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thecheeseman
03-03-2008, 16:46
Lets just say I'm not the strongest-I did my certification on a 63 and had enough trouble. My divemaster suggested I switch to a 80 for a longer dive I am doing. Is this worth it? I suck alot less air then most, and I know i'll have trouble in the surf zone with an 80.

What is your opinions on this?

Thanks people!

rye_a
03-03-2008, 16:54
If you can dive as long on a 60 as your buddy dives, stick with what is comfortable.

SkuaSeptember
03-03-2008, 18:05
Your post is a little light on info, and I would agree with Rye in general. If however your goal is to dive longer, a full AL80 weighs only about 4lbs more, a HP steel 80 weighs about 5lbs less than the 63 you were using. Spend some time looking at the charts related to tank weights and bouyancy characteristics on ST and you will find a balance that is right for you!

CompuDude
03-03-2008, 18:06
More importantly, is the 60 enough gas for BOTH of you, given the dives you are doing? What if your buddy goes OOA?

Unless you're diving with someone who has similar air consumption, I'd consider hitting the gym so you can handle a normal size tank.

cummings66
03-03-2008, 18:48
Considering the weight difference I don't think you should have problems. I'd switch to the 80 myself.

rfb3
03-03-2008, 21:04
More importantly, is the 60 enough gas for BOTH of you, given the dives you are doing? What if your buddy goes OOA?


I agree with CD. If your buddy and you run out (not all the way) at the same time after a nice enjoyable dive, then you are ok. I have a (girl) friend that can out breath me with a 60, and I'm on an 80, so we do ok.

texdiveguy
03-03-2008, 21:53
On the other hand....the OP may be a small person whom is best suited for a 63cf tank--and there is nothing wrong with that at all....he indicates his consumption rate he feels is pretty good. When diving with another diver whom has a larger tank and similar gas consumption then he will be the 'handicap' of the pair, and again no shame there...profiles and gas management are based on those limits. There is no such thing as a normal sized tank...as we all have our own indv. limits. If the OP is comfy in the 63cf and feels this is a safe size for the diving environment he is in...then I say stay with it for now and monitor your progress as you gain additional experience.

CompuDude
03-03-2008, 23:13
On the other hand....the OP may be a small person whom is best suited for a 63cf tank--and there is nothing wrong with that at all....he indicates his consumption rate he feels is pretty good. When diving with another diver whom has a larger tank and similar gas consumption then he will be the 'handicap' of the pair, and again no shame there...profiles and gas management are based on those limits. There is no such thing as a normal sized tank...as we all have our own indv. limits. If the OP is comfy in the 63cf and feels this is a safe size for the diving environment he is in...then I say stay with it for now and monitor your progress as you gain additional experience.

As long as they are actually doing the math, analyzing their consumption rates, and determining turn pressures based on the diver with the smallest amount of gas, I can agree with that.

But two divers diving mismatched tanks simply because that way "they come out even" (not saying the OP is doing this, but it's a common refrain) is not the way to go.

Mycroft
03-04-2008, 14:01
On the other hand....the OP may be a small person whom is best suited for a 63cf tank--and there is nothing wrong with that at all....he indicates his consumption rate he feels is pretty good. When diving with another diver whom has a larger tank and similar gas consumption then he will be the 'handicap' of the pair, and again no shame there...profiles and gas management are based on those limits. There is no such thing as a normal sized tank...as we all have our own indv. limits. If the OP is comfy in the 63cf and feels this is a safe size for the diving environment he is in...then I say stay with it for now and monitor your progress as you gain additional experience.

As long as they are actually doing the math, analyzing their consumption rates, and determining turn pressures based on the diver with the smallest amount of gas, I can agree with that.

But two divers diving mismatched tanks simply because that way "they come out even" (not saying the OP is doing this, but it's a common refrain) is not the way to go.

Remembering that the turn point is based upon the diver breathing more using the last 1/3 of the diver using lesses' tank.

So, for example, when I dive my 130, and I'm diving a cavern with a buddy using an 80, we turn when his last 2/3 tank = the gas I used to get to that point, plus his remaining third. This does not = 2/3 of his tank! Cavern class covered this (at least mine did) and then I wrote a program to calculate the amounts for differing size tanks. The program is available freeware for some Palm pilots. Go to the Aquadivelog site to download it.

cummings66
03-04-2008, 16:53
Man, you make that sound complex, I think it'd be far easier to say you turn when you hit a certain volume of gas. So if you determined that you'd need 23 cf of air then that's an easy conversion to psi for his tank.

in_cavediver
03-04-2008, 17:18
Man, this feels odd but before we go to far on the complex gas management - what types of dives are being done here? While I believe all divers should know and understand the concept of Rock Bottom - we have to be equally intelligent in its application. Some times we try to over think things and the simple rules actually do work.

More importantly, what level of gas management is really needed? I haven't seen enough info given to really say. We can all agree there is a big difference between 30ft and 100ft and OW vs Overhead.

So, lacking any definitive information - that means my stock answer of 'it can't be done without doubles and a deco bottle. (stage too if you have one!)'

cummings66
03-04-2008, 17:59
There's a point where you don't need to worry about it, that's certain. I think there's things to consider for thirds and rock bottom. Sometimes you'll do rock bottom calc's for thirds too. Each dive merits it's own plan in other words and for some dives that's as simple as get in and come up before we run out of air.

solodiver
03-04-2008, 19:37
I use 53's, 6y3's and 80's Depending upon what I am diving. I do a lot of shallow diving, jetties and springs, when I do that I prefer the smaller lighter tanks, they are enough, Deeper dives I use the 80's

http://forum.scubatoys.com/southeast-florida/9991-dive-boat-project-florida-pan-handle.html

TommyB
03-04-2008, 20:15
Man, you make that sound complex, I think it'd be far easier to say you turn when you hit a certain volume of gas. So if you determined that you'd need 23 cf of air then that's an easy conversion to psi for his tank.

Couple that come in handy


Dissimilar Tank Turn-around Formula:
Step One:

1. You must first determine the cubic ft per 100 psi for your tank or as it is called the "Baseline."

Formula: (Tank Size/Tank Working Pressure) x 100 = Baseline

Example: (104 cuft/2640 psi) x 100 = 3.9 cuft per 100 psi.

For Doubles multiply baseline by 2.

Step Two:

1. Now you take the cuft consumed (1/3 of starting pressure) by the smaller tank and divide the number by the baseline of the larger tank then multiply the answer by100.

Formula: (Small Tank cuft consumed/Large Tank Baseline) x 100 = Allowable consumption of Larger Tank.

Example:

a. Diver A is diving a single Steel 95 @ 3000 psi
b. Diver B is diving a single Steel 104 @ 3000 psi

Diver A consumes 1/3 of starting pressure =1000 psi
1000 psi of steel 95 = 36 cuft

(95 cuft/2640 psi) x 100 = 3.6 cuft per 100 psi. This equates to 36 cuft per 1000psi.

Diver B can only consume the same amount of cuft not psi.
Divide smaller tank cuft (36cuft) by larger tank baseline (3.9 cuft) then multiply by 100.

(36 cuft/3.9cuft) x 100 = 923 psi

Turn-around for Diver B would be approximately 2073 psi. This is obviously to small to register, so for conservatism Diver B would round up to 2100 psi and this would be hi adjusted dissimilar tank turn-around.



Little more info incase some out that are curious as to what the heck these people are talking about :)

Sometimes you may wish to figure out how many cubic feet you have in your tank at any given pressure. To do that you can use to following formula:
Supplemental Formula:


(Baseline x Tank Pressure) /100

Example: Let us say that you are diving a steel 104 @ 3600 psi. The baseline for a 104 is 3.9 cuft.

(3.9 cuft x 3600 psi) /100 = 140 cuft.

Baseline Quick Reference List:

AL = Aluminum Tank. AA = Steel Tank. GEN = Genesis Tank.

1. 50 cuft AL = 1.66 cuft. 2 Tanks = 3.3 cuft
2. 71.2 cuft AA = 2.9 cuft. 2 Tanks = 5.8 cuft
3. 80 cuft AL = 2.7 cuft. 2 Tanks = 5.4 cuft
4. 80 cuft GEN = 2.3 cuft. 2 Tanks = 4.6 cuft
5. 100 cuft AL = 3.0 cuft. 2 Tanks = 6.0 cuft
6. 100 cuft GEN = 2.8 cuft. 2 Tanks = 5.6 cuft
7. 95 cuft AA = 3.6 cuft. 2 Tanks = 7.2 cuft
8. 98 cuft AA = 3.7 cuft. 2 Tanks = 7.4 cuft
9. 104 cuft AA = 3.9 cuft. 2 Tanks = 7.8 cuft
10. 108 cuft AA = 4.1 cuft. 2 Tanks =8.2 cuft
11. 120 cuft GEN = 3.4 cuft. 2 Tanks = 6.8 cuft
12. 120 cuft AA = 4.5 cuft. 2 Tanks = 9.0 cuft
Or as Larry likes to dive... "When SPG = Zero, Dive = Over:smiley2:

Hollywood703
03-04-2008, 21:25
I'll just stick with 1000 PSI and its time to start upward...granted im Diving a 119, so thats quite a while....I dive the 119, most Buddies dive 95's so...I dive to their bottle, and when they say its time to go.......thats when we go. My Bottle is also the extra Air in case of emergencies...along with a Pony. I am Fit enough to carry, so I do....so others who cant dont have to strain. Its only an issue into and out of the water...once it....it doesnt matter.

texdiveguy
03-04-2008, 21:50
WOW this is all so heavy.
:)

thecheeseman
03-07-2008, 15:35
Oh wow I had no idea of the weight comparison!! That's not bad at all!!! See, this is why i love ST-two pages of advice!!!! :D Thanks everyone-I agree with your points about OOA, we're going to swim out pretty far (on the surface with a snorkel), so it might be a good idea to use a 80.

THANKS!!!!

thecheeseman
03-07-2008, 15:37
Man, this feels odd but before we go to far on the complex gas management - what types of dives are being done here? While I believe all divers should know and understand the concept of Rock Bottom - we have to be equally intelligent in its application. Some times we try to over think things and the simple rules actually do work.

More importantly, what level of gas management is really needed? I haven't seen enough info given to really say. We can all agree there is a big difference between 30ft and 100ft and OW vs Overhead.

So, lacking any definitive information - that means my stock answer of 'it can't be done without doubles and a deco bottle. (stage too if you have one!)'

I'm going about 50-60 feet (not bad), We're swimming out 300-400 feet on the surface, to conserve air with a snorkel then diving down. (Coldwater diving)

We have out DM usually take a Spare air, but it would really only help him, and I think most of us have octos.

CaptainRon
03-08-2008, 00:10
My daughter (13) considered buying a 63 because that was what she used while in class. She went ahead and got the 80 because the weight was not that much different and it works well for her. She doesn't really notice any difference.