What's your SurfGF and how does it compare to your (Rec) GFHi?

[Wibble]

I've had DM's ask me why I was hanging around longer than three minutes at the cluster around the anchor line on some trips. "Were you doing deco!?" Had one particularly pesky dive leader on one trip who I basically told to back off after showing that I was in "Recreational" mode.
But they have the power, and all you can do is not use their boat on the next trip.

Every dive is a deco dive.

Some DiveMasters can be so up themselves.

 

[stuartv]

Yeah, yeah, but you forgot to include the context:



-- and nobody in their right mind is going to tell you that "anywhere below X is safe for you personally" based on the value of X. There is nothing personal in the algorithm and the whole point of gradient factors was to let individual diver do what you describe. But you knew that.

He didn't ask about him personally. He said "a typical rec diver".

I may not be in my right mind, but I have no problem answering his question by saying "Medium Conservatism, on a Shearwater (in Nitrox Recreational mode) - which is GF40/85. That is generally considered safe, for a typical rec diver. But, what works for you is personal, so you should understand that Medium Conservatism, or even High Conservatism MIGHT not be conservative enough for you and your personal physiology and circumstances."

 

[stuartv]

Every dive is a deco dive.

Some DiveMasters can be so up themselves.

I agree, but I also try to be a little empathetic. A lot of them have very little experience as a DM and none with technical diving or actual deco theory. A lot of times, I think what comes across as "up themselves" is just them TRYING to do their job as best they can, while actually not knowing a lot about it. They'd rather err on the side of caution than face their boss and try to explain how somebody had to go to a chamber on their watch. Their training may even have them convinced that something like "going into deco" is a REALLY dangerous thing and they may be genuinely concerned for the other person's health/well-being. Born of ignorance, of course, but still - they're trying to do what they think is the right thing.

 

[Wibble]

I agree, but I also try to be a little empathetic. A lot of them have very little experience as a DM and none with technical diving or actual deco theory. A lot of times, I think what comes across as "up themselves" is just them TRYING to do their job as best they can, while actually not knowing a lot about it. They'd rather err on the side of caution than face their boss and try to explain how somebody had to go to a chamber on their watch. Their training may even have them convinced that something like "going into deco" is a REALLY dangerous thing and they may be genuinely concerned for the other person's health/well-being. Born of ignorance, of course, but still - they're trying to do what they think is the right thing.

You're absolutely correct.

Can never accept that you can have the title of DiveMASTER when you've no experience, knowledge nor skills. It's the level of nonsense that we expect from **** for brains know-nothing politicians.

 

[Wibble]

And gradient factors... (stop yawning at the back)...

Interesting to see such high values for GF-hi mentioned. Received wisdom now has GF-hi being reduced below 80.

By definition a recreational dive is a non-decompression dive, so they should be keeping their SurfGF within the generally accepted limits. Kind of implies that their decompression stops safety stop isn't being followed.

Shouldn't recreational divers use a low GF-hi, e.g. <70, to keep them safe and out of decompression obligations?

(Or just accept that all dives are deco dives then plan and execute the dives accordingly)

 

[stuartv]

And gradient factors... (stop yawning at the back)...

Interesting to see such high values for GF-hi mentioned. Received wisdom now has GF-hi being reduced below 80.

By definition a recreational dive is a non-decompression dive, so they should be keeping their SurfGF within the generally accepted limits. Kind of implies that their decompression stops safety stop isn't being followed.

Shouldn't recreational divers use a low GF-hi, e.g. <70, to keep them safe and out of decompression obligations?

(Or just accept that all dives are deco dives then plan and execute the dives accordingly)

I just want to point out here that most recreational dive computers do not use Buhlmann with Gradient Factors. Many, over the years, have used the DSAT algorithm (as one example). Those that use DSAT do not have a reputation for bending their divers. I.e. it SEEMS (anecdotally, anyway) that DSAT is a reasonably safe algorithm for recreational diving. And, DSAT has been shown by many anecdotal reports to give NDLs that are very close to what you get with a Shearwater when using a GF Hi in the 90 - 95 range.

So, do recreational divers REALLY need to use a GF Hi of 70 or less to be safe? I kinda don't think so... I suspect many recreational divers could dive GF95/95 without ever getting bent. ("many" meaning, probably the younger, more fit ones, that don't have a PFO or any other predisposing factors) But, I would NOT recommend to anyone to start there. How a person's body responds to different GF settings is very personal, so anyone that is wondering where to start should definitely start with something less aggressive and work their way towards more aggressive - IF they want to - while paying attention to their body over the course of numerous dives to decide what GF settings work for them.

 

[Nemrod]

I've had DM's ask me why I was hanging around longer than three minutes at the cluster around the anchor line on some trips. "Were you doing deco!?" Had one particularly pesky dive leader on one trip who I basically told to back off after showing that I was in "Recreational" mode.
But they have the power, and all you can do is not use their boat on the next trip.

I try to do 5 minute safety stops. I usually do a deep stop or pause at half depth approximate for dives below 60 feet. I ascend at 60 fpm to half depth and from there wander upward at snail pace and certainly no more than 30 fpm.

I had a popular east Florida operation who I really like to dive with fuss at me for doing so. The DM insisted I break the surface and was yelling (with exaggerated hand signals) and then when I complied and surfaced that if I did not surface within one hour it was THE LAW that the captain had to call the CG! I am calling BS on that. I was doing a long safety stop as this was the third dive and they were all fairly deep and because there were at least 12 divers stacked ahead of me to the ladder. And with my camera I prefer to be first or last so I do not need to rush or delay the other divers with my camera OCD. So I was just hanging out slowly frog kicking to keep position about 15 feet aft of the ladder at 10 feet. As well I prefer to avoid the usual CF on the tag line with divers doffing their fins and getting blown off, kicking each other in the face and other assorted mayhem as they try to overhand the line with fins on their elbows. So they are going to call the CG? And tell them what, that Nemrod will not come up! And when I set my tank in the rack it still had 800 plus psi on the clock! What was the big deal? But I just soaked it all in, politely nodded I understood and basically ignored him, politely. Hence forth I will break the surface with them at 59 minutes and 59 seconds!

N

 

[rsingler]

...it SEEMS (anecdotally, anyway) that DSAT is a reasonably safe algorithm for recreational diving. And, DSAT has been shown by many anecdotal reports to give NDLs that are very close to what you get with a Shearwater when using a GF Hi in the 90 - 95 range.

So, do recreational divers REALLY need to use a GF Hi of 70 or less to be safe? I kinda don't think so... I suspect many recreational divers could dive GF95/95 without ever getting bent.

As this thread gets longer, we seem to have lost the bubble. When @Jay first started this conversation over two years ago, I think he was reacting to the surprising finding once SurGF was introduced as an available datum.
Whether you dive 30/85, 50/70 or 95/95, it is surprising that in my experience, the vast majority of regular recreational dives end up with GF99 upon surfacing between 40 and 60. In other words, you could dive 100/100 and there would be no effect on your safety.
It's only as recreational diving has begun to push the envelope that these gradient factor discussions have merit. It's only when you start doing repetitive dives that are long (CCR) or deep or maybe on trimix that the argument has much possibility of being worth pursuing.

For me, it's cumulative risk that I'm trying to reduce. When I'm on Helium with my CCR, I understand that I need to be conservative. But it's the other half of my diving that I'm really worried about. Cold water California diving is beautiful, but a lot of prep and driving and cleanup to do every weekend. So when I have the chance, I pack 25 dives into a week in some tropical paradise. And it's those dives where I want an approach that will keep me out of trouble. Yeah 95/95 will (statistically) work for our 40 min bounce dive to 120 feet and the 40 foot second dive that afternoon, with a pair of 60 footers tomorrow before I go home.
But what system should I have used to do twenty-five 80-100' dives in a row, 4-5 a day (counting night dives), as I drank in the sights of the second dropoff on Bonaire last September?
It wasn't DSAT, and it wasn't 95/95.

 

[dmaziuk]

In dive computers - software there's a fun little threadlet in which the poster comes up with a dive plan that saturates the 19-minute tissue compartment and goes from an hour NDL to mandatory deco by simply changing the ascent rate. The math works exactly the same way for back-calculated surfacing GF: you could come up from the exact same dive with SurfGF of 102 or 42, you just need to get your hypothetical tissue loading exactly right to land on the border between two imaginary tissue compartments, and then all it takes is to spend an extra minute coming up to the safety stop, to tip it over one way or the other.

 

[jborg]

goes from an hour NDL to mandatory deco by simply changing the ascent rate

I think that's a mischaracterization of what Subsurface does. The difference is only whether he arrives at 10m with a teensy-tiny deco obligation (Subsurface rec planner says go to the surface after clearing the seconds or whatever of deco) or with no deco obligation (Subsurface rec planner says you can stay at 10m until gas runs out, because the NDL there is really long).

you could come up from the exact same dive with SurfGF of 102 or 42, you just need to get your hypothetical tissue loading exactly righ

That seems worrying and not how I understand the algorithms to work. Can you give an example of how that would happen?