30/30 ?

[Nimrod Chen]

hi
i'm thinking of starting using 30/30 for rec dives with no deco and would like to hear from anyone who is diving it , do you just use min deco or do you change your profile ?
any one had problems with it ?

Nimrod

[lamont]

hi
i'm thinking of starting using 30/30 for rec dives with no deco and would like to hear from anyone who is diving it , do you just use min deco or do you change your profile ?
any one had problems with it ?

Nimrod

We dive it almost just like 32% and don't have any issues with it -- doing 1s from 1/2 max depth, and usually 3 @ 20 fsw, 3 @ 10 fsw for good measure (for coming directly up from 120 we usually start the stops at 70 fsw, though -- saturated tissue compartments at 120 fsw have a ppInert of 75 fsw). For an "NDL" we typically use 30 mins at average depth of 100 (generally 110 -> 90 non-reverse profile). I don't know if you're tech 1 or not, but 1-1-1-3-5-10 is a deco-on-backgas profile that we use if we're pushing the NDLs to stay conservative. Often, though, we're shorediving and will do a level of 10-15 mins @ ~50 fsw and take 10-15 mins coming up from 30 fsw. For tech 1 divers, you can clean up on 100% O2. If we're doing support diving on 30/30 running up against the NDLs we'll clean up with 10 mins of 100% as well because of the likelihood of throwing heavy gear around after we get out. If exposure times are getting longer (roughly over 40-45 mins), and especially if you are diving a squarer profile at 120, you probably want to use 21/35 and 100% O2 for deco anyway to reduce ppO2 (the deco benefits of 30/30 over 21/35 at 100-120 fsw are not that great). We'll use 30/30 to 120 fsw and a ppO2 of 1.4 but that is max depth on profiles that range from 90-120 and average out closer to 100.

Generally, if we're within the "NDLs" for 32%, then we consider 1s from 1/2 max depth to be an option, but usually are never in that much of a hurry to get out, so we add more shallow deco time (which is actually how we usually dive 32% as well...).

[rjack]

30/30 works just like 32% for me, although I have recently started experimenting with 25/25 using only -10% EAD. This is to be able to take advantage of my banked 32% more than anything.

Lamont's 30/30 profiles are heavily padded on the shallow stops partly because they have shallow protected waters to extend those stops in.

On more than one occasion I have done 1 min stop per 10 ft ascents (starting at 50% of average depth) from 100ft (30m) with no noticable adverse affects. If my NDL plan anticipates this kind of ascent I will usually back off the time by 5 minutes to be conservative. The boat is frequently a bit far away from real medical support services. I still almost always do 2 (sometimes 3) minutes at 20ft (6m) and 10ft (3m). But I rarely do 10+ mins at 10ft/3m when doing a free ascent in some current.

If you are trying to be conservative, IMO it is easier to trim a few minutes off your NDLs than to bring O2 (at least for the unattended boat diving I do).

[lamont]

Lamont's 30/30 profiles are heavily padded on the shallow stops partly because they have shallow protected waters to extend those stops in.


not always. we do 1-1-1-3-3 a lot on boat dives with 30/30. but yeah, this is low current and good surface conditions -- although i do recall one dive to 80 fsw for 40 mins on 30/30 that was 1s from 50 and out and that treated me fine...

[rjack]

Oh I know, but for those who don't know the area the

1-1-1-3-5-10 is a deco-on-backgas profile that we use if we're pushing the NDLs to stay conservative


is a "nice to have" deco with stuff to see and protected waters to poke along in. Its certainly not a "must have" profile for a 30 min dive at 100ft/30m.

[lamont]

Oh I know, but for those who don't know the area the


is a "nice to have" deco with stuff to see and protected waters to poke along in. Its certainly not a "must have" profile for a 30 min dive at 100ft/30m.

Oh, no, that's generally just contingency. Here's an example scooter run that we do:

http://www.scriptkiddie.org/Sna225.png

That was a dive appx 3,500 ft out and back on gavins using 30/30 as backgas with no accellerated deco. The plan was 3-5-10 for deco which would allow for 10 minutes of contingency time at depth -- even though we didn't use the contingency we still did the deco. We wound up doing something more like 3-5-20 because we were practicing gas switching at 10 fsw (that's what all the bobbling up and down at the 10 foot stop is). The 30 foot stop also turned into a 27 foot stop because that was the depth of the base of a really cool piling to look at... I think we've done prettier profiles than that one, but I don't have any of the others online...

[rjack]

Good example. The 1st and 2nd halves are like mirror images of each other :-).

In this case you could have probably surfaced at 48 mins (~14 min ascent, average depth ~108ft, BT = 28 mins). Nice to do that 20 mins of shallow stops, but not required IMO.

Padding is good, and if I were Nimrod I'd pad my shallow stops too, especially to start. But rock bottom relys on having a feel for "required" vs. "nice to have stops". Personally, I would calculate rock bottom assuming a 9 minute ascent and a NDL of 25 mins at 110ft (33m).

Richard

[lamont]

Good example. The 1st and 2nd halves are like mirror images of each other :-).

if you look closely though you can see where my shortbody was starting to slow down a little bit though on the way back...


In this case you could have probably surfaced at 48 mins (~14 min ascent, average depth ~108ft, BT = 28 mins). Nice to do that 20 mins of shallow stops, but not required IMO.


yeah, that was all drilling, plus we need to extend the runtime out to >60 mins or it doesn't count... If the shit was really hitting the fan, I would have just continued with 1's to the surface (although with all the gas we have by the time we hit 30 fsw I can't really think of a situation which would require this short of a medical crisis).

i believe one of the lundgren's posted awhile back about testing 1's to the surface from 50 fsw after X minutes at 100 fsw on 30/30 and IIRC below 60 minutes was asymptomatic, 60-65 was fatigue-hits and 70 mins was a type 1? (i can't seem to find it again, so i'm going from memory). that suggests to me that these profiles at around 100-110 for ~30 mins have quite a bit of safety factor built in...


Padding is good, and if I were Nimrod I'd pad my shallow stops too, especially to start. But rock bottom relys on having a feel for "required" vs. "nice to have stops". Personally, I would calculate rock bottom assuming a 9 minute ascent and a NDL of 25 mins at 110ft (33m).

Richard
I still try to figure rockbottom allowing for the deco time using standard rockbottom plus 400 psi / 10 mins for 2 divers at the shallow stops to keep it conservative. Generally we burn about ~1200 psi total per run which leaves 1100+ psi left over after two runs (in double 130s). I wouldn't start out on a 3k line run with less than about 2400 psi, and there's definitely no way to get 3 of these dives off a fill...

[rjack]

yeah, that was all drilling, plus we need to extend the runtime out to >60 mins or it doesn't count...

Doesn't count?

I still try to figure rockbottom allowing for the deco time using standard rockbottom plus 400 psi / 10 mins for 2 divers at the shallow stops to keep it conservative.

So that's why you're diving the 130s :)

Actually on dive 1, I usually turn on time and dive 2 is substantially shallower and I turn on pressure. E.g last friday I did a 109ft dive at KVI tower and we multi-leveled from 109ft up to 50ft. 1min stops up from 40 ft.

Dive 2 was at the Maury barges in ~55 ft of water. We started our ascent with ~600 psi, 1min stop at 30, 3min at 20 and 1 min at 10 (since Melody was a tad light in her new double 80s) Surfacing with ~500psi.

RB +400 is more conservative than I usually plan. But as you can see, in 55ft of water you don't need 900 psi in double 85s (12L) tanks to get you and your buddy to the surface either.

Generally we burn about ~1200 psi total per run which leaves 1100+ psi left over after two runs (in double 130s).

Isn't 1100 psi enough for a $$ break on the next fill at 5thD?

[lamont]

Doesn't count?


dives shorter than 60 mins don't count... =)


So that's why you're diving the 130s :)

Actually on dive 1, I usually turn on time and dive 2 is substantially shallower and I turn on pressure. E.g last friday I did a 109ft dive at KVI tower and we multi-leveled from 109ft up to 50ft. 1min stops up from 40 ft.

Dive 2 was at the Maury barges in ~55 ft of water. We started our ascent with ~600 psi, 1min stop at 30, 3min at 20 and 1 min at 10 (since Melody was a tad light in her new double 80s) Surfacing with ~500psi.

RB +400 is more conservative than I usually plan. But as you can see, in 55ft of water you don't need 900 psi in double 85s (12L) tanks to get you and your buddy to the surface either.


Right. I usually only use 1,000 psi or less on typical recreational profiles in double-130s for the entire dive as well, often much less if it bottoms out at 80 fsw or so. On sunday the posession point wall dive was to a max depth of 96 fsw and at 20 mins into it we were on our way above 70 fsw to the top of the wall around 50 fsw -- my buddy was on EAN32 and I was diving 30/30. I'll typically be okay starting a dive with 1800 psi in double-130s on a normal recreational profile (basically starting with a single-130, although I don't count on the last few hundred psi). I can typically get 3 purely recreational dives off of a fill in the double-130s and typically use 1,000 psi or less over the entire dive (800-900 is pretty typical), and use 700 psi as absolute rockbottom, but I can't remember the last time I've been at depth (90-120 fsw) and had less than 1,000 psi.

The 3k line runs tend to consume more gas because we're usually a little deeper and a little more aggressive. We're also 3,000 ft from home and I like to plan on having a 10 minute delay at depth and being able to hit all our stops with gas to spare. Even though we're not treating the line as a cave, and not dropping deco gas, I don't like to shave it that close since I'd like to make it home rather than bailing somewhere down the line...

Although one time I recall we started with one full set of doubles and one 1800 psi set of doubles and we just went out 3k and then peeled off and did a shallow contour at around 30-50 fsw back to cove 3... That was a planned bailout off the line though...


Isn't 1100 psi enough for a $$ break on the next fill at 5thD?

yup, that's another good point... 2 line runs or 3 recreational dives and then i'm topping 30/30 from 1000 psi and i get a break on the gas already in the tanks...

[rjack]

and use 700 psi as absolute rockbottom,
That would be a close shave for me in LP85s/HP100s. At least it would be much below 60ft.

but I can't remember the last time I've been at depth (90-120 fsw) and had less than 1,000 psi.

Me neither, I'm usually leaving these depths with 1500 or more (in doubles).

I did a dive with Limeyx a month ago on 30/30 in an AL80 stage with 1400 psi remaining of 18/45 backgas. 105ft, 25 mins, 1 min stops up to 30 and a few extra mins at 20 and 10. We both surfaced with ~500 psi in the stage and never touched the backgas (although I used ~100 psi for bouyancy).

I guess in this case we were starting up with 800-900 in the stage (I don't remember exactly).

[Nimrod Chen]

i was thinking of doing what we do for 32% -
1m' per min from 21 and 1@12 ,1@9 , 3@6, 3@3 for a bottom time of up to 30-35 min at 30-33 meters .


Nimrod

[rjack]

I have done that and it works for me. You might want to cut back on the bottom time to start. I don't know your experience or skill level, but starting out conservatively is wise - especially if you are doing a free ascent and might not be able to hold the shallow stops very well.

Richard

[lamont]

i was thinking of doing what we do for 32% -
1m' per min from 21 and 1@12 ,1@9 , 3@6, 3@3 for a bottom time of up to 30-35 min at 30-33 meters .

Nimrod

Yeah, that's basically what we're doing, but we start doing 1 min stops from 21m, particularly at 33-36m max depth.

[rjack]

They not going to kill you, but those first stops down at 21m are not helping you much either. My max stop depth on 30/30 is 18, usually 15m (since I don't dive this gas to 36m by and large).

On these shallow dives ratio deco is a bit 'off' IMO (and others think so too).
http://www.hhssoftware.com/v-planner/decomyths.html
And a plan via decoplanner, regardless whether depth is 33 or 36m has a max stop depth of 18m.

But if it slows the game down a bit and gets things under control for the subsequent stops that's good. No harm done with the gas supplies you've got.

Richard

[lamont]

They not going to kill you, but those first stops down at 21m are not helping you much either. My max stop depth on 30/30 is 18, usually 15m (since I don't dive this gas to 36m by and large).

On these shallow dives ratio deco is a bit 'off' IMO (and others think so too).
http://www.hhssoftware.com/v-planner/decomyths.html
And a plan via decoplanner, regardless whether depth is 33 or 36m has a max stop depth of 18m.

But if it slows the game down a bit and gets things under control for the subsequent stops that's good. No harm done with the gas supplies you've got.

Richard
Yeah, 21m/70ft is about where ppInert is going to be, so you have no overpressure driving gradient at that point. I like to slow it down there, though, because 1 min spent at that depth only costs you 1 min in additional overall runtime (aka there's no deco penalty for adding a stop there) and you've got lots of gas. Its also still 50 ft/15m off the bottom (120ft/36m) which is close to the 66ft/20m delta of the bottom that rossh suggests there, and I'm a little more paranoid about forming larger bubbles containing helium deep than v-planner is... On these kinds of profiles v-planner will take you directly to 20-30ft/6-9m... Plus, it does start to ingraine doing 1 min stops from 70ft/21m, which is not bad from a training perspective... YMMV...

[Nimrod Chen]

I have done that and it works for me. You might want to cut back on the bottom time to start. I don't know your experience or skill level, but starting out conservatively is wise - especially if you are doing a free ascent and might not be able to hold the shallow stops very well.

Richard
holding the stops is not a problem (i'm tech1 ) - i think i'll give it a try -
the only problem now is what if i like it :p

thanks for your help

Nimrod

[rjack]

As you can tell, we use 30/30 alot in the cold dark waters of Seattle