Rock Bottom for Solo Divers

[MXGratefulDiver]

I think that's the answer right there.

If you're diving somewhere that you're not likely to ever run into another diver, then you just need enough gas to deal with whatever issues you may have as a truly solo diver. If you're at any kind of halfway popular divesite then one of the issues that you may have is a diver you don't know with really big eyes showing you a gauge way into the red. I know it has happened locally around here before. That means you need all the gas you need as a buddy.

Good call ... it's happened to me more than once. In fact, I haven't had to share air with my dive buddy since I was a very new diver. I've had to share air with divers who weren't my dive buddy a few times since then ...

... Bob (Grateful Diver)

 

[Steve50]

not to mention the stranger who shows up out of air, if not solo, may very well have a buddy who's also low...

 

[GrumpyOldGuy]

not to mention the stranger who shows up out of air, if not solo, may very well have a buddy who's also low...

That scenario (2 uninvited buddies, one OOG one LOG) crosses over into the 2 failure mode, which rec divers don't plan for.

Even though you might have enough gas to ascend with 3 divers, the chances of the 2 idiots (both buddies being LOG/OOG is a real good indicator of Darwin at work) overwhelming your ability to manage the situation could kill all 3 of you. Some instructors might have the skills necessary to pull this one off, regular divers like me, its really questionable.

 

[divengolf]

I believe that the simpliest approach is the best. I use just one RB rule: depth X 10 plus 300. Regardless of whether I'm solo or buddied and if I'm carrying a pony or not. Even I can do that calculation at depth.

Note I'm using either an 80 or 100 CF tank.

BTW Lamont: Thanks for your RB write-up. I've used it for years.

 

[Steve50]

That scenario (2 uninvited buddies, one OOG one LOG) crosses over into the 2 failure mode, which rec divers don't plan for.

Even though you might have enough gas to ascend with 3 divers, the chances of the 2 idiots (both buddies being LOG/OOG is a real good indicator of Darwin at work) overwhelming your ability to manage the situation could kill all 3 of you. Some instructors might have the skills necessary to pull this one off, regular divers like me, its really questionable.

Actually I was thinking it would be a good reason to have a Knife

 

[GrumpyOldGuy]

I believe that the simpliest approach is the best. I use just one RB rule: depth X 10 plus 300. Regardless of whether I'm solo or buddied and if I'm carrying a pony or not. Even I can do that calculation at depth.

Note I'm using either an 80 or 100 CF tank.

BTW Lamont: Thanks for your RB write-up. I've used it for years.

That rule-of-thumb is easy to use and reasonable accurate for the typical AL80, but like many rules-of-thumbs, they work well in a narrow range of conditions. Simpler is not always better.

When you try to apply it to a pony (from the OP) it does not work. Ditto as you get into the large tanks / doubles. As a solo diver, you are by definition "outside the norms" and I am hesitant to rely on rules-of-thumb. I have a printout of my RB pressures on my dive log to check before my dive. (Right next to my medical release, next-of-kin contact info, etc... which are there to remind me to take my solo dives seriously.)

 

[MXGratefulDiver]

That scenario (2 uninvited buddies, one OOG one LOG) crosses over into the 2 failure mode, which rec divers don't plan for.

Even though you might have enough gas to ascend with 3 divers, the chances of the 2 idiots (both buddies being LOG/OOG is a real good indicator of Darwin at work) overwhelming your ability to manage the situation could kill all 3 of you. Some instructors might have the skills necessary to pull this one off, regular divers like me, its really questionable.

Actually I was thinking it would be a good reason to have a Knife

Actually, it's a good reason why you don't count your redundant air supply into your gas plan. If that eventually were to occur, you put one diver on your pony and share air with the other.

I've never had to do that before ... but when I dive solo my planned reserves would easily accommodate it ...

... Bob (Grateful Diver)

 

[lamont]

That rule-of-thumb is easy to use and reasonable accurate for the typical AL80, but like many rules-of-thumbs, they work well in a narrow range of conditions. Simpler is not always better.

When you try to apply it to a pony (from the OP) it does not work. Ditto as you get into the large tanks / doubles. As a solo diver, you are by definition "outside the norms" and I am hesitant to rely on rules-of-thumb. I have a printout of my RB pressures on my dive log to check before my dive. (Right next to my medical release, next-of-kin contact info, etc... which are there to remind me to take my solo dives seriously.)

If you check what I wrote up (which the poster referenced) there's all kinds of qualifications on that rule-of-thumb in that it works best for Al80s, LP80s, and HP100s at depths shallower than 100 feet (and the poster referenced tank size as well), with a minimum cutoff of 500 psi at any depth.

I'd encourage everyone to slog through the math and be able to play with the calculations and arrive at their own numbers -- but given that some people legitimately have issues with mathematics and struggle with it, I'd prefer them to have a simple formula available and know where it applies.

It is vastly better than "be back on the boat with 500 psi" as a gas planning technique.

 

[bkotheimer]

I think that's a great rule to follow (depth x 10 + 300 psi) and easy to remember. It actually matches pretty well for an AL80 with the example tables in the link I referenced. And not to push the issue, but for a solo diver, even depth x 10 WITHOUT adding the 300 is still much more conservative than halving the values from the AL80 column OR extrapolating the pony bottle values to one's backgas.

And again, that's the only reason I mentioned pony bottles at all in this thread -- because I was thinking that the whole "one diver, one reg" situation actually (sort of) applies to your backgas if you're by yourself. However, the stress factors and "unplanned buddy" situations mentioned by other posters in this thread are a good argument for following the "two diver" calculations anyway.

When in doubt... Depth x 10 (+ 300) with a minimum of 500. Good one.