Feedback on recent two-tank and dive limits

[Blackcrusader]

Prior to 1988 most recreational divers generally used either the US Navy or British Navy dive tables. Again, it worked well if used conservatively. Lots of old divers can testify to this. All of a sudden, we have these Buhlmann dive computers with GF. According to the experts, It's supposed to make no decompression limit (NDL) recreational diving easier and safer. I am not convinced.

My question, why does a recreational diver who executes NDL 60ft or perhaps the odd 100ft dive, require GFs. Even if they are on multilevel or multiday dives. If you want to make recreational diving safer, keep it simple (KIS principle). KIS will never be outdated.

I did my OW and BSAC Sports diving 86 -88 so used older tables I did not have the BSAC 88 tables.
Later on did Nitrox and Padi Rescue. When I go on dive vacations I willl often do 10 or more straight diving days of 3 or 4 dives a day. I was using a Suunto with RGBM for a time until the pressure sensor failed in 2018. I had several hundred dives logged but when I bought a new laptop after a hard drive failure lost those logs. No big deal really.

Anyway I saw 6 instructors / technical divers on a dive boat wearing Perdix. When I saw how easily they could be seen when diving I asked them about the Perdix. The all stated was a great DC. I told them I would buy one as my Suunto had just died. They all agreed it was a great DC for me even as a recreational diver. I have not been happier as a diver than with my Perdix and yes GF's. I would recommend Shearwater / Garmin to anyone who wants to have a great DC. I see many vacation divers who dive with no DC and just depend on their guide or dive buddy. Do vacation divers even need a DC one could ask? After all I started diving when we used a watch and did tables.

Should we ignore features like GF99 and SurfGF? They are not required either but I love that I have that information on my Perdix. The real issue is that many divers buy a DC and do not really understand its features and settings. The issue is not using a DC with GF's but not taking the time to study up on them and how it benefits a diver.

For multilevel NDL diving over many days is a DC with RGBM (Reduced Gradient Bubble Model) better than a DC using Bühlmann and gradient factors? My Suunto was too limiting for me. Glad it died and I bought the Perdix. BTW most recreational dives I do start with dives to 30m unless there is a seabed that prevents deeper diving.. Around one third of my dives I will do 30m to 40m ( sometimes deeper ) on most dive vacations. If you watch the video posted by Dr Simon Mitchell and the studies done he decided to dive GF over RGMB models.

So a diving technical doctor who does research has valid reasons for using GF's. Yes he is a saturation diver which I am not. But it seems that using GF factors gives one safer diving as you are not doing deep stops as much where you are still on gassing.

 

[old frogman]

I did my OW and BSAC Sports diving 86 -88 so used older tables I did not have the BSAC 88 tables.
Later on did Nitrox and Padi Rescue. When I go on dive vacations I willl often do 10 or more straight diving days of 3 or 4 dives a day. I was using a Suunto with RGBM for a time until the pressure sensor failed in 2018. I had several hundred dives logged but when I bought a new laptop after a hard drive failure lost those logs. No big deal really.

Anyway I saw 6 instructors / technical divers on a dive boat wearing Perdix. When I saw how easily they could be seen when diving I asked them about the Perdix. The all stated was a great DC. I told them I would buy one as my Suunto had just died. They all agreed it was a great DC for me even as a recreational diver. I have not been happier as a diver than with my Perdix and yes GF's. I would recommend Shearwater / Garmin to anyone who wants to have a great DC. I see many vacation divers who dive with no DC and just depend on their guide or dive buddy. Do vacation divers even need a DC one could ask? After all I started diving when we used a watch and did tables.

Should we ignore features like GF99 and SurfGF? They are not required either but I love that I have that information on my Perdix. The real issue is that many divers buy a DC and do not really understand its features and settings. The issue is not using a DC with GF's but not taking the time to study up on them and how it benefits a diver.

For multilevel NDL diving over many days is a DC with RGBM (Reduced Gradient Bubble Model) better than a DC using Bühlmann and gradient factors? My Suunto was too limiting for me. Glad it died and I bought the Perdix. BTW most recreational dives I do start with dives to 30m unless there is a seabed that prevents deeper diving.. Around one third of my dives I will do 30m to 40m ( sometimes deeper ) on most dive vacations. If you watch the video posted by Dr Simon Mitchell and the studies done he decided to dive GF over RGMB models.

So a diving technical doctor who does research has valid reasons for using GF's. Yes he is a saturation diver which I am not. But it seems that using GF factors gives one safer diving as you are not doing deep stops as much where you are still on gassing.


View attachment 913236

Those early tables used by the BSAC were actually based on the British Royal Navy (RN) dive tables.

They were called BSAC RPNL dive tables (Repetitive Pressure Group and Nitrogen Loading).

In the original RN dive tables, the depth increments were in 5 metres units. The BSAC RPNL dive tables depth increments were in 3 metres units. At the time, it was recommended by the BSAC to use the next longer time or depth increment when planning dives to allow for a safety margin when conducting strenuous dive activities/cold water diving.

The British Royal Navy dive tables were slightly more conservative than the US Navy Dive tables for dives up to 100ft (30 m).

In 1988 the BSAC RPNL dive tables were replaced with the BSAC 88 dive tables which facilitated multi-level diving. At about the same time PADI Introduced the Recreational Dive Planner (RDP). Personally, the RDP was a much easier to use than the BSAC 88 dive tables. The RDP could be adapted to multi-level diving to a degree during the dive.

 

[Blackcrusader]

Found this thread on old tables.

Thread 'Vintage Dive Tables?'

Aug 13, 2009

Has anyone collected vintage dive tables?

On another board someone mentioned being in Italy and finding a 70 year old dive table with NDL figures for 70 meters (230 feet) being 5 minutes.

I'd be interested to learn more about what the NDL times were.

• gcbryan
• Replies: 15
• Forum: Vintage Diving & Equipment

 

[Mobulai]

An „idiot proof“ user modifiable conservatism Bühlmann computer IS always GF based

If that’s too complex and confusing for you, don’t use it

Others seem to be ok with it

 

[Belzelbub]

All of a sudden, we have these Buhlmann dive computers with GF. According to the experts, It's supposed to make no decompression limit (NDL) recreational diving easier and safer. I am not convinced.

That's clear. Not certain anything will convince you. If Buhlmann with GFs was so bad for recreational diving, then why don't we see a huge increase in DCS incidents with divers using them?

My question, why does a recreational diver who executes NDL 60ft or perhaps the odd 100ft dive, require GFs. Even if they are on multilevel or multiday dives.

Why are you so afraid of GFs? You seem to keep ignoring the fact that computers running DSAT or RGBM also offer the user with the ability to select different conservatism settings. GFs does the same. For a novice recreational diver, simply selecting one of the available presets will work just fine. It will simply add a buffer against the theoretical limits, thus reducing NDL when compared to a less conservative setting. That's exactly the same thing that happens with computers running other algorithms.

The main thing is that the computer running Buhlmann with GFs can grow with the diver. It can be used for simple single recreational dives, multiple dives a day, and multi-day trips, and so on.

I know you'll not be using one. I don't think anything will ever convince you.

 

[Nick_Radov]

All of a sudden, we have these Buhlmann dive computers with GF. According to the experts, It's supposed to make no decompression limit (NDL) recreational diving easier and safer. I am not convinced.

Yes, if you are technical diver trained and qualified, doing long and/or deep dives I can see the logic of GFs. That is where they belong - technical diving.

My question, why does a recreational diver who executes NDL 60ft or perhaps the odd 100ft dive, require GFs. Even if they are on multilevel or multiday dives.

No one cares whether you're convinced or not, or even what's required: the free market has spoken. The "default" new recreational dive computer runs the Bühlmann ZH-L16C algorithm with configurable gradient factors. This is largely a commercial decision because ZH-L16C is easy to implement and generally not encumbered by IP licensing fees. Garmin, Apple, and Huawei now sell millions of smart watches every year which have that functionality built in or available in a downloaded app so we're increasingly seeing OW students showing up for the first day of class already owning a basic dive computer suitable for open circuit air/nitrox dives within the NDL. Those computers have preset conservatism options but they're implemented using gradient factors.

Perhaps this isn't an ideal situation but empirically it seems to be fine. There hasn't been an epidemic of DCS among recreational divers using those computers. And in practice the few DCS cases that do occur seldom seem to depend on the fine nuances of one algorithm (or conservatism setting) versus another: it's usually some more fundamental problem like a PFO where variations in individual physiology make accurate mathematical modeling an exercise in futility.

If you'd like to make a positive contribution instead of complaining online then here's a suggestion. Come up with a deco model more accurate than ZH-L16C (plus gradient factors) and prove it using a large-scale controlled clinical trial. The bubble focused models such as RGBM and VPM never seemed to work very well in practice but they were probably on to something that the neo-Haldanian models missed, so perhaps you can use those as a starting point for improvement. Then release the new model for free use by any dive computer manufacturer. I'm sure they'd be thrilled to have a better alternative.

 

[grantmac]

Plenty of divers have been bent running "NDL" dives on pure Bühlmann or other tables. If anything I'd bet the instances of DCS per dive hour has decreased since computers with adjustable conservatism.

 

[old frogman]

No one cares whether you're convinced or not, or even what's required: the free market has spoken. The "default" new recreational dive computer runs the Bühlmann ZH-L16C algorithm with configurable gradient factors. This is largely a commercial decision because ZH-L16C is easy to implement and generally not encumbered by IP licensing fees. Garmin, Apple, and Huawei now sell millions of smart watches every year which have that functionality built in or available in a downloaded app so we're increasingly seeing OW students showing up for the first day of class already owning a basic dive computer suitable for open circuit air/nitrox dives within the NDL. Those computers have preset conservatism options but they're implemented using gradient factors.

Perhaps this isn't an ideal situation but empirically it seems to be fine. There hasn't been an epidemic of DCS among recreational divers using those computers. And in practice the few DCS cases that do occur seldom seem to depend on the fine nuances of one algorithm (or conservatism setting) versus another: it's usually some more fundamental problem like a PFO where variations in individual physiology make accurate mathematical modeling an exercise in futility.

If you'd like to make a positive contribution instead of complaining online then here's a suggestion. Come up with a deco model more accurate than ZH-L16C (plus gradient factors) and prove it using a large-scale controlled clinical trial. The bubble focused models such as RGBM and VPM never seemed to work very well in practice but they were probably on to something that the neo-Haldanian models missed, so perhaps you can use those as a starting point for improvement. Then release the new model for free use by any dive computer manufacturer. I'm sure they'd be thrilled to have a better alternative.

Who's complaining? Nothing wrong with GFs when used as they were intended to by its designer Erik Baker (that is technical diving). Mate, you need to stop situating the argument to suit your agenda. And, I have not seen you offer any nth degree proof supporting your opinions. Yet you make intimidating demands that people who have a contrary or challenging opinion prove their statement to the nth degree.

At best all approaches to diving are an "educated guess" that some people inject the word "science" into the conversation to make an "educated guess" sound important.

In the past when people were diving navy tables, many decompression problems occurred as a result of repetitive diving. Also, many divers were not using the tables conservatively, for example, strenuous diving or cold water diving. To address this problem PADI introduced the DSAT/Spencer tables which were more conservative and also included a safety stop (optional or as required). This reduced the incidence of DCS.

 

[David Carron]

Who's complaining? Nothing wrong with GFs when used as they were intended to by its designer Erik Baker (that is technical diving). Mate, you need to stop situating the argument to suit your agenda. And, I have not seen you offer any nth degree proof supporting your opinions. Yet you make intimidating demands that people who have a contrary or challenging opinion prove their statement to the nth degree.

At best all approaches to diving are an "educated guess" that some people inject the word "science" into the conversation to make an "educated guess" sound important.

In the past when people were diving navy tables, many decompression problems occurred as a result of repetitive diving. Also, many divers were not using the tables conservatively, for example, strenuous diving or cold water diving. To address this problem PADI introduced the DSAT/Spencer tables which were more conservative and also included a safety stop (optional or as required). This reduced the incidence of DCS.

Isn't it just "directly user settable gradient factors" that you don't like?

I mean, when a diver buys a ZHL16-based dive computer they get gradient factors in very much the same way that they get γ₀ when they buy an RGBM one: user-visible or not, they're parameters to the algorithm.

Although it seems unlikely to me that a rec diver is going to be in a very good position to make an informed choice about the precise values for these parameters, that doesn't seem to imply that they shouldn't have indirect control over them through some manufacturer designed "safety level"

 

[MarkA]

Those early tables used by the BSAC were actually based on the British Royal Navy (RN) dive tables.

They were called BSAC RPNL dive tables (Repetitive Pressure Group and Nitrogen Loading).

In the original RN dive tables, the depth increments were in 5 metres units. The BSAC RPNL dive tables depth increments were in 3 metres units. At the time, it was recommended by the BSAC to use the next longer time or depth increment when planning dives to allow for a safety margin when conducting strenuous dive activities/cold water diving.

The British Royal Navy dive tables were slightly more conservative than the US Navy Dive tables for dives up to 100ft (30 m).

In 1988 the BSAC RPNL dive tables were replaced with the BSAC 88 dive tables which facilitated multi-level diving. At about the same time PADI Introduced the Recreational Dive Planner (RDP). Personally, the RDP was a much easier to use than the BSAC 88 dive tables. The RDP could be adapted to multi-level diving to a degree during the dive.

This is the RNPL/BSAC tables that you are referring to. Copied from my qualification record book.



Understood that RNPL stood for Royal Naval Physiological Laboratory.