ascent rate

[declan long]

Hi Guys

So last night i was thinking about ascent rate. Normally i use ten metres per minute throuought the dive. But i was watching a vid and some guys where ascending at 1 m/m which to me seemed like a good idea.

What ascent rate do you use and when do you change it?

Does it really make a differnce, i would have thourght that a faster ascent is good interms of less deco time but bad in more risk of dcs? is this correct theory?

So, when choosing an ascent what do you look for and how do you choose it?

thanks

 

[TSandM]

Whatever the decompression model is that you are using, it should be prescribing the ascent rate to use during each phase of the decompression.

 

[declan long]

Whatever the decompression model is that you are using, it should be prescribing the ascent rate to use during each phase of the decompression.

Thanks for your reply,

I mainly follow my dive computer, would it be safer ascending at say three m/m and doing the extra deco?

Also i believe v planner using vpm lets you alter ascent rate?

thanks

 

[boulderjohn]

So last night i was thinking about ascent rate. Normally i use ten metres per minute throuought the dive. But i was watching a vid and some guys where ascending at 1 m/m which to me seemed like a good idea.

Why does that seem like a good idea?

For your final ascent from your last stop, I can see it, but I don't see any benefit to it at any other point in the ascent. Do you have any research that shows that an ascent that slow is preferred?

I agree with TSandM that you should use the prescribed ascent rate for the decompression model you are using. Do you know any decompression models that advocate 1 m/min?

 

[declan long]

Why does that seem like a good idea?

For your final ascent from your last stop, I can see it, but I don't see any benefit to it at any other point in the ascent. Do you have any research that shows that an ascent that slow is preferred?

I agree with TSandM that you should use the prescribed ascent rate for the decompression model you are using. Do you know any decompression models that advocate 1 m/min?

Hi thanks for your reply boulderjohn

so i am thinking this because when ascending as ambient pressure drops bubbles increase so therefore have more chcnce of dcs?

i think that this is why it would be a good idea. normally you hear the slower the ascent the better.

if you was to ascend from a given depth at thirty m/m and still make stps you would have a bgger vhance of dcs thats my reasoning. it is only a thoery.

thnaks mate

declan lonng

 

[Akimbo]

I would not be surprised if future decompression algorithms support variable ascent rates. A short deep dive with faster rates through deeper parts of the ascent can make sense. The idea is some tissues can actually absorb more gas during a slow ascent. One problem is putting a decent user interface on it.

A letter in the Winter 2014 Alert Diver Magazine discussed it on page 59-60

 

[PfcAJ]

An variable ascent rate is what GUE has been teaching for years now. 30fpm, 20fpm, 10fmp, and 3fpm are all things taught in their tech curriculum.

 

[Makhno]

(1) What the deco model tells me, until (2) I've switched to EAN50 at 21 meters. Then 3 meters per minute until I've switched to O2 at 6 meters. Then after I've finished all my deco, (3) 1 meter per minute to get to the surface.

If the deco model doesn't tell me to stop at 18, 15, 12 & 9 meters, I input those as 1-minute stops just so the program knows I'm doing the 3 meters/minute ascent rate. Usually it tells me to stop at each of those for a minute or longer anyway unless it was a really short, shallow dive.

The 1 meter/minute crawl to the surface after my deco is done is just a way to pad the final stop and add conservatism. I tell the deco program that I'm going to do those additional 6 minutes on O2 so it can calculate my O2 exposure properly. That 1 meter/minute thing is fairly common among technical divers here in SE Asia -- but let me reiterate that it's only for the ascent from the 6 meter stop to the surface, and is just for added conservatism after all the required deco is done.

Sent from my GT-I9300 using Tapatalk

 

[Redshift]

Variable ascent rates have been implemented in diving computers for many years already.
I don't know which computer the OP is using, but maybe it's doing something like that.

The ascent rate is a trade-off between absorbing more gas and not allowing bubbles to grow in a way that makes it impossible to release them.

 

[boulderjohn]

Hi thanks for your reply boulderjohn

so i am thinking this because when ascending as ambient pressure drops bubbles increase so therefore have more chcnce of dcs?

i think that this is why it would be a good idea. normally you hear the slower the ascent the better.

if you was to ascend from a given depth at thirty m/m and still make stps you would have a bgger vhance of dcs thats my reasoning. it is only a thoery.

thnaks mate

declan lonng

No, you do not normally hear that the slower the ascent rate the better, at least I have never heard that idea expressed among any of the people with whom I have trained. The ascent rate you use needs to balance the need for some of your tissues to off gas at a safe rate with the fact that some of your tissues are still ongassing at that depth. If you ascend too slowly, then (in overly simple terms) your tissues are ongassing more than they are offgassing. A study of bubble formation in ascent rates at the recreational level found that 10 m/min (30 FPM) was superior to 3 m/min.

Some of the posters have talked about a variable ascent rate, which is gaining popularity. The idea is that the deeper you are, the faster you can safely ascend safely. I think one of the biggest problems many technical divers have is that they ascend much too slowly in the first part of their ascent. Conversely, they ascend too rapidly in the last part.