Ascending without a dive computer

[txgoose]

At 2ft a minute, buying back time all along the way, I'd surface with a fair amount of air and highly doubt I'd ever hit NDL.

Okay, so even a blind squirrel can find a nut. I think I got lucky with my two foot guess. I went and found my SSI tables, this gets me mildly back on topic. Based on the data there, for rec diving you need to stay at 130 less than five minutes; then ascend at 2ft/min back to 80ft (fine minutes per ten feet); where you can slow down to 1ft/min to 60ft; where you can slow down to half a foot a minute up to 50 ft; and then it begins to get crazy slow as might be expected. This would allow you to brush up against NDL in a quasi responsible way.

My formula was Distance to travel divided by time allowed = ascent rate = (current depth - next higher depth on the chart) / (NDL time allowed at higher depth - time already burnt at lower depth(s))

 

[boulderjohn]

Okay, so even a blind squirrel can find a nut. I think I got lucky with my two foot guess. I went and found my SSI tables, this gets me mildly back on topic. Based on the data there, for rec diving you need to stay at 130 less than five minutes; then ascend at 2ft/min back to 80ft (fine minutes per ten feet); where you can slow down to 1ft/min to 60ft; where you can slow down to half a foot a minute up to 50 ft; and then it begins to get crazy slow as might be expected. This would allow you to brush up against NDL in a quasi responsible way.

My formula was Distance to travel divided by time allowed = ascent rate = (current depth - next higher depth on the chart) / (NDL time allowed at higher depth - time already burnt at lower depth(s))

If you I am understanding you right, you are saying it is OK if reach the time for the NDL for a specific depth even if you have spent the entire time below that depth. Is that right? Are you saying that if the NDL for 60 feet is 60 minutes, it is OK to be below 60 feet for all of those 60 minutes?

 

[txgoose]

Here is a way to think about it by carrying it to an extreme. Let's say you are using the PADI tables to guide your dive. (I am using that example because I can give you specific numbers.) You are at 100 feet for 20 minutes, the maximum NDL time for that depth. You begin to ascend at 5 FPM. After 2 minutes, you arrive at 90 feet and have now spent 22 minutes between 90-100 feet. You have essentially gone into deco, although a table as no way to calculate it. You reach the 90 foot mark at just about the NDL for 90 minutes, but you have spent that entire time below that depth.

Now we will be getting way off topic. But isn't this what our computers are doing when we talk about riding the NDL, or riding the computer? Granted I have only been in this situation once but the wife and I approached NDL, we ascended and bought back time, on the second ascent we/me actually hit turn pressure first (we staged ourselves and arrived at the mooring line at my turn pressure).

 

[txgoose]

If you I am understanding you right, you are saying it is OK if reach the time for the NDL for a specific depth even if you have spent the entire time below that depth. Is that right? Are you saying that if the NDL for 60 feet is 60 minutes, it is OK to be below 60 feet for all of those 60 minutes?

I am here learning. I am picking no fights. I am exploring the knowledge of SB.

But to your point, what about staying at 60 feet for 59 minutes and ascending very slowly? Never hit NDL. When do I hit NDL?

 

[boulderjohn]

Now we will be getting way off topic. But isn't this what our computers are doing when we talk about riding the NDL, or riding the computer? Granted I have only been in this situation once but the wife and I approached NDL, we ascended and bought back time, on the second ascent we/me actually hit turn pressure first (we staged ourselves and arrived at the mooring line at my turn pressure).

Computers do something similar to that, but it is not the same because the values are not the same. For your table to work for 60 minutes at 60 feet, every one of those minutes must be shallower than 60 feet. Think that one through and you will see the difference. Your computer is recalculating your dive constantly, as if you are doing a series of different dives to different depths. That is something a table cannot do. There is therefore no correlation between the numbers on a table and the way a computer is able to recalculate your dive during ascent. With a table, you cannot have any depth deeper than the NDL for that depth; with a computer you can. Therefore, the time limit for each depth on a table has no relation to what a computer give you when you "ride" the computer to the surface.

 

[txgoose]

Computers do something similar to that, but it is not the same because the values are not the same. For your table to work for 60 minutes at 60 feet, every one of those minutes must be shallower than 60 feet. Think that one through and you will see the difference. Your computer is recalculating your dive constantly, as if you are doing a series of different dives to different depths. That is something a table cannot do. There is therefore no correlation between the numbers on a table and the way a computer is able to recalculate your dive during ascent. With a table, you cannot have any depth deeper than the NDL for that depth; with a computer you can. Therefore, the time limit for each depth on a table has no relation to what a computer give you when you "ride" the computer to the surface.

 

[txgoose]

I am not advocating for anyone to “ride a table“ like they might “ride a computer.“ I also like computers. I think buying a pack on sale for $100 is a no brainer for most people who don’t own a computer yet.

My question revolves around the proposed minimum a cent rate of 9 feet per minute. That seems incredibly fast for a minimum when we are allowed to help her with zero change during other parts of the dive. I was trying to calculate a facsimile Closer to what I suspect is reality than 9 ft./m. That is all I am trying to do. Would you agree that the slowest minimum a cent rate would be closer to 2 ft./m than 9 ft./m? Of note, I am using Siri. Apologies for awesome AutoCorrect’s.

 

[boulderjohn]

I am not advocating for anyone to “ride a table“ like they might “ride a computer.“ I also like computers. I think buying a pack on sale for $100 is a no brainer for most people who don’t own a computer yet.

My question revolves around the proposed minimum a cent rate of 9 feet per minute. That seems incredibly fast for a minimum when we are allowed to help her with zero change during other parts of the dive. I was trying to calculate a facsimile Closer to what I suspect is reality than 9 ft./m. That is all I am trying to do. Would you agree that the slowest minimum a cent rate would be closer to 2 ft./m than 9 ft./m? Of note, I am using Siri. Apologies for awesome AutoCorrect’s.

The ascent rate recommended by just about everyone today is 30 FPM. If you are going slower than that, you are needlessly on-gassing in the slower tissues. You mentioned the SSI tables--30 FPM is the rate you are supposed to use with them. 2 FPM is absurdly slow.

 

[txgoose]

The ascent rate recommended by just about everyone today is 30 FPM. If you are going slower than that, you are needlessly on-gassing in the slower tissues. You mentioned the SSI tables--30 FPM is the rate you are supposed to use with them. 2 FPM is absurdly slow.

I don’t want to belabor the point. The discussion was about a stated minimum limit. I probably have beaten my curiosity on this one. I’ll call it three feet for impractical practical purposes. You and Doc and Bluetrin have been great. I appreciate your contributions here and all over SB.

 

[barth]

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

There are many options I think. This options I did use:

1

This table you can use for some dives, but it depends on the profile

http://dir-diver.com/pdf/minimum-deco-tables/english_metric_A.pdf
http://dir-diver.com/pdf/minimum-deco-tables/english_imperial_A.pdf

Here is the text about average depth
DIR-diver.com - Average depth for deco?

2

Using deco software on smartphone

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.

1 The wrecks I did it was clear what I wanted to see and which depth it was. Sometimes i need to do photography of some objects. Planning a wreckdive makes it easer for me to do what I want to do at the wreck. It is much easier to discuss a plan at the surface than spending time at to bottom to communicate what we want to do. If I want to measure torpedo things or do photography and should be back at the line after a certain time I should do a panning before the dive starts.

Maybe we have different goals underwater, there is nothing wrong with that. I did wreck dives in croatia and the northsea this year. Most of the dives were projectdives. Planning is verry clear before the dive start, and different divers have different tasks.

The same for cavediving. Before the dive starts we have a plan and know the depths of the cave. We also have a plan were we want to do photography and/or filming.

I think what works for me maybe doesn't work for you.

2 If it is a reef dive I would have probably done the same dive. (Sometimes the plan is really simple like when I hit 100 bar I will go to 18 meter and when I hit 50 barI will go to ten meter and only minimum deco, no more deco,) I can change the plan if there is a reason for it. Maybe a few minutes shorter/longer and/or a few minutes more stops. But I don't think your dive or profile would be much different than mine.But if somebody is using another computer and/or computersettings his/her dive wouldn't also not be exacly the same.