Blown Ascent Rates and Somersalts

[Marie13]

MacDive is very nice.

 

[gcarter]

I’m a frisky diver: diving style has been compared to a seal. When I look at my logged dives in my Oceanic Datamax Pro Plus (now Pro plus 2), it usually shows a blown ascent rate, despite the fact I creep pretty slowly up the water column on actual ascent. Recently in the pool I thought, well standards have changed (60 feet per min to 30 feet per min above 30 feet, maybe I AM coming up too fast. So I inched up watching the ascent rate meter and it didn’t show any marks. Later looking at the log—totally blown ascent rate, in the red and flashing. Huh? But then I remembered I was somersaulting into my BC at the bottom (doff/don exercise) and I wondered if it could be that. Also if I bring my console rapidly up to look at it, could that do it? Anyone else have this problem?

I have had logged rapid ascent rates because of arm movement on my Oceanic Veo 2.0. I do notice it less with my Petrel 2. I would not worry about momentary ascent speed fluctuations.

 

[aquacat8]

I have had logged rapid ascent rates because of arm movement on my Oceanic Veo 2.0. I do notice it less with my Petrel 2. I would not worry about momentary ascent speed fluctuations.

Thanks, pretty sure that’s it for me too, good to hear from another Oceanic user.

 

[scubadada]

Oh dear I have no idea how to download dive, and I’m on a Mac.

So, at 62 minutes, I apparently exceeded 30 ft/min for at least some portion of the 30 second sample, the manual does not say for how long

 

[Eric Sedletzky]

The idea that anyone can be a diver, even people who are scared of the water, scares ME!

That’s why they invented solo diving.

 

[Johnoly]

.....totally blown ascent rate....

Remember your OW training.......Where does the GREATEST per foot pressure change difference occur?

I dive the ProPlus 2 also and will 'push' the accent indicator from 115 up to 60 hitting the alarms. But that last 30 feet, I just very slowly wrap the string around a thin stainless steel eye bolt attached to my SMB on the surface to 'slo-poke-it' up. It's the bubble size that matter's and the bubbles get big at the top, not the bottom. There's another huge other discussion on multi-dive tissue sat that I'll ignore for this post. Just shoot an SMB at 30 ft and practice slow wrapping. If you are not shooting an SMB at 30 on every dive (even with other divers) then that's the 1st correction you need to make.

 

[aquacat8]

Yeah good advice... I just started shooting an SMB when I moved here and began drift diving Florida trips. Before I moved to the east coast I never shot one, often we would do like a 15 minute “swimming safety stop” swimming back underneath, after ascending to 15-20 feet on these handy ascent lines called kelp stalks (which I’m pretty sure would make spaghetti of an SMB line). Sigh, I miss Nature’s Ascent Lines.

 

[aquacat8]

@Johnoly may I ask, since you used the same computer, do you ever experience mysterious blown ascent rates in the log, looking after the dive, even though during ascent you did not crack the ascent rate? That is what I see, and that’s why I was wondering about hand movements and somersaults.

 

[Johnoly]

@Johnoly may I ask, since you used the same computer, do you ever experience mysterious blown ascent rates in the log, looking after the dive, even though during ascent you did not crack the ascent rate? That is what I see, and that’s why I was wondering about hand movements and somersaults.

Yep,,,,especially if I'm coming up and then also pick up my PP2 to read it. Just moving the computer from your waist to your eye level can blow it. It's very sensitive and will almost always blow the ascent rate. But that's also a good thing because it's extremely accurate on it's depth readings, for example 21 foot versus 20 foot which starts your SS countdown timer. Watch if you are coming up faster than your bubbles.

 

[dmaziuk]

@Johnoly may I ask, since you used the same computer, do you ever experience mysterious blown ascent rates in the log, looking after the dive, even though during ascent you did not crack the ascent rate? That is what I see, and that’s why I was wondering about hand movements and somersaults.

You have to realise that if your computer recalculates every, say, 2 seconds, then moving its pressure sensor up by over one foot will be a "momentary" ascent rate violation. You can't program it to beep on every one of those, if only because nobody wants the computer that beeps all the time and you'll lose customers. So these "momentary" violations don't generate an alarm -- but they still get logged because computers are dumb like that, they just log what is and you did move more than a foot in 2 seconds.

(In reality it's even worse because if you move up and down between 2 sensor readings it will not even realise there was an up movement. So the part of the program that decides to sound the alarm if there was an actual violation has to average over several readings and somebody has to decide how many is "too sensitive" and how many is "too risky".)

My logs are also peppered with yellow triangles in subsurface.