YD Scuba Diving Forums banner

1 - 10 of 10 Posts

·
Registered
Joined
·
366 Posts
Discussion Starter · #1 ·
Imported post

Two dives both to just below 20m on air, dive 1 34mins ( including 3mins @ 5m ) dive 2 38mins ( including 3mins @ 5m )

Rounding up on the RDP to 22m, it looks like I exceeded my NDL for the second dive if I work out the pressure group using the PADI RDP.  

Looking at the output from my Vyper dive computer, I don't see anything screaming about exceeding NDL.

Outcome is to ensure dive 2 is "shallow", but as a learning experience I'm guessing the RDP errs on the side of caution, but I was probably sailing close to the wind on dive 2 ?

Comments please  ?

Andy ( ancl )
 

·
Registered
Joined
·
1,922 Posts
Imported post

My guess would be the fact that the RDP only works exactly for a true "square profile" dive whereas the Vyper tracks and continuously recalculates nitrogen loading. If you have Suunto Dive Manager have a look at the simulated screen on the graph page to see what the Vyper calculated your NDL as for the second dive.

Dom
 

·
Registered
Joined
·
366 Posts
Discussion Starter · #3 ·
Imported post

Just looking at the graph for the second dive, following the profile, doesn't appear that I exceeded NDL, also the bar graph on the left hand side during the dive and the dive manager profile ( need to grab the manual and review ) didn't go past the yellow or red marks.

So no need to be concerned this time around ?

Cheers

Andy ( ancl )
 

·
Registered
Joined
·
280 Posts
Imported post

<font color='#0000FF'>hi mate
if your computer is not screaming or shut down and still works you seem to be ok
tip
either dive a computer or tables but never try to use both you will get well confused and end up worrying all the time
computer says your ok so you will be ok99.999% of the time


ps what was your surface interval
 

·
Moderator
Joined
·
3,293 Posts
Imported post

[b said:
Quote[/b] (ancl @ Feb. 22 2004,20:32)]Comments please  ?
<font color='#000080'>Hi

Stop diving on air.

Andy

PS You'd have to look at the computer profile but as others have said, it probably wasn't square and didn't have all that time at 20 mtrs.
 

·
Exiled in Scotland...
Joined
·
6,286 Posts
Imported post

<font color='#000080'>As was said to me when I bought a computer by one of the more senior divers in my club,

'divers just seem to use tables, then swtich over to a computer when they buy one and ignore the tables other then to work out their Current Tissue Code, there after.'

As has been said, you will have not dived a square profile, which is what tables are based on for the most conservative prediction of your Current Tissue Code. You should have been aiming for a nice ramp up from the deepest point during your dive. Try comparing your dives recorded on your computer with what your (square profile) tables yeild. Once you have a few dives under your belt you'll begin to have a better idea as to what differences there are between your computer and your tables. Of course your dive profiles for the compared dives, will have to be very similar for this to work.

Dave C
 

·
Jonah
Joined
·
7,366 Posts
Imported post

[b said:
Quote[/b] (ancl @ Feb. 22 2004,20:32)]Two dives both to just below 20m on air, dive 1 34mins ( including 3mins @ 5m ) dive 2 38mins ( including 3mins @ 5m )
Hi Andy -

Remember that with the PADI RDP, bottom time is defined as "The time from the beginning of descent until the beginning of a direct continuous ascent to the surface or safety stop".

Let's assume you ascended directly from the bottom (max depth) to your safety stop- that would have taken at least a minute, probably quite a bit longer. So knocking off the ascent and stop times, you have a bottom time of 30 mins for Dive 1 and 34 for Dive 2. No problems.

HOWEVER - does the dive time you give for Dive 2 reflect the actual time you spent underwater, or does it also include your Residual Nitrogen Time from Dive 1? If  the latter, then unless you had a pretty long surface interval, then you might have gone over the table limits.
 

·
Registered
Joined
·
609 Posts
Imported post

<font color='#0000FF'>Had you done a square profile dive your computer probably would have told you it was a no-no. Your computer is most likely set to be more conservative than your PADI table, meaning that doing a square profile on a computer will give you shorter actual bottom time at say 22 meters. The thing is that your computer will punish you if you stay down and reward you as you slowly ascend by giving you time back. What you're actually doing is a multilevel dive and had you done your calculations and planned a multilevel session accordingly you probably would have been inside the limits of your PADI tables.

There are two ways to dive on computers:
- Follow tables and use the computer as a monitor for safety measure.

- Follow computer and use charts as backup, meaning that should your computer go bust you must have the table in your head and calculate your NDL according to deepest level you've been on. That could mean that you'll have to go into deco in case your computer passes out late in the dive.

I do the latter. I'm sure many would object to that, but at least I know my tables (not every detail obviously) and have a plan what to do should my computer die on me. For that I have a bottomtimer as a backup.
I'm quite sure that's more than most computerdivers actually have.  


Kyrre
 

·
Registered
Joined
·
366 Posts
Discussion Starter · #9 ·
Imported post

[b said:
Quote[/b] ]
HOWEVER - does the dive time you give for Dive 2 reflect the actual time you spent underwater, or does it also include your Residual Nitrogen Time from Dive 1? If  the latter, then unless you had a pretty long surface interval, then you might have gone over the table limits.
Time is actual time underwater, doesnt include RNT.

Thanks for the replies, I think a refresher review of the PADI OW manual is in order tonight.

Andy ( ancl )
 

·
Jonah
Joined
·
7,366 Posts
Imported post

sorry, I meant 'if the former' of course. DOH.
 
1 - 10 of 10 Posts
Top