Maximizing bottom time safely

[admikar]

edit: @admikar beat me to it! anyway, great book

SLOWPOKE!

 

[lowwall]

I was thinking more of examples of people he's seen do this. I understand the theory.

Ascent rate errors are pretty common. Shearwater's deco calculations assume an ascent rate of 10m/minute. Bust that either way and you are potentially creating problems.

BTW, go a lot slower than that from the last safety stop to the surface.

We shouldn't gloss over the buddy issue either. Even if you can convince a buddy to try this, how are you going to handle it on an actual dive? It's highly unlikely you'll end up with identical deco profiles.

 

[lowwall]

You can thank me later.

Let's try it this way, the forum software messes up straight Amazon links:
Deco for Divers by Mark Powell

 

[Wibble]

Ascent rate errors are pretty common. Shearwater's deco calculations assume an ascent rate of 10m/minute. Bust that either way and you are potentially creating problems.

Is that a problem in reality?

Of course that's a real issue with deep decompression dives where your surface GF is many hundreds of percent when you start the ascent and you've a long ascent where you're still on-gassing. i.e. the ascent time to "half way" is a significant fraction of the total bottom time.

This is not the case on a NDL/just into deco type dives where the "half way" ascent isn't far and the ratio of the time spent travelling to "half way" is a tiny fraction of the total bottom time.

 

[Wibble]

Deco for Divers by Mark Powell

Mark Powell has done various lectures on Gradient Factors which are available on YouTube.

There's a stepped graph of "tissue tension" vs "ambient pressure" which takes a bit of concentration to understand, but is a very good description of what's going on and the affect of different gradient factors.


Coupled with that would be to download some decompression calculation software such as MultiDeco or SubSurface. Then run various scenarios through that to see what comes out.

 

[Angelo Farina]

Ption w

I recently got a peregrine and I’ve been enjoying all the extra information that it’s showing me. I was thinking that I could use the info to maximise my ndl bottom time while managing risk. I’m eventually going to move to tech diving and have recently bought a Twinset and i have done some training on it.

So I’m thinking that I have two options to maximise my down time and manage risk.

Option one is to set conservatism to minimum (gf high 95), and then stay on my safety stop until surface gf is 75, or I decide to go up. I won’t know my tts with this option.

Option two is to set conservatism to max (35/75 I think), ensure that my surface gf doesn’t go above 95 and that my tts is within my available gas. This is technically a deco dive, but only because of conservatism settings.

Option one doesn’t violate any rules as the computer shows me as within ndl at all times, but option two gives me more information and I think could be a more reliable way to achieve my goal. Option two also gives me some practice in following a proper deco profile.

What are your thoughts?

Please note that this thread is a dogma free zone. I’m keen to hear opinions backed by logic or personal experience , but please refrain from saying I’m going to die because this isn’t what is being taught.

Option 2, definitely.
A dive planned as "deco", with good conservatorism, proper deco equipment and done by a deco-trained diver is much safer than a dive planned as "no deco" but conducted with small conservatorism on the edge of NDL, by a diver not equipped for deco and not trained for it.
If any minor events happens delaying the ascent, the "no deco" dive suddenly becomes an ""unplanned deco" one, which is an emergency situation.
If you had trained by an European agency (Cmas, Bsac) you would already know this.
Here already during OW course deco procedures are taught, and each student gets the information that "each dive is a deco dive".
Here we consider truly dangerous the approach of "riding the NDL". We prefer to plan always for diving with some mandatory deco stop. Of course this means being properly equipped (redundant gas supply, additional tanks suspendend under the boat, etc.) and trained.
So if you did not get yet proper training, I suggest that you get some deco training.
No need to go to true tech level, a recreational deco/deep course is plenty enough for your goals.

 

[scubadada]

...Using something like GF 80/95 will maximize your BT within NDL; spending as much time as you have gas for at your SS will minimize your risk...

Hi @Bazzathemammoth

You saw my post in the other thread. Most of my diving is no stop. I have been using GF 80/95 for nearly 4 years now. I use SurfGF to control my surfacing GF and make my final ascent over at least a minute to control the final significant increase in GF99

Using GF99 and SurGF

This popped up in my Chrome feed Excellent article about Shearwater computers and GF99 and SurGF https://scubatechphilippines.com/scuba_blog/shearwater-dive-computer-settings/

scubaboard.com

 

[100days-a-year]

If staying within NDL GF is largely irrelevant.
If doing deco dives, it is key to know the effects of changing GFs has on decompression profiles with respect to safety.
A n ntro tech class at least would be the best course forward. Reading up on deco theory, learning the computer's operation and diving with more experienced buddies as mentors will also help.
I've seen divers bent well within their computer's profile but typically its people riding the max GF over multiple dives or days.

 

[Wibble]

@Bazzathemammoth

Deco For Divers is an interesting read and should give you the info you need.

 

[tursiops]

If staying within NDL GF is largely irrelevant.

Maybe you mean GF-lo is largely irrelevant? GF-hi sets your NDL....