Recreational Ascent Rate in the last 15 feet

[W W Meixner]

Can't say, but as a general rule, s-l-o-w.

I know that anecdote, not even in plural, is data, but I almost quit wanting to stop for a nap during my drive home when I stopped corking from my safety stop.

Agreed...s-l-o-w...

Looking up there's usually a line-up at the boat ladder...plus if it's the last dive of the day...or the last dive of the trip...I'm in no hurry to surface...or get out of the water period...and always have a sufficient reserve...usually well over 1000 PSI...

W...

 

[stepfen]

Do you agree that a diver can go straight to the surface from a NDL dive without injury, assuming reasonable ascent rate and no breath hold?

Even in this case, during the ascent (with or without reasonable ascent rate) decompression is taking place, hence every dive is a decompression dive. Like it or not.

Just my 2c and I will leave this discussion here. Regards.

 

[Jay]

...

Just my 2c and I will leave this discussion here. Regards.

I hope that topic is left there. I don't know why that boring oft heard bomb was lobbed by @happy-diver

Back to the question, any ideas / analysis re this:

I'm still intrigued by this. When I play with your SS and enter a near NDL limit dive it seems the %AoM (SurfGF) is near GFHi.
Can you replicate the GFHi of 75 versus a 92% SurfGF in your SS?
FWIW I played a bit with SubSurface and those results are also near GFHi (for a dive just out of deco). <--EDIT/ADD and it should be obvious what I mean: when the model/computer says a 'deco' value of zero / does not display and 'deco' value.

 

[happy-diver]

it's called going up man
at a particular speed, man
spread some thinking dudes

 

[EFX]

I'm still intrigued by this. When I play with your SS and enter a near NDL limit dive it seems the %AoM (SurfGF) is near GFHi. Can you replicate the GFHi of 75 versus a 92% SurfGF in your SS?
FWIW I played a bit with SubSurface and those results are also near GFHi (for a dive just out of deco).

I replicated baker's dive profile from "Decolessons" in my ss. His total DT adding in the initial ascent to the first stop is 96 minutes. My spreadsheet shows 106 minutes using the starting depth for ascents and descents in the calculation for inspired inert gas pressure. One reason for the greater DT in the ss is I switch to the (2) deco gases at a shallower depth (the switch depth is non-selectable). There are some other minor differences as well that affect the overall DT. I will be posting a major revision soon. In the new version I added EAD and a choice to show the surface GF or current GF as Baker calculates it. Baker came up with a GF of 91.2% upon surfacing. The ss came up with 91%. Selecting Surface for the %AoM column produced 63% which comes under the GFHi of 75%.

 

[Ayisha]

...If I read a dive book that said all dives were deco dives, I would immediately toss it, because getting something so basic wrong is inexcusable.

A deco dive requires decompression. A dive that doesn’t require a mandatory deco stop is not s deco dive.

Don’t spread misinformation...

Yes, every dive is a deco dive.

Do/did you subscribe to training that involves dive planning and pressure groups?

If you are in a pressure group at any point in a dive, and especially at the end of a dive, then you incurred decompression stress.

Why would anyone need to have a surface interval between recreational dives? Because they incurred decompression stress.

If you don't have decompression stress in a recreational dive, then why do a safety stop at all?

Have you ever heard bubbling divers on Doppler after recreational dives? I have. Our Canadian DND has presented some interesting Doppler studies on recreational divers and the sound can be surprisingly alarming.

You're kidding yourself if you think you're not incurring decompression stress during recreational dives.

People who subscribe to "Minimum Deco" and "every dive is a deco dive" don't train for NDL dives or optional/safety stops. Every dive has a minimum amount of deco to be done. Of course, decompression theories are theoretical, so where anyone draws a line in the sand as to when, how long or at what depth stops "should" be done is debatable. That there is decompression stress appears to be pretty prevalent no matter what you call it.

 

[NAM001]

When I talk to people about very basic deco . I tell them that every dive is a deco dive., The onlly difference is how the deco iis done, It is a ballance of on gassing time vs off gassing time. if you are going to ascend at 30 fpm that gives you x time to off gass. if you need more time you have to get it by either doing a stop or slowing the ascent to aquire the additional time needed. as our standard so to speek is 30 fpm , in order to prevent having to do a stop you have to control exposure which is on gassing. that exposure time limit is called NDL.

Some where there is a way to put in 2 givens to get teh 3rd compunent. IE i want to go to 130 feet for 25 minutes what is my ascent rate to foster a non stop ascent to the surface. the answer may be 12 fpm who knows but is is calculable. our tables and computers force certain givens like ascent rate of 30 and 60 fpm and our depth is a given and gives the corrosponding NDL. I would also bet you can calculate a dive to 100 ft for 5 minutes and get what the max constant ascent rate allowed would be to safely get to the surface. that may be 75 fpm. Or system and training does not include the alternate possibilities as its goal is to keep it simple and that is done by doing 30 fpm or less and using tables based on that ascent rate. Its simple the product of functions a and b gives c. we only choose to use one aspect of that concept in OW and AOW training. Is there more science than that in deco. YES there is but the fine details do not change the big picture.

 

[happy-diver]

THE FIVE WAYPOINTS AND SIMPLE ASCENT BEHAVIOR

 

[dmaziuk]

There's 3 kinds of people: those who get math and those who don't. Ascent from 39 to 26 metres in 1.5 minutes at the rate of >= 9 m/min means it's time to go buy a better watch.

I'm not disagreeing with the concept, but seriously: at these depths it's just easier to go < 9 m/min to your "running stop", whichever way you define it, and not worry about ascent rate switch. E.g. on reef dives to 20-ish metres, half-pressure "running stop" puts you around the no-limit depth, from there you can have an extended safety stop and watch your 99 grapefruits for as long as your gas and schedule allows and all that.

 

[dmaziuk]

Some where there is a way to put in 2 givens to get teh 3rd compunent. IE i want to go to 130 feet for 25 minutes what is my ascent rate to foster a non stop ascent to the surface. the answer may be 12 fpm who knows but is is calculable. our tables and computers force certain givens like ascent rate of 30 and 60 fpm and our depth is a given and gives the corrosponding NDL. I would also bet you can calculate a dive to 100 ft for 5 minutes and get what the max constant ascent rate allowed would be to safely get to the surface. that may be 75 fpm.

This is probably non-linear because of the switch in the leading tissue compartment. I expect you can smooth it out by using more tissue compartments up to the infinite number of infinitely small ones, a la integral. With Buhlmann's idea of deriving M-values from properties of the gases, this may actually be doable, and modern cellphone-level CPU shouldn't have a problem running it in what passes for real time in our case. Well, except those Buhlmann's numbers turned out to be too much and had to be tuned down in the middle compartments...

I bet it's so much easier to calculate the upper bound... which may just happen to be 30 fpm.