Trailing negative tanks and using a leash
- Thread starter Daniel Dilley
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other option that I've done is to keep the AL80's *Luxfer infinitely preferred over Catalina*, and only pump them up to 2000/2200 or so. 2200lbs still gives me about 56cf of gas in the bottle, but it takes 1.6lbs of gas out of the cylinder which really helps the way it floats. With safety margins on a deco bottle it gives me 44cf of usable O2 and about 35 minutes of O2 decompression. For the mid gas bottles I'll use them as travel gas on the way down which helps with deco time as well as getting the tanks lighter. Both deco bottles will then go to the butt. Dive Rite used to have a really good article about it on their website, but I can't find it.
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Daniel Dilley
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Hi Everyone
Thank you all for your responses, i appreciate the time and effort from you to answer my question.
Could i as you adv tmx OC divers out there. When you complete a dive requiring three stages do you ever use a full tank of rich mix and trail it or do you always use less deliberately so the tank is more positive. what about you out there using nitrox80?
Thank you all for your responses, i appreciate the time and effort from you to answer my question.
Could i as you adv tmx OC divers out there. When you complete a dive requiring three stages do you ever use a full tank of rich mix and trail it or do you always use less deliberately so the tank is more positive. what about you out there using nitrox80?
PfcAJ
Contributor
I just use full tanks. With al80 and/or 40s for deco/ stages it's no big deal.
In my opinion, I'd rather come home with unused gas than be stuck underwater wishing I had brought more gas, so I would go with full tanks.
Luxfer tanks have decent buoyancy characteristics. And on dives that require three deco gases, one of the tanks should have some helium in it solving the negative buoyancy issue.
But as I believe I said earlier in this thread, I wouldn't get carried away on dives that require lots of deco in the open ocean. Let's take a deep wreck in 270' as an example. For a 20 minute dive on that wreck, the difference in deco by using three gases as opposed to two is less than ten minutes. Personally, I wouldn't want to do a much bigger bottom time in the open ocean than that without substantial in water support, and the ten minute deco delta is not worth bringing three bottles.
Luxfer tanks have decent buoyancy characteristics. And on dives that require three deco gases, one of the tanks should have some helium in it solving the negative buoyancy issue.
But as I believe I said earlier in this thread, I wouldn't get carried away on dives that require lots of deco in the open ocean. Let's take a deep wreck in 270' as an example. For a 20 minute dive on that wreck, the difference in deco by using three gases as opposed to two is less than ten minutes. Personally, I wouldn't want to do a much bigger bottom time in the open ocean than that without substantial in water support, and the ten minute deco delta is not worth bringing three bottles.
PfcAJ
Contributor
IMO, the big advantage to bringing 3 gases is the reduced
minimum gas needed.
The amount needed to go from 270 to 70 is a lot.
minimum gas needed.
The amount needed to go from 270 to 70 is a lot.
Valid point. You could easily run it on 120' and 20' gases and still keep the bottle juggling minimum and only pay a five minute penalty.
Yes, it's not optimal, but neither is racking up a ton of deco in the open ocean. There's too much crazy stuff out there...
Yes, it's not optimal, but neither is racking up a ton of deco in the open ocean. There's too much crazy stuff out there...
PfcAJ
Contributor
Curious as to what parameters you're using to derive those numbers. I plugged it into deco planner and i did not get a 10mins difference. I ended up with a 34min difference (20,70,120 vs 20,70). Bottom gas 12/70, 30/70gf. 30min difference with 20/85gf, and 26min difference with vpm+2.
Different gases?
It's got to be the bottom mix, or instant descent to depth.
I calculated with a bottom mix of 15/55 (po2 1.4, end 100'), and used 270' being the sand for selecting it (I was thinking about the RBJ when I threw this hypothetical dive out there). Deco gases were 120' of 35/30, 70' of 50% and 20' of 100%. Buhlman Zhl-b with 50/85 gf. Descent rate of 100' per min, so would hit the sand at 3 minutes in and begin ascent 17 minutes later.
20 minutes to begin of ascent gives a runtime of just under 90 minutes for all 3 gases, 95 for 50%/100%, 103 for 120'/100% and 100 minutes for 120'/70'.
Beginning ascent at 23 minutes to give a full 20 minutes at 270' gives me 103 for all 3 gases, 112 for 50/100, 120 for 120'/100% and 118 for 120'/70'.
Using your bottom mix, all three deco gases on my original schedule give a 102 minute rt, 50/100% gives 117, 120'/100% gives 118 and 120'/70' gives 115 using the 50/85 gf. That's a 12-15 minute delta.
I'm using multideco on android and pretty comfortable with the 50/85 gf, it's been working pretty well for me; I did a five mile run this morning at my normal pace after diving with Charlie yesterday at D2.
I calculated with a bottom mix of 15/55 (po2 1.4, end 100'), and used 270' being the sand for selecting it (I was thinking about the RBJ when I threw this hypothetical dive out there). Deco gases were 120' of 35/30, 70' of 50% and 20' of 100%. Buhlman Zhl-b with 50/85 gf. Descent rate of 100' per min, so would hit the sand at 3 minutes in and begin ascent 17 minutes later.
20 minutes to begin of ascent gives a runtime of just under 90 minutes for all 3 gases, 95 for 50%/100%, 103 for 120'/100% and 100 minutes for 120'/70'.
Beginning ascent at 23 minutes to give a full 20 minutes at 270' gives me 103 for all 3 gases, 112 for 50/100, 120 for 120'/100% and 118 for 120'/70'.
Using your bottom mix, all three deco gases on my original schedule give a 102 minute rt, 50/100% gives 117, 120'/100% gives 118 and 120'/70' gives 115 using the 50/85 gf. That's a 12-15 minute delta.
I'm using multideco on android and pretty comfortable with the 50/85 gf, it's been working pretty well for me; I did a five mile run this morning at my normal pace after diving with Charlie yesterday at D2.
PfcAJ
Contributor
All in the GFs 
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