Pressed Steel Decision, Help!

[wedivebc]

The first dive that I calculated my average SAC throughout the whole dive for, it came in at 1.1 cuft/min. And that was without thinking I was gonna die, and it was the average. n00bs can breathe pretty heavy...

I plan on being able to deal with the situation that I'm at 100 fsw and some new diver that shouldn't be down there winds up ripping my reg out of my mouth because they ran out of gas...

I don't know how many times you have calculated it but that sounds pretty high given your experience. You should probably do some more trys at it and takle the overall average. On a cold working/current dive with doubles and stages I can do .6cuft/min and given that I'm 6'3" and 240lbs I'm a bit of a hoover myself.

 

[Hoosier]

Bfenne,

I don’t understand your hesitation. What is the primary purpose to set up the double tank? Is it more air, right? In the same context, if you can handle the size, weight, and price, it is not a difficult decision to make. Go with the bigger one. You are not comparing AL tanks with Steel tanks. It is all good tanks for all purpose in the current market. Moreover, in reality, there is no guarantee that you can get the full fill on site. It always takes longer than AL tanks’ refill. Sometimes, you have to leave it at the shop to ensure the max. fills.

In my case, I go with E8-130. But, for the double setup, I go with AL 80 tanks.
You know why, I can't handle the weight of two 130s even though I can afford.

Hey, make simple. We are living in the weird complexed world though.

 

[triton94949]

Nope, rock bottom. 2.0 SAC rate (OOA buddy) @ 100 fsw:

1 min to solve problem + 3 mins to ascend @ 30 fpm + 3 min stop @ appx 2.5 ata:

2.0 SAC * 2.5 ata * 7 mins = 35 cu ft

which is what i should have said. 48 cu ft is for 130 fsw:

2.0 SAC * 3 ata * 8 mins = 48 cu ft

If you are at 100 fsw, then presumably you are diving nitrox, if you are a well trained modern diver. Your EAD will be around 80 ft. Your first stop should be at 40 ft for 1 min according to NAUI's recently new doctrine of "deep stops" for NDL diving. Your second stop should be at 15 ft for 3 mins. At 2 cu ft per min for both of you, this would consume the following from the moment of your OOA air sharing:

100 ft to 40 ft = 60 ft
60 ft / 30 ft per min = 2 min
Aver 70 ft / 33 + 1 = Aver 3.1 ATAs
3.1 x 2 min x 2 cu ft per min = 12.4 cu ft

40 ft / 33 + 1 = 2.2 ATAs
2.2 x 1 min x 2 cu ft per min = 4.4 cu ft

40 ft to 15 ft = 25 ft
25ft / 30 ft per min = 1 min
Aver 27 ft / 33 + 1 = 1.8 ATAs
1.8 x 1 min x 2 cu ft per min = 3.6 cu ft

15 ft = 1.5 ATAs
1.5 x 3 mins x 2 cu ft per min = 9 cu ft

15 ft / 30 ft per min = 0.5 mins
Aver 7 ft / 33 + 1 = Aver 1.2 ATAs
1.2 x 0.5 mins x 2 cu ft per min = 1 cu ft

Thus I get total nitrox required for the combined OOA buddy ascent = 30 cu ft

That is pretty close to your 35 cu ft above.

 

[triton94949]

The first dive that I calculated my average SAC throughout the whole dive for, it came in at 1.1 cuft/min. And that was without thinking I was gonna die, and it was the average. n00bs can breathe pretty heavy...

I plan on being able to deal with the situation that I'm at 100 fsw and some new diver that shouldn't be down there winds up ripping my reg out of my mouth because they ran out of gas...

With a little jogging and swimming, and conserving your energy underwater, you can probably bring this RMV-SCR down to 0.75 soon. I used to be over 1.0 myself a long time ago. The most important thing is to relax and minimize your effort during the dive. The second most important thing is to vent your CO2 for a couple of minutes at the surface before you begin your dive. The third most important thing is to exercise regularly and get into shape. Trying to reduce your RMV-SCR is a good goal to motivate you to jog every other day for about half an hour. It works great!

 

[triton94949]

Honestly, I disagree with GUE and don't see the point to a 50' stop on a 100 fsw NDL dive...

Actually NAUI agrees with them on this.

As far as the separate OOA issue goes, that is a part of dive planning.

You have already computed that you need about 35 cu ft of air/nitrox for an air sharing ascent from 100 ft. Make sure you have that much reserved gas on hand at all times in your single tank (and pony if needed).

 

[triton94949]

WOW,

Thanks for all the great feedback. I guess I forgot some personal info. I am 5'10" at 250lbs and it is not sloppy... yet!!!lol I dive wet in Dutch Springs Quary, no deeper than 100' and an occassional Atlantic Ocean Dive. I don't know what my breathing rate is but with an AL80 I am good for about 50min. Oh, I also dive with a backplate and harness setup so I am ready if needed for doubles in the future.

Let me ask you all this...If you were setting up doubles are the e7-100's overall for most recreational needs the better choice or are the e8-119's? I am just trying to cover as many bases as I can so if i decide in the future to dive doubles I am ready.

Thanks again.

Well you are my height, but bigger. So it may make sense for you to have 100s or thereabouts for single tank NDL diving. Why you would need 120s or 130s for single tank NDL diving even on nitrox is not clear to me BFENNE. I would suggest that you get a total of 3 single tanks, all of the same size, all around 100 cu ft. Then for your doubles, definitely look at twin 130s. Two sets of twins ultimately, since many tech charters these days are doing 2 deco dives with a 2 to 3 hour surface interval.

 

[reubencahn]

Well it's simple, since an OOA situation is somewhat of an emergency I would probably forgo the 50,40,30,20 ft stops that reubencahn suggested since we are talking about diving within NDL limits. I would not assume my buddy was hoovering back 2.0 cuft/min during the ascent like lamont suggested and if he was he could carry those big scuds around as independant doubles that way he would not likely have an OOA situation. There is no way I am going to carry around 130cu ft of gas just so I can do staged "safety stops" on an NDL dive that an al80 would do just nicely.

If it's skip my stops or drown, I'll skip my stops. But why put myself in that position? As I said before, I can easily dive an E7-100 and have plenty of gas to do full bottom time on a 100 fsw NDL dive and have a rock bottom reserve that will allow me to do all my stops even with a panicking buddy who is hoovering gas. Why not give myself that security? Will I dive that dive with an AL 80? Yes, I have many times while travelling. But these tend to be multilevel dives so I'm unlikely to have a 100 foot ascent ahead of me late in the dive. If I'm diving to 130, well I definitely don't want to skip my stops. Maybe I'm just too old and cautious. As for the E7-130s, I think if you need that much gas for a 100fsw dive, you probably shouldn't be diving to those depths.