Computer VS. Tables

[tursiops]

Everybody in the team has spare air, enough for executing safe ascend with all the stops.

What do you mean by spare air...i.e., how many cu ft?
If you mean Spare Air, a trademark, you are NOT diving safely.
If you mean some extra air, how much? Is it part of your dive plan, or just for emergencies?

 

[mrdre]

...
Do you know how to calculate the amount of gas you will need for this dive? How is your buoyancy? Can you really hold a 15-20 minute stop at 20 feet in rough seas? Can you do a succession of 10 foot stops without losing buoyancy control and bouncing to different levels? Can you do this in a blue water ascent, which is difficult for a person with lots of technical training? Do you know what to do in case of a catastrophic gas loss at depth? If a first stage O-ring blows--what will you do? Will your buddy have enough gas to bring both of you to the surface safely during a 25 minute ascent? Do the math, and you will see that is a lot of gas--how will you carry it all? If you are using extra tanks, do you have the ability to change tanks safely during a decompression stop without losing control of buoyancy and possible rocketing to the surface too soon?

Yes, yes, and yes, yes to all that.

---------- Post added August 26th, 2014 at 11:47 AM ----------

What do you mean by spare air...i.e., how many cu ft?
If you mean Spare Air, a trademark, you are NOT diving safely.
If you mean some extra air, how much? Is it part of your dive plan, or just for emergencies?

Either 20 or 40 cft. Only for emergencies, not part of the plan.

 

[boulderjohn]

Yes, yes, and yes, yes to all that.
.

OK, then, let's try it. Let's start with two questions.

1. How much gas will you and a buddy need for the first dive, and how did you calculate that?

2. How will you carry that gas? (Be specific in terms of tanks and sizes.)

 

[mrdre]

OK, then, let's try it. Let's start with two questions.

1. How much gas will you and a buddy need for the first dive, and how did you calculate that?

2. How will you carry that gas? (Be specific in terms of tanks and sizes.)

OK, using Baltic Lite app (ZHL16-B model):

Dive 1:

100 fsw - 22 minutes bottom time - air .

1 minute - descend
22 minutes - bottom

on ascend: first 1 minute stop is at 60 fsw. Then 1 minute stop on every 30 feet. (Or say 30 feet per minute ascent).
9 minute last stop on 20 fsw.

Total air required - 82 cft = 65 for the dive and 17 for ascent. 0.7 RMV assumed for bottom and 0.6 RMV assumed for stops.

Carry a single 100 cft main tank, so have 17 cft extra for sharing. I carry 19 cft spare for emergency.

Buddy has the same.

 

[Storker]

I got into a raging debate regarding just this topic on dive planning and why knowing SAC rates wasn't needed for rec dives even those to deep depths. Is it nice to know? Sure. But's it's not necessary.

Thanks for the kudos, but I think I disagree ever so slightly here. It may be because I'm a data geek, but I've been tracking my SAC/RMV rate ever since I got my AI Suunto Cobra, and I've been doing min gas calculations on my desktop PC to check whether I'm gas limited or deco limited at extended depths. It's because of those SAC numbers (in the range of 15-20 SLM, or 0.5-0.7 cuf/min) and my Excel calculations that I know that if I'm using a normal Euro capacity tank (10L 300 bar, or 15L 200 bar) and I'm below some 15-20m I'm generally NDL limited, so I won't have to worry about gas. Even if I do a proper min gas calculation with doubled SAC rates for both myself and my buddy to whom I'd be donating gas in case the bovine manure should make contact with the rotating ventilation device.

And no, I don't have any training even approaching tech or advanced level. My highest cert is a PADI AOW, I dive single tanks and overheads - be they virtual or physical - are way beyond my personal comfort zone.

 

[boulderjohn]

OK, using Baltic Lite app (ZHL16-B model):

Dive 1:

100 fsw - 22 minutes bottom time - air .

1 minute - descend
22 minutes - bottom

on ascend: first 1 minute stop is at 60 fsw. Then 1 minute stop on every 30 feet. (Or say 30 feet per minute ascent).
9 minute last stop on 20 fsw.

Total air required - 82 cft = 65 for the dive and 17 for ascent. 0.7 RMV assumed for bottom and 0.6 RMV assumed for stops.

Carry a single 100 cft main tank, so have 17 cft extra for sharing. I carry 19 cft spare for emergency.

Buddy has the same.

I don't understand this:

on ascend: first 1 minute stop is at 60 fsw. Then 1 minute stop on every 30 feet. (Or say 30 feet per minute ascent).
9 minute last stop on 20 fsw.

It seems to me you are saying you have a one minute stop at 60 feet, and then not another one for 30 feet, and then a 9 minute stop at 20 feet. Is that correct? So this program says that your total ascent time according to this as 12 minutes, compared to 19 for V-Planner. Is that correct? It is unusual for a program to have a 30 foot jump after the first stop--in fact, I have never seen this before. That's why I ask.

Because I am not sure I understand what you wrote, I will continue as if we were using the V-Planner schedule as defined above and determine what to do if you blow an O-ring at 100 feet.
Dec to 100ft (2) Air 50ft/min descent.
Level 100ft 20:00 (22) Air 0.85 ppO2, 100ft ead
Asc to 40ft (24) Air -30ft/min ascent.
Stop at 30ft 2:00 (26) Air 0.40 ppO2, 30ft ead
Stop at 20ft 15:00 (41) Air 0.34 ppO2, 20ft ead
Surface (41) Air -30ft/min ascent.

Standard technical diving calculations assume that in a situation like this, the diver's SAC rate will be 1.0, and it will take a minute to solve the problem at depth. Your first move will be to switch to the pony and begin your ascent to the first stop. That would be planned at needing 7 cubic feet (4 cubic feet solving the problem at depth + 3 for the ascent). The two minutes from 40-30 feet would take about 4 more cubic feet. The 15 minutes at 20 feet would require 24 cubic feet, so you will need to switch to your buddy's pony after you have used about 7-8 cubic feet--you cannot empty a tank at depth. You will need to use just about every breath of your buddy's pony in addition to yours. You should surface out of air.

V-Planner assumes that you will need over 90 cubic feet for the dive, so your buddy will be just about out of air as well.

Hope there are no other problems.

 

[EFX]

Thanks for the kudos, but I think I disagree ever so slightly here. It may be because I'm a data geek, but I've been tracking my SAC/RMV rate ever since I got my AI Suunto Cobra, and I've been doing min gas calculations on my desktop PC to check whether I'm gas limited or deco limited at extended depths. It's because of those SAC numbers (in the range of 15-20 SLM, or 0.5-0.7 cuf/min) and my Excel calculations that I know that if I'm using a normal Euro capacity tank (10L 300 bar, or 15L 200 bar) and I'm below some 15-20m I'm generally NDL limited, so I won't have to worry about gas. Even if I do a proper min gas calculation with doubled SAC rates for both myself and my buddy to whom I'd be donating gas in case the bovine manure should make contact with the rotating ventilation device.

And no, I don't have any training even approaching tech or advanced level. My highest cert is a PADI AOW, I dive single tanks and overheads - be they virtual or physical - are way beyond my personal comfort zone.

It's great you know how to calculate and use SAC rates. From your response you are not using SAC rate to plan a dive but to check a dive you already did. Here's a simple dive plan: dive to 90 feet for 25 mintes and start the ascent at 900 psi stopping at 15 feet for 3 minutes. One diver reaches 900 psi after 15 minutes with a remaining NDL of 10 minutes. He's gas limited. Another diver reaches a remaining NDL of 1 minute with 1000 psi. She's NDL limited. Amazing! No SAC rates needed.

 

[fnfalman]

Back to the OP's question as to how to put which data into the dive log.

I don't log dives, hence I have no issues or problems with what information goes into which box.

 

[boulderjohn]

Yes, yes, and yes, yes to all that.

I wanted to make a separate comment on this.

You seem to be saying that you have already achieved all the skills and knowledge taught in beginning technical diving classes, and from everything else in this thread, I gather you did so without the help of any instructor.

Good for you!

I did not do so well. I was already a full scuba instructor when I started technical diving training, and realizing how challenging those skills were was among the most humiliating experiences in my life. It took my quite some time to convince my first tech instructor that I had achieved the level you believe you have already reached without having to go through training at all. My hat is off to you.

Now, are you saying that all other recreational divers have achieved this level of skill and knowledge on their own as well? You seemed to be saying that everyone should all follow your lead in not paying attention to NDLs and doing deco dives on their own--or isn't that what you have been advocating?

 

[mrdre]

I don't understand this:


It seems to me you are saying you have a one minute stop at 60 feet, and then not another one for 30 feet, and then a 9 minute stop at 20 feet. ...

My bad. 1 minute stop every 10 feet. 10 feet per minute ascend. My mistype. It's this metric/imperial mess. Keep multiplying everything by 3.