Rule of Thirds & Shallow Rec diving

[victorzamora]

Jumping off the boat without a predetermined and pre-calculated dive plan is nothing to worry about. A little story to show how its done.

Just a little background: I'm not a GUE diver, I've done plenty of dives where the last thing I do before surface is realize I've sucked the tank DRY. I've done plenty of dives where the plan was "blow bubbles until tank runs out" and I have nothing against it in particular. However, I have PLENTY wrong with your scenarios. First of all, the tone was pretty grouchy and inappropriate. I'm not offended by it, but there's no need to become offensive or offended. Secondly, Lynne mentioned that the articles she linked to alluded to gas planning as a "techie" thing....not that you did. Thirdly, I think they're wildly misrepresentative of all parties involved. Most vacation-only rec divers don't swim in circles around the boat and make a successful b-line back when their gas gets low. Most swim in random directions (mostly away from the boat) until they hit 30b and then surface....only to have a half-mile surface swim back. As for the tech divers, I'm not sure about Lynne or anyone else on the board....but I don't plan meticulously like that for simple rec dives. What I do, however, is something closer to what your rec divers do. I keep a mental note of about how far I am from the boat and my depth. I know about how much gas it takes to get me and a buddy to the surface from where I'm at, and about how long it takes to get back to the line. I also keep track of depths between me and the line. The gas it takes to get two of us up to the surface calmly is my "absolute minimum" before I start ascending. I then know about how long it takes me to get to the line, and I add gas to my turn pressure the further away I get. I know on a wall dive I turn halfway to my "absolute minimum" pressure, and fiddle with it based on current. It's something you can discuss quickly with a buddy just before the dive, and it's something you could/should be responsible for if you're leading the dive.

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I'm interested to hear from some of the technical divers posting here suggesting that the way in which the novice divers conducted their dive in the story was unacceptable. Please explain. Why was it unacceptable?

To be clear, I believe that most people don't object to the novice divers methodology prescribed in your story. I know I don't. However, it's a LOT more planning than the majority of divers do. The "average" novice diver doesn't follow all of the depth/time/direction limits you described YOUR novice divers doing. They get in the water and swim until their tanks are empty, and then they surface. Knowing the depth, keeping track of position in the water, and returning with sufficient gas is all good and is all more planning than "no planning" and way more than most people do.

And all that without the need for a calculator or having a predefined route.

I don't need a calculator OR a predefined route on any of my recreational dives. Gas planning doesn't have to be down to the single PSI if you have good practices instilled and you're used to the basics.

 

[NAM001]

Out of curiosity... What would your gas management plan be for a dive in a 10 acre lake with a physical max depth of 30-40 ft.
I know mine would be go in play till I hit 4-500 and surface. Then surface transit to my entry point.

The point is that there is a place and time for gas management. Some dives need more, some need next to none. That is why beginner divers dive in beginner environments. Those of you that have beach locations will have an entirely different view on the plannig of a dive than the land loclked folks have. Most of the diving I see are at lakes with dive shops or at least fill stations present. You pay 20 bucks for the day and go for it. I am not saying this to deminish the need for safety. However most locations do not have issues of overhead. deep, deco, wreck, currents and certainly not a reachable NDL. The beach front divers would probably NOT call this real diving and more of a training location, but reality is that a large majority of diving is done in these types of waters. I have been trying to get intrest on a person to start diving. Thier fears are that they arent smart enough to do all the planning they have heard about that is necessary to dive. Thier only expoxure has been the tech divers and cave divers who willingly discuss all the complexities of the sport, and it scares them. They get the impression that you have to be a master to learn.

The more comlex the dive requires more comlex planning. A simple lake does not need a plan beyond play till you get 4-500 and surface for lunch and a gas fill. Next dive will be the sunk grayhound bus on the north side of the pond.

 

[boulderjohn]

I'm interested to hear from some of the technical divers posting here suggesting that the way in which the novice divers conducted their dive in the story was unacceptable. Please explain. Why was it unacceptable? .

I am a tecyhnical diver, and as I said in my previous post, proper diving planning caries by the site and the purpose of the dive. One size does not fit all.

Most vacation-only rec divers don't swim in circles around the boat and make a successful b-line back when their gas gets low. Most swim in random directions (mostly away from the boat) until they hit 30b and then surface....only to have a half-mile surface swim back. ...
The "average" novice diver doesn't follow all of the depth/time/direction limits you described YOUR novice divers doing. They get in the water and swim until their tanks are empty, and then they surface. Knowing the depth, keeping track of position in the water, and returning with sufficient gas is all good and is all more planning than "no planning" and way more than most people do.

I agree with Victor. If you go to Key Largo, you will find most dives are done in ways similar to what you describe but with even less planning. The boat crews are used to it. They will tell divers something along the lines of "when you are half way through your gas, swim to the surface, locate the boat, and start heading back." That can work out well for most divers because of the nature of the site. With a little more skill and experience, it all can be done a lot more efficiently than that, but people are not going to be dropping like flies under those conditions. Now, start adding levels of complexity a little at a time, and each level will call for adjusted planning. If "swim around aimlessly until you are half way through your air and then surface to find the boat" is the only dive plan you know, then you will eventually find yourself in a dive that is beyond your ability.

 

[muteki]

Every dive trip I've taken, we've been told to do our safety stop with 500psi / 50bar. I've always stuck to that, and I'm also a big believer that technology is not always accurate, and can fail (stemming from years in tech support). I wouldn't want to get down to 10bar and then realize that the SPG was wrong and wind up out of air. Better safe than sorry.

 

[victorzamora]

Out of curiosity... What would your gas management plan be for a dive in a 10 acre lake with a physical max depth of 30-40 ft.
I know mine would be go in play till I hit 4-500 and surface. Then surface transit to my entry point.

My gas management plan would include how much gas it would take to get me and a buddy to the surface safely and calmly....probably 500psi per tank, maybe a little lower if I'm having fun and I'm in SM and with the right buddy. However, that's still gas management plan. I've figured out that from 40ft, a buddy and I can make it up with 500-700 psi nice and slow. If things go really wrong, I can CESA from much deeper than that. The point isn't that you need to have hundreds of slates and tables with pre-plotted gas plans and "lost gas" backup scenarios and intricate run lists planned out....you just need to be aware that not every scenario allows for "hit 500psi, then hold your inflator button down" type of diving.

Like I said, I'm VERY against uninformed diving.....but I've sucked a tank DRY (like, completely OOA) on a dive before. Actually, I've done it a few times. My "main buddy" did the same thing several times at the same dive site. I don't always have to surface with 1200psi and a full pony for me to consider it a safe and successful dive.

 

[Foxfish]

Bob (Grateful Diver), no one is saying that the tech diving approach to a dive is a waste for all kinds of diving. The little story was intended to show that some aspects are not appropriate in the recreational context. Apart from what you claim is a 'cocky attitude', you haven't been able to identify one problem with the way the novice divers in the story.

 

[MXGratefulDiver]

Bob (Grateful Diver), no one is saying that the tech diving approach to a dive is a waste for all kinds of diving. The little story was intended to show that some aspects are not appropriate in the recreational context. Apart from what you claim is a 'cocky attitude', you haven't been able to identify one problem with the way the novice divers in the story.

... that's because I don't see a problem ... I believe I've already said that a couple times. Go back and read my first response in this thread ... I think my position's clear.

Your method has some limitations ... but so do the dive profiles you're applying it to. No big whoop. But what happens when you decide to apply your method to more aggressive profiles?

On the other hand, you seem to be of the opinion that applying a more precise method is somehow unduly rigorous. I can assure you it's no more rigorous than driving down a road, seeing a sign indicating the next gas station is 150 km ahead, looking at your fuel gauge, and determining whether you have enough in the tank to make it ... takes about 10 seconds, and most people can do it in their head.

Those tech divers in your scenario would more likely have been in the water while you were still putting your gear on ... because they'd have thought their dive out long before they got to the dive site.

Let me come back to you with a scenario ... a local dive profile that's completely within recreational limits, and has bitten a couple of our locals with fatal results. We have a pair of coves with a fishing pier in between them. To keep divers away from the pier, we've installed a boundary rope that goes along the bottom from about 2 meters in one cove down to about 30 meters, across in front of the pier, and up to about 2 meters in the other cove. It's about a 15-minute swim to depth on either end, and about 8 minutes across the fishing pier at 30 meters. You're using a 12L tank.

Do you have enough gas for that dive? If so, how did you determine that you did?

For extra credit, how much gas will you need to get you and your buddy to the surface safely if something goes wrong while you're crossing in front of the pier?

At what pressure level would you determine that you can't make it, and decide the better part of valour would be to turn back?

My AOW students can answer all of those questions ... without needing more than a minute or two to think about it. OK ... the slower ones might need a few minutes. But that's what dive planning is for.

Can you determine whether or not you have adequate gas for that dive, using your methods? And if not, would you really consider it a safe dive for you to do?

Why or why not?

... Bob (Grateful Diver)

 

[Foxfish]

First of all, the tone was pretty grouchy and inappropriate. I'm not offended by it, but there's no need to become offensive or offended.

I thought I was being restrained. Could have had the tech divers thrown over board by the skipper and other divers in the story. The story was intended to highlight how ridiculous it would be to follow some of the things tech divers need to do on more difficult dives in a recreational context.

Thirdly, I think they're wildly misrepresentative of all parties involved. Most vacation-only rec divers don't swim in circles around the boat and make a successful b-line back when their gas gets low. Most swim in random directions (mostly away from the boat) until they hit 30b and then surface....only to have a half-mile surface swim back.

If not having a predefined route and losing the boat worries you then swimming away from and then back to the boat in circles is one way to navigate.

To be clear, I believe that most people don't object to the novice divers methodology prescribed in your story. I know I don't. However, it's a LOT more planning than the majority of divers do. The "average" novice diver doesn't follow all of the depth/time/direction limits you described YOUR novice divers doing. They get in the water and swim until their tanks are empty, and then they surface. Knowing the depth, keeping track of position in the water, and returning with sufficient gas is all good and is all more planning than "no planning" and way more than most people do.

Don't know if you're exaggerating here but most of our novice divers don't dive this way. They manage to get back to the boat in good time.

Trying to force the same kind of rigor sometimes needed on a tech dive onto recreational divers is problematic for several reasons. Firstly it is usually logistically impossible given the vagaries of the way we dive. Once divers have worked this out it would then be easy to go to the other extreme and disregard even the most simple forms of gas management. A really good way to freak out a novice diver who struggles with mathematics is to tell them how to calculate their air consumption rate, how to calculate a dive plan based on that rate and then tell them if they don't do that before a dive they won't be safe.

---------- Post added November 27th, 2013 at 07:16 PM ----------

Those tech divers in your scenario would more likely have been in the water while you were still putting your gear on ... because they'd have thought their dive out long before they got to the dive site.

We dive about 20 km off shore in an area I'd guess is 8 km by 10 km. None of the divers know where we'll end up for the dive until a few minutes we get to the location.

I don't think they'd be allowed to jump in the water before I got my gear on. The boat would still be moving.

Can you determine whether or not you have adequate gas for that dive, using your methods? And if not, would you really consider it a safe dive for you to do?

One way would be to calculate average depth and air consumption rate and then work out how long you've got on a tank of air. BUT...

What is the problem with surfacing part way through the dive. If it was unsafe due to say shipping in the area I'd probably avoid the dive. It's not my idea of a recreational dive. AND..

If you've never done the dive before how do you know how long it will take to swim the legs? If you have done the dive before then why do you need to do a gas management plan?

---------- Post added November 27th, 2013 at 07:27 PM ----------

Like I said, I'm VERY against uninformed diving.....but I've sucked a tank DRY (like, completely OOA) on a dive before. Actually, I've done it a few times. My "main buddy" did the same thing several times at the same dive site. I don't always have to surface with 1200psi and a full pony for me to consider it a safe and successful dive.

I've spent the best part of the day diving with no air in my tank, with no tank in fact and no BCD.

 

[MXGratefulDiver]

We dive about 20 km in an area I'd guess is 8 km by 10 km. None of the divers know where we'll end up on the dive until a few minutes we get to the location.

I don't think they'd be allowed to jump in the water before I got my gear on. The boat would still be moving.



One way would be to calculate average depth and air consumption rate and then work out how long you've got on a tank of air. BUT...

What is the problem with surfacing part way through the dive. If it was unsafe due to say shipping in the area I'd probably avoid the dive. It's not my idea of a recreational dive. AND..

If you've never done the dive before how do you know how long it will take to swim the legs? If you have done the dive before then why do you need to do a gas management plan?

Do they not teach you anything about dive planning in Australia? Or did you sleep through that part of the training?

When I dive a site I've never dived before, I make it a point to find out as much about the profile as possible before I get in the water. This is often done prior to arriving at the dive site ... particularly if I'm not diving off a live boat.

It's something that, here in the states at least, we teach as part of our Open Water curriculum. Not sure about Oz ... sounds like you mates just jump in the water and splash about until it's time to abort the dive ...

... Bob (Grateful Diver)

 

[Hatul]

Sorry I did not read all the posts, but the rule of thirds was designed, I believe, by Sheck Exley for cave diving. The analogous rule for open water rec diving is the Rock Bottom -- always have enough gas to make a direct safe ascent while sharing air with your buddy, with a safety stop. A simple rule to meet this requirement is to always have in PSI at least (depth in feet)*10+500. At say 90 feet this works out to 900+500=1400 psi.