LP50 Doubles and/or Backmount Independent Doubles Accepable for ITT & AN/DP/HT?

[-JD-]

TL : DR Looking for authoritative responses - jump down to the two bold-underline questions below if you aren't interested in the whys.


I'm working on recovery from a severe disk herniation and have too much time on my butt. So I've been thinking about my eventual return to diving, dealing with my expected limitations, and preventing re-injury; while also moving on to my end goals which will be ITT and AN/DP/HT for OC (I'm thinking RB eventually, but that is really for another thread)

I'm mostly asking for feedback from instructors that work at this level, but if you have relevant experience in this as a student please join in.

Please no "do it in sidemount." I do want to get sidemount training along the way to expand my capabilities, but backmount is likely more practical in my expected dive environments at this point.

I was going in this direction anyway because moving full size banded twinsets around was already doing a number on me before my disc issue slammed me. I could (can?) happily carry 2 HP120s one in each hand, and lift one at a time for shelving, filling etc., but the weight and awkwardness of the full size banded twins is just not happening for handling loading in and out of vehicles, fill tank, etc.

I have a set of LP50 baby doubles and filled with love they give me a good 120 cuft. I may be able to buy-back the twins twins so I might have 2 sets in the end.

Bench to water and back was OK with my HP100 twins. it was the off-back handling that was making me "unhappy." I'm hoping that I will be able to to handle double HP100s again once they are on the rig.


So specific questions:

1) Would backmounted LP50 Manifolded (but preferably isolated) doubles be acceptable for ITT and AN/DP/HT

2) Would backmounted independent HP100 doubles be acceptable for ITT and AN/DP/HT (if not, please, why not - since independent sidemount seems acceptable.)


TIA!

 

[Akimbo]

What is ITT & AN/DP/HT?

 

[rddvet]

What is ITT & AN/DP/HT?

Intro to tech and advanced nitrox/decompression procedures/helitrox

 

[runsongas]

intro to tech, advanced nitrox/decompression procedures/helitrox

@-JD- for TDI it is up to the instructor, but both lp50 doubles and independent doubles meet the minimum requirements provided the capacity is sufficient. you will need to check with the instructor and calculate your expected consumption if 120cf is enough to carry out the planned training dives

 

[-JD-]

intro to tech, advanced nitrox/decompression procedures/helitrox

@-JD- for TDI it is up to the instructor, but both lp50 doubles and independent doubles meet the minimum requirements provided the capacity is sufficient. you will need to check with the instructor and calculate your expected consumption if 120cf is enough to carry out the planned training dives

Thanks!

I guess that may mean some additional instructor shopping when the time comes. I'd prefer that not to be the deciding factor in my choice, but y'a got to do whatcha got to do ...

 

[-JD-]

What is ITT & AN/DP/HT?

Actually, would you mind moving this over to Tech? Sorry for being a dope.

 

[Akimbo]

Actually, would you mind moving this over to Tech? Sorry for being a dope.

Done, no worries.

 

[sabbe]

TL : DR Looking for authoritative responses - jump down to the two bold-underline questions below if you aren't interested in the whys.

So specific questions:

1) Would backmounted LP50 Manifolded (but preferably isolated) doubles be acceptable for ITT and AN/DP/HT

2) Would backmounted independent HP100 doubles be acceptable for ITT and AN/DP/HT (if not, please, why not - since independent sidemount seems acceptable.)


TIA!

I’m an ITT instructor but not yet AN/DP.

Almost anything is acceptable for ITT and most instructors will give leeway letting you dive what you own now. It’s like the discover scuba of tec diving.

For AN/DP double 50s don’t have enough gas to get into deco and have enough redundancy to get you and buddy out of trouble. Buddies won’t want to dive with you because you’d be limited with half the gas they’re carrying.

If an instructor allowed you to use double 50s at all, it would likely need to be done as a private one on one class.

You would probably be allowed to use double 50s for AN/DP training dives where you’re simulating deco but the checkout dives will require something bigger. My helitrox instructor required double 100s minimum. Someone with incredibly low SAC could get by with slightly less, but it would take a pair of divers with really low SAC rates, typically tiny females to actually do deco dives with such small tanks. Again, because if you’re stuck with a ceiling in deco you need redundancy for you and your buddy.

Two suggestions:
1. Find a instructor and boat willing to let you take off gear in the water.
2. Look at Helitrox instead of AN/DP. The work is the same and you have more options when done.

Sam

 

[Jim Lapenta]

TL : DR Looking for authoritative responses - jump down to the two bold-underline questions below if you aren't interested in the whys.


I'm working on recovery from a severe disk herniation and have too much time on my butt. So I've been thinking about my eventual return to diving, dealing with my expected limitations, and preventing re-injury; while also moving on to my end goals which will be ITT and AN/DP/HT for OC (I'm thinking RB eventually, but that is really for another thread)

I'm mostly asking for feedback from instructors that work at this level, but if you have relevant experience in this as a student please join in.

Please no "do it in sidemount." I do want to get sidemount training along the way to expand my capabilities, but backmount is likely more practical in my expected dive environments at this point.

I was going in this direction anyway because moving full size banded twinsets around was already doing a number on me before my disc issue slammed me. I could (can?) happily carry 2 HP120s one in each hand, and lift one at a time for shelving, filling etc., but the weight and awkwardness of the full size banded twins is just not happening for handling loading in and out of vehicles, fill tank, etc.

I have a set of LP50 baby doubles and filled with love they give me a good 120 cuft. I may be able to buy-back the twins twins so I might have 2 sets in the end.

Bench to water and back was OK with my HP100 twins. it was the off-back handling that was making me "unhappy." I'm hoping that I will be able to to handle double HP100s again once they are on the rig.


So specific questions:

1) Would backmounted LP50 Manifolded (but preferably isolated) doubles be acceptable for ITT and AN/DP/HT

2) Would backmounted independent HP100 doubles be acceptable for ITT and AN/DP/HT (if not, please, why not - since independent sidemount seems acceptable.)


TIA!

1 . Yes, they would meet the standards for ITT and AN. DP/HT? I don't really see how unless you are planning very short dives with limited depth. Remember you don't just need to have enough gas for you. You need to carry sufficient gas depending on you and your buddy's rates of consumption, to have sufficient reserve in case of a catastrophic gas loss to get you and them to the surface with all required stops. Also, two of the DP dives need to be in excess of 100 ft. When I taught DP we planned the 2 dives to 125-130. You also need to demonstrate shutdown drills. If you can do it with 50's that's fine. I would personally be leery of independent cylinders because, in an OOA situation, you'd need to show me you have managed the gas well enough that if you do need to donate, there will be enough gas in that cylinder to do so. So you'll need to be switching regs just as if you were on sidemount.

2. Yes, with the caveat above. Are you switching cylinders at the planned intervals? Which one are you donating from? How much gas are you leaving in it. If you run low are you prepared to buddy breathe with the person you are donating to? Sidemount divers plan for a gas reserve in the long hose cylinder to donate. As well as having sufficient gas in the other cylinder so that they don't run low. You'll also need to be carrying a deco cylinder for DP of sufficient size to share. On one of the dives you will do a final stop buddy breathing off that cylinder to simulate a loss of deco gas.

Now that said, would I allow independent LP50's for a deco class. That would depend on who you are buddied with. If your buddy shows up with LP85's or HP 100's expecting nice long dives with time to really drill, I don't see how that would work. Unless they agreed beforehand, IMO it's not fair to them to limit the dives that much. Depending on SAC rates. So probably no. A private class? Probably not as well. If I'm going to the effort to put on a class I want to enjoy the dives also.

I have to also consider that you may not be able to get those nice fills and so, there is not going to be sufficient gas in those tanks for decompression dives. Given that an alternative to a loss of deco gas is deco'ing on back gas. Will you have enough to do that?

I generally require a minimum of LP72's for deco procedures. I use 75.5's and LP 85's. If a person is a gas hog, then 95- 100 cu ft cylinders minimum.

.
Just for giggles, Run the numbers on this dive, using your SAC rate, 120 ft for 25 minutes with a conservative descent using 100% O2 for deco. How much gas do you need? How much will you need if we need to share air 20 minutes in that effectively doubles the SAC rate on that supply to get to the surface. My SAC is .42. How much gas do you have left in the cylinder you are going to donate to me? Will you now have enough in your cylinder for the ascent with the required stops until we can get on our deco gas?
This is what I need for that dive. So I need to be carrying a minimum of 150 - 160 cu ft of gas to also take the rule of 3rds into account. If I get a good fill in my 75.5s I'll have 170 cu ft +. If I can't get a good fill I'll run my 85's.
Decompression model: VPM - B
DIVE PLAN
Surface interval = 1 day 0 hr 0 min.
Elevation = 0ft
Conservatism = + 3
Dec to 120ft (4) Air 30ft/min descent.
Level 120ft 21:00 (25) Air 0.95 ppO2, 120ft ead
Asc to 50ft (27) Air -24ft/min ascent.
Stop at 50ft 0:05 (28) Air 0.52 ppO2, 50ft ead
Stop at 40ft 3:00 (31) Air 0.46 ppO2, 40ft ead
Stop at 30ft 4:00 (35) Air 0.40 ppO2, 30ft ead
Stop at 20ft 4:00 (39) Oxygen 1.59 ppO2, 0ft ead
Stop at 10ft 5:00 (44) Oxygen 1.29 ppO2, 0ft ead
Surface (44) Oxygen -20ft/min ascent.
Off gassing starts at 85.1ft
OTU's this dive: 38
CNS Total: 16.1%
Gas density: 5.4g/l
55.1 cu ft Air
5.1 cu ft Oxygen
60.2 cu ft TOTAL

 

[-JD-]

@sabbe & @Jim Lapenta

Thank you both for the advise and analysis (Jim, super detail appreciated)!

I expect that most of my work will be land based, so my concern has been gearing up and walking in from a distance. The LP50s are roughly equivalent to an HP120 in effective capacity and from a carrying perspective, so hopefully, I should be able to handle them (If not, I'm getting toward the realm of diving with accommodations for even basic stuff) That would allow me to work through the ITT and maybe AN portions without bogging things down.

If, and how long it will be before, I can carry double HP100s on my back for any significant distance is an unknown I don't want to be stupid and re-injure. In part it will depend on if recovery is through PT & plain healing or if I end up with surgery. Carrying my tanks down and assembling by the water could be an option, even donning/doffing in the water if necessary. I'd prefer not to because it would be somewhat disruptive to the class. But I do absolutely get the need for sufficient gas capacity. So I guess that will have to be made part of the known equation going in.

I am also absolutely aware of the need to correctly, and conscious of reserve, alternate breathing when on independent cylinders. My thought has been that backmount ID or sidemount differ by mounting position not breathing technique. I plan to have this worked out and practiced before starting down the classes.

Given my current circumstances, I see the ITT & AN/DP/HT sequence serving me in 4 ways.
1) Honing buoyancy, propulsion, planning, etc skills and training beyond my expected operational limits.
2) The ability to safely execute planed dives with very short deco and/or execute dive profiles that would otherwise be no-stop, but with enhanced conservatism that puts me into limited deco.
3) The ability to deal with OH SH*T circumstances to the best of my available gas resources (beyond just blindly following the stop by stop directions on my dive GPS)
4) Aspirational at this point, but I think a RB may be in my future if I can make the economics work out. (I'm an engineer and long--lapsed SEL private pilot so I would enjoy the rigor and RBs are way cheaper). This is a stepping stone to RB.