments on 'diving is expensive get used to it or dont dive' are insulting. Diving is not just for the rich. There are a lot of divers out there who can just about afford to do it. To tell them you shouldent do it unless you have shead loads of mony to burn like me are inflamatory but i have tried not to rise to the bait.

Why is it insulting?

If you couldn't afford to get the brakes on your car fixed, would you drive your kids to school?  

Like most people I do not have as much money to spend on diving as I would like. But I cut my coat according to my cloth. I pick and chose the trips I do with great care, and if I need to get in the water, but can't afford to get on a boat, which happens more often than I would like - I go to a muddy puddle somewhere and train.

I fully accept that life is not ideal but I am a patient person, and highly risk averse. I'd much rather chicken out today and do two dives later, than have this one be my last...  

And as for the agressive dives thing - I forgot to say that I'd do it on 15/55 back gas, 35/25, 50 and O2, otherwise I wouldn't be able to do the deco on 7l stages. On a 30/85 it gets me out of the water in 94 minutes. Of course were I doing dives like this, I'd hold off until I could afford a scooter and do it then!

Chris

[Rob Evans]

Originally Posted by [b

Quote[/b] ]It's probably this rebreather:

Megalodon Rebreather

Absolutely right Chris, it was just me being flippant.  In all likelihood piloted by Christina Campbell & Chris Hutchinson.  Hell of a dive eh?  Still, 6.5 hrs deco. Rather them than me.

[Finless]

The answer to the question of how much deco gas to carry, with reference to allowing for your buddy, relates directly to your comparative strength or speed of finning.

If you are by far the strongest, or fastest finner out of you and your buddy, then you really only need to carry enough backup/deco gas for yourself.

[Mark Chase]

Originally Posted by [b

Quote[/b] (Tibbs @ Sep. 23 2003,12:35)]

Originally Posted by [b

Quote[/b] ]
If you couldn't afford to get the brakes on your car fixed, would you drive your kids to school?  

That is obviously a safety issue. We are not discussing a safety issue we are discussing alternitive aproaches to safety. If you want a safety / car analagy why not say If your Ford Focus needs new breaks you should fit four piston floating caliper Brembos with ceramic disks and Fidaro racing pads. shoulds only cost you about 2 grand. And no one could argue that they will stop you quicker than the standard breaks on a Focus and are therefore safer. So obviously any one who couldent afford to do the above upgrade is in your opinion not fit to dirve their kids to school?

Diving is expensive not only in terms of mony but also time. As a result I will always try to maximise the potential of any dive. It IS insulting to say diving is expensive get used to it. I know its expensive but that is no excuse for wasting money on unused gas and patheticly short bottom times.

Originally Posted by [b

Quote[/b] ]I fully accept that life is not ideal but I am a patient person, and highly risk averse. I'd much rather chicken out today and do two dives later, than have this one be my last...  

I have two kids and as a result I dont take uncalculated risks.
I dont consider the diving I am doing to be high risk. Every dive I do has a bail out contingancy planned into the profile. Usualy this will be in the travel gas and on deeper dives a drop tank. The travel gas is a simple nitrox fill which is cheep and can be decanted into my wifes single tank and the drop tank can be used over and over again. This system is economical, maxes the potential for the dive and is IMHO a safe system.

Originally Posted by [b

Quote[/b] ]And as for the agressive dives thing - I forgot to say that I'd do it on 15/55 back gas, 35/25, 50 and O2, otherwise I wouldn't be able to do the deco on 7l stages. On a 30/85 it gets me out of the water in 94 minutes. Of course were I doing dives like this, I'd hold off until I could afford a scooter and do it then!

Chris

Three stages increases task loading and increases the posibuility for error but its your choice for me 70m just dosent justifie the use of a third stage. I used a third but redundant gas on my deep dives as bail out to first deco but it wasnet in the gas plan and has never actualy been used. It was back mounted and breathable at max depth.

Your comment on the scooter is interesting. You should talk to a few divers who use scooters. Most of the time the viz is not good enough to use them so be prepaired to bin a lot of dives.

When you have actualy done a season of deep mix diving i would be interested to read your post again. The first deep dives I did were with 25min bottom times but with 5min decents a 20mins on the bottom I soon found that to be no where near long enough to compensate for all the efort. So I upped to 30 then 35 and now 40+min run times I now feel like I have actualy dived the wreck rather than bounced the deck and glanced about for a couple of mins.

Maby it's just me but i would be interested to see what your up to in the future anyway.

ATB

Mark Chase

[And]

<font color='#0000FF'>Hi

Just a few things. This 90 minute rule is not as strict as all that, and is a guideline which acknowledges that ocean dives are significantly shorter than cave. You don't need to ensure that your runtime is below 90 minutes as long as the conditions allow. They did not dive the britannic with 90 minute runtimes and many deep wrecks also break that guideline.

Tibbs, there would be little need for 3 stages on that dive to 70 mtrs (why does every discussion turn into a dive plan for 70 mtrs, tunnel vision thats why ), get rid of the 35/25 as you wouldn't push that pp02 over a 1.4, deco gasses start with the 50% at 21 mtrs and you only go to 1.6 po2 when you hit 21 mtrs. It makes little difference to your profile if you check. I fell into that trap on an earlier thread. Best not to get involved in this stuff as it only gets picked on by others.

Mark, there is no travel gas as we have discussed before, it is a waste of a bottle. And you use AIR as your bailout to first stop, again which we have discussed is not required in a proper buddy diving system. The gasses you use inherently make the dive more complicated than it needs to be, with little real benefit. Sorry, but thats what I think.

Pierre, with deco gasses there are choices. As with all DIR diving you also have ample bailout for your buddy and so you need enough deco gas to be able to complete the dive safely with you and your buddy. AL80's are favoured which will have plenty of gas at 20 mtrs for most dives. You could buddy breathe or do a 6 on, 6 off or something. You could also deco on back gas as that will surely be one of the possible plans bearing in mind you will have plenty left. There is NEVER an occasion where you need to leave your buddy as the stops are the same. You can also use the yellow smb protocol which signals surface cover to get you oxygen or whatever you have agreed. Loads of choices Pierre, and the answers are determined in your own dive plan. The initial suggestion which you stated about gas quantities seems logical.

Andy

[Pierre Farrugia]

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

What we considered as well was a pair of 2nd stages on deco bottle. So if sh''t happens just breath from it. I know about free flows but till now I never encountered one and if I have one I just use my buddy's gas. But then I can just use travel gas and bail out on it. Drop tanks are a big problem as normally here you would be diving from a boat with others and I will never rely on boat man for this unless we are a very small group. Here we normally use 10 liters with 232bar in and I always come up with plenty of gas.

[Mark Chase]

Originally Posted by [b

Quote[/b] (wetlettuce @ Sep. 23 2003,15:21)]

Originally Posted by [b

Quote[/b] ]Mark, there is no travel gas as we have discussed before, it is a waste of a bottle. And you use AIR as your bailout to first stop, again which we have discussed is not required in a proper buddy diving system. The gasses you use inherently make the dive more complicated than it needs to be, with little real benefit. Sorry, but thats what I think.

I dont folow this, what do you meen?

Travel gas just gets you from the surface down to back gas thus saving back gas and then it gets you up from the deep stops to the shalow deco stops. It is also used when the back gas is below life suport in 02 content. &nbsp;

The final job of travel gas is to reduce the 02 spike by preventing a drop to avery low ppo2 on back gas up to 6m then suddenly whacking 100% in your mouth and hitting 1.6

Doing a 60 -70m dive on a single deco mix without travel gas is not advisable IMHO

I use 32% generaly but I would vary this to suit the dive if required. I dont like the 50% option as you cant get on it deep enough for the mix to offer any bail out from the bottom but thats just my personal thing and I know a lot of 50% users.

The bail out gas would suit the dive. Both the dives where I use it were 56 to 58m to the top of the wreck which is where I will be at the end of the dive and I am happy to breath air at these depths whilst imediatly ascending. If it were deeper I would use mix. Now I own a whip I would decant the last of my 18/40 into it and air top it and use that. I didnt have a whip on my last trip.

If you are saying that 50% is not a travel gas and you are just running two deco gas mix's then thats fine but the generic term for all gas under deco mix for the 6m stop is travel gas. If you were using 32% and 50% then 50 % would be the deco gas.

The reasion we generaly refer to 60 or 70m dives is the necesity for the correct gas balance and the deco comitments become much more acute after 60m. A 45 -55m dive can easily be done on Nitrox or Air let alown Trimix and multiple stages so whats the point of using that as a comparison.

On the subject of stages:

Two 7ltr stages:

Cheeper than 10s
Will do most dives
Wastes less gas on re fills
Lighter than 10s
Smaller than 10's
Easier to mount both on left if you rearly have to dive like that.


Two 10 ltr stages

More gas greater safety margin on dive
Less need for good high bar fills
Will cover most if not all recreational dive depths

ATB

Mark Chase

[jasondrake]

I just dive solo and save myself a fortune. Less gas, less messing about and fewer binned dives. And I get to make all the decisions. Luxury.