Buddy Air Balancing?

[Nemrod]

While it is true that the STRICT application of the Rule of Thirds to open water tropical, shallow, clear water diving is overly restrictive the INTENT of the Rule of Thirds is still applicable. That being, all dives should have some sort of plan and your air supply should be divided into that which is needed for the outbound and inbound legs and safety stop and adequate reserve--for that dive. The greater the depth, potential dangers, variables, the closer to actual division by 3 of the air supply the diver should apply--more conservative. For a resort reef snoozer dive it might go 1200/1200/600 or it might just be an agreement among the buddy team where to turn and where to surface. Nonetheless, they are applying the intent of the rule. Diving without a plan and without dividing your air supply could leave you having to surface far from the boat, not having enough air to swim back under the surf or get back to a safety exit point etc even if it was not the original entry point. The OP was not a tech dive post or an airshare pratice, it appears to be an extension of the dive by using your buddy's air supply.

N

 

[MikeFerrara]

While it is true that the STRICT application of the Rule of Thirds to open water tropical, shallow, clear water diving is overly restrictive the INTENT of the Rule of Thirds is still applicable. That being, all dives should have some sort of plan and your air supply should be divided into that which is needed for the outbound and inbound legs and safety stop and adequate reserve--for that dive. The greater the depth, potential dangers, variables, the closer to actual division by 3 of the air supply the diver should apply--more conservative. For a resort reef snoozer dive it might go 1200/1200/600 or it might just be an agreement among the buddy team where to turn and where to surface. Nonetheless, they are applying the intent of the rule. Diving without a plan and without dividing your air supply could leave you having to surface far from the boat, not having enough air to swim back under the surf or get back to a safety exit point etc even if it was not the original entry point. The OP was not a tech dive post or an airshare pratice, it appears to be an extension of the dive by using your buddy's air supply.

N

I don't disagree but there isn't always a boat and the dive doesn't always even involve an out and back. Some dives just cover a pretty small area where you really aren't going anyplace. Or they may be a one way dive, like drifting. That's why I make the three seperate distinctions. Those, I can ascend anyplace (just rock bottom reserved), those I'd like to get back to the entry point but it really doesn't matter (halves after rock bottom is backed out) and those that really do require the rule of thirds.

There are those dives that really don't neatly fall into any of those catagories but common sense can handle those with the bottom line being that I need enough gas to me and my buddy both out of the water.

 

[Thalassamania]

I think that we call all agree that we should be turning back with no less that twice the amount of air that would be reasonably required to finish the dive. I always tell me students that they must have more than twice the amount of air needed to exit the dive (plus a modest reserve) in their tank and when they actually hit that value (what we refer to as Bingo Air) it's mandatory to thumb the dive.

 

[Cacia]

wow..that's a lot of air. I flunk that test. By those standards, we would all need doubles to do the Sea Tiger. About 75 people dive it everyday with
Al 80's.

Is this for "students" or everybody? I would say we cut it closer than that.

I will say, on a shore dive vs a pick-up, I would allow that much. Too many vaiables like current.

 

[Thalassamania]

wow..that's a lot of air. I flunk that test. By those standards, we would all need doubles to do the Sea Tiger. About 75 people dive it everyday with
Al 80's.

Is this for "students" or everybody? I would say we cut it closer than that.

I will say, on a shore dive vs a pick-up, I would allow that much. Too many vaiables like current.

Sorry a bad choice of words. I edited to fix and then realized that might clarify with your post here.

By "twice the amount of air needed to complete the dive (plus a modest reserve)" I mean twice the amount of air that you'd need if you thumbed the dive at this instant (that's what I mean by complete, exit is perhaps better ... but still unclear).

 

[MikeFerrara]

wow..that's a lot of air. I flunk that test. By those standards, we would all need doubles to do the Sea Tiger. About 75 people dive it everyday with
Al 80's.

Is this for "students" or everybody? I would say we cut it closer than that.

I will say, on a shore dive vs a pick-up, I would allow that much. Too many vaiables like current.

The idea is this...What if you or your buddy suffer a total gas loss at the furthest point in the dive?

If you don't mind doing a direct ascent wherever you happen to be, then all you need is enough gas for both divers to ascend on one tank. On the other hand, if you really need to get back to where you started, you need enough for two divers to do it.

That's a minimum reserve and assumes that you can get back using no more gas than you did going out. The fact is that when there are problems, you are likely to use more.

Yes it can be a lot of gas and, there are recreational divers all over the world doing dives with 80 cu ft tanks that I wouldn't touch on that size tank. Usually, the worst (one of you losing all your gas at the furthest point) isn't going to happen but it only takes once.

 

[Charlie99]

.... I make the three seperate distinctions. Those, I can ascend anyplace (just rock bottom reserved), those I'd like to get back to the entry point but it really doesn't matter (halves after rock bottom is backed out) and those that really do require the rule of thirds.

the bottom line being that I need enough gas to me and my buddy both out of the water.<emphasis added.>

The situation where I have most often extended dive time by air sharing early in the dive has been drift dives in Cozumel. Rock bottom and/or ascent pressure has been determined in advance, and air sharing earlier in the dive doesn't impact that calculation. When either of us hit the ascent pressure, we ascend. What has gone on earlier in the dive is not relevant. Easy to handle.

Air sharing on a shore dive or dive from moored boat, where getting back is nice, but not essential, is a bit trickier, since your turnpoint does depend upon consumption up to that point, and air sharing complicates monitoring of that. On a practical basis, it isn't really all that hard, particularly since air shares are normally done when the heavier breather hits 1500 - 1800psi (assuming 3000psi start). I note the delta in our pressures, and then we dive using only my tank until my tank is about 2/3 of that delta lower than his. If done right, we would both hit our rock bottom simultaneously if our dive continues that long.
In practice, in most of my diving the return trip takes less time and gas than the outbound, either because I'm coming back shallower, or because I'm coming back directly rather than wandering about.

For a dive that actually requires using the rule of thirds I would not do this sort of air sharing because the results of miscalculation are too severe.

Charlie Allen

 

[Cacia]

If done right, we would both hit our rock bottom simultaneously

and that is a beautiful thing! Striving for that precision brings you along as a diver, I have found.

yes, I find the type of dive factors in...I guess it shouldn't by the book, but I am much more conservative when I need to navigate back. Lucky for me, few dives are like that as we tend to go down the line and straight back up in clear water. When I used to lead..say a night dive, for example, with a group, I would allow PLENTY since the limiting diver requires me to return the group safely. (And compass work requires "extra" gas!)

 

[Nemrod]

My only actual OOA MikeF was a drift dive. I did not call the dive when the DM had instructed me to because I was distracted by other "buddys" that had been stuck with my wife and I. I have told the story before.

I am not dissagreeing with you MikeF on your previous post, you are planning your dive even if your not splitting your air up (mentally--well--actually you are) but your just rearranging your procedure to account for a drift dive that does not have a return leg. I understand that and agree with your thoughts.

Many resort locations only ask that you be back up with 500 psi--but again--still, they have a plan, very loose but usually sufficient for shallow resort dives.

As to others who are doing deeper and more aggresive diving without a plan (and we include an air plan in that) then your just rationalizing away the need for either 1) limiting your dives to less depth or shorter time or both or 2) carrying more air capacity.

It works like this, you want to make dive X. Dive X is a certain depth and you plan for a certain bottom time. You plan also for possible deco/safety stop needs and then you work out your required amount of air(techies call it gas) to complete that dive with safe reserves. THEN---THEN, you choose your equipment and size your tanks (single, double, pony, stages--all that) to accomplish that. It is a rational approach that SHOULD be taught in all scuba courses.

OK, you go through your plan and determine that you cannot do this dive on an aluminum 80, well, you either get more tanks capacity or you DON'T do the dive--or--you dive dangerous and rationalize away this requirment with things like, well, other people do it, or, I cannot do dive X and I want to--wah--wah.

N<---some people say I am a dangeous diver, I am still here and I plan my dives--sorta, mostly but what the heck, safety is way over rated, die young and beautiful

 

[Cacia]

I plan my dives--sorta, mostly but what the heck,

...hey! are you allowed to say that?
Looking for someone you know on the ascent line is an option.

The other day this Instructor was telling me he had a diver with 500 pounds on the Corsair when they arrrived. He couldn't imagine how the heck he did it. So he traded gear with him, put him on the line, turned his group around and leached off the entire group for the 110 ascent and safety stop. I thought that was pretty creative.

I'm not sure why he chose to do it that way, but I guess he was worried that his 2500 psi might not cut it since the guy had burned up about that on the way down. (working against the current, on the surface too long?)