ascent rate

[declan long]

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.

thanks for that post, so can i clarify you are saying that from example one hundered metres ascend to the first stop at ten per min then the same again. from say twelve or fifteen metres ascend at 3 per minute, this would be good?

 

[boulderjohn]

thanks for that post, so can i clarify you are saying that from example one hundered metres ascend to the first stop at ten per min then the same again. from say twelve or fifteen metres ascend at 3 per minute, this would be good?

As TSandM said, you have to do what your decompression plan calls for. When you create a plan using a specific theory, it calculates each stop based on the assumption that you are ascending at a specified rate. If you are ascending at a different rate, then everything is off.

For example, two of my friends got bent on a dive in which they were using a plan that assumed they would ascent at 30 FPM (10 m/min) until they reached their first stop. They were using computers in gauge mode as bottom timers, so they were able to look at the actual dive profile later on. When they did, they found they had made a downright leisurely ascent at a fraction of that rate before their first stop, meaning that they had in effect accumulated more bottom time than their plan called for. The profile showed they had made other errors in their profile, but that one was huge.

If you are using a program like V-Planner to plan your dive, it will include both a planned ascent rate and a planned descent rate. Both are important. For example, if you drop like a rock at twice the planned descent rate to a 300 foot maximum depth, you will accumulate several more minutes of actual bottom time than your plan calls for. If you ascend more slowly than it expects, you are adding more bottom time. If you ascend more rapidly than it expects, then it affects the planned length of the deco stops as well.

 

[declan long]

As TSandM said, you have to do what your decompression plan calls for. When you create a plan using a specific theory, it calculates each stop based on the assumption that you are ascending at a specified rate. If you are ascending at a different rate, then everything is off.

For example, two of my friends got bent on a dive in which they were using a plan that assumed they would ascent at 30 FPM (10 m/min) until they reached their first stop. They were using computers in gauge mode as bottom timers, so they were able to look at the actual dive profile later on. When they did, they found they had made a downright leisurely ascent at a fraction of that rate before their first stop, meaning that they had in effect accumulated more bottom time than their plan called for. The profile showed they had made other errors in their profile, but that one was huge.

If you are using a program like V-Planner to plan your dive, it will include both a planned ascent rate and a planned descent rate. Both are important. For example, if you drop like a rock at twice the planned descent rate to a 300 foot maximum depth, you will accumulate several more minutes of actual bottom time than your plan calls for. If you ascend more slowly than it expects, you are adding more bottom time. If you ascend more rapidly than it expects, then it affects the planned length of the deco stops as well.

With out this sounding patronising that is an excellent post, thankyou very much that is clear now.

Another question then please if you don't mind. say i am to ascend from a given depth at ten per min, i have a sw petrel comuter which shows ascent using arrows or chevrons, it shows one arrow as three per min so three of theese is only 9 per min, four would mean twelve per min, how can i do my ascent accuratel using this?

also when i dive i aslo cary a bottom timer, this shows the ascent slightly different to the comp, which should i follow?

thanks

 

[boulderjohn]

With out this sounding patronising that is an excellent post, thankyou very much that is clear now.

Another question then please if you don't mind. say i am to ascend from a given depth at ten per min, i have a sw petrel comuter which shows ascent using arrows or chevrons, it shows one arrow as three per min so three of theese is only 9 per min, four would mean twelve per min, how can i do my ascent accuratel using this?

also when i dive i aslo cary a bottom timer, this shows the ascent slightly different to the comp, which should i follow?

Those slight differences between deco stops will not make enough difference to worry about. Just do your best to follow the prescribed plan. Your Petrel documentation should tell you what it wants you to do, and that should be your target.

 

[Diver0001]

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

As a general rule of thumb you can split your dive into two main zones. Deeper than the depth whereby the deco limit corresponds to your bottom time, and the "shallow" part above that.. On the deeper part you really should ascend with about the speed dictated by the model you're using.

ON the shallower part, you can slow down some depending on the total bottom time up to that stop. Normally on an hour long dive I'll ascend from depth to 18 metres at 10m/min, from 18 to 6 metres with 3m/min and dead slow after that. If the dive was up to 90 min, I'll still ascend to 18 metres for the first stop according to the deco model but I don't extend that stop. the first extended stop in that case will be the 15 metre one notwithstanding a compelling reason.

I don't make dives that are longer than 2 hours and I don't make dives that require stops deeper than what I would define as the shallow zone... but keep in mind that this is possible so my method *will* break down if you make extreme dives.

Carrying on: from 6m to the surface you can extend your stops indefinitely without incurring any additional decompression obligation. I would advise ascending from 6m to the surface at "dead slow", regardless of scenario.

There are various reasons why I say this and I really should get around to posting about it in more detail but the main thing to remember is that the closer you get to the surface the slower you can (and should) be ascending.

R..

 

[rivers]

declan, have you read Mark Powell's 'Deco for Divers'? If not, I strongly suggest you do. It's an excellent resource that answers many, if not all of the questions you have been posting in your various threads.

 

[OMANDIVER]

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

with V planner you have to set the ascent rate in metres per minute. It doesn't tell you what the rate is.

 

[ajduplessis]

80, 30 and 10 feet per minute

 

[eelnoraa]

..... But i was watching a vid and some guys where ascending at 1 m/m which to me seemed like a good idea.

If you do this for the whole ascent, you will need a lot of gas even for a simple 100ft(30m) dive.

declan, have you read Mark Powell's 'Deco for Divers'? If not, I strongly suggest you do. It's an excellent resource that answers many, if not all of the questions you have been posting in your various threads.

Yes, this. Read this book.

 

[OMANDIVER]

thanks for that post, so can i clarify you are saying that from example one hundered metres ascend to the first stop at ten per min then the same again. from say twelve or fifteen metres ascend at 3 per minute, this would be good?

try this in V planner and see what it looks like; bottom to OG point 9metres per minute; 6 mpm to switch; 3mpm to 3metre stop and then 1mpm to surface. Also look at Erik Browns V planner tutorial; google Team Blue Immersion and you will find it.