Ascending without a dive computer

[barth]

I am going to take a wild guess as to what this might mean. I am going to guess that you are saying that some people dive in ways that don't require the advantages of a computer. In that case, I agree with you. If you want to be limited in your diving and not use those advantages, you are free to do so.

For example, you are free to dive the bottom time limits of a table rather than the extended limits of a multi-level dive. I did 3 dives in Palau on May 10, with roughly a 1 hour surface interval between the 1st and the 2nd and roughly a 1.5 hour interval between the 2nd and 3rd. Please calculate them on your dive tables of choice and tell me what limits I would have had following the 1st dive if I had chosen to use the tables instead. (All dives were done on EANx 32.)

First dive: 91 feet for 66 minutes.
Second dive: 87 feet for 70 minutes
Third dive: 96 feet for 63 minutes.

What I mean is that diving without a computer doesn’t change anything for me. My dives would be the same, I can change my plan underwater. I can do a multilevel dive.

It also doesn’t effect my safety.

I agree that a computer is easier for most divers. It is also safer for most divers. But that’s because most divers don’t know what they are doing. Their safety depends on the computer.

But if you really want to spent time in watching your dive profiles after the dive, make your own divetables in wetnotes, do your planning with a smartphone before a dive. Make a good diveplan before the dive. Than the dives would probably the same when you are using a bottomtimer or computer.

For me a computer/bottomtimer is just a tool to do the dive(s).

I don’t understand that people here seems to believe that it is not safe to dive without a computer and/or you can’t do the same dive.

 

[doctormike]

For me a computer/bottomtimer is just a tool to do the dive(s).

I don’t understand that people here seems to believe that it is not safe to dive without a computer and/or you can’t do the same dive.

I don't think that anyone said it wasn't safe to dive without a computer.

What you can't do is get "credit" for time spent above the planned bottom depth, or above any of your planned levels. If you really do stick to square dive profiles, then not much different, other than the logging feature. It's probably more conservative to dive tables, if anything, since you are assuming more N2 loading than you actually have, if you stay above your planned maximum depth.

Of course, it's also more conservative to end your dive when your NDL hits 20 rather than letting it get closer to zero, but most people prefer to have a longer dive time if it can be done safely.

 

[boulderjohn]

I can do a multilevel dive.

How? Most people who say they do multi-level dives are using a system that is not valid using the tables.

But if you really want to spent time in watching your dive profiles after the dive, make your own divetables in wetnotes, do your planning with a smartphone before a dive. Make a good diveplan before the dive. Than the dives would probably the same when you are using a bottomtimer or computer.

That is yet another limitation. It only allows you to do dives where you know ahead of time exactly what you are going to do.

Example One: When I do a wreck dive, whether it is a simple recreational dive or a technical dive, I can't be sure how much time I will spend at different depths. It depends upon the wreck and where I will go on it. That is especially true if I am visiting a wreck I have never dived before.

Example Two: Once on a dive in Hawai'i, we planned a dive and started out. I have no memory of the actual plan, because what we did was so very different. As we began our descent, we saw something we had not expected--a manta ray being cleaned at a cleaning station at about 100 feet. We headed over to it and watched until the manta felt sufficiently cleaned and headed off. We were about to do the same when an eagle ray came by for a cleaning. We watched that for a while until our computers indicated we should start an ascent. We were heading up the slope when we encountered a helmet conch stalking a decorator urchin. We saw the actual capture by the conch, and then went up to finish off the dive at the top of the reef. It remains one of the most interesting recreational dives of my life, and it was only possible because we did not follow our plan whatsoever.

 

[Chris Richardson]

Ok, ok, guys! Right, l have bitten the bullet and bought a used Suunto Gekko dc in the interim. I do plan to still use my Divemaster watch, RDP and eRDP as it would be stupid to let them go to waste. Thanks for your help, input and advice guys

 

[MaxBottomtime]

I am going to guess that you are saying that some people dive in ways that don't require the advantages of a computer. In that case, I agree with you. If you want to be limited in your diving and not use those advantages, you are free to do so.

For example, you are free to dive the bottom time limits of a table rather than the extended limits of a multi-level dive.

During my first five or six years of diving I was making local shore dives where my depth rarely exceeded 45 feet. I never made more than two dives per day. A computer would not have given me any more bottom time. In three decades of diving I have still never made more than three dives per day. I do get an advantage by using a computer but I would be able to dive without one if I wanted to.

 

[boulderjohn]

I do plan to still use my Divemaster watch, RDP and eRDP as it would be stupid to let them go to waste.

How?

A couple of decades ago, I did my first dive trip after certification in Cozumel. After my first multi-level, DM-led dive, I dutifully pulled out my tables to log the dive, figure my pressure group, etc. I saw that I was already well off the tables. As I sat there puzzled, one of the others divers told me that my tables would make a decent Frisbee. I bought a computer after that trip.

I have no idea how many recreational dives I have done around the world in the ensuing decades (check my profile), but my attempt to use my tables after that dive remains the only time I have seen a recreational diver attempt to use any tables other than on training dives.

 

[doctormike]

. It remains one of the most interesting recreational dives of my life, and it was only possible because we did not follow our plan whatsoever.

Yeah, this is a common misconception. "Plan the dive and dive the plan" is fine, but I think that some people take it to mean that following a plan is an end in itself. I am happy to deviate from a plan based on new information, as long as I can remain safe. Now that I think of it, that's good advice for pretty much any human activity.

Reminds me of an old Stephen Colbert line, about a politician. "If he believes something on Monday, he still believes it on Wednesday. No matter what happens on Tuesday."

 

[boulderjohn]

People often scoff at recreational divers who enter the water with no other plan than to return to the surface when their SPGs reach a certain level or when their computers get close to NDL. "These people don't know how to plan a dive," they sneer.

These people will often point to cave diving as a primary example of people who plan their dives, even though they often have no other plan than to return to the surface when their SPGs reach a certain level.

There are different ways to plan a dive. Just because someone else's plan does not look like yours does not mean it is not a plan.

 

[txgoose]

First off, let me clarify, I am not challenging anybody's knowledge or expertise. Simply trying to be a bit geeky and dive into the details so that over time I absorb more and more of this information.

See my post #34 for more information.

You seem to be assuming that all tissues are off-gassing as you ascend.

I guess I am. I am surprised that we have tissues that are so sensitive to pressure that even a few inches of water pressure will keep them on-gassing. It seems like those tissues would by default be the fast tissues. What compartment, in my scenario, or any scenario at a microscopic level cannot off gas during the apropriate partial pressure of an ascent? For my question, a _very_ slow, possibly impractical ascent? Even if the off gassing is incredibly slow, there has to be some depth along the ascent path where each tissue's partial pressure is met, no? At some point on the ascent, if slow enough, won't every tissue reach a partial pressure equilibrium for the current depth and begin to off gas if that depth is reduced? This is why I asked if we were talking about a "practical for scuba" sweet spot of ascent rate vs a law of physics sweet spot. I guess I figured that a really slow ascent rate would be the perfect form of decompression. Slow tissues are allowed to off gas slowly and near zero chance of a bubble forming. I am not suggesting that all tissues would reach equilibrium at the same time, only that if an ascent was slow enough, all tissues would reach ambient saturation seconds and inches below the surface.

Those slower tissues will one-by-one reach equilibrium and then begin to off-gas as you ascend,

Agreed. Wholeheartedly. This is also the assumption you said I made above.

but you will not be off-gassing in ALL tissues until you are on the surface.

But you and I just agreed that they would? At least at any practical level. If an ascent were slow enough, wouldn't any practically measurable tissue that had nitrogen in it at a depth of a foot or two be at ambient pressures?

I understand the different compartment idea, admittedly at a very amateurish level. At the extreme, even the fast tissues would have an elevated nitrogen equilibrium at a foot of depth. Maybe immeasurable, but there. This is why I asked about a _very_ slow ascent. I am still working my head around a "too slow ascent rate." I remember the SB thread that contained a really nice on-gassing computer simulation. (Which I didn't find with a cursory look. I think that you were a contributor.) It explained this really well but I don't think it addressed anything like a too slow ascent rate. I understand that equilibrium will be reached at different depths for different tissues. Again, in my proposed scenario, we are talking about a possibly impractically slow ascent. I was just surprised that a diver could ascend too slowly. Just digging for an understanding.

Let me ask it in a different way. This doesn't tie directly to my original question but it is possibly a more practical question. Is scenario two actually at a higher risk of DCS than scenario one?
Scenario 1) I am doing a 60 minute dive to 45' depth, I stay there the maximum amount of time to allow for a safe "industry standard" ascent to the surface, 53 minutes. Then ascend normally at 30ft per minute. (2 minute descent. 3 min safety stop, 90 second combined ascent, so a 53+ minute bottom time)
Scenario 2) I am doing a 60 minute dive to 45' depth. It take two minutes to descend to 45'. At that time, I take 58 minutes to at ascend 45 feet smoothly to the surface. Roughly an ascent rate of .8 feet per minute.

 

[doctormike]

First off, let me clarify, I am not challenging anybody's knowledge or expertise. Simply trying to be a bit geeky and dive into the details so that over time I absorb more and more of this information.

I'm not quite sure I understand the point of confusion in your post, but I think that you are wondering about increasing DCS risk from a slow ascent. When you are at your NDLs on a recreational dive, not all of your tissue compartments are fully saturated - specifically, the slower ones. So if you ascend slowly, there will still be a pressure gradient for these compartments during part of the ascent, and they will continue to ongas. So with a slow enough ascent, your N2 load will possibly be great enough for one of these to become the leading compartment and put you into deco.

Or am I misunderstanding the question...?