Maximizing bottom time safely

[L13]

If staying within NDL GF is largely irrelevant.

GF-High is essential to NDL diving on any computer that uses GF's to set conservatism, which is most new computers on the market.

GF-Low on the other hand is largely irrelevant as you say (until you accidentally go into deco, the highly relevant again).

 

[uncfnp]

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.

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I think what you are trying to describe here is a version of what some call “light deco” and to some extent I have done this as well.

Light deco?

As a corollary to a recent post/poll regarding advancing from recreational to technical diving Happy to always dive advanced within recreational limits, forever ? [Poll], I would like to know if you use the term light deco. If you do, I would appreciate it if you would supply your definition for...

scubaboard.com

"Riding your Computer Up" vs. "Lite Deco"

A recent pony thread got me to thinking back to an amazing thread from days gone by, can't think of any search terms, fuzzy recollection... Yes! Just found it! Doing 'Light Deco' as a recreational diver Please read posts 1, 16, and 31. :snicker: Do that and you will most likely end up...

scubaboard.com

Doing 'Light Deco' as a recreational diver

On a recent trip to dive some wrecks off Nanaimo I found that some of the people on the dive had their computers show a deco obligation. My buddy and I had planned our dive profiles rather carefully before the trip and we decided on 20 min at 100 for dive one, a 2 hour SI and 20 min at 80 for...

scubaboard.com

 

[broncobowsher]

Changing computer setting still doesn't change physics.
The computer models are like weather forecasts, which are also computer models. The new ones are pretty good, but still sometimes wrong.

I may have missed it, didn't see it in the original post. How deep is the OP planning on diving? Nitrox is one way to change the physics. That might be a better way to get more bottom time?

 

[Bazzathemammoth]

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.

I know the one. It was a bit of an ah-ha moment for me with understanding Gradient factors. I have a hard time spending $60 on a book, but I’ll look into it. Nice to know there’s one that is so well regarded. As below I’ve been running dives through the peregrine planner to get an understanding of what my gas obligations etc could be. A few extra minutes of bottom time adds up quickly at depth!

Ption w

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.

Yes! My favourite dive buddy is a cmas instructor. My experience of diving with him and talking about recreational deco has shifted my perspective a bit. We have done some planned “deco light” dives, hence my comment earlier about never accidentally going past ndl. I asked him to certify me in the cmas system, but because he’s not based in France anymore, or with his club it wasn’t an option (or some reason like that). He’s taught me gas planning etc.

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.

I’ve done intro to tech, and I know how to plan deco dives on the peregrine. It’s got a really nice planner, it even works out gas usage if you put in your Rmv.

I also dive nitrox for more bottom time. Its expensive, and can take a while to get a fill, so I don’t use it that often

 

[tursiops]

OP, your options for increasing bottom time are:
1) increase GF-Hi to 95; dive within NDL
2) Nitrox; Dive within NDL
3) planned deco

(2) is your best bet for significant increases in BT. If you don't like the cost, wait until you start doing planned deco...

 

[Bazzathemammoth]

OP, your options for increasing bottom time are:
1) increase GF-Hi to 95; dive within NDL
2) Nitrox; Dive within NDL
3) planned deco

(2) is your best bet for significant increases in BT. If you don't like the cost, wait until you start doing planned deco...

Nitrox is a hassle here. The last two times I got it they had issues. There’s only one place here that’s does it.

First time the shop filled the tanks with air, then ran out of o2. It took over a week for the fill.

Second time they stuffed up the fill and it was a way lower o2 percentage than I wanted. That took a week from drop off to ready to pick up.

If you combine that with the fact that our dives are all open ocean and very subject to weather it can be pretty frustrating. Weather forecasts are only accurate 3 days out here and it takes a week to get a nitrox fill. My last 2 dive trips have been canceled due to weather conditions.

Getting a practice dive at the lake with $50 of nitrox on my back isn’t something I want to do if I can avoid it, which can happen if the dive trip I got the nitrox fill for a week earlier gets canceled and I still want to get wet.

 

[tursiops]

Nitrox is a hassle here. The last two times I got it they had issues. There’s only one place here that’s does it.

First time the shop filled the tanks with air, then ran out of o2. It took over a week for the fill.

Second time they stuffed up the fill and it was a way lower o2 percentage than I wanted. That took a week from drop off to ready to pick up.

If you combine that with the fact that our dives are all open ocean and very subject to weather it can be pretty frustrating. Weather forecasts are only accurate 3 days out here and it takes a week to get a nitrox fill. My last 2 dive trips have been canceled due to weather conditions.

Getting a practice dive at the lake with $50 of nitrox on my back isn’t something I want to do if I can avoid it, which can happen if the dive trip I got the nitrox fill for a week earlier gets canceled and I still want to get wet.

If you are planning air dives with deco, and longish bottom times, you may want to rethink your strategy. Deco'ing on air is terribly inefficient...you probably want at least Nitrox for a deco gas, if not 50% or 100% O2.

 

[grantmac]

I might draw some flak on this but you may wish to look at doing your own partial pressure blending if nitrox is such a challenge in your area.

 

[Bazzathemammoth]

I might draw some flak on this but you may wish to look at doing your own partial pressure blending if nitrox is such a challenge in your area.

Yea, I know a local diver who blends their own nitrox. He’s offered to teach me. Long term I want to move to somewhere that’s better setup for diving, so I’m probably just going to carry on as is for now.

 

[Brett Hatch]

How far away is the fill shop from your home/work/dive sites? If it's reasonably close to any of these, then I'd say a couple more tanks would be a better solution than your own blending gear, or planned deco dives for that matter. If you've got 4 tanks, then diving 2 tanks a week while the other 2 are parked at the shop waiting around for slow-ass fills isn't so bad, I used to do it that way all the time. Used tanks are just as good as new ones, and cheaper.

Deco dives without sufficient training and redundancy are not a good idea. Doing trust-me dives with your friend who does have the training isn't a good idea either. Get the training, the skills and the redundancy going, sure, maybe it's a good option for you. What depths are you typically diving?