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superkingkong
11-07-2007, 20:55
Hi guys,

For example, say you want to go 100ft for 20mins.

do u start counting your 20mins the moment u start to descend from the surface? or the moment u touch down at 100ft?

Also, when do u stop counting?

the moment u leave the 100ft spot?
or when u reach 5m for safety stop?
or safety stop time also included in your 20mins?

thanks

texdiveguy
11-07-2007, 21:09
Dude.... this is your second question posed in the past moments that really bring question in my mind as to are you really certified or are you just playing games???????? Your bio shows you have 25-50 dives as a certified diver....come on now???!
Not being rude but just being honest!

superkingkong
11-07-2007, 21:42
ok, i ask this question, because i do not know. maybe i'm stupid, i have a list of "wanna ask questions" with me.

well, if it's not appropriate, i'll stop.
thanks and sorry.

BouzoukiJoe A.K.A. wrecker130 AKA Chuck Norris AKA joeforbroke (banned)
11-07-2007, 21:49
Dogma is beginning of descent to beginning of ascent. Nobody remembers everything, but they should have taught you this in your cert class.

texdiveguy
11-07-2007, 21:55
ok, i ask this question, because i do not know. maybe i'm stupid, i have a list of "wanna ask questions" with me.

well, if it's not appropriate, i'll stop.
thanks and sorry.

I have just been looking at your questions all over the board in several different sub forums....not trying to discourage you questions....but some are just SO simple in terms of the answer that I would EXPECT a diver whom is certed with 25-50 dives to know the answers. If I am over reacting to your numerous threads than maybe I am missing the point.
**Again I would sugg. a refresher class from an instructor...that is a super way to review and bring your basic skills and knowledge back up to speed before your future dives.

TommyB
11-08-2007, 05:27
Hi guys,

For example, say you want to go 100ft for 20mins.

do u start counting your 20mins the moment u start to descend from the surface? or the moment u touch down at 100ft?

Also, when do u stop counting?

the moment u leave the 100ft spot?
or when u reach 5m for safety stop?
or safety stop time also included in your 20mins?

thanks
You start the minute you head down. And stop counting when you finish your saftey stop.
Example plan for doing a dive to 130 using air



Dec to 130ft (2) Air 50ft/min descent.
Level 130ft 5:24 (8) Air 1.01 ppO2, 130ft ead
Asc to 90ft (9) Air -30ft/min ascent.
Level 90ft 5:00 (14) Air 0.77 ppO2, 90ft ead
Asc to 50ft (15) Air -30ft/min ascent.
Level 50ft 5:00 (20) Air 0.52 ppO2, 50ft ead
Asc to 20ft (21) Air -30ft/min ascent.
Stop at 20ft 0:00 (21) Air 0.33 ppO2, 20ft ead
Level 15ft 3:00 (24) Air 0.30 ppO2, 15ft ead
Surface (25) Air -30ft/min ascent.

OTU's this dive: 12
CNS Total: 4.7%
56.7 cu ft Air
56.7 cu ft TOTAL
At 2 mins into the dive I should be at 130.
at 5 mins and 24 secs into the dive , I should be at 90 feet
etc , etc
at 21 mins into the dive, I should be at 20 feet doing saftey stop, and at 25 mins into the dive, done and on the surface.
This is multi-level dive planning.

But the long and short of it, time starts when you begin your descend, and time ends on surface.

BouzoukiJoe A.K.A. wrecker130 AKA Chuck Norris AKA joeforbroke (banned)
11-08-2007, 06:52
So I guess the definition of bottom time depends on how you are making your nitrogen loading calculations. If you're using the PADI RDP (square profile, assumes all time spent at the deepest depth) bottom time ends when you begin your ascent to the safety stop.

Zenagirl
11-08-2007, 09:02
I have to agree with Joe. When using the tables, bottom time is defined as the time from when you begin your descent to the time you begin your ascent to end your dive. It does not include the time between your deepest depth and the surface.

Another reason I really like having a dive computer.

robanna
11-08-2007, 09:24
Gee texdiveguy, for such a simple question, there sure is some conflict of answers.

And by the way, do you have anything to contribute to the tread or are you just going to keep flaming the guy for posting question that you consider elementary?

I start on descent and stop at the surface.

DougNR
11-08-2007, 11:11
Gee texdiveguy, for such a simple question, there sure is some conflict of answers.

And by the way, do you have anything to contribute to the tread or are you just going to keep flaming the guy for posting question that you consider elementary?

I start on descent and stop at the surface.

That's fine as your personal preference - as it does provide for an extra level of safety, but it is not the way the tables were designed. I would assume you then calculate the time of ascent from your planned depth plus safety stop and subtract that from your table no decompression bottom time.

I'm also surprised this question got so many variations as others have expressed. I wonder if this is a symptom of the ubiquitous Dive Computer? It's been 35 years since I took OW training and it wasn't even called OW at the time, but we sure as heck got that concept drilled into our heads - of course we were going 100% off the USN dive tables.

Question - Do OW classes today teach the tables or is that more in the realm of AOW training?? I can't fault the OP for his question if the later is true and perhaps he has not advanced to that training as yet.

FYI I have no beef with computers - luv 'em, use 'um, but I sure as hell have a backup plan that came from a good 'ol table for every dive.

IMO this could be one of the more interresting threads in a while!

Doug

D

BG9879
11-08-2007, 11:20
I know PADI OW still teachs the tables. And PADI uses the start of the decent to the start of the ascent. (Time you leave the surface until you start coming back up).

RoadRacer1978
11-08-2007, 11:24
Ok, I don't have a computer and do it the old fashioned way. If I am calculating for a square profile then I use the standard method of start upon descent and stop upon ascent. If I am diving a multi-level profile, which I do most of the time I error on the side of safety and start upon descent and stop when I reach my safety stop. I do not include my safety stop into my total bottom time. And calculate depth as my max depth obtained. (Man I can't wait to get a computer. Sure will lengthen my bottom time :) )

RoadRacer1978
11-08-2007, 11:28
Question - Do OW classes today teach the tables or is that more in the realm of AOW training?? I can't fault the OP for his question if the later is true and perhaps he has not advanced to that training as yet.

FYI I have no beef with computers - luv 'em, use 'um, but I sure as hell have a backup plan that came from a good 'ol table for every dive.

IMO this could be one of the more interresting threads in a while!

Doug

D

I took my PADI OW course back in 1994 and computers wern't mainstream, so we focused on the tables considerably. I ust recently took AOW this last sumer and the tables were not assressed at all and I was even the only person diving without a computer. I asked the LDS about the tables and he said they are rarely touched on anymore because of the frequent use of computers. I feel this is a great short coming. It is teaching students to rely too heavily on thier computer. :( And not on their brain.

DougNR
11-08-2007, 12:14
I asked the LDS about the tables and he said they are rarely touched on anymore because of the frequent use of computers. I feel this is a great short coming. It is teaching students to rely too heavily on thier computer. :( And not on their brain.

I agree 100%.

I also have no intention of blowing a dive because a computer failed. Falling back on my watch, a backup depth gauge, and tables might shorten my dive but not put an end to it.

Doug

in_cavediver
11-08-2007, 18:50
First, to define bottom time, you have to define its intended use. For me, BT is the Dive time I log. I use a 'puter predominantly and when I don't, its runtime tables. (IE, Be here at this time tables). Given that, my definition I use most of the time and yours can vary greatly.

Now, if you use IANTD, NAUI or PADI tables - you should use their definition.

Now for the really good part. How much does it really matter if you are off by a minute or two? Practically speaking, it doesn't make that much of a difference. Everything in deco theory is gray area not distinct lines. Your actual loading and how close you fit the model changes from day to day, dive to dive. Time is just one more source of error (that you should try to minimize) in the 'how close is the model to my body' analysis. You should understand what information you are getting and what it means.

For instance, do a dive to 80ft and come withing 3 minutes of the NDL for the table. For practical purposes, you are so close to the line of deco that you can't be sure what side your on for a given day, dive etc. In that case, you want to really control your ascent profile. Now, do a 50' dive for 15-20 minutes, you are well clear of the NDL area and likely can get away with a much more aggressive ascent profile.

If you still don't believe me, download GAP (free) and create a series of dive profiles and see for yourself. (of course, this is yet another model trying to predict reality)

CompuDude
11-08-2007, 19:18
PADI's RDP does indeed call for the dive to be timed from the moment you drop underwater to the moment you begin your ascent. This gets really messed with if you're diving a V profile (off a gently-sloping beach, for instance) and not a square one, but frankly on a shallow V profile it won't matter much anyway.

You should learn the rules for whatever tables you are using. If you are using a computer, the computer takes care of it all, and it's irrelevant, unless the computer dies.

PADI still teaches tables, but less and less importance is given to them. Some agencies, such as SDI, no longer teach tables, other than as a historical footnote. A tragic loss, in my mind.

BouzoukiJoe A.K.A. wrecker130 AKA Chuck Norris AKA joeforbroke (banned)
11-09-2007, 11:31
When I took PADI AOW (this year) we had to log the dive using tables even if we were using a computer. The instructor would not sign the log sheet unless your calculations were correct. A lot of people had forgotten how to use them and had to rework their calculations.

I have no idea if this is a PADI thing or just a good instructor.

quasimoto
11-09-2007, 15:55
Now for the really good part. How much does it really matter if you are off by a minute or two? Practically speaking, it doesn't make that much of a difference.

Great point!! You aren't go to put yourself into jeopardy by counting bottom time either way. Also if you are diving a computer a lot of them vary as well. I have worn my Cochran and Atmos 2 and came up with a minutes difference.

Something else that was noticed last weekend at the quarry was that three different computers calculated three different bottom times.

By definition BT is from decent till ascent. Scuba 101.

mitsuguy
11-10-2007, 01:49
When I took PADI AOW (this year) we had to log the dive using tables even if we were using a computer. The instructor would not sign the log sheet unless your calculations were correct. A lot of people had forgotten how to use them and had to rework their calculations.

I have no idea if this is a PADI thing or just a good instructor.

my instructor does the same thing... as some have mentioned, it's extremely important...

however, diving with a computer kinda dumbs it down for everyone... then my calculations don't work (they would if I had exact times at each level, but I don't record those because I use the computer)... the computer definitely extends down time, but it is hard to cross one to the other...

also, I was taught beginning of descent to beginning of ascent, but honestly, it is a little confusing the way you log it in the book...

Splitlip
11-10-2007, 05:26
My kid just completed her OW with PADI. They had computers but skill with the tables was still mandatory.

Splitlip
11-10-2007, 06:09
Gee texdiveguy, for such a simple question, there sure is some conflict of answers.

And by the way, do you have anything to contribute to the tread or are you just going to keep flaming the guy for posting question that you consider elementary?

I start on descent and stop at the surface.

Texdiveguy can reply for himself, but I too at first thought this was a Troll. It is an elementary question.
OP might benefit, as TDG suggeseted, from a refresher course.
Not flaming. I took one when I got "stale".

moosicman
11-10-2007, 08:16
i had to think hard before leaving this post--i say that to say this is not meant to flame anyone, OP, Texdiveguy or otherwise, so please read with that in mind...

it is an elementary question, & i am glad Splitlip wrote his humble post above, as it is worded in a nice & kind manner & is good advice for all who aren't as frequent a diver as they may like (although i must admit, i don't know what a TROLL is, don't spank me for not knowing:) )LOL......i just read this thread today (11-10-7) & i noticed that the OP hasn't posted back in this thread since he was kinda scolded for not knowing, which to me could indicate that he took what was said rudely.....let me put in my dime's worth & say i'm glad OP asked it, wether he was suppose to know it or not. if one were suppose to know it and didn't, then maybe now they do know it & it has saved them from trouble down the road. i hope that we can have a place where we can ask anything we feel would help us become better divers, even if it is something that is common knowledge. perhaps someone didn't have the world's best instructor or is still hazy about some facts (yeah it can happen). its a good thing to suggest a refresher course to someone. we can do this in a way that won't belittle the person. the goal is for nobody to die or get DCS right?? what if the person asked a ? that they were EXPECTED to know? if the goal is to help them stay safe & alive, & our answer could help or assist in that, then what a mighty act we have done!!

who knows....maybe this forum could be all our "refresher course" everyday!! now THAT is safe AND cool!!

So here is to you OP. Ask your questions without fear! If you need to know something but it seems rudimentary so you are afraid to ask, have no fear. i have plenty myself and i will ask them so that i don't get myself killed.

No persons were flamed in the making of this post! ;)

paintsnow
11-10-2007, 11:50
just because PADI should teach it to you doesn't mean they did.

my instructor pushed me over the edge of the boat after 0 pool time.
later into the dive he proceeded to leave me with a DM in training to ascend and get a discover scuba guy.

at the time i had no clue that was breaking more violations that i have fingers.

what i did after was go on scubaboard (pre scubatoys forum) and ask questions and read, read and read some more.

i agree with the poster above me, this can be used as somewhat of a refresher course.
if you forget a few things why pay for an instructor that might not even help you?

im not trying to flame anyone with this post, i was just stating a different perspective.

id like to see this forum stay friendly and kind, even towards the new divers with elementary questions. its the reason i dont even have scubaboard in my browser history anymore.

and remember, the only stupid questions are the ones that are never asked.

wgt
11-10-2007, 13:50
Excellent analysis as usual, C-Dude.


You should learn the rules for whatever tables you are using. If you are using a computer, the computer takes care of it all, and it's irrelevant, unless the computer dies.

Perhaps to change the spin of the discussion, though, the "death" of a computer at depth calls for normal ascent protocols, beginning the moment that the death is noted. Assuming that one frequently checks the device, this should preclude flirting with the No Decompression Limits. However, when I have used the term "computer failure" (or similar terms) on this board in the past, others have perhaps assumed that I was referring to sudden computer death.

I have seen two computers that were failing underwater (perhaps malfunctioning is a better term). In both cases, the divers were unaware of the failures, as the displays looked normal. In one of these cases, the computer was confirmed to be reading a full three meters shallow and computing No Decompression Limits according to the shallow reading. The busting of the No Decompression Limit was prevented by the buddy system.

In the second case, the computer was inaccurately calculating time. Although the computer was only underestimating time by about 2 minutes per hour, the conditions under which the failure was detected were eye-opening. The computer was being tested after the diver had been stricken with DCS.

Was the failing computer instrumental in the expression of DCS? I suspect not, as the victim had been diving with a reliable buddy and under supervision. However, this case does emphasize the risks of shutting down your brain to let a non-redundant device plan your life. Information given by computers, should always be interpreted with caution and good sense. The good sense may depend for its expression on a solid open water course that emphasizes, at a minimum, the understanding of valid planning models, perhaps as represented in tabular form.

superkingkong
11-10-2007, 14:52
i had to think hard before leaving this post--i say that to say this is not meant to flame anyone, OP, Texdiveguy or otherwise, so please read with that in mind...

it is an elementary question, & i am glad Splitlip wrote his humble post above, as it is worded in a nice & kind manner & is good advice for all who aren't as frequent a diver as they may like (although i must admit, i don't know what a TROLL is, don't spank me for not knowing:) )LOL......i just read this thread today (11-10-7) & i noticed that the OP hasn't posted back in this thread since he was kinda scolded for not knowing, which to me could indicate that he took what was said rudely.....let me put in my dime's worth & say i'm glad OP asked it, wether he was suppose to know it or not. if one were suppose to know it and didn't, then maybe now they do know it & it has saved them from trouble down the road. i hope that we can have a place where we can ask anything we feel would help us become better divers, even if it is something that is common knowledge. perhaps someone didn't have the world's best instructor or is still hazy about some facts (yeah it can happen). its a good thing to suggest a refresher course to someone. we can do this in a way that won't belittle the person. the goal is for nobody to die or get DCS right?? what if the person asked a ? that they were EXPECTED to know? if the goal is to help them stay safe & alive, & our answer could help or assist in that, then what a mighty act we have done!!

who knows....maybe this forum could be all our "refresher course" everyday!! now THAT is safe AND cool!!

So here is to you OP. Ask your questions without fear! If you need to know something but it seems rudimentary so you are afraid to ask, have no fear. i have plenty myself and i will ask them so that i don't get myself killed.

No persons were flamed in the making of this post! ;)

thanks moosicman and all.
to tell you the truth, yesterday i was "scared" to come in and even read the replies.
well, guess it ain't that bad.

and thanks for all the replies. now, i will remember... calculate from start of decend until start of ascent :)

thanks. indeed... it's a "refresher thread" :)

superkingkong
11-10-2007, 14:54
Excellent analysis as usual, C-Dude.


You should learn the rules for whatever tables you are using. If you are using a computer, the computer takes care of it all, and it's irrelevant, unless the computer dies.

Perhaps to change the spin of the discussion, though, the "death" of a computer at depth calls for normal ascent protocols, beginning the moment that the death is noted. Assuming that one frequently checks the device, this should preclude flirting with the No Decompression Limits. However, when I have used the term "computer failure" (or similar terms) on this board in the past, others have perhaps assumed that I was referring to sudden computer death.

I have seen two computers that were failing underwater (perhaps malfunctioning is a better term). In both cases, the divers were unaware of the failures, as the displays looked normal. In one of these cases, the computer was confirmed to be reading a full three meters shallow and computing No Decompression Limits according to the shallow reading. The busting of the No Decompression Limit was prevented by the buddy system.

In the second case, the computer was inaccurately calculating time. Although the computer was only underestimating time by about 2 minutes per hour, the conditions under which the failure was detected were eye-opening. The computer was being tested after the diver had been stricken with DCS.

Was the failing computer instrumental in the expression of DCS? I suspect not, as the victim had been diving with a reliable buddy and under supervision. However, this case does emphasize the risks of shutting down your brain to let a non-redundant device plan your life. Information given by computers, should always be interpreted with caution and good sense. The good sense may depend for its expression on a solid open water course that emphasizes, at a minimum, the understanding of valid planning models, perhaps as represented in tabular form.

Don't trust your computer 100% :) your brain is still no.1 :smiley2:

Zenagirl
11-11-2007, 07:50
I have seen two computers that were failing underwater (perhaps malfunctioning is a better term). In both cases, the divers were unaware of the failures, as the displays looked normal. In one of these cases, the computer was confirmed to be reading a full three meters shallow and computing No Decompression Limits according to the shallow reading. The busting of the No Decompression Limit was prevented by the buddy system.

In the second case, the computer was inaccurately calculating time. Although the computer was only underestimating time by about 2 minutes per hour, the conditions under which the failure was detected were eye-opening. The computer was being tested after the diver had been stricken with DCS.


This is exactly why my buddy and I compare computers a couple of times during each dive. We compare time and depth, so if something is off we can deal with it immediately. But I agree that you shouldn't be checking your brain at the door when you get a computer.

frankc420
11-11-2007, 08:08
The response from texdiveguy is exactly why I do not hang out as often on Scubaboard, it was an unnecessary flaming. The whole purpose of this board is to be different than the 'other guy' and be helpful even when/if it may be a stupid question to one person but not another.

The guy could have 300 dives, if he has a question that is scuba related it should be considered valid.

robanna
11-11-2007, 09:01
That was my first thought about texasdiveguy; very SBish responses.
Only flame, no usable content.

RoadRacer1978
11-11-2007, 12:19
Lets all give TexDiveGuy a small break. Maybe he was having a bad day. Usually his posts are very helpful and informative. Any new members, please do not take his response here as the norm for TexDiveGuy or this board. Another thing for all the new members, the only stupid question is the one you do not ask. Please ask away.

robanna
11-16-2007, 12:19
ABT actual bottom time/bottom time. The number of minutes that a diver spends underwater on a particular dive, calculated from beginning of descent to beginning of direct ascent to the surface or a safety stop. Used in calculating the repetitive group designation on a dive table.

moosicman
11-16-2007, 12:31
i do agree with roadracer...part of keeping this board friendly is just keeping things in check, but not kicking someone when they may have crossed the line. lets all play nice and fair!:)

ReefHound
11-16-2007, 13:10
ABT actual bottom time/bottom time. The number of minutes that a diver spends underwater on a particular dive, calculated from beginning of descent to beginning of direct ascent to the surface or a safety stop. Used in calculating the repetitive group designation on a dive table.

That's why one of the critical attributes of a PADI 5-point ascent is to check your time.

mm2002
11-18-2007, 16:51
I know I've posted some very elementary questions on this board, just because I like to learn from other peoples experiences. Texdiveguy has always been more than helpful. I don't know the dude outside of his posts on this forum, but we all have bad days.
Now, what our PADI instructor taught us is to start the time on ascent, and end when the ascent is started (just like in the manual), but he also stated that if we wanted to include the ascent time, it would give us an extra margin of safety when using the tables. Being the kind of person that errs on the conservative side, I always include my ascent time. That may be technically wrong, but I sure don't see any harm in it.

navyhmc
11-18-2007, 19:56
SKK: For starters as noted, bottom time starts at descent (when you begin to have nitrogen loading) to the start of Ascent (when you start off gassing). Now, I calculate my bottom time and my total dive time differently. ABT is what I use for dive planning and subsequent dives that day and I log my entire dive time (that is when I logged dives, I haven't for a while.)

If you are not familiar with working the tables (RDP) make it a point to practice with it. To me square profiles are the best to start with. Just think of 3-4 dives you've done and putthem together or make some up. Remember though it's better to start with your deepest dives first and gradually go to your more shallow dives. Why? Well, try then the other way and comare bottom times/no deco limits and RNT's

Here are a few to work with:

110' for 8 minutes. 1:45 surface interval

90' for 15 min 3:00 surface interval (lunch and the boat's moving)

50' for 40 minutes.

Answer the questions just like in class. What goup when you surface? what when you hit the water? What's your RNT? Max no deco? Make up dive profiles and work 'em out. **disclaimer** I didn't have my RPD with me when I wrote this so my second and third dive may be in Deco time frames, If they are, adjust accordingly.

I still don't have a computer so the table are my life-literally!

Computers are nice, but the brain is better. Plan you dive(s) and dive your plan(s).

BouzoukiJoe A.K.A. wrecker130 AKA Chuck Norris AKA joeforbroke (banned)
11-19-2007, 12:53
I use the tables for planning and logging.

I also always have a watch and RDP (and EAD table if diving Nitrox) with me in case my computer fails. I learned on the tables and see no need to stop using them just because I have a computer.

SiscoKid
12-04-2007, 08:03
Hi guys,

For example, say you want to go 100ft for 20mins.

do u start counting your 20mins the moment u start to descend from the surface? or the moment u touch down at 100ft?

Also, when do u stop counting?

the moment u leave the 100ft spot?
or when u reach 5m for safety stop?
or safety stop time also included in your 20mins?

thanks
If you or in the Dallas aria I would get hold of a good instructor, Woody Scuba Toys, refresh on dive tables, set up a deco course with him. All your questions will be answered.