Modern research/thoughts on Ascent Rates

[Heat Miser]

GF high of 80 or 85. I can't recall which. My Perdix which recorded my dives during that time won'y turn on. I need to get the button repaired for the 2nd or 3rd time.

and if you compared it to your traditional ratio deco profile. would your ascent have been faster or slower? Thanks

I'm a ratio deco illiterate

subsequent edit ----------------

I've done a bit of reading (30ish minutes) about ratio deco .... Mark Powells Deco for divers... And I think what you are saying is Ratio Deco with is slightly slower ascent rate has served you well, despite a tendency to deeper stops?

Im sorry about your hit ... just watched GUE.TV Simon Mitchell 3rd installment .... hope you got to a chamber < 6hrs

 

[Akimbo]

Anecdotal: I think I did exactly 90 straight days diving in 2018 (most of them deco between 100 and 250 feet) before I got bent.

Do you recall about how many dives/day during the last week or so? My impression is that the hit rate is significantly higher on liveaboards is higher after several days of multiple no-deco dives than at the beginning of the trip.

Adjusting your GF/conservative settings might be worth considering for a long strings of repetitive dives.

 

[Trace Malinowski]

and if you compared it to your traditional ratio deco profile. would your ascent have been faster or slower? Thanks

I'm a ratio deco illiterate

When comparing ratio decompression, VPM+2, and Buhlmann with a GF 40/85 the decompression plans are very close. GF 40/85 is usually more conservative around the 20-foot and 10-foot stops. The difference between ratio deco and both VPM+2 and Buhlmann GF 40/85 is that you usually start making deep stops deeper than the other two models.

Research began suggesting that we might be forming more bubbles by doing deep stops. This would be like a GF Low of 20. The recommendation became to ascend to shallower depths before stopping. Divers set their GF Low to 40, 50, or greater.

To put it in simple terms, my question for scientists would be if we are forming more silent bubbles by doing deep stops would the bubble model theory still hold up regarding tension, and would the tension on those bubbles still place a diver at a lower risk than if the diver ascended higher in the water column, possibly forming less bubbles, but would less tension on fewer bubbles still make it more likely that one bubble could cause a problem. I haven't been following advances in science on the matter because I've been busy trying to recover physically for 4 years, so my understanding might be flawed. I've returned to recreational diving using DCIEM tables. But as I gain experience post-injury by returning to technical diving, a thorough understanding of current vs. past theories would be a central focus of my personal growth.

 

[Trace Malinowski]

Do you recall about how many dives/day during the last week or so? My impression is that the hit rate is significantly higher on liveaboards is higher after several days of multiple no-deco dives than at the beginning of the trip.

Adjusting your GF/conservative settings might be worth considering for a long strings of repetitive dives.

I remember doing 2 - 3 dives a day most of the time. Yeah. I'm okay with ultra-conservative GFs. I've returned to recreational depths staying well within the DCIEM tables and only doing 1 dive per day. I've also got my Shearwater set to GFs that are more conservative than the default setting.

 

[Trace Malinowski]

and if you compared it to your traditional ratio deco profile. would your ascent have been faster or slower? Thanks

I'm a ratio deco illiterate

subsequent edit ----------------

I've done a bit of reading (30ish minutes) about ratio deco .... Mark Powells Deco for divers... And I think what you are saying is Ratio Deco with is slightly slower ascent rate has served you well, despite a tendency to deeper stops?

Im sorry about your hit ... just watched GUE.TV Simon Mitchell 3rd installment .... hope you got to a chamber < 6hrs

Yes, to ratio deco working for me without incident for more than a decade.

Would you believe I surfaced just 30.0 yards from the center of the wreck I was on to the back door of a hospital? The symptoms hit me about a mile's drive down the road, though. I returned to the hospital where the P.A. in the E.R. wouldn't give me O2 with a mask, and he listed me as a non-emergency transport. The paramedics did three non-emergency runs between that hospital in the 1000 Islands and the hospital in Syracuse, NY, that had the chamber before they picked me up. I didn't get chambered for 7 hours. Had I driven myself or called a friend instead of going into a hospital, I would have arrived at the chamber in about 90 minutes.

 

[inquis]

As this is a thought experiment, and assuming the RELATIVE rate of change of absolute pressure is the important part (R = Pdot/P)

I wanted to circle back and acknowledge this assumption is incorrect. Since V is inversely related to P under the ideal gas law, the critical ratio to maintain in order to maintain the same rate of bubble expansion is actually R = Pdot / P^2. Working through things from there, we arrive at a depth-dependent ascent rate (imperial units) of:

• Ascent Rate = Reference Rate * ( (Depth + 33) / (Reference Depth + 33) )^2

This clearly backs up the overwhelming consensus that one should slow WAY down during the final ascent. With a reference rate of 30 ft/min and reference depth of 30 ft, the rate when nearing the surface should be about 8 ft/min to maintain the reference rate of bubble expansion. The flip side to this, however, backs up the comments by @Superlyte27 that you can basically ascend as fast as your scooter can take you when very deep. (The calculation evaluates to more than 1000 ft/min when passing through 333 ft, so anything slower than that results in SLOWER bubble growth than you have at 30 ft!)

(Metric folks should use 10 instead of 33 in the bulleted expression. The ascent rate when nearing the surface is 2.5 m/min assuming a reference depth of 10 m and reference rate of 10 m/min.)

To be clear, I'm not recommending that anyone depart from their training, and the choices you make on your own dive are your own. Again, this is merely a thought experiment, and like the OP, I find the question interesting. (The validity of the above assumes the rest of the ideal gas law terms -- particularly the number of gas molecules -- does not significantly increase over the timescales in question. I have no evidence that is true.)

 

[Nick_Radov]

This is why I get annoyed at dive computers with fixed ascent rate alarms regardless of depth. If I'm down at 200 ft and scooter up over a rock I don't need it beeping at me.

 

[dianna912]

GF high of 80 or 85. I can't recall which. My Perdix which recorded my dives during that time won't turn on. I need to get the button repaired for the 2nd or 3rd time. When I get it back, the log will be reset so all that info will be lost.

Oh, no, I hate to hear this! I'm having an issue with the button on my Perdix AI. I've had it for 18 months and I'm sending it for warranty work now. Can you give any feedback on how the warranty works for their work? Are their repairs warrantied for a certain period of time? I'm worried that I don't have enough time underwater to assess it before the 2 year warranty is up, and we've got 3 weeks planned to Indonesia in November!

 

[grantctobin]

Oh, no, I hate to hear this! I'm having an issue with the button on my Perdix AI. I've had it for 18 months and I'm sending it for warranty work now. Can you give any feedback on how the warranty works for their work? Are their repairs warrantied for a certain period of time? I'm worried that I don't have enough time underwater to assess it before the 2 year warranty is up, and we've got 3 weeks planned to Indonesia in November!

It gets shipped to Divetronix, fixed, depth tested, and is generally back within a week good as new (or new). Obv ask for rough estimate on repair time as my most recent experience was a few months ago, but you'll be impressed.

 

[dianna912]

It gets shipped to Divetronix, fixed, depth tested, and is generally back within a week good as new (or new). Obv ask for rough estimate on repair time as my most recent experience was a few months ago, but you'll be impressed.

Sorry, I should've been more clear: do they warranty their work? So if I have an issue at 23 of 24 months of the warranty and get it back, and the same issue arises at month 25, will they still cover it? Trace's report of the button malfunctioning multiple times worries me.
Also, how hard should the button need to be depressed? Mine is non-usable with gloves on. Without gloves, if I hit it just right in the dead center, it has a 50% chance of working. If I use my knuckle (without gloves) it works more consistently. Our last two trips, I couldn't get it to work at all and had to rely on pressure to get it to turn on. Couldn't use compass or anything. We tried a fresh battery once, and that didn't work, but just tried one again and now it seems to be at that 50% functionality, which seems super strange to me. It seems like button issues are usually hardware issues with these, but that wouldn't explain it intermittently working.