dive to 300 ft

[USVet96]

Ok I understand. Thanks guys for taking the time to explain.

I appreciate it.


USVet

 

[nadwidny]

40 cu feet of a gas that will be first breathed at 120 feet, 40 cu feet of gas that will be first breathed at 50'

As this is the DIR forum I suspect nadwidny may have made a mistake? (Is such a thing even possible? ) Normal deco gas would be 50% O2 that can be breathed at 70'

Yup. My bad. The football game was starting and I was in a hurry. A 40 of 50% that is started at 70'.

 

[MXGratefulDiver]

I haven't gone to 300 feet ... but when I was doing deep dives fairly regularly we used a support diver on any dive deeper than 200 feet. They'd meet us at the 70' stop with a spare bottle of EAN50 ... stick around till everyone made the switch, collect scooters, stages, etc. and take 'em back to the boat ... then meet us at 20' with a spare bottle of O2 ... wait till everyone made the switch, collect the 70' bottles and take 'em back to the boat ... then come back and stick with us until we surfaced ...

... Bob (Grateful Diver)

 

[Kevrumbo]

Good day,

In the thread Accidents and Incidents > Cozumel Incident 9/4/11 it has been contended that some divers planned to dive to 300 ft on a single AL 80 or AL 100. Regardless of what happened in Cozumel and irrespective of whether or not these rumours are correct, I am curious how properly trained DIR divers would execute a dive to 300 ft. Let's say for a max bottom time of 10 minutes - just go to 300 ft, hang out there for 10 min, then head back. I am not interested in a recipe and I won't be trying this on my own. I'd be curious in a sketch based upon healthy divers with decent SAC rates. For example, would you likely have doubles plus stage bottles? Eight bottles per diver? Trimix? Deco obligations totaling eight hours? Support divers?

Again, please don't waste too much time. I just want to see how very different a DIR approach would be from a "bounce dive."

Thanks.

Quick overview on the gas plan for Rock Bottom: Figure 2200 litres needed for 10 min at 90m (300') for a SCR of 22 L/min (0.75 cf/min) --that's equivalent to one ENTIRE 11 litre (AL80) tank; need around 6300 litres to get an Out-of-BackGas Buddy from 90m to the first deco stop at 21m, which would require another aluminium 11 litre stage bottle of bottom mix together with at least double aluminium 11 litre backgas tanks of bottom mix for each teammate. This totals roughly 8800 litres of bottom mix for each of the three-man team.

Better option would be larger capacity doubles (15 to 17 L) and the use of at least one more intermediate deco mix starting at 36m --minimum gas reserve from 90m to 36m would be reduced to roughly 4000 litres.

http://www.scubaboard.com/forums/te...9-analyzing-90-m-trimix-dive-dahab-egypt.html

 

[danvolker]

First, I think bounce dives are foolish, and doing something like this with a single tank is crazy.
But no one benefits by discussing the proposed 300 foot dive with incorrect ideas on how crazy people would do this...

First, if you were foolish enough to do this, the descent would be fast falling, more around 100 feet per minute, as this was more typical of bounce dives in the old days....second, the people that used to bounce on air in the old days, would use "blow and go" from 300 to 100, meaning a fully inflated bc would rocket them from 300 to 100 in seconds..so they would have far more air left than is being predicted by v-planner and others...air will not cause significant bubbling in the 300 to 100 maneuver, especially after such a short bottom time. I would think someone foolish enough to bounce to 300, would potentially be aware of this technique, as it makes using a single tank less retarded ( still retarded, just less so )

That said, even at the most foolish point in my 4 decades of adventure diving, I would NEVER have bounced to 300 on a single tank.
I have done body recoveries to 280 where I used less than 70 cubic feet of gas, this being essentially a bounce, but with a working issue due to lifting....Even with trimix, the ascent can be faster than V-planner projections, if the duration was very short and the need for faster ascent due to dangerous conditions, warrants this.

 

[MXGratefulDiver]

Tough to respond to the OP, since this is in the DIR forum ... and bounce diving isn't DIR. I think Brian gave the best answer ... if you're gonna go that deep, you're gonna plan it with sufficient gas reserves and appropriate gases. That'd mean big-ass doubles, a stage, and three deco bottles ... all filled with gases that are appropriate for the depths you plan to use them. Each team member plans adequate gas reserve to cover a back gas failure at depth (assume a shared-air ascent from 300 feet to the first deco switch) ... or the worst-case loss of one deco bottle ... whichever requires more gas.

Bouncing to 300 feet on air and a single tank ... ... that topic just doesn't belong in the DIR forum ... or even on ScubaBoard, to my concern ... StupidBoard, perhaps ...

... Bob (Grateful Diver)

 

[Slamfire]

[Almost] Every time I post here I do this disclaimer: I'm not DIR trained.

Therefore more than an answer, this post is a question. Would the profile below be an acceptable DIR profile? Please critique it and tell us what could be better. Thanks.


MV-Plan 1.5.2
Settings: GF=35-80 Factors:1.0/1.0 ppH2O=2.041 ftsw ZHL16B
=========================================================
DESC:100ft for 01:40 [ 2] on Trimix 35/25
DIVE:100ft for 00:00 [ 2] on Trimix 35/25
DIVE:100ft for 00:00 [ 2] on Trimix 10/70
DESC:300ft for 03:20 [ 5] on Trimix 10/70
DIVE:300ft for 10:00 [ 15] on Trimix 10/70
ASC :160ft for 04:40 [ 20] on Trimix 10/70
DECO:160ft for 00:20 [ 20] on Trimix 10/70
DECO:150ft for 01:00 [ 21] on Trimix 10/70
DECO:140ft for 01:00 [ 22] on Trimix 10/70
DECO:130ft for 02:00 [ 24] on Trimix 10/70
DECO:120ft for 02:00 [ 26] on Trimix 10/70
DECO:110ft for 01:00 [ 27] on Trimix 35/25
DECO:100ft for 02:00 [ 29] on Trimix 35/25
DECO: 90ft for 02:00 [ 31] on Trimix 35/25
DECO: 80ft for 02:00 [ 33] on Trimix 35/25
DECO: 70ft for 02:00 [ 35] on Nitrox 50
DECO: 60ft for 03:00 [ 38] on Nitrox 50
DECO: 50ft for 04:00 [ 42] on Nitrox 50
DECO: 40ft for 06:00 [ 48] on Nitrox 50
DECO: 30ft for 09:00 [ 57] on Nitrox 50
DECO: 20ft for 12:00 [ 69] on Oxygen
DECO: 10ft for 21:00 [ 90] on Oxygen

Gas estimate based on Dive RMV =0.7, deco RMV =0.6cuft/min
Nitrox 50 : 33.1cuft
Oxygen : 28.0cuft
Trimix 10/70 : 132.3cuft
Oxygen Toxicity - OTUs: 106 CNS: 63%
Trimix 35/25 : 19.0cuft

 

[Slamfire]

I just noted that MV-Plan is having me switch to 35/25 at 110' not 120'. It is calculating MOD for 35/25 to 118'. That would probably be a change, do the 35/25 switch at 120' not 110'.

 

[nadwidny]

Quickly looking at it I would change the GF to a 30/90 or a 30/95. I would not use a "travel gas". I would lengthen the 70' stop and shorten the 40. Combine the 20' and 10' stops into one 20' stop with back gas breaks. There are some other tweaks but those are the main ones.

 

[johnkendall]

Good day,

In the thread Accidents and Incidents > Cozumel Incident 9/4/11 it has been contended that some divers planned to dive to 300 ft on a single AL 80 or AL 100. Regardless of what happened in Cozumel and irrespective of whether or not these rumours are correct, I am curious how properly trained DIR divers would execute a dive to 300 ft. Let's say for a max bottom time of 10 minutes - just go to 300 ft, hang out there for 10 min, then head back. I am not interested in a recipe and I won't be trying this on my own. I'd be curious in a sketch based upon healthy divers with decent SAC rates. For example, would you likely have doubles plus stage bottles? Eight bottles per diver? Trimix? Deco obligations totaling eight hours? Support divers?

Again, please don't waste too much time. I just want to see how very different a DIR approach would be from a "bounce dive."

Thanks.

Ignoring the nonsense about single tanks and 100m diving, I'll give you the outline of a plan. This is how we are going to be doing a dive next month on a deep wreck in the english channel. Our plan for 2 bottom teams with 1 team doing 17mins and the other 20mins @ the bottom.

Gas load. D18s 10/70, Al80 10/70, AL80 21/35, AL80 50%, 7L 100%
Safety bottles - 1 x 21/35 per team, 1 x 50% per team, 1 x 100%

2 support teams, 1 will be meeting us at around 24m and the other at 9m

Roughly 3 hours in water time.

HTH
John