Modifying rule of thirds

[Sludge]

Oh,a softball team from Illinois.

No, it's Southern Illinois University, in general. It's just that the site you were sent to showed the current athletic schedule, and it just happens to be softball season.

I happen to know three cave divers that are SIU graduates.

[billybones519]

Gas planning for simple swim only solo dives is relatively straight forward. The modifying that you are pobably refering to is equating the size of your buddy bottle to the size of your back gas. For example:

Back gas lp95's filled to 3600psi.
Buddy bottle is an al80 filled to 3000psi.

Since the gas in the buddy bottle equates to only 1100psi of back gas, maximum penetration should be no less than 2500psi.

Hope this helps.

[Sludge]

It was suggested that the rule of thirds be modified when diving solo.

I mentioned something to that effect in an earlier post; perhaps that's what you're talking about.

In my view, modifying for solo entails adding a buddy bottle that contains twice as much gas as you'll need to get to your nearest gas source. This gas is not touched except in an emergency.

[Kelly Jessop]

Hey Kelly,I cant figure out your avatar.Is it a sports team or something?

http://en.wikipedia.org/wiki/Southern_Illinois_Salukis
http://www.youtube.com/watch?v=hFThX...eature=related
Go Dawgs Go!!!

[chimie007]

It was suggested that the rule of thirds be modified when diving solo. I'd like to hear suggestions for modifying this rule.

To me it means diving SM. No reason to adjust because you are diving solo. Cave conditions are reasons to adjust but not the fact that you are on your own.

If diving backmount solo (I don't do that) then it means a buddy bottle and limiting penetration to the buddy bottle content which in most cases would be less than a 1/3rd.

Why should gas management need to be adjusted when diving solo vs team based ? Realistically, there are two reasons that one would need to share gas.

1- Delayed exit. A buddy won't be much help since he will be about out of gas when you are since you are diving together.

2- Equipment failure. In the case of SM, it is statistically impossible to loose more than half your gas supply. That means that if proper gas management is followed (1/3 in high flow, less in no flow, less in low vis, etc) the loss of one tank can be dealt with. If diving backmount, the buddy bottle provides a fully redundant gas source in case of total loss of back gas.

[contender]

2- Equipment failure. In the case of SM, it is statistically impossible to loose more than half your gas supply. That means that if proper gas management is followed (1/3 in high flow, less in no flow, less in low vis, etc) the loss of one tank can be dealt with.

Hmmm.... Not so sure about statistically impossible!

[Sludge]

That would be "statistically insignificant."

[RN]

Use thirds with a buddy bottle, fourths without bottle and sixths when scootering. JMO

What about scootering with a buddy bottle?

[Gary]

What about scootering with a buddy bottle?

It's pretty easy to add a single bottle to a scooter ride. Generally very worth the effort even if the dive plan doesn't require it.

Generally better to divide the air use up so that any single failure causes no more of a problem then any other one. So some dive plans that would mean using the buddy bottle. When dropping the bottle the air in it may be of less use to a person a couple thousand feet farther along so that using more of it then the gas with you might make sense.

When diving a manifold and solo I would expect the buddy bottle to be limiting. Although unlikely anything that can take both manifolded tanks out at one time leaves one with only the buddy bottle. Leaving that bottle untouched and limiting the dive to safe exit on that bottle is possible.

If solo scooter without a backup scooter planning the exit as a swim out becomes necessary. This could easily mean 6ths for many faster scooters. Combined with longer in water times, cold and deco obligations it may make swim out impossible even with 6ths.

More gear equals more failures. Extended range diving I think makes it necessary to at some point look beyond a single failure situation. Dual failures put almost any dive on more then simple thirds. When solo at least 4ths even with independent tanks and no scooter. Looking at combined failures that include both a scooter and a manifold for a swim out on only a buddy bottle could be impossible for a solo diver. If rebreathers are run off backgas then does a single failure disable both the rebreather and the OC supply? and does that provide enough for a diver to get out?

[RN]

I just started scootering recently, and because of scheduling conflicts and some sinus issues with my regular buddy, most of my scootering has been solo. I'm diving sidemount in a high flow (again) system and have yet to come close to 1/3s during the penetration (barely reaching 1/4s). My first few scooter dives were within the penetration distance I had made swimming the system when the flow was down. Once I hit 3000' I started carrying a buddy bottle, not a stage. This leaves me with 3200psi plus whatever is left in the SM bottle left should one of the SM bottles have a total gas loss. I don't think the buddy bottle is completely necessary since I'm turning my dive with over 3/4s of my starting gas. But better to have it and not use it than need it and not have it. Besides, it really doesn't create any additional drag. I managed to increase my travel speed by 10fpm during my last dive.