Steel HP100 or HP120 and reserve air in tank?

[Flashgun66]

Hi,

I’ve completed a solo course and enjoy the freedom of taking pics at my own pace, but would like to increase tank size. I shore dive with a slung 40, and a single aluminum 80. Leaving a reserve in my main tank has been leaving me a bit limited. So .. lately I’ve been diving using my older back mounted al30 as the reserve (attached to the 80 with a bracket), and using my main al80 as normal ending dive with 500psi., while still slinging the 40 - so three tanks. Really would like to upgrade to a single larger steel tank and leave the 30 at home. I also would like to stick to one tank on my back and the slung 40 configuration. My concern is reserve volume in the main tank.

I’ve never dove steel, but the 100 looks shorter, and the 120 longer/heavier.

I’m 6’1”, 215 lbs. , SAC rate .45 ft3/min.

Do you think 20 ft3 of air reserve is enough in the steel 100 (using around 80 ft3 for a dive)?

What about following the rules of thirds?

If I dive with the 120 + slung pony, I could use 100 ft3 for dive with 20 ft3 as reserve, or 90 ft3 for dive and 30 ft3 as reserve?

Looking forward to your thoughts.

 

[inquis]

Look up Minimum Gas or Rock Bottom. My reserve is tied to my depth (among other things). Also consider what you need the reserve for (e g., is entanglement likely where you dive).

 

[Gonad]

Hi,

I’ve completed a solo course and enjoy the freedom of taking pics at my own pace, but would like to increase tank size. I shore dive with a slung 40, and a single aluminum 80. Leaving a reserve in my main tank has been leaving me a bit limited. So .. lately I’ve been diving using my older back mounted al30 as the reserve (attached to the 80 with a bracket), and using my main al80 as normal ending dive with 500psi., while still slinging the 40 - so three tanks. Really would like to upgrade to a single larger steel tank and leave the 30 at home. I also would like to stick to one tank on my back and the slung 40 configuration. My concern is reserve volume in the main tank.

I’ve never dove steel, but the 100 looks shorter, and the 120 longer/heavier.

I’m 6’1”, 215 lbs. , SAC rate .45 ft3/min.

Do you think 20 ft3 of air reserve is enough in the steel 100 (using around 80 ft3 for a dive)?

What about following the rules of thirds?

If I dive with the 120 + slung pony, I could use 100 ft3 for dive with 20 ft3 as reserve, or 90 ft3 for dive and 30 ft3 as reserve?

Looking forward to your thoughts.

I’ve got 4 scuba pro steel 90’s I don’t use, if it’s cost worthy. This might be a solution. Less weight on belt, low pressure high volume,

 

[rjack321]

I guess you need to decide what is the reserve for? What depth will the problem(s) occur at? How long will the problem last? Then how long will the ascent take. Those decisions will dictate the volume you need.

There are many threads about minimum gas and rock bottom on SB but most of those are addressing 2 divers with one of them being OOA.

 

[rx7diver]

I’ve never dove steel, but the 100 looks shorter, and the 120 longer/heavier.

I’m 6’1”, 215 lbs. , SAC rate .45 ft3/min.

If I dive with the 120 + slung pony...

@photoJim ,

I am 6'2" with long legs. My PST HP 120 is too long for me to comfortably dive as a single. FWIW.

Also, I have an OMS (Faber) LP 121/126, an 8" OD cylinder that is a bit longer than my HP 120. My one attempt to dive it as a high-capacity, BM single was extremely unpleasant. (Although some of this unpleasantness might actually have been the STA that I used for that dive.)

Have you considered diving a set of small doubles, instead of a high-capacity single + pony bottle?

rx7diver

 

[undrwater]

Leaving a reserve in my main tank has been leaving me a bit limited.

Perhaps define this a little better. If you're worried that 120 would also be "limited", it sounds like you may be headed into doubles territory.

Look up Minimum Gas or Rock Bottom

I've been wondering how well these concepts apply to solo dives.

 

[inquis]

I've been wondering how well these concepts apply to solo dives.

They apply exceedingly well. Think of an issue and the time you would need to fix it. Your reserve gas gives you that time. When solo, you obviously don't have to worry about a buddy's issues, but that only cuts the odds of having an issue in half, and you also don't have the buddy to help you get out of whatever jam you're in. The SAC rate during ascent will be different from the typical buddy scenario, but you still need to get up. The "problem evaluation/solving" time at depth might be different (e.g., an entanglement), but it's still gotta happen before you can start the ascent.

 

[tursiops]

Hi,

I’ve completed a solo course and enjoy the freedom of taking pics at my own pace, but would like to increase tank size. I shore dive with a slung 40, and a single aluminum 80. Leaving a reserve in my main tank has been leaving me a bit limited. So .. lately I’ve been diving using my older back mounted al30 as the reserve (attached to the 80 with a bracket), and using my main al80 as normal ending dive with 500psi., while still slinging the 40 - so three tanks. Really would like to upgrade to a single larger steel tank and leave the 30 at home. I also would like to stick to one tank on my back and the slung 40 configuration. My concern is reserve volume in the main tank.

I’ve never dove steel, but the 100 looks shorter, and the 120 longer/heavier.

I’m 6’1”, 215 lbs. , SAC rate .45 ft3/min.

Do you think 20 ft3 of air reserve is enough in the steel 100 (using around 80 ft3 for a dive)?

What about following the rules of thirds?

If I dive with the 120 + slung pony, I could use 100 ft3 for dive with 20 ft3 as reserve, or 90 ft3 for dive and 30 ft3 as reserve?

Looking forward to your thoughts.

I'm sorry your solo class did not cover this kind of planning.

The point of the redundant tank (a 40 for you) is to get you comfortably to the surface in case your main tank cannot supply any gas; is a 40 more than you need? How much DO you need?
The point of the reserve in your main tank is....what? Until you can answer that, you cannot say how much you need. Why have you been using 500 psi? Where does that number come from?

 

[rjack321]

Assuming you need or want the gas, the hp119 and the hp130 are both far more popular single tanks in the Puget Sound / BC region than the long skinny hp120. In rough order of popularity you'll find for hp exemption tanks

a) hp100, 119
b) 130
c) 80
various combinations of double hp100s/119s/130s
double lp85s



then wayyyyy down the list is the
g) hp120

 

[Flashgun66]

Assuming you need or want the gas, the hp119 and the hp130 are both far more popular single tanks in the Puget Sound / BC region than the long skinny hp120.

Thanks for the info