Precision diving and table use

[LastSquire]

I'm just completing my open water course, and I’m very displeased with how layback, and imprecise the course has been. When I ask for more in-depth information for contingencies or a better understanding, they always respond that I shouldn't put myself in a position where I need to know or do what I'm suggesting. While I don't expect that I'll ever unintentionally put myself in a situation that's over my head. I would like, at least, to be prepared with the knowledge necessary so that I can get my way out of such a situation, whatever it may be. This is my first question. Where do I need to go, or what books do I need to read in order to be better prepared, and know my equipment better and how it can be uses, not as intended to help out extreem situations.

Secondly, more specifically, I'm wondering about dive tables. I've been told that if I want to do a multiple depth dive accurately, without being conservative and using only the deepest depth, that I need a computer. I think this is bull. Maybe it isn't? But I don't see why I can't cycle around the tables using the 10 min SIT time for going from one depth to another. As is, for some reason the 3rd table (RNT and AMDT) seems to be between 2 to 6 minutes high on the RNT, or short on the AMDT--I figure that this probably an adequate safety margin for every change of depth. Is there some way to do what I'm suggesting? I'm only interested as a backup incase my computer fails and again there's a reson for me to stay down longer or go to a deeper depth. Normally I would do what they recommend and abort the dive, but I figure if I'm on top of my depths and times, then I don't see why I can't do manually, what a computer does. Any insight here would be most appreciated. Thanks.

 

[PerroneFord]

I know where this one is headed!

Very good questions, and there are answers to them all. Hopefully one of the experienced divers will come along and answer them all for you. OW these days is really just an intro to diving. Your education is FAR from finished. The training and answers you seek are all out there if you want them.

 

[chrisch]

I'm just completing my open water course

I am humbled by your experience.

Think of the OW as a driving test. Sure you can make a left turn and an emergency stop. But you are not Michael Schumaker.

The course is laidback in order to give as many people as possible an entry into the sport. The idea of a computer is to make up for the fact most people cannot work a dive table or do maths. That's the idea behind the Dell I'm using right now!!

I applaud your desire to learn more. Before attacking your current training and posting hard to understand questions about the tables stop and think. The more advanced courses are there if you work up to them. How about "Technical Diver"? Only a few years away.... And if you want to understand tables you need to understand decompression theory. Albert Buhlmann has a few books you might want to read.

Chill out, go see some stuff. Read. Research. Progress. Realise the OW course is just a begining and a long way from being a qualified diver.....

Chris

 

[mixdiver]

Secondly, more specifically, I'm wondering about dive tables. I've been told that if I want to do a multiple depth dive accurately, without being conservative and using only the deepest depth, that I need a computer. I think this is bull. Maybe it isn't? But I don't see why I can't cycle around the tables using the 10 min SIT time for going from one depth to another. As is, for some reason the 3rd table (RNT and AMDT) seems to be between 2 to 6 minutes high on the RNT, or short on the AMDT--I figure that this probably an adequate safety margin for every change of depth. Is there some way to do what I'm suggesting? I'm only interested as a backup incase my computer fails and again there's a reson for me to stay down longer or go to a deeper depth. Normally I would do what they recommend and abort the dive, but I figure if I'm on top of my depths and times, then I don't see why I can't do manually, what a computer does. Any insight here would be most appreciated. Thanks.

What cert agencie are you going thru. The best way to multi level dive is with a computer. It calculates your exact time and dept and shows exactly how long you can stay at that dept. If you insist on using tables the best way to multilevel dive is with the padi wheel. Using the 10 min Sit will not work that is time you are off gassing you are not able to do this at all. You might get yourself hurt. Take a multi level diving class. The wheel is not hard to use but you must be on top of your timing and your dive planning to do it saftly. Since you are not certified yet. Please don't push yourself to soon diving to max is a quick way to get hurt if you are not trained. Get a few dives under belt using the standard table and then when you are ready move on. just my 2cents worth. Enjoy your class and enjoy diving.

 

[Charlie99]

The "zero SI" method which you seem to be describing will accurately keep track of the one Haldanean compartment that is tracked by the table. This means that you can accurately track the pressure group to aid in planning repetitive dives.

The zero SI method will not properly track the faster compartments that set the NDLs for all dives 50' and deeper. Using this method can result in dives that slightly exceed the underlying decompression model. Usually this doesn't result in DCI, but does result in increased risk beyond a dive that is within the table/model limits.

The PADI wheel addresses this problem by having slightly shortened NDL limits that are used, along with restriction on the allowable combinations of depths.

I suggest that you buy or borrow a PADI Wheel and instruction book.

 

[melfox26]

What cert agencie are you going thru. The best way to multi level dive is with a computer. It calculates your exact time and dept and shows exactly how long you can stay at that dept.

Given that this is the DIR forum, please do not give non-DIR answers.


Mel

 

[LastSquire]

What cert agencie are you going thru. The best way to multi level dive is with a computer. It calculates your exact time and dept and shows exactly how long you can stay at that dept. If you insist on using tables the best way to multilevel dive is with the padi wheel. Using the 10 min Sit will not work that is time you are off gassing you are not able to do this at all. You might get yourself hurt. Take a multi level diving class. The wheel is not hard to use but you must be on top of your timing and your dive planning to do it saftly. Since you are not certified yet. Please don't push yourself to soon diving to max is a quick way to get hurt if you are not trained. Get a few dives under belt using the standard table and then when you are ready move on. just my 2cents worth. Enjoy your class and enjoy diving.

I entierly agree, I don't want to get hurt at all. And I understand that I'm not offgassing at all. But if you look at the tables and you use the 10 min SIT time you never drope a letter, and infact like I said it actually adds time to your dive/RNT. I'm using the NAUI tables but for an example they say you can go to 40ft for 130 min max prior to needing a deco stop. But say you go for 30 min and then you do what I'm suggesting, or actually do surface and have a 10 minute off gass time, it says that you exit as a "D" diver, and that you go back down as a "D" diver, but that you now can only go to 40 ft for 93 minutes. 93+30=123, which is 7 minutes shy of 130min. Thus I think it can be done, so long as you start the clock on entry and stop it on exit.

Actually the tables are kinda weird this way. The course teaches if you have a surface time less than 10 minutes you must treat it as a continuous dive... so that means you can continuously surface and go down as many times as you can staying at depths less than 40 feet for 130 minutes before you need a deco. But if you do 5 minute time intervals, then you can only stay down for a fraction of that time, because each time you surface, if you count your 1 second of surface time as 10 minutes you actually gain a few minutes of RNT each time.

Iduno... maybe there's a reason for this, but it just seems like they are accounting for people who aren't timing their dives from start to finish. Is there something else I'm not aware of?

 

[miketsp]

..snip..
I'm using the NAUI tables ...
..snip..
Thus I think it can be done, so long as you start the clock on entry and stop it on exit.
..snip..

Just my curiosity, I never used NAUI tables but I was told they timed from start of descent to start of 1st/safety stop?

 

[Charlie99]

Is there something else I'm not aware of?

Hopefully you are aware that sawtooth profiles, or repeated surfacing is generally a very bad idea.

Since I just realized this is the DIR forum, I'll step aside and see what sort of advice you get from DIR divers.

 

[Doc Intrepid]

I'm just completing my open water course, and I’m very displeased with how layback, and imprecise the course has been. When I ask for more in-depth information for contingencies or a better understanding, they always respond that I shouldn't put myself in a position where I need to know or do what I'm suggesting. While I don't expect that I'll ever unintentionally put myself in a situation that's over my head. I would like, at least, to be prepared with the knowledge necessary so that I can get my way out of such a situation, whatever it may be. This is my first question. Where do I need to go, or what books do I need to read in order to be better prepared, and know my equipment better and how it can be uses, not as intended to help out extreem situations.

Secondly, more specifically, I'm wondering about dive tables. I've been told that if I want to do a multiple depth dive accurately, without being conservative and using only the deepest depth, that I need a computer.... I don't see why I can't do manually, what a computer does. Any insight here would be most appreciated. Thanks.

Your profile is a bit sparse, but if you just completed your OW course you may have what, 5 or 6 dives? Actually, while you think your instructors might be condescending, there is some wisdom to what they say: until you have a few more dives, you should be avoiding putting yourself in situations where emergency response might be called for! (Not to be a dick or anything )

Most emergency response in diving consists of planning so that you're informed of, aware of, and avoid most of the bad situations, and practicing with fundamental skills and your equipment (e.g. being able to turn your tank valve on and off) so that if bad situations occur you've thought the response requirements all the way through and are able to respond appropriately.

Thats about it - preplanning, pre-thinking and discussion with your buddy, ensuring your gear is working fine, being aware throughout the dive, communicating, and last, while you're doing your three minute safety stop, practice the skills most divers don't - take your mask off and replace it, find a lost regulator, practice an OOA drill with your buddy, etc.

Most of these things simply require experience. Just getting out and diving. Reading articles and books is good, and SB can provide lots of reading lists and insight, but really at this point in your diving career you simply need to get out and dive a lot - the right way. Since this is the DIR forum, here is one book you may want to look at, about halfway down - "Doing It Right: Fundamentals of Better Diving", find it here:

http://www.gue.com/catalog/order

With respect to the tables, you already demonstrate quite a bit of familiarity with them. Don't fall into the trap of thinking that conservativism is a bad thing, or that using the tables to stretch out every dive to the max NDL allowable is a good thing. Part of being a good diver means knowing when to thumb a dive, there will always be another dive. Same with tables - plan your dives to a max depth and time. Plan square profiles for now. Screw conservativism. Do three or four dives a day, esp. if you are not in the same physical condition as a US Navy Diver, and it won't be so conservative, I assure you. Get into the habit of using your tables prudently. If you want longer bottom times, take a Nitrox course - don't try to use your tables to work multi-level dives to stretch every dive to its longest possible duration.

I'm not a computer-hater, computers have their places. If I were on a liveaboard vacation, for example, doing 5 dives per 24 hr period for 5 days in a row a computer might come in handy to track residual nitrogen more accurately.

But IMHO no beginning student should be taught that computers are "the only way to dive", and I do believe that computers "rot the brain" as Uncle Pug says - divers who use them end up believing them and letting the computer dictate the dive instead of taking the time to plan the dive themselves. That is dangerous. You're doing the right thing by going with tables first, and possibly getting a computer sometime in the future. Just don't try to use a table to do what a computer does. Use a table the way a table is meant to be used.

Best,

Doc