Planned deco on a recreational dive?

[MXGratefulDiver]

The post I answered was the proof of the inability to two people to surface from 110' on 800 psi in an AL100. Absolute calculations that showed you couldn't do it. And absolute nonsense. I don't have to calculate it I know I can do it.

You can do it ... but if your buddy swam up to you at 110' and slashed his hand across his throat, would you have enough to share? Or is the buddy on his own?

Most people who "know I can do it" are planning for everything going right ... but that's not how to make a dive plan ...

... Bob (Grateful Diver)

 

[Lorenzoid]

I don't think I have done gas planning in over 20 years unless you call starting your ascent with 500-700psi gas planning.

I think it IS gas planning in a sense; it's just that you last ran the numbers years ago--or maybe you never actually ran the numbers but figured out from trial and error (not recommended) that 500-700 psi is sufficient for the dives you do, and nowadays when you do the same kind of dive you know that 500-700 is still sufficient. A less experienced diver might be well advised to actually go through the calculation and see if he arrives at "500-700" or some other number--that's planning. Maybe he will decide he wants to reserve more gas, or not. I don't interpret "planning" as meaning one has to do arithmetic before every dive. As I see it, gas planning is giving some reasoned thought in advance of the dive to how much gas you would like to have remaining at least at the point of beginning the ascent if not at one or more additional waypoints in the dive.

 

[Bob DBF]

And it's not unusual for divers to get so focused on the objective that they neglect to turn when they should ...

Sounds like turn pressure is better than a dive plan in your example.

Personally my turn pressure is much more important to me, especially when hunting and salvage, or any diving when distraction is present.


Bob

 

[MXGratefulDiver]

Actually, what you said and what Bob said are quite different. You said in certain situations "Gas Planning" can become an afterthought and I agree with you. I don't think I have done gas planning in over 20 years unless you call starting your accent with 500-700psi gas planning. Bob changed that to say "Breathing" in not an afterthought. Of course it's not but that's not what you said.

Actually that's not what he said. He said "With no stop diving, follow your computer and monitor your air. Gas planning is an afterthought."

Monitoring your air is well and good ... and we should all do that. However, unless you have some idea of how quickly you go through your air it doesn't mean much. It's like driving across the wilderness while monitoring the gas gauge in your car. It's all well and good, but unless you also know your miles-per-gallon and how much gas your tank holds you have no way of knowing whether or not you'll make it.

In diving you need more information that what your gas gauge tells you, because we all go through our gas at different rates, and 700 psi means something very different depending on the size of the tank you're diving.

You've done enough diving to know what your "miles-per-gallon" is ... and because you mostly (or completely) dive on vacations, you tend to use the same size tank all the time (besides, as I recall, you carry a pony). So you do gas planning ... you just have enough information from previous experience to apply the needed criteria without overt effort.

... Bob (Grateful Diver)

 

[MXGratefulDiver]

Sounds like turn pressure is better than a dive plan in your example.

Personally my turn pressure is much more important to me, especially when hunting and salvage, or any diving when distraction is present.


Bob

Depends on the dive profile and circumstances. As an example, I recently did a dive on a wall that's known for current. The reality of the current that day bore little resemblance to the prediction, and we found ourselves kicking against it on the return. Had I relied strictly on turn pressure I would not have made it back to the exit point without running out of air.

Turn pressure's just one of several criteria that needs to be applied to a gas plan. One must also factor in the exit strategy if things don't go as expected ... and "up" isn't always the best option, even on open-water, no-deco dives ...

... Bob (Grateful Diver)

 

[BRT]

You can do it ... but if your buddy swam up to you at 110' and slashed his hand across his throat, would you have enough to share? Or is the buddy on his own?

Most people who "know I can do it" are planning for everything going right ... but that's not how to make a dive plan ...

... Bob (Grateful Diver)

Yes. If my wife comes up to me OOA at 110" and I have 800# we will have air to go up.

 

[MXGratefulDiver]

Yes. If my wife comes up to me OOA at 110" and I have 800# we will have air to go up.

Sounds pretty risky to me ... but I wish you both luck with that ... I wouldn't, personally, choose to cut my margins that thin ...

... Bob (Grateful Diver)

 

[boulderjohn]

... but in the real world, reaching an objective is often a big part of the plan

And often it isn't. In fact, the situations I described in my comparison are the norms in my experience. I have done several hundred wreck dives in my time, and I have rarely seen anyone with any objective other than to look around. With my cave diving, I have only had a goal of reaching a specific location on perhaps a third of my dives. In the majority of cases, i was just going to go into the cave and come back, enjoying the scenery along the way.

"Turn the dive at" a specific pressure isn't planning ... it's reacting.

I am therefore baffled as to what I should be doing differently on the dives mentioned. Please explain how those dives should be planned.

 

[MXGratefulDiver]

Reacting works just fine, as long as you remember when to react.

In my experience, people who go OOA/LOA usually are so focused on other things (like taking pictures or catching lobsters) that they neglect to monitor their gauge. When that happens, turn pressure doesn't mean much.

Having a dive plan always works better than relying on a data point to manage your dive. It gives you much more information to work with, and comes with better feedback to help you manage what you're doing.

... Bob (Grateful Diver)

 

[Fastmarc]

Reacting works just fine, as long as you remember when to react.

In my experience, people who go OOA/LOA usually are so focused on other things (like taking pictures or catching lobsters) that they neglect to monitor their gauge. When that happens, turn pressure doesn't mean much.

Having a dive plan always works better than relying on a data point to manage your dive. It gives you much more information to work with, and comes with better feedback to help you manage what you're doing.

... Bob (Grateful Diver)

Would you give an example using one of the above two you mentioned of how you would plan that dive?