Overshooting NDL and mandatory deco stops
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In fairness, many recreational diver's computer training consists of little more than instructions not to exceed the NDL and how to use planning mode. There isn't an in-depth discussion of what the computer is doing and why it's important to understand how the computer is working. Many of the concepts that we're discussing here are introduced for the first time in early technical training.
If he is going to buy a $1000 dive computer, I'd think he would at least R the FM. And find out -- even in recreational mode -- it has the choices of low, medium, or high conservatism.
He has the nerve to ask the default setting of his own computer!Oh c’mon! The vast majority of recreational divers don’t know there are different algorithms for deco much less what GF or setting they are using. I realize this is Advanced but i don’t think Dale’s statement really calls for that many explanation points -
Edits: typos
I do not have a Perdix but I am pretty sure the manual will explain everything that the owner ought to know. In this case what happen when exceeding ndl.
JBFG
Contributor
Heck if you don’t want to read the computer there are YouTube videos on how to use the Perdix. No excuses to not know.
divinh
Contributor
I did read the manual but apparently I didn't understand all the concepts:
-----
DEEP STOP
In order to avoid the risks related to the micro bubbles formed during the ascent, Giotto is able to suggest a DEEP STOP of one or two minutes (in case of decompression dives) at variable depth depending on the dive profile. During the dive, if the profile requires it, DEEP STOP is displayed and an acoustic signal is issued. The stop icon with the depth and the time minutes is displayed. In case the dive omits the Deep Stop, the warnings will be deleted and the computer recalculates the ascent planning without that stop.
REMARK: Verify that the deep stop is enabled (see paragraph DIVE SET)
REMARK: In this case, the maximum depth can be displayed by pressing the right (>) button.
-----
By default, the Cressi Giotto has DEEP STOP on. On the particular dive I mentioned, the DEEP STOP did flash on, but we, the dive group, proceeded to the safety stop depth to clear our deco obligation. From the text, it sounds like the DEEP STOP could be skipped and the computer will recalculate the deco obligation.
-----
DIVING OUTSIDE THE NO DECOMPRESSION LIMITS
DANGER: do not use this device to dive beyond the no decompression limits! Cressi discourages the use of this device for decompression dives. However, if during the dive, due to negligence or emergency, you have exceeded the no decompression limits, Giotto will provide specific information related to a correct ascent and to the decompression information.
Upon violating the limits, the computer will issue an audible alarm and the screen on the display will change to look as indicated in the following picture providing the diver with the following information:
1) Stop icon with the word DECO showing that the no decompression limits have been violated and that decompression must be performed. The arrow indicating UP will flash.
2) Depth of first decompression stage (the deepest), indicated in metres (m) or feet (ft). This can vary from a maximum of 24 m to a minimum of 3 m by steps of 3 m in 3 minutes.
3) Duration in minutes for the first decompression stage (the deepest).
4) TOTAL icon, indicating the total ascent time, that is the time required to ascend to the deepest stage, respecting the ascent rate, PLUS the stop time at that depth and any other subsequent stop (indicating the deep stop if necessary), PLUS the safety stop time, PLUS the time required to reach the surface after completing the decompression stages.
5) “DIVE.T” icon giving the total time spent while diving.
REMARK: In this case, the maximum depth can be displayed by pressing the right button.
REMARK: In case the deepest stage is a Deep Stop, by pressing the right key you will see, always on the right top corner , the depth and duration of the first stage, not Deep Stop.
DANGER: NEVER ascend above a decompression depth. To avoid this situation, you should ascend at a depth slightly below the recommended decompression stop depth.
Please remember that under these conditions, the amount of air you need to complete your dive increases.
-----
The above paragraph follows the paragraph about DEEP STOP's. To me, when the DECO icon flashes, I'm in mandatory deco and I'm expected to go to the depth indicated (2) and wait until the computer clears (3). Step (4) seems to indicate that there may be more than one deep stop, then the safety stop, to clear subsequently.
After looking up Deep Stop, I /think/ I understand where I misunderstood. Deep Stops were developed by Richard Pyle to be decompression stops done in /addition/ to computer calculated ones:
Alert Diver | Deep Stops
If I go into DECO, the decompression stops indicated by the computer are in addition to these DEEP STOP's, or rather, the DEEP STOP's get added to the decompression obligation. If I set the computer to have DEEP STOP's, then I will be doing the mandatory decompression stops and DEEP STOP's.
Did I get that right? Please correct me, as that's why I'm here.
For most of my diving, I have plenty of No-Deco time.
-----
DEEP STOP
In order to avoid the risks related to the micro bubbles formed during the ascent, Giotto is able to suggest a DEEP STOP of one or two minutes (in case of decompression dives) at variable depth depending on the dive profile. During the dive, if the profile requires it, DEEP STOP is displayed and an acoustic signal is issued. The stop icon with the depth and the time minutes is displayed. In case the dive omits the Deep Stop, the warnings will be deleted and the computer recalculates the ascent planning without that stop.
REMARK: Verify that the deep stop is enabled (see paragraph DIVE SET)
REMARK: In this case, the maximum depth can be displayed by pressing the right (>) button.
-----
By default, the Cressi Giotto has DEEP STOP on. On the particular dive I mentioned, the DEEP STOP did flash on, but we, the dive group, proceeded to the safety stop depth to clear our deco obligation. From the text, it sounds like the DEEP STOP could be skipped and the computer will recalculate the deco obligation.
-----
DIVING OUTSIDE THE NO DECOMPRESSION LIMITS
DANGER: do not use this device to dive beyond the no decompression limits! Cressi discourages the use of this device for decompression dives. However, if during the dive, due to negligence or emergency, you have exceeded the no decompression limits, Giotto will provide specific information related to a correct ascent and to the decompression information.
Upon violating the limits, the computer will issue an audible alarm and the screen on the display will change to look as indicated in the following picture providing the diver with the following information:
1) Stop icon with the word DECO showing that the no decompression limits have been violated and that decompression must be performed. The arrow indicating UP will flash.
2) Depth of first decompression stage (the deepest), indicated in metres (m) or feet (ft). This can vary from a maximum of 24 m to a minimum of 3 m by steps of 3 m in 3 minutes.
3) Duration in minutes for the first decompression stage (the deepest).
4) TOTAL icon, indicating the total ascent time, that is the time required to ascend to the deepest stage, respecting the ascent rate, PLUS the stop time at that depth and any other subsequent stop (indicating the deep stop if necessary), PLUS the safety stop time, PLUS the time required to reach the surface after completing the decompression stages.
5) “DIVE.T” icon giving the total time spent while diving.
REMARK: In this case, the maximum depth can be displayed by pressing the right button.
REMARK: In case the deepest stage is a Deep Stop, by pressing the right key you will see, always on the right top corner , the depth and duration of the first stage, not Deep Stop.
DANGER: NEVER ascend above a decompression depth. To avoid this situation, you should ascend at a depth slightly below the recommended decompression stop depth.
Please remember that under these conditions, the amount of air you need to complete your dive increases.
-----
The above paragraph follows the paragraph about DEEP STOP's. To me, when the DECO icon flashes, I'm in mandatory deco and I'm expected to go to the depth indicated (2) and wait until the computer clears (3). Step (4) seems to indicate that there may be more than one deep stop, then the safety stop, to clear subsequently.
After looking up Deep Stop, I /think/ I understand where I misunderstood. Deep Stops were developed by Richard Pyle to be decompression stops done in /addition/ to computer calculated ones:
Alert Diver | Deep Stops
If I go into DECO, the decompression stops indicated by the computer are in addition to these DEEP STOP's, or rather, the DEEP STOP's get added to the decompression obligation. If I set the computer to have DEEP STOP's, then I will be doing the mandatory decompression stops and DEEP STOP's.
Did I get that right? Please correct me, as that's why I'm here.
For most of my diving, I have plenty of No-Deco time.
Generally speaking, the depth of stops will be calculated based on the algorithm in use. It seems that your computer is running a deeper algorithm, but will switch to a shallower algorithm if it senses that you are skipping the deep stop (most likely due to gas concerns).
IF you do the deep stop, that time will reduce the time spent shallower by a little, at the expense of gas consumed. If you skip it, then you will spend longer at the shallow stop.
What makes reading the manual really useful is this: In many cases, a stop indicated is NOT optional, and if it is a ceiling then ascending past it will cause issues. Now you know that in the case of your computer, if it says "deep stop" then you can omit that and continue till the depth indicated under "Stop" without any issues. A fine distinction to try make underwater while stressed etc, much easier with a manual on a couch with a cup of coffee.
If you have a 'recreational dive computer', then it is totally legitimate not to know what table the computer is using.
If you have a computer that is designed for technical diving, i.e. that uses GF to adjust the decompression algorithm. You should know, what the GF settings are - and how aggressive your profile is.
These computers are really designed for those with technical diving training where GF are taught and discussed, at length.
A conventional recreational dive computer is generally very conservative (bend risk low). A technical diving computer can be set (or shipped) for very aggressive profiles which result in a high bend risk.
The VR3 (which has now been overtaken by time), out of the box, the default GF settings where very aggressive - arguably too aggressive to use safely (in the same way that pro planner was too aggressive with its default settings.
IF YOU HAVE GF check the settings, and ensure they are appropriately set.
If you have a computer that is designed for technical diving, i.e. that uses GF to adjust the decompression algorithm. You should know, what the GF settings are - and how aggressive your profile is.
These computers are really designed for those with technical diving training where GF are taught and discussed, at length.
A conventional recreational dive computer is generally very conservative (bend risk low). A technical diving computer can be set (or shipped) for very aggressive profiles which result in a high bend risk.
The VR3 (which has now been overtaken by time), out of the box, the default GF settings where very aggressive - arguably too aggressive to use safely (in the same way that pro planner was too aggressive with its default settings.
IF YOU HAVE GF check the settings, and ensure they are appropriately set.
Efka76
Contributor
Deep stop is so called Pyle stop is not mandatory. Some literature says that this stop help significantly to reduce bubbles in a body, other literature says that there are no sufficient evidences. There is a very good book "Deco for divers" by Mark Powell where you can find information about Pyle stop, bubbles and various algorithms.
When I was doing my TDI Decompression procedures training I developed a deco diving plan by using software and Buhlmann algorithm and had this plan on my slate. This plan included many stops for 1-2 min at various depths and decompression by using EAN 50. I also had 2 Cressi Newton computers, which support 2 gases (up to 100% oxygen). The purpose was to use these computers for measuring the depth and dive according to the plan. Also, wanted to see how recreational computers will react to decompression. So, I was diving at 40 m depth strictly according to scheduled plan and computers showed that NDL expired and I am in deco (showed that I need to some specific depth and stay there for 8 min.... do not remember exact depth and deco timing). However, I was still diving according to my plan and start ascending by doing planned 1-2 min stops at planed depths. When I was at 18 m. depth I switched to my deco gas - EAN 50, and also, switched gas on one of my computers (other computer intentionally left as it is and computer thought that I am diving on air). When I reached 5.9 m my first computer was cleared of deco and showed that I need to do safety stop for 3 min. Another computer wsa showing deco violation. Deep stop functions were disabled on my computers, however, I ultimately did deep stop as my ascent included many stops for 1-2 min.
When I ended the dive first computer showed that I was in deco mode and that's it. I was able to use it for another dive and it was normally, however, another computer showed that there is a deco violation and I need to wait 48 h hours until computer will be unlocked. When I was doing a second dive I also used my both computers. First was working as supposed to work, another was still working as bottom timer (showed depth, dive time and etc. but did not show data related NDL). Also, after second dive this computer rest non-diving period to 48 h.
When I was doing my TDI Decompression procedures training I developed a deco diving plan by using software and Buhlmann algorithm and had this plan on my slate. This plan included many stops for 1-2 min at various depths and decompression by using EAN 50. I also had 2 Cressi Newton computers, which support 2 gases (up to 100% oxygen). The purpose was to use these computers for measuring the depth and dive according to the plan. Also, wanted to see how recreational computers will react to decompression. So, I was diving at 40 m depth strictly according to scheduled plan and computers showed that NDL expired and I am in deco (showed that I need to some specific depth and stay there for 8 min.... do not remember exact depth and deco timing). However, I was still diving according to my plan and start ascending by doing planned 1-2 min stops at planed depths. When I was at 18 m. depth I switched to my deco gas - EAN 50, and also, switched gas on one of my computers (other computer intentionally left as it is and computer thought that I am diving on air). When I reached 5.9 m my first computer was cleared of deco and showed that I need to do safety stop for 3 min. Another computer wsa showing deco violation. Deep stop functions were disabled on my computers, however, I ultimately did deep stop as my ascent included many stops for 1-2 min.
When I ended the dive first computer showed that I was in deco mode and that's it. I was able to use it for another dive and it was normally, however, another computer showed that there is a deco violation and I need to wait 48 h hours until computer will be unlocked. When I was doing a second dive I also used my both computers. First was working as supposed to work, another was still working as bottom timer (showed depth, dive time and etc. but did not show data related NDL). Also, after second dive this computer rest non-diving period to 48 h.
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