Computer VS. Tables

[mrdre]

Storker, boulderjohn, why are you guys assuming that if somebody is thinking about other ways of approaching the planning it means he is not capable of doing some skills? I wasn't discharged from mental institution yesterday. Do you guys really think the "dive planning" you are talking about only few chosen ones are capable of mastering?

What I was saying, that if you treat every dive as deco dive and plan as a deco dive, then the whole issue of NDLs goes away. You are just adding another task: planning and executing deco-stops. Although it's not a good idea for new divers, but it's not really that hard and anybody with 100 dives is capable of doing it. I hit NDLs often, I have low SAC rate and this strategy allows me to stay longer underwater.

That doesn't mean I can't really take a dive computer with me and "plan" like "we'll go 80' then look at the fish for 15 minutes, then ascend to 60', look at the fish more and once we hit 1000 PSI or my computer will tell me to - ascend". C'mon, guys. If I'm talking about checkers that doesn't mean I can't play chess.

 

[Storker]

Do you guys really think the "dive planning" you are talking about only few chosen ones are capable of mastering?

Poor attempt at strawmanning there. You are arguing against the exact opposite of what we're saying.

Did you read our posts? Do you understand what "it ain't rocket science" means?

It seems as if someone is lacking in the reading comprehension department, and I don't think it's me...


--
Sent from my Android phone
Typos are a feature, not a bug

 

[mrdre]

Poor attempt at strawmanning there. You are arguing against the exact opposite of what we're saying.

Did you read our posts? Do you understand what "it ain't rocket science" means?

It seems as if someone is lacking in the reading comprehension department, and I don't think it's me...


--
Sent from my Android phone
Typos are a feature, not a bug

"I'm sorry that the subset of the diving population you know isn't able to plan and execute a dive without risk of getting bent"

It's from your post.

 

[Storker]

...omitting "because up here it's a requisite to get certified." Nice misquoting, there.

If "I'm sorry that the subset of the diving population you know isn't able to plan and execute a dive without risk of getting bent because up here it's a requisite to get certified." in your mind means 'a chosen few', I'm becoming more convinced as how to who of us is lacking in the reading comprehension department. Alternatively, you might be desperately trying to derail the discussion, because you're losing.

---------- Post added August 26th, 2014 at 08:10 AM ----------

Now, to get back to topic, and to follow up on boulderjohn's examples of simple rec dive planning, let me add a couple of examples of the type of planning I like to do:

Boat dive, wall without hard bottom at rec depths, return to boat:
"I'd like to dive the deep part going out and the shallow part going in. Okay with you? How long are we gonna be in the water? 40min? 50? an hour? Max 50? OK. What's your max depth for today? 25? No? 30? We won't get half of 50 minutes at 30, so let's do a little shallower. What about 25? Fine. 25m first level. Let's see, 25, that's... (takes out RDP) 29min max. Let's say 25. First level, 25 meters 15 minutes. With 10L 300bar tanks, gas shouldn't be problem, but minimum pressure at 25m is 110 bar. Then we ascend to max 16 after 25min or 110bar pressure, turn around and swim back to the boat. We have... 30 minutes left at 16m, so that's OK. There's some nice kelp forest from 10m to 5m, so let's just go slowly shallower on the return leg so we can see it. Safety stop just below the boat, there are some nice corals on the wall there to watch."

If I had planned this as a square profile dive, I would have exceeded my no-stop limit by about 20 minutes. According to the Norwegian navy tables I'd need 5min deco at 6m and 15min at 3m. That's 20 more minutes, by which time I'd be freezing and would have peed myself. Which I don't like to do, especially in a DS...

Shore dive, sloping bottom:
"How long are we gonna be in the water? 40min? 50? an hour? Max an hour? OK. What's your max depth for today? 25? No? 30? OK. Let's go quickly to around 30, we have... max 20 minutes at 30. Let's say 15. At 15min, we start to go shallower, and at 20min we should be no deeper than 15. Min pressure at 30 is 130 bar. Turn back at 25min, go gradually shallower on the return leg and muck about in the shallows at around safety stop depth until the time is up or we reach 50 bar."

If I had planned this as a square profile dive, I would have exceeded my no-stop limit by about 40 minutes. According to the Norwegian navy tables I'd need 5min deco at 9m, 10min at 6m and 30min at 3m. That's 45 more minutes, by which time I'd be hypothermic and out of gas.

Scallop dive, almost flat bottom:
"I'm usually getting cold after about an hour when the water is this temperature, so that's my limit. The scallops start at around 12-14m here, but let's go a little deeper first. No need to go deeper than 20, there's enough of them. So, max 20m for max 30 minutes, then max 15m for max 30 minutes."

If I had planned this as a square profile dive, I would have exceeded my no-stop limit by about 15 minutes. According to the Norwegian navy tables I'd need 5min deco at 6m and 5min at 3m. That's 10 more minutes, and my fingers would have been uncomfortably cold, and probably so stiff that I'd have serious problems doffing my weights before climbing aboard.



All of these are real-world examples, very similar to dives I've done. They were planned using my PADI tables and the method I linked to in my post #10. Haven't been bent yet, haven't broken my Suunto's no-stop limits and haven't spent one minute in deco.

It ain't rocket science, and divers who actually are competent to plan and execute a dive shouldn't have much of a problem to do this. Especially if they take, e.g. the PADI multilevel dive specialty.

 

[mrdre]

......you might be desperately trying to derail the discussion, because you're losing........

Dude, I'm not "losing" anything as I'm not trying to "win" anything. The time I care about winning is when my money is on stake. I'm very glad that you haven't been bent, are confident in your planning and executing the dives. I really am. Good for you. But I would really prefer to leave my humble persona alone together with my abilities to read, understand, think, etc. Also I don't think my certifications, medals, diplomas or lack of those really matter for the argument.

You don't cross NDLs, good for you. I do cross NDLs all the time and so I do deco-dives. And I never been bent either. I'm discussing how to implement some of the elements of deco diving in recreational diving. We are crossing NDLs by not large margin and so the models I'm using don't require long deco-stops. Tops 15 minutes. They are easy to execute. That's what I'm trying to discuss.

 

[boulderjohn]

You don't cross NDLs, good for you. I do cross NDLs all the time and so I do deco-dives. And I never been bent either. I'm discussing how to implement some of the elements of deco diving in recreational diving. We are crossing NDLs by not large margin and so the models I'm using don't require long deco-stops. Tops 15 minutes. They are easy to execute. That's what I'm trying to discuss.

So the issue for you finally comes out. You violate NDLs frequently, and you want everyone to say it is OK to do that.

To a large extent, that is how things used to be done. The only tables really being used by much of the recreational world were the U.S. Navy air tables, and they progressed from NDL dives to serious deco dives simply by telling you when you had to start adding deco stops, how deep to do them, and how long to do them. Of course, U.S. Navy divers had the training and equipment to make the progression safely. The world of recreational divers? Not so much. Those days went away long ago, and they went away for a reason.

Let's take a 100 foot dive for 20 minutes followed by that oxymoron of a required "optional" safety stop, which is a NDL dive according to the PADI RDP and, I suspect, almost all dive computers. Make it a 22 minute dive and you are in deco. If you are using a standard, basic recreational computer, it will tell you how much time you have to add to the safety stop to clear deco. Not too bad. I suspect a lot of people will do that. If something goes wrong and they have to surface before completing that obligation, they will probably be OK.

As you increase the decompression obligation, though, you will at some point have enough of an obligation that surfacing too soon will mean almost certain DCS and potential death. Where is that point? When you reach that point, wherever it is, you are definitely in the realm of technical diving. Technical divers have special equipment and training designed to ensure that they can complete decompression obligations, no matter what problems may arise. That is the main idea of the difference--recreational divers should always be able to head for the surface in an emergency, and technical divers will be able to deal with problems while staying at depth.

You want to do away with that distinction. You want to be a technical diver without going through the trouble of getting the right equipment and training. I pointed out the trouble with your definition in my first response to you. You then said that when you talked about doing away with the whole idea of NDL dives, you were only talking about NDL dives. When you said to treat all dives as if they were decompression dives, you were not talking about decompression dives. How are we to know the difference in your system?

The reason for the difference is this. Researchers have determined that up to a certain point, divers experiencing difficulties while diving within these limits can go to the surface safely. After that, it becomes increasingly likely that divers going directly to the surface will experience problems, including potential fatalities. That is why special training and equipment is considered a prerequisite for diving beyond those limits.

 

[mrdre]

So the issue for you finally comes out. You violate NDLs frequently, and you want everyone to say it is OK to do that....

No, I don't want everyone to say "OK" to that. I want everyone to criticize me (I mentioned it in my first post), as I'm interested in the arguments against. Moreover, I'm not advocating doing this to anyone. It's just me and my butt. (well.. and my buddies' who do the same, but I know my training, I know their training, I know the equipment we have).

OK, you gave these arguments and offered an example. Let's stay with that example. There is a wreck laying at 100'. We are doing 2 or 3 dives to that wreck in a row (1 hour SI). NDL limit is 20 minutes (for the sake of argument let's assume regular air). But I'm thinking staying there for 22 minutes. I will cross NDL. I'm running a dive planning software ahead of the dive and I know I will be required to do (let's say) 3 minutes deco (it's just an example) - not a "safety stop", but mandatory stop.

On the second dive I also decide to stay 22 minutes. Now I'm planning my dive and the software tells me I need 6 minutes deco and so I do it. Then maybe I will do the 3rd dive, and I will be required to do 15 minutes stop. I will know ahead of the time my dive plan precisely. Now, suppose I will be diving around 80, then ascend to 70, then descend to 90 - it won't matter, as I used 100 for calculations.

Everybody in the team has spare air, enough for executing safe ascend with all the stops.

Let's say now that we realized that we used more air than we planned to in the middle of the dive for whatever reason, then obviously we head to the surface earlier, but will still execute the same deco strategy. So we plan only for the main tank (I'm assuming single tank dive - "recreational" diving). The spare air is for catastrophic failure of the main tank and for sharing air with another diver.

In this scenario I'm not even using my dive computer, I don't need to. I'm using it just as a bottom timer. I know what I'm gonna do ahead of the dive, I don't need my dive computer to tell me about NDL, I don't care about NDL anymore.

I'm interested to hear criticism of this strategy. Is it "tech diving"? I don't think so. Are the risks too high? I don't think so, but I'm interested in the arguments.

 

[Basking Ridge Diver]

I don't think so, but I'm interested in the arguments.

No Arguments from me - you seem to have made up your mind. Why try to change that?

If you know the risk and accept it - tell your family about your decision - because they too will be involved when something bad happens.

For anyone else reading this thread - this is a classic case of you will only hear what you want to believe - go back to your training and stay within your comfort zone.

 

[EFX]

There is a tendency on SB for experienced highly trained divers to apply their training and tools to dives that don't require them. I got into a raging debate regarding just this topic on dive planning and why knowing SAC rates wasn't needed for rec dives even those to deep depths. Is it nice to know? Sure. But's it's not necessary. I wish storker and Boulderjohn were there in that thread. They could have said what they're saying here: simple dive plans that meet the objective using a dive computer running algorithms based on NDL's is enough. The argument by mrdre appears to be that same argument. That, more complex planning is needed for (relatively) simple dives that don't require it. The more unnecessary complexity you add the greater risk that something will go wrong. I think KISS is a good principle. K.I.S.S. = keep it simple stupid.

 

[boulderjohn]

In this scenario I'm not even using my dive computer, I don't need to. I'm using it just as a bottom timer. I know what I'm gonna do ahead of the dive, I don't need my dive computer to tell me about NDL, I don't care about NDL anymore.

I'm interested to hear criticism of this strategy. Is it "tech diving"? I don't think so. Are the risks too high? I don't think so, but I'm interested in the arguments.

Yes, this is in the realm of tech diving, but it is at the edge. Many tech divers do use software that pre-plans deco stops and use bottom timers or computers in gauge mode. I will be teaching a student how to do that in a couple of weeks. Your example is a bit off, though. Here is what the most popular dive planning software, V-Planner, says for a 22 minute dive to 100 feet on air:

Dec to 100ft (2) Air 50ft/min descent.
Level 100ft 20:00 (22) Air 0.85 ppO2, 100ft ead
Asc to 40ft (24) Air -30ft/min ascent.
Stop at 30ft 2:00 (26) Air 0.40 ppO2, 30ft ead
Stop at 20ft 15:00 (41) Air 0.34 ppO2, 20ft ead
Surface (41) Air -30ft/min ascent.​

So you will have decompression stops starting at 40 feet, for a total ascent time of 19 minutes, with 15 minutes at 20 feet.

For your second dive, you will have a similar profile, with 25 minutes of decompression. I did not calculate your third dive.

Do you know how to calculate the amount of gas you will need for this dive? How is your buoyancy? Can you really hold a 15-20 minute stop at 20 feet in rough seas? Can you do a succession of 10 foot stops without losing buoyancy control and bouncing to different levels? Can you do this in a blue water ascent, which is difficult for a person with lots of technical training? Do you know what to do in case of a catastrophic gas loss at depth? If a first stage O-ring blows--what will you do? Will your buddy have enough gas to bring both of you to the surface safely during a 25 minute ascent? Do the math, and you will see that is a lot of gas--how will you carry it all? If you are using extra tanks, do you have the ability to change tanks safely during a decompression stop without losing control of buoyancy and possible rocketing to the surface too soon?