How to Use the Shearwater Perdix with GF99 & SurGF- Expert Guide to Safer Diving with Shearwater
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- Опубліковано 6 сер 2024
- Mastering Safety with Shearwater Dive Computer GF99 & Sur99 | Expert Guide to Safer Diving
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Welcome to another exciting Friday message by Benjamin Hadfield, a noted technical diving instructor with Teach Me to Dive. In this must-watch video, Benjamin dives deep into the world of diving safety, and how the Shearwater Dive Computer's GF99 and Sur99 features can revolutionize your underwater adventures. Dive into this informative video for a comprehensive understanding of these essential tools for divers.
TIMESTAMPS
0:00 - Introduction
0:42 - The Importance of Dive Safety
0:57 - Exploring the GF99 & Sur99 Features
1:24 - Understanding the GF99 and "On-Gassing"
1:45 - Nitrogen's Impact on Your Tissues
1:59 - Vacuum Sealing Analogy for Dive Pressure
2:38 - Off-Gassing and Bubble Formation
3:05 - Pressure Difference and Bubble Formation
3:32 - Balancing On-Gassing and Off-Gassing
4:02 - Achieving Optimal Nitrogen Release
4:21 - Balancing On-Gassing and Off-Gassing
4:35 - Visualizing GF99 During a Dive
4:46 - Interpreting 0% on GF99
5:00 - Super-Saturation and Risks
5:14 - Understanding Percentage Values
5:25 - Navigating Nitrogen Levels
5:41 - Red Flags and Decompression Sickness
5:54 - GF99 Display During Your Dive
6:08 - Monitoring Percentage for Safe Ascent
6:19 - The Role of Gradient Factors
6:31 - Setting Preferred Gradient Factors
6:41 - Applying Safety Margin to Diving
6:52 - Explaining Gradient Factors 50/80
7:08 - The Significance of Gradient Factors
7:38 - Monitoring GF99 for Safe Ascent
7:59 - Lower GF99 for Safer Diving
8:18 - Importance of Objective Data
8:43 - Using O'Dive Monitor for Accuracy
9:00 - Differentiating GF99 and Gradient Factor
9:18 - SurGF: A Dive Safety Crystal Ball
9:33 - Empowering Dive Decision-Making
9:48 - Real-Time Control and Monitoring
10:05 - Predicting Supersaturation and NDL
11:27 - The Relationship Between GF99 and SurGF
11:42 - The Impact of Nitrogen Removal Speed
11:59 - Optimizing Ascents and Reducing Risk
12:12 - The Balance of Off-Gassing Speed
12:33 - Understanding Bubble Removal
12:58 - The Impact of Physical Condition
13:19 - Real-Time Dive Progress
13:40 - Equilibrium and Decompression
14:03 - Allocated Bottom Time and NDL
14:18 - Ascent and Supersaturation
14:31 - Rising in the Water Column
15:04 - Controlling Supersaturation
15:44 - Balancing Bubble Removal
15:52 - Importance of Ascent Rate
16:05 - The Role of Safety Stops
16:24 - The Value of Additional Safety Stops
16:43 - Predicting Your Dive's Future
17:08 - Conclusion: Shearwater Dive Computer for Safer Diving
Don't miss this comprehensive guide to dive safety with Shearwater's GF99 and Sur99 features. Like, share, and subscribe for more exciting content from Benjamin Hadfield and Teach Me to Dive. Stay safe, stay informed, and dive into the magic beneath the surface!
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If I understand correctly, when your SurfGF exceeds your GFHi, you've exceeded your NDL.
I like how you've split the GF99 into ranges. It makes it easier to understand how fast you're off gassing.
I always try to keep the GF99 below my GFLo, with my GF set to 45/75. I'm not a fit person, so I definitely need more conservatism.
When the SurfGF exceeds 100% you have exceeded the Bulmann absolute NDL limit and are on the very edge, with no conservativeness at all. If your GFSurf exceeds your GF High, you have exceeded your interpretation of the NDL that takes into account your desired level of conservativeness. :)
@@TeachMeToDive When your SurfGF exceeds your GF High you get into deco mode. If you do your deco correctly you keep the same level of conservativeness...
@@alaincaspar2148 that is correct, but remember, the GF high is your interpretation of the max m value you are willing to achieve and is a safety margin
@@TeachMeToDive To state it more clearly, your SurfGF is a percentage display of what your supersaturation or critical supersaturation level would be at the surface, at that particular moment in relation to the M-Value line. Since M-Value is 100%, a display of less than 100% is more conservative and above 100%, you’re at substantial risk of DCS or already could be in trouble.
I agree David, i haven't found such an in depth explanation, yes the subject is completed but Benjamin, you made it a little more easier on the brain. Thank you. Keep up the good work dear friend
Awesome!!! I am so glad you liked it. Make sure to post and share as much as you can :)
Very helpful and easy to understand
Not many recreational diver know this but it’s vital
Cheers
Glad it was helpful! Make sure to check out the next video in this series. Diving Safety Secrets: 10 Exclusive Tips Revealed - ua-cam.com/video/7F6piEeousM/v-deo.html and Share them with your friends :)
such a great video
Thank you
Amazing explanation and great video! Could you add anything in regards to how the GF99 is determined in regards to the different tissue compartments though? Is it based on your average tissue saturation rates or the most/least conservative?
Sure thing! In the Bulman model that most every computer uses, there are 16 "compartments" that have different speeds at which they "off-gass" AKA Diffuse gas. The challenge with looking at a 2D chart of this, is that you can only see one of the compartments actions. In reality, it should be 3d, showing all compartments. The model for GF99 and supersaturation is lead by, or controlled by what we term as the "controlling" tissue. This is the tissue, within the model that has reached the point of the most "super-saturation" and has the largest "off-gassing/diffusion" of all of the tissue compartments. Another way to look at this compartment is this. The controlling tissue is producing the largest Nitrogen bubbles out of all of the compartments and is the most dangerous one for creating DCS. The Bulman model sees this, and show a recommendation to slow down or stop in an effort to control the size of those bubbles and keep them under control. We would say that it's goal is to keep all the bubbles at bubble seeds to silent bubbles and not allow them to grow in size and become "symptomatic" bubbles :) I hope this helps :) Make sure to keep watching and share our channel often:)
You suggest keeping GF99 at 50% of preset GF low, however, Andy Davis suggests keeping GF99 between 1/3 and 1/2 of your preset GF high. Are you just erring on the more conservative side or do you have another reason for that suggestion?
Neither way is certainly wrong. The GF99 is a measure of how high your supersaturation is past the total m-value. By keeping that a little lower, you are not allowing bubble growth to become quite as large during the ascent phase and creating less tissue stress. Both concepts will get you where you would like to be, but with a little more care and conservatism, you will feel better after the dive and add just a little more safety. Remember, the GF99 is also sort of a gauge idea of how large the bubbles will be as you ascend :) Smaller bubble good, bigger bubbles bad lol
As a minor aside, you may want to take a look at Doolette's talk about VGE in Portugal at Diving Talks regarding your mention of the use of O'Dive as a helpful tool. TLDR, based on the retrospective study he led (on top of his career worth of work in the field), observation/measurement of VGE provides no useful information to act upon at an indidual diver level. There's just too much noise/variability dive-to-dive even with identical profiles and conditions.
We tend to agree. Using the odive is very much like using a Garmin device. Over the course of time, it does reveal interesting patterns, but using it for just a few dives isn't enough data to make any adjustments, just interesting observations
Could you provide the source of the information given from 5:26 to 5:38 please? Ive not learned of this before and would like to know where it comes from
This comes straight for the Perdix Manual. :) A good practice for GF 99 is to keep it at 1/2 or less of your GF low.
@TeachMeToDive I've just been though the manual for my perdix 1 and that info is not contained within. Has the manual been updated maybe? Could you give me the page number? Thank you
@@petercaron3799 Email me directly and we can chat :)
@TeachMeToDive thanks will do. I'm also wondering why you would aim a GF99 of half the GF low... Will drop you an email :)
@@petercaron3799 Great question. GF99 is a measurement of how fast the nitrogen is leaving your tissues and entering the veins Another way to look at this is it is a measurement of the size of the bubbles. :) The larger the number, the larger the bubbles and the faster they are entering your system from the tissue compartments. Keeping this number lower means smaller and less bubbles. A larger number means more and larger. Using a guiding factor like the measure of half of your GF low allows you to keep a low target for your GF99. Keeping these bubbles as small and manageable as possible should be your goal. So, I like to use the visualization, when teaching, that the GF99 is a numeric value of the bubble size. if your GF99 is half of your GF low (IE 50 meaning you keep your GF low at 25 or less) your bubbles will only be reaching 25% of m-value. It isn''t really the big picture, but it gives a clearer visualization of what is potentially happening, and increases safety as well as reduces symptoms after a dive.
GF99 ... unless you have some ( metabolic data ) or ( physiological data) on the diver -- now correct me if I am wrong in my 30 years of ER medical knowledge... we are just taking a [container] at depth and applying data... Unless we are using the AI and then ( hoping there is NO leaks ) because that will count against our PO2 AND SAC rate (which the "insert descriptive noun" in Vancouver calculate every 18600 microseconds) ... yes I also CODE...
Stating the above am I lying that the numbers being calculated for GF99 and sur99 are just the standard Bulhman ( which has not changed since 1994 when it was presented/refined ) AND the use of VCM for microbubbles... packaged in a [implementation] which every dive company does with a level of safety they ( align ) in compliance to their legal teams expected liability....
In short it is a Litmus based on use for a box -- respective of data collected at depth over time only as viable as the sampling rate used.... [ in a nutshell this is correct ]
Lastly the differences between Perdix2 GF 50/85 and Garmin 50/85 is 1.) sampling and 2.) coding via legal liability
I have not seen a dive log in subsurface before or after from Apeks, but I have in ad-nauseam cross coded export, transformation and import filters for divesoft garmin uwatec shearwater suunto mares and ratio... [ in short without O2 and heartrate plus true PO2 saturation via consumption ] doing a volume calculation is also including putting air into a BCD filling a lift bag and any and ALL gas loss... (truth hurts)
All which the computer knows is ( how long you are down and pressure on you ) WITH AI ( assumption based on volume of gas used + depth and time )
In some ways your are right, it is a general algorithm. But that is where GF's come into play. With the Gradient Factors, you are able to personalize this information to you as well as increase your safety margin. So, as you look at your GF99, you are now looking at the closest recommendation to your desired anticipated M-Value as possible. ALL of this is far more accurate that a dive planner or tables since it is now able to monitor you Nitrogen load on the fly and give you credit for time not spent at your ulitmate depth and penalize you for the time that you exceeded your planned depth (as well as the time). With GF99, you now have a more accurate window into the future of your dive, based on the actual dive, rather than the hope you placed into the dive prior to it. :) While, yes, having a pulse ox meeter and other sensing equipment could have the and affect on this data, the challenge here is that we still know very little about bubble formation, how bubbles are really formed or some of the major key indicators that can and do cause DCS. In studies, we have seen divers do the same dive with wildly different results, even though the dives were the same and the divers had very similar characteristics. We have also see the same diver be able to do the same, exact dive twice and return fine from one, and bent from another. Much of deco is really in theory still and the is far more that we don't know, than we do know. But, again, I will take a dive computer and trust the GF99 to give me a sense of where I am at over tables and dive planning software any day of the week :)
@@TeachMeToDive
this adds to my point... I think we are sayign the same thing.. The point I am making is shearwater is not the god of Gf99 Sur99 ... that on off gas credit bubble system has been toyed with and twisted over the past 25 years... I remember the first introduction to the GUE (children) in 2001 the only thing they were missing was jack boots and armbands... Wkpp should ring a bell to some.. [the reason] one can do a dive 1 time and be good and another and be bent has nothing to do with GF or Sur...
it comes to WOB + heartrate that atttribute to tissue ( on gassing ) [not to be confused with GF or SUR] I will explain and give examples...
Variables + computer + environment
1.) surge 7M waves 2~3 Atm dive so 66~99
2.) Calc volume air used ( be it lift/bcd or consumption ) -- no heartrate data no 02sat no ability to calc ( TRUE PO2 ) guesstimation based on rapid or slow on/of gas [hardcoded fudge table]
3.) this data comprises the dive
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Examples as promised SAME dive
Okinawa June vs Okinawa November
June 1M waves light current low tide 20~30M dive 45 minutes
November ( SAME DIVE location ) 7M waves pending Craft Advisory Heavy churn current 5M shift at 25M 30 minute dive cut short , but difference was 2700 PSI consumed at depth in 15 minutes vs 45 ------
One would be correct to assume the GF on gassing is different w AI and without AI on Perdix [because it WAS WAAY different]
I dive 3 computers those dives were on Perdix 1 w AI 1 w/o AI -- yes shearwater does clown data with AI affecting Deco
1. valid use and invalid use {if all gas is pulled from the tank then the SAC calc is true data and valid for use in Calc}
2. assumption is the mother of all incidents que shearwater [if calc data is based on tank volume and there is a incident the calc based on data flaws deco adding un-nessary deco during emergency]
Math or no math Fact is take any of the laws we learned about partial pressure and pressure at depth -- application is clear change in SAC affected on/off gas of nitrogen.. Next outside calc Heart rate ( and why Garmin ) in tests was "lagging" is the O2sat was turned off AND it was not getting pulse readings during the dive.
Recommendation quit holding Perdix as the GOLD standard just like the tech field held EMC because they ( coined a phrase ) and crippling all competition because THEY need to be kneecapped to meet the bar the perdix Cannot exceed...
I hope this makes some sense when it comes to GF and SUR it is a slide rule so 55/85 your calc is low 55% and set high at 85%...
If you want to see magic do a diveplan ( less environment ) with Dos dive planner [yes been doing tech that long was kicing around with Iantd in the late 80s ] -- then run a multideco plan ... then prep the dive... using the computers ( review the dive log after UDDF or XML)
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since 1996 I dove with reefnet units (time temp depth every 3 seconds ) vs computers and runtime dive plans calc the dive on the slate w grease
The only thing preventing a diver from injury is being not being relaxed "steady state", increased heart rate, increased breathing which increases PO2 ... I can hit 1.6 at 10ft with 21%... just up the heart to 140~160 go from 4 breaths per minute to 15 you will push CNS to peak..
you ask how or make the statement same dive one good one bad one DCS one not. It is not magic it is knowing all the data points... no vendor for dive computers will Qc a clean deco because they do not have all the data ( until they have o2 tissue sat before during and after a dive )
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Apologies for the bibles
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Shearwater has a good logging might as well be reefnet.ca with a display and interactive.. Garmin add O2 and Pulse
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Divesoft/ratio/garmin/oh and shearwater all do GF/Sur [shearwater] just happened to be in the community for 20 years. using the 30 year old algorithms and adding the vcm high low bit known as GF Sur .... all may I add based on ass-um-tions and math taking in little to no physiological data.
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in closing this novel and I apologize for that
all mfg are guilty even the tried and true ( plan your dive and dive your plan ) has misgivings due to stress/wob/heartrate/hydration/bodyfat/constrictive or non constrictive clothing/cold or hot water/depth * I would be lying if I said any one computer can properly calc this information.. that is why I always call my dive computer my ( FLIGHT RECORDER ) and always want the data to be pulled to the RAW data in UDDF or XML
WTF is "Sur99" in the title? Correct that.
Good Catch. Thank you