How deep/long before you start running 80's for deco?

[texdiveguy]

So how common is it to not have access to a shop with a booster pump for O2 fills?

Location- location- location....$$-$$-$$.

In my local LDS area, 90% of the dive shops would be clueless as to what a booster is!

Feel lucky....

 

[Gilldiver]

The only shop that I know of in New England that has a Booster is New England Dive Center in Wallingford, CT. Even the local DIR/GUE shop guys go to it to get boosted gas or to get fills where they don't have to dump whatever is already in their tanks.

So one shop in the 6 New England states.

 

[Gilldiver]

I am more then willing to be corrected, anyone know of a shop in Mass with a booster?

 

[battles2a5]

I have to drive 2 hours for boosted gas. Booooooo.

 

[ucfdiver]

After cave training and personally seeing people loose deco gas or at least the abilty to use the deco gas they carry I have decided to always dive thirds on all gas including deco gases unless a certain situation calls for different protocol.

This means carrying larger tanks but usually I can stash them anyway. For this weekends dive I will be using an 2 40's of 40% and a 40 of 100% for a 215' multilevel mission orientated dive.

Curious, why dive to 1/3 on o2 for the majority of cave dives? Since you don't have any penetration on it, wouldn't reserving an extra 50% make more sense?

Example-
15min o2 deco for this dive, and one deco bottle fails.

You would do 2/3 of your deco on o2, (10min) and then pass the bottle off to your buddy, who has been on back gas for 10 minutes. Now, you've done 10 out of your 15 minutes, and he's done 5 out of his 15 minutes (since 32% takes basically 2x the deco time o2 does, we cut it in half) at this point.

This leaves you with 5min of o2 deco, so you'll need to stay on 32% for 2x that time, or 10 minutes. Your buddy has done 10min of 32%, so he'll need 10 minutes of o2 deco. You will both finish deco at the same time.

Am I missing something here?

 

[Meng_Tze]

I have never had the need to use an al80 for O2. An al40 will last me about one full hour on O2. If you have to stay on O2 for one full hour you either have not planned deco properly or are doing such big dives that you should consider other means to make the dive more efficient.

Carrying 2 al40's for redundancy make better sense than one al80 to share...

Obviously other deco/stage gases do come in al80's.

 

[DA Aquamaster]

UCF is on the money. There is no need for a thirds rule with O2 from a lost gas perspective, and with half in reserve, you will have badly overstayed the deco to need it all and will be in back gas trouble long before then.

Even with a moderately long dive where O2 may be the only deco gas (figure a 60 minute cave dive with mean depth of 110 ft for 60 minutes), you are only going to have about 25 minutes of deco, with 15 on O2 and use around 9 cu feet of O2 - maybe 12-15 if you I am in some flow. That still leaves at least a 50% reserve in an AL 40 and I won't come close to using that even if I double my bottom time to 120 minutes (in which case I would have needed staged bottom mix anyway) as the time at 10 and 20 feet is still only 36 minutes, using about 20 cu ft of O2 - still a 50% reserve.

In that situation the 10' and 20' stops don't get that much longer, the initial stop depths just get deeper so a 2/3 reserve of O2 is pretty useless.

An AL 80 and planning with thirds might make sense with a 50% deco mix, as the amount used in the example above jumps from 18 cu feet to 54 cu feet with 50%, but using a 50% deco gas with a 32% backgas almost never makes sense and fixing that flaw again eliminates the need for thirds.

In short, using a thirds rule on deco gas just for the sake of using it does not make much sense.

 

[flareless]

This is the method I prefer:

HOG stage rigging

Now that's what I'm talkin' about! Actually I got my rigging info here. I like it because it's step by step, simple to do and I didn't manage to screw it up. In addition, I carry the material to make another rigging in my tool box.

The important point is that should the need arise, you want to be able to cut that clip loose.

 

[DA Aquamaster]

I've see that site too. Basically the same thing, they use a more complicaed approach to tying off the end, but it is slightly cleaner and the bolt snap stays attached if you remove the stage strap.

I still prefer clear hose over the rope. I have also used tubular webbing rather than innertube over the hose clamp and it seems to hold up better.

You can tension the cary handle with pressure pushing the snug but not yet tight hose clamp down the bottle. If you also do this with the line pre-soaked and fully saturated, it will stretch a bit more. It will be quite tight when dry but just snug when wet with less slop. Its not required with a used rope but some new nylon rope can stretch quite a bit initially.

 

[flareless]

If you also do this with the line pre-soaked and fully saturated, it will stretch a bit more. It will be quite tight when dry but just snug when wet with less slop. Its not required with a used rope but some new nylon rope can stretch quite a bit initially.

Excellent tip! Thanks.