Dive Planning Excersize: Check My Work?

[reubencahn]

Again any one feel free to correct me if I'm wrong but what I've seen taught in a DIRF was 1 minute stops at 30, 20 and 10. Beyond no-stop limits there's a lot more to talk about.

Also a deliberate pause at 80% of max ATMs, not a real stop, just a pause followed by a pause every ten feet to make certain you're sticking with the ascent rate.

 

[bwerb]

Sorry...I made a blunder...1000 psi is RB for an AL80 dive to 100 feet...:blush:

Here's the calculation:

1 minute to solve the problem @ 100 feet
1 minute per ATM ascent rate
-pause- at 80% ATM's (70 feet)
1 minute per ATM ascent rate
1 minute at 30
1 minute at 20
1 minute at 10

6 minutes of gas needed x 2 divers = 12 minutes of gas needed
Surface SAC is based on 1 cf/minute
Multiply SAC by average depth = 2 ATM = 2 cubic feet per minute

12 minutes x 2 cubic feet per minute = 24 cubic feet gas needed

tank is an AL80 = 77 cubic feet divide by working pressure of 3000 psi x 100 = 2.5

24/2.5 = 10 (rounding up for conservatism) x 100 to get 1000 psi = rock bottom

 

[deep_6]

Pardon my post earlier. It was a very innocent question. No offense meant. It did appear very technical. I just thought that this was a usual thing for divers to do.
Thanks

 

[deep_6]

Pardon my post earlier. It was a very innocent question. No offense meant. It did appear very technical. I just thought that this was a usual thing for divers to do.
Thanks

I'll be more carefull with my posts next time. :whack:

 

[lamont]

Okay, how about this for EAN32 to 80fsw:

Dive to 80 fsw on EAN32:

Descent to 80 fsw @ 60 ft/min:
- Air = .6 SAC * 1.3333 min * [ ( 40 fsw / 33 ) + 1 ]
- = 1.76968

47 min @ 80 fsw - 3.42424 atm
- PO2 = 1.09575
- PN2 = 2.32848
- Equiv Air Depth = 64.26552 fsw
- NDL: 47 min
- RMV = .6 SAC * [ ( 80 fsw / 33 ) + 1]
- = 2.05454 cu ft
- Air = .6 SAC * 47 min * [ ( 80 fsw / 33 ) + 1 ]
- = 96.56356 cu ft

Ascent to 0 fsw @ 30 ft/min:
- Air = 2.0 SAC * 2.66666 min * [ ( 40 fsw / 33 ) + 1 ]
- = 11.79794 cu ft

Stop @ 50 ft (80% max atm) for 1 min:
- Air = 2.0 SAC * 1 min * [ ( 50 fsw / 33 ) + 1 ]
- = 5.03030 cu ft

Stop @ 30 ft for 1 min:
- Air = 2.0 SAC * 1 min * [ ( 30 fsw / 33 ) + 1 ]
- = 3.81818 cu ft

Stop @ 20 ft for 1 min:
- Air = 2.0 SAC * 1 min * [ ( 20 fsw / 33 ) + 1 ]
- = 3.21212 cu ft

Stop @ 10 ft for 1 min:
- Air = 2.0 SAC * 1 min * [ ( 10 fsw / 33 ) + 1 ]
- = 2.60606 cu ft

Rock bottom = 26.46460 cu ft

Solving for tank capacity:

Min air for NDL limit dive w/halves = 26.46460 + 2 * ( 96.56356 + 1.76968 ) = 223.13108 cuft
Min air for NDL limit drift dive = 26.46460 + 96.56356 + 1.76968 = 124.79784 cuft

Solving for bottom time and turn pressure by tank:

Usable capacity for AL80 w/halves = ( 77.4 - 26.46460 ) / 2 = 25.46770 cuft
Bottom time for AL80 w/halves = 25.46770 cuft / 2.05454 cuft/min = 12.73385 min
Turn pressure for AL80 w/halves = 3000 * (26.46460 + 25.46770) / 77.4 = 2012.85 psi

Usable capacity for AL80 drift dive = 77.4 - 26.46460 = 50.93540 cuft
Bottom time for AL80 drift dive = 50.93540 cuft / 2.05454 cuft/min = 24.79163 min
Turn pressure for AL80 drift dive = 3000 * (26.46460) / 77.4 = 1025.75968 psi

Usable capacity for E8-130 w/halves = ( 130 - 26.46460 ) / 2 = 51.76770 cuft
Bottom time for E8-130 w/halves = 51.76770 cuft / 2.05454 cuft/min = 25.19673 min
Turn pressure for E8-130 = 3442 * ( 26.46460 + 51.76770 ) / 130 = 2071.35058 psi

Usable capacity for E8-130 drift dive = 130 - 26.46460 = 103.53540 cuft
Bottom time for E8-130 drift dive = 103.53540 cuft / 2.05454 cuft/min = 50.39347 min (XXX: >NDL)
Turn pressure for E8-130 = 3442 * 26.46460 / 130 = 700 psi

 

[Spectre]

47 min @ 80 fsw - 3.42424 atm
- PO2 = 1.09575
- PN2 = 2.32848
- Equiv Air Depth = 64.26552 fsw
- NDL: 47 min
- RMV = .6 SAC * [ ( 80 fsw / 33 ) + 1]
- = 2.05454 cu ft
- Air = .6 SAC * 47 min * [ ( 80 fsw / 33 ) + 1 ]
- = 96.56356 cu ft
[...]
Min air for NDL limit dive w/halves = 26.46460 + 2 * ( 96.56356 + 1.76968 ) = 223.13108 cuft
Min air for NDL limit drift dive = 26.46460 + 96.56356 + 1.76968 = 124.79784 cuft

What's your 'halves' concept? You've figured 47 minutes at the bottom, which requires the [I would say] 100 cuft. The 'halves' concept would be 1/2 of your BT/gas reserves, so turn at 23 minutes or after using 50 cuft... whichever comes first. If you are diving overhead or otherwise -must- get back to your anchor line, then you'd dive 3rds, 33 cu ft out, 33 back with 33 in reserve for your buddy.

I tend to dive halves in OW. If something happened during the dive, I can turn it and head back to the anchor. Since I'm mostly doing wreck dives, it's usually pretty quick back to the anchor if I have to head back; I can pay attention to my pressure and if I don't think we'll make it before we hit rock bottom, thumb and free ascend from wherever I'm at when I make the call.

I would also take the descent out of the equation. Make that 50 minutes at 80 feet.

I would calculate in some 'checking' numbers, e.g. 10 minutes in what -should- my PSI be. 20 minutes in? makes it so you recognize dives with high consumption early so you can adjust accordingly.

Taking it a little further lets talk 2 dives on one set of doubles, I ignore rock bottom for the first dive. I calculate out a normal ascent requirement for me only, and add that to 1/2 of my tanks. [all numbers pulled out my... <whistle>] So say rock bottom is 500 psi, and I need 150 psi for my ascent normally; Tanks have 3000 psi in them. First dive 'rock bottom' would be 1650, turn pressure would 2350 [yea, threw the extra 50 psi in the return]. If a problem occurs, I might end up under 1500 when I get to the surface, but most likely we won't be doing that second dive anyway.

If everything goes perfect, on the boat with 1500 psi. Second dive is as expected... 500 psi rock bottom, turn at 1000 psi; free ascend if there's a problem and I'm getting close to 500 psi without reaching the ascent line.

 

[cnidae]

Okay, how about this for EAN32 to 80fsw:

Dive to 80 fsw on EAN32:

Descent to 80 fsw @ 60 ft/min:
- Air = .6 SAC * 1.3333 min * [ ( 40 fsw / 33 ) + 1 ]
- = 1.76968

47 min @ 80 fsw - 3.42424 atm
- PO2 = 1.09575
- PN2 = 2.32848
- Equiv Air Depth = 64.26552 fsw
- NDL: 47 min
- RMV = .6 SAC * [ ( 80 fsw / 33 ) + 1]
- = 2.05454 cu ft
- Air = .6 SAC * 47 min * [ ( 80 fsw / 33 ) + 1 ]
- = 96.56356 cu ft

Ascent to 0 fsw @ 30 ft/min:
- Air = 2.0 SAC * 2.66666 min * [ ( 40 fsw / 33 ) + 1 ]
- = 11.79794 cu ft

Stop @ 50 ft (80% max atm) for 1 min:
- Air = 2.0 SAC * 1 min * [ ( 50 fsw / 33 ) + 1 ]
- = 5.03030 cu ft

Stop @ 30 ft for 1 min:
- Air = 2.0 SAC * 1 min * [ ( 30 fsw / 33 ) + 1 ]
- = 3.81818 cu ft

Stop @ 20 ft for 1 min:
- Air = 2.0 SAC * 1 min * [ ( 20 fsw / 33 ) + 1 ]
- = 3.21212 cu ft

Stop @ 10 ft for 1 min:
- Air = 2.0 SAC * 1 min * [ ( 10 fsw / 33 ) + 1 ]
- = 2.60606 cu ft

Rock bottom = 26.46460 cu ft

Solving for tank capacity:

Min air for NDL limit dive w/halves = 26.46460 + 2 * ( 96.56356 + 1.76968 ) = 223.13108 cuft
Min air for NDL limit drift dive = 26.46460 + 96.56356 + 1.76968 = 124.79784 cuft

Solving for bottom time and turn pressure by tank:

Usable capacity for AL80 w/halves = ( 77.4 - 26.46460 ) / 2 = 25.46770 cuft
Bottom time for AL80 w/halves = 25.46770 cuft / 2.05454 cuft/min = 12.73385 min
Turn pressure for AL80 w/halves = 3000 * (26.46460 + 25.46770) / 77.4 = 2012.85 psi

Usable capacity for AL80 drift dive = 77.4 - 26.46460 = 50.93540 cuft
Bottom time for AL80 drift dive = 50.93540 cuft / 2.05454 cuft/min = 24.79163 min
Turn pressure for AL80 drift dive = 3000 * (26.46460) / 77.4 = 1025.75968 psi

Usable capacity for E8-130 w/halves = ( 130 - 26.46460 ) / 2 = 51.76770 cuft
Bottom time for E8-130 w/halves = 51.76770 cuft / 2.05454 cuft/min = 25.19673 min
Turn pressure for E8-130 = 3442 * ( 26.46460 + 51.76770 ) / 130 = 2071.35058 psi

Usable capacity for E8-130 drift dive = 130 - 26.46460 = 103.53540 cuft
Bottom time for E8-130 drift dive = 103.53540 cuft / 2.05454 cuft/min = 50.39347 min (XXX: >NDL)
Turn pressure for E8-130 = 3442 * 26.46460 / 130 = 700 psi

Ok, now do it without a calculator and without a table and post your answer.

 

[lamont]

What's your 'halves' concept? You've figured 47 minutes at the bottom, which requires the [I would say] 100 cuft. The 'halves' concept would be 1/2 of your BT/gas reserves, so turn at 23 minutes or after using 50 cuft... whichever comes first. If you are diving overhead or otherwise -must- get back to your anchor line, then you'd dive 3rds, 33 cu ft out, 33 back with 33 in reserve for your buddy.

I think I've been horribly confused about what 'halves' are. You're actually supposed to use both of those halves right? What you're figuring on is a dive where you descend, swim for X mins, turn, swim back for X mins and then ascend (with the restriction that you could ascend at any time if you had to, so no caves). So, if you're doing a dive where you descend, swim for 3 mins, screw around for 25 mins *and* you will be no more than 5 mins from your ascent line, turn, swim back and ascend -- then you turn at 5 mins + RB?

 

[Spectre]

If your in open water; yes, you are supposed to use both of the halves, because in the open water situation, you have the option to ascend at any point in the dive. In the situation where you don't have, or want to plan out that option, then you plan it like an overhead, and dive thirds. 1/3 out, 1/3 back, 1/3 for your buddy if you're sharing on the way back.

You plan your rock bottom for you and your buddies ascent. You plan your bottom to get -you- back to the ascent line before rock bottom. If you have a problem even at the turn point, you can try and get back with your gas reserved for your return, and ascend if you can't make it.

Since, as you say, you often are taking your time on your way out, and really don't need as much gas and time to return; that's why you have the shot to get back to your ascent point in case of a problem. e.g. 20 minutes leisurely enjoying a dive could really be 5 minutes back if your focused on getting back, not checking out the scenery.

Most of my plans have turn pressures, but they really are "It's your responsibility to keep eye of your gas and where we are on the wreck to ensure that you turn us at a point where we we be back at the line with XXX gas left".

Of course all my numbers have padding. e.g. if I'm saying 900 rock bottom, it's really gonna be 700 or so, with a couple hundred padded in.

For example, this is an excerpt from one of my plans :

Planned penetration if all is well upon arrival on wreck. Tie in outside and drop down one of the hatches. I'll lead and run the line. 10 minutes max in, 400 psi max. 20 minutes/800 psi max inside.

900 psi rock bottom leaves 1700 useable. 1200 needed for penetration. 250 travel. 2350 necessary for penetration w/ 400 psi turn. If between 2200 and 2350, penetration turns of 300 psi [400 out + 400 back + 300*3 inside = 1700].

Numbers to know: 900 Rock Bottom. 2350 and 2200 for 400 and 300 penetration respectively.


The above example you'll see a planned bottom time of 30 minutes. 5 minutes [250 psi] to the penetration entry point, and 5 minutes [250 psi] back to the ascent line. Then we have 20 minutes planned inside using the rule of thirds, 400 psi in, out , reserve. Then the 900 psi rock bottom for the ascent.