Ascending faster than 60ft/minute

[Fish_Whisperer]

Slowing ascent rate, the closer to the surface you get, is because of Boyle's Law and its affect on the nitrogen bubbles, correct?

 

[Fish_Whisperer]

A routine stop for 3 minutes at half your dive depth (plan or no plan, slate or no slate) will do you much more good than blowing off everything that's left in your tank at 15 feet or less.

This is how we did it when we dove (dived?) the Spiegel-Grove. Stops at 70, 50, 30, and 15.

 

[DandyDon]

Just curious, we cant change the ascend rates in our dive computers.

How then can we gauge this 20ft/min?

I don't think so. When I'm coming up a mooring line, I'll count "one thousand one, one thousand two" for each foot about 60 ft - and that is creeping. On swimming ascents, I watch the variable ascent rate on my Oceanic computer and try to keep it in the 2-3 bubble range.

Well, yes, you can ascend too slowly from depth. And if your plan calls for deep stops, you had best be following the plan on your slate. My point was that from 15 feet to the surface, there is no reason not to take a lot of time to offgass as that is where the fastest rate of offgassing will occur.

Yep - in addition to very slow ascents, I like a deep stop, safety stop, shallow stop like yours for a minute or two anyway after the safety stop, then floating effortlessly on the surface for a minute or two before climbing a ladder - which is another fast off-gassing level to consider.

Even for the times a fast ascending diver doesn't get bent or embolism, you can be left excessively exhausted. I guess it's too much Nitrogern = not enough Oxygen leading to fatigue...?

 

[Thalassamania]

My wife and I did a Padi course in January, books stated 60 ft/min max ascent rate. One person in class had to wait a session to receive her books, as a fresh batch was coming in. Her's used 60 ft/ min also. Our instructor made a point of saying that was a "max", and slower was better. Safety stops were also "strongly urged", and simulated at 5' inthe pool. OW dives with another PADI shop always used a safety stop @ 15' partly to instill it in us, and partly to send up a marker, and check for boat traffic before finishing ascent.

This is the kind of thing I'm talking about. Here we have outdated information bing spread under the auspice of the best known recreational training agency. Is this because the Instructors involved don’t not know any better, because they don’t want to go against "the book” or … ?



Minimizing diving risk requires practice, practice with your gear, practice of your skills and practice with your mind. You must stay current. None of us always succeed … we all learn new thing every day. But for an instructor to not be conversant with something so mainstream that it was up on the DAN website in 2004 is, I fear, negligent.

 

[uglyredshoes]

interesting read so far. reading the threads has helped me to understand the functioning tables behind my comp.

looks like in any case, ill just dive my comp since it takes into consideration deep stops, and allows me to change my safety stop to 20ft which i prefer.


besides, its easier. dam these small little gadets are smart!

 

[Charlie99]

Just curious, we cant change the ascend rates in our dive computers.

How then can we gauge this 20ft/min?

What works for me is that when I start my final ascent I make a judgement call about how long of total ascent time is appropriate.

Then, looking at the current dive runtime on my computer, I pick out the times at which I will leave 40', 25', and 15'.

Obviously, the time of leaving 10' or 15' is my chosen total time of ascent (typically 5 to 9 minutes) added to current runtime.

The runtime for leaving 40' is calculated from an average of 30fpm ascent from my starting point, plus a minute or so stop at 40'.

Then the "leaving stop" time for the 30' or 25' stop is my 40' point + 2 or 3 minutes.

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A concrete example: I've done a dive to 130' for a few minutes, then up to 90 foot, then, then puttering around 60-70' for another 15 minutes. I'll ignore the deeper portion, since I've been at 65' for quite a while. My overall loading is reasonably high, so I choose 8 minutes total ascent time.

OK. Lets say my computer says 52 minute runtime. 8 minute total ascent time obviously means that I intend to surface at 60 minutes. Everything easily falls out from that decision.

It takes me a minute to get to 40', add another minute to hang there. I leave 40' at 54 minutes. A couple of minutes after 40' stop means I leave 25' at 56 minutes.

I leave the shallow safety stop at 52+8=60 minutes. In practice, I start the safety stop at 20', and slowly ascend so that I'm at 8 to 10' depth when the computer runtime hit 60 minutes.

It sounds much more complicated when reading it than it is in real life. Particularly, since I do basically the same ascent after every dive, with just minor tweaks back and forth ---- very heavy N2 loading gets me to add a few minutes. For example, when starting an ascent directly from the deck of a 100' wreck the 40' stop becomes a 50', 25' stop moves to 30' or 35.

I don't worry too much about the instanteneous ascent rate, other than just keeping things under control. In practice, what happens after a while is you get used to doing a very slow slide or glide between the 3 depth/time checkpoints of the ascent.

 

[proyce]

I have a Suunto Gekko, set to P1. If I ascend at 60ft/min it will beep at me and tell me to slow down. It will also require a safety stop between approx 18 and 22 feet, and another one around 15 feet.

 

[Thalassamania]

Slowing ascent rate, the closer to the surface you get, is because of Boyle's Law and its affect on the nitrogen bubbles, correct?

No. Boyle's Law states that under conditions of constant temperature and quantity, there is an inverse relationship between the volume and pressure for an ideal gas. What you need to do to minimize decompression risk is keep bubbles from forming. When you descend breathing compressed air, your body uses the oxygen, but the nitrogen is dissolved into your blood. When you ascend, the water pressure around you decreases. If this pressure change occurs too fast, dissolved nitrogen separates out in your blood of other tissues and forms bubbles. Since the blood pressure is lower on the venous side, and the vessels get larger with direction of flow until the lungs are reached, bubbles in the blood are usually not a problem. The capillary beds in lungs filter them out and they exchange over a relatively short time without much more effect than tiredness or shortness of breath (shortness of breath or the “chokes” is an extreme symptom of this). When a nitrogen bubble forms elsewhere, it can cause decompression sickness, or the bends, so named because the ensuing joint pain can double you over.

So what you want to do is keep the nitrogen in your body just below the level of bubbling off and thus have maximum driving force for offgassing while NOT forming bubbles. It appears that the best way to do this, on an approximate basis, is through the use of “deep stops” (half your dive depth) rather than shallow stops (20 ft or less).

Boyles law comes into play in the treatment of both air embolism and decompression sickness where increased external pressure, supplied by a chamber, Is used to “crush” the bubbles and then oxygen therapy is used to wash the nitrogen out.

 

[Thalassamania]

Please, do not just dive your computer. Make a conscious effort to do a three minute stop at one half of your max depth, then follow your computer on up. Your spinal cord will thank you. Bowel, bladder and sexual function are worth preserving ... and that ... along with your very life ... is what you may be risking.

 

[Fish_Whisperer]

Thank you, Thalassmania. This is partially what I had in mind, when I was thinking of a DCS hit and embolism. The additional info you provided is very helpful, too. Thanks again.