RMV Spinoff from Accident & Incident Discussion - Northernone - aka Cameron Donaldson

[lv2dive]

I used to dive air to 130’ (NC) but now I generally have He in the mix if going deeper than 100’. That being said, I understand that He isn’t cheap and narcosis is less of a problem in warm clear waters. While I wouldn’t dive to 150 on air, I don’t judge those who do.

While I am a big advocate of diving gas, and with ALL due respect, I am constantly surprised to hear that people would consider air at 45m / 150ft so thick, or 'cold' - in the above context - to give them the shivers, if you get my drift. That is, air below what, 40m (or even 30m for GUE, no?) is to be avoided almost no matter what? No offence meant, as this is a general comment i.e. not directed at the poster - but methinks way too much "cool-aide" has been drunk since helium became popular.

 

[rjack321]

While I am a big advocate of diving gas, and with ALL due respect, I am constantly surprised to hear that people would consider air - especially in warm clear water - at 45m / 150ft so thick, or 'cold' - in the above context - to give them the shivers, if you get my drift. That is, air below what, 40m (or even 30m for GUE, no?) is to be avoided almost no matter what? No offence meant, as this is a general comment i.e. not directed at the poster - but methinks way too much "cool-aide" has been drunk since helium became popular.

Nope not koolaid, science
Gas density guidelines
There's a sharp inflection of Co2 related problems above 6gm/L. The data mostly comes from the CCR universe but OC isn't physiologically different. Also note post #17 in that thread, unpublished data supports this conclusion for OC as well.

Is air at 150ft insane? No not really. Is it "one more little thing" most likely yes.

 

[Kay Dee]

True, but you'd be in the deep current very briefly, and if deemed dangerous an experienced diver would proceed to surface (I assume)..........

Not a correct assumption. There are currents that can defeat the best of scooters, let alone a swiming diver, and they do with you what they will, be it up, down, or sideways, and all during the same 'experience' sometimes. You may have no say in the matter. A recreational dive of such an example familiar to me is off Roca Redonda in the Galapagos Isl. with a self explanitory name called 'The Washing Machine'. Another in Palau. Another in the Solomons. Actually, there are many places notorious for them. Caveat (or in this case, diver ) Emptor.

 

[johndiver999]

As we don't know Cameron's dive profile, his usual RMV, or his computer settings, it is not possible to begin to estimate his possible gas use.

It is quite simple to calculate the gas requirement for a hypothetical air dive to 150 feet, with a RMV of 0.5, that results in about 30 min of deco when a computer is set at 50/85. Any of the variables can be easily changed. In this example, the 21 minute dive would have a gas requirement that is well below that available in two AL80s.
View attachment 510878

Thanks, that is a smaller rmv than I was using, but it is exactly what I was asking. Now if someone runs a profile that includes diving over the shallow reef for x minutes and returning over over the same reef from 70 feet and shallower to the shoreline, we would get a better estimate. Any time spent on the reef before or after the deep, solo excursion, would require more air than the straight up and down.

It might also be useful to estimate the gas use (elevated rmv) should a scooter die or if it was insufficiently powerful and required any degree of kicking and exertion to offset the very unusual current that was apparently there that day.

Do tech divers plan deco dives in strong currents using an rmv of 0.5? If a diver must maintain a very low air consumption rate to complete a dive with a scooter, then it would seem that failure of the scooter would negate the overall air consumption predictions or plans.

 

[rjack321]

Do tech divers plan deco dives in strong currents using an rmv of 0.5? If a diver must maintain a very low air consumption rate to complete a dive with a scooter, then it would seem that failure of the scooter would negate the overall air consumption predictions or plans.

No not usually. Depends on the diver but in someplace like Coz an RMV of 0.75 for planning purposes would be typical for me. But my normal OC RMV is 0.55ish. If Cameron's normal RMV was 0.35 (unusually good but not unheard of) then 0.5 might be a reasonable planning level.

EDIT: a SAC of 0.23 suggests quite a bit of skip breathing to me. But I'm not qualified to judge.

Planning for a scooter failure in open water is relatively rare. But in open water its also unusual when the currents are so strong that you're going to get washed away forever if the scooter fails. In Puget Sound (for instance) you are never going to be that far away from shore or passing boats that you'll be washed out to sea.

 

[boulderjohn]

EDIT: a SAC of 0.23 suggests quite a bit of skip breathing to me. But I'm not qualified to judge.

I know some extremely well known and highly regarded divers with great SACs who absolutely do skip breathe. They won't admit it in a public forum like this because of the expected reaction, but they do it.

 

[Kay Dee]

Do tech divers plan deco dives in strong currents using an rmv of 0.5?

I would certainly hope not.

 

[scubadada]

Hi @johndiver999

OK, my last attempt at an estimate. As before, we cannot estimate Cameron's gas consumption because we don't know his profile, RMV, or computer settings

So, in our hypothetical dive we spend 40 minutes on the shallower reef, say around 60 ft, and come close to NDL. We then make a brief dive over the wall, down to 150 ft, until we have almost a half hour of deco. We satisfy our deco obligation while getting back to shore and end the dive. So, this dive is done with conditions that make the dive doable. Any of the previously mentioned factors could make this dive undoable, such as ripping current, strong downdrafts, scooter failure... That would nullify any chance at an accurate estimate. The first half of this dive is under reasonably benign conditions, one eighth of the dive is the deep portion, three eighths are deco and return to shore. Again, arbitrarily, 50/85 is used. The first table uses an average RMV for the entire dive of 0.5 cf/min, the second table uses an RMV of 0.75 cf/min for the entire dive. You can judge for yourself how to interpret these RMVs, I consider both on the high to very high side for a doable dive. At the lower RMV, there would be plenty of gas in two AL80s to complete the dive. With the higher RMV, there would be insufficient gas to complete the dive. Though extremely artificial, this exercise was useful for me.

 

[lv2dive]

A former dive buddy of mine consistently had a RMV of .25-.27 in Mexico caves (in a drysuit!). He was a tall male and it drove me crazy bc I was ALWAYS the one who called the dive.

The reason I figured out our RMV was that I felt like an air hog. After measuring, i realized my gas consumption (RMV .40-.45) was reasonable, his was atypical. He wasn’t skip breathing, either, he was just that relaxed in the water. I imagine Cameron was similar.

No not usually. Depends on the diver but in someplace like Coz an RMV of 0.75 for planning purposes would be typical for me. But my normal OC RMV is 0.55ish. If Cameron's normal RMV was 0.35 (unusually good but not unheard of) then 0.5 might be a reasonable planning level.

EDIT: a SAC of 0.23 suggests quite a bit of skip breathing to me. But I'm not qualified to judge.

Planning for a scooter failure in open water is relatively rare. But in open water its also unusual when the currents are so strong that you're going to get washed away forever if the scooter fails. In Puget Sound (for instance) you are never going to be that far away from shore or passing boats that you'll be washed out to sea.

 

[Kay Dee]

I think he told me on several occasions that his sac was in the mid to high .2s on cave dives with a camera and no scooter and his mom was around .23.

I don't mean to be offensive or disrespectful, but I find those rates extremely, reapeat extremely, hard to believe.