Gradient Factors

[caverkevin]

The Internet is a powerful resource. Have you hugged your Internet connection today?

Richard Pyle's paper on deepstops was one of the first things I read in regards to deco different to standard USN dive tables. Thinking about venting the gas from the fish kinda put things into perspective for me. I Googled and came up with this link for you.

http://www.bishopmuseum.org/research...deepstops.html

Then I would google some of the references.


Cheers!!

Kevin

Quote: (Originally Posted by neilh)

I'll admit that while I find these threads interesting, most of the content goes way over my head because deco theory, gradient factors, etc are all a mystery to me! Your point about reading and research is a good one - any suggestions for some good places to start?

[Mark Chase]

There is loads of info here:

ftp://ftp.decompression.org/pub/


Click on Baker and read his stuff on deep stops especially column 3 page 2.

Winky is also well worth a look

Here is an article on Gradient factors attempting to explain them simple:

http://www.rebreatherworld.com/gener...adient+factors

VPM is discussed Here:

http://www.decompression.org/maiken/...m_Site_Map.htm

And this is an excellent article on deco myths and legends:

http://www.hhssoftware.com/v-planner/decomyths.html

HTH

Mark Chase

[LCF]

Thanks, Mark, for the link to the gradient factor article.

[peter_steinhoff]

Quote: (Originally Posted by Gledders)

So - what do you use, what have you experimented with in the past, and what have you learned from it (Don't do it like this, you get bent is an acceptable response )

I started by using 30/100 and added the deep stops myself. I then started to shave the O2 stop basically running GF 120. I never had any problems on wreck profiles but later got unclean deco when doing long multiday diving on nitrox with O2 for deco. Switching to 30/30 took care of that.

After a couple of years and some problems that I believe was dehydration and sleep related I started to think about what the purpose of doing short deco was. As a general rule I always just made it as short as I knew work but for instance diving in warm water what is the benefit? So I started to add some deco back in again. What that would be in gradient factors I can't say.

Best,
Peter

[Clare Gledhill]

Quote: (Originally Posted by peter_steinhoff)

After a couple of years and some problems that I believe was dehydration and sleep related I started to think about what the purpose of doing short deco was. As a general rule I always just made it as short as I knew work but for instance diving in warm water what is the benefit? So I started to add some deco back in again. What that would be in gradient factors I can't say.

You are right to point out that it is not a race. My investigations started when considering gas planning for the deeper sections of a dive in an OOG scenario, and GFs obviously have a significant impact on these. In an 'all is well' scenario - particularly if the water is warm and gas is plentiful - of course more is fine but we need to know what the base line is in order to know what we are 'padding' in the first place.

[EBT]

What defines "padding" vs "new deco shape"?

I'd argue that what most DIR folk is doing is the latter. So at this point, how relevant is GF? I'd have thought its becoming pretty irrelevant, what you guys do is to use GF as a baseline for runtime, then you reshape all the deco to fit the basic tenets of DIR deco practise.

Peters post pretty much shows this in action and as he says "I've no idea what GF this ends up at"

[Mark Chase]

Quote: (Originally Posted by Gledders)

You are right to point out that it is not a race. My investigations started when considering gas planning for the deeper sections of a dive in an OOG scenario, and GFs obviously have a significant impact on these. In an 'all is well' scenario - particularly if the water is warm and gas is plentiful - of course more is fine but we need to know what the base line is in order to know what we are 'padding' in the first place.

The base line is surely 100/100GF

50m 18/45 30min bottom time 50% for deco = 30mins

1@ 21 (purely for the gas switch)
2 @ 12
5 @ 9
8 @ 6
14 @ 3


The BASE line for any dive means getting shallow ASAP to conserve gas and pushing the bubble gradient as hard as you dare.

Curves and deep stops have no relevance in emergency situations, get shallow as soon as possible and save as much gas as possible to extend your 3m stop as long as gas reserves last. Then get out of the water and accept that its likley going to hurt but at least your still alive.

When I ran tables I always had a set of 100/100 GFs planned for the dive. If the emergency was not that bad I could always pad out the profile manually.

This sort of logic is not quite so apparent on a 50m dive but on a 80mdive with deep stops costing you say 140lpm of gas on a 20 SAC 60m stop depth
its importance starts to become more apparent.

ATB

Mark Chase

[graham_hk]

There is no mystery to deco - take a starting point (maybe deco planner), use widely distributed knowledge on deco (articles on www.wkpp.org are a good start) and do some diving - see how you feel and adjust as necessary. Personally, if I was getting good results with 30/85 I wouldn't adjust?

I rarely see the need shave time off deco - that resulted in plenty of bends in these parts a few years ago when everybody was racing to do "george deco" - what they (those who were racing) failed to realise is that you have alot more scope to shorten on longer exposures than the short bounce dive typified by ocean diving.

Search quest or gavin scooters and you will see that George actually does longer deco than common deco planner profiles for short bottom times. I was talking with a few folks in Florida last week about this and it is a major misunderstanding that taking a class (insert any agency here) will give you the magical formula for "deco".
The only thing that works is diving

Graham

[graham_hk]

Quote: (Originally Posted by Mark Chase)

Curves and deep stops have no relevance in emergency situations, get shallow as soon as possible and save as much gas as possible to extend your 3m stop as long as gas reserves last. Then get out of the water and accept that its likley going to hurt but at least your still alive.

Rubbish!

That is asking for trouble: much better you do the deep stuff properly and then blow off the shallow (By rushing to the shallows you are asking for serious bends - by doing the deep stuff give yourself a chance). Better still carry a suitable amount of gas on you and your buddies.

Graham

[vid]

Quote: (Originally Posted by Mark Chase)

Curves and deep stops have no relevance in emergency situations, get shallow as soon as possible and save as much gas as possible to extend your 3m stop as long as gas reserves last.

i agree and in some types of emergency you might ignore deco entirely - which is a personal risk assessment

but i think it's slightly different for OOG situations and planning the dive

if, for example, i use 15/85 GF, then there's a trade off between

• carrying sufficient bail-out to run that dive profile in all contingencies or
• limiting my gas which might push me nearer to 100/100 GF or thereabouts

Personally, I'd carry the gas and not alter my dive baseline

vid