first stop = 80, last stop = 6 ??

[Mark]

Originally Posted by Mark Chase

Is the £40 I paid Ross for Vplanner any worse than the fee you have to pay GUE to get your hands on oficial ratio deco info?

No one pays GUE just to get ratio deco. It is just part of the Tech-1/2 course theory (a very handy part at that!)

I wouldn't pay £40 for the software as I don't need it. The profiles that Andy & I do work pefectly well without any further verification.

Regards,

Mark.

[Mark Chase]

Originally Posted by Mark

No one pays GUE just to get ratio deco. It is just part of the Tech-1/2 course theory (a very handy part at that!)

I wouldn't pay £40 for the software as I don't need it. The profiles that Andy & I do work pefectly well without any further verification.

Regards,

Mark.

Sorry my mistake:

Is the £40 i paid Ross any worse than the £450 I have to pay GUE?

If its free as you claim can you post me to where I can get it as I only have the shalow diving version


ATB

Mark Chase

[Mark]

Originally Posted by Mark Chase

Is the £40 i paid Ross any worse than the £450 I have to pay GUE?

I'd have to say that you get what you pay for when comparing the two.

Tech-1 costs £650 plus gas, b&b and boat fees, plus DIR-F, plus many training/practice sessions, plus DIR gear (ie a major commitment to DIR). You get rather more for your time, effort and money than just how to calculate deco.

£40 buys you a computer program that you can't take underwater. Whoop-de-doo

Regards,

Mark.

[rossh]

Originally Posted by And

To counter the 'mistakes' page on your website you have my dive profile. ..

Hello Andy, Are we certain we are talking a "mistake" here? If we check the article, it says "plan the slow ascent".. and "this is perfectly OK"...The point is to prevent some from applying one aspect without all the considerations... that would be a mistake. The myth is that the bottom section can be adjusted without penalty - not so... leading to a mistake.

If we take your plan and push your bent and twisted ascent into the deco model .. your plan is precisely as required. so what does this mean??
1/ all the fluff and extras added onto plans, amount to zero, as they do not depart from the basic bubble model,
2/ any suggestion that bubble models are inadequate, are null and void, given that your current plans are still within the bubble model..
3/ the adjustments made have a penalty, and need to be considered through the whole ascent.

To substantiate my view that the algorithm does not understand physiology,

And the digital human being will never exist.. get over it .. models are models .. they simulate conditions using physics and math .. very accurately.
.

I included a quote from Erik Maiken stating that the way that VPM deals with helium is 'dubious'. In fact when you read the history of the algorithm you can see that it has become a bit of a 'Frankenstein' of sorts. The VPM-O (which incidentally was forced to comply within the Navy Tables limits) was changed to include Boyles Law and became VPM-B and then with VPM B/E it now extends shallow stops a la Buhlmann. IMO it has become largely empirically based and has moved further away from the original science, which was of course, based on jelly Andy

You had to dig deep for the quote... it applies to all models in general.. and it still does not validate your point of view.

The VPM original was calibrated to a narrow range. VPM-B investigated and corrected the range limitation, and is valid across all depths, including NDL interception. VPM-B/E is a convenience for divers with many hours of deco wanting combined plans with deep stops and Haldainian. read more here

Andy.. Your own deco methods.. are validated against bubble models and GF.. why would you try to convince us that the original source of your deco is defective?? In fact Bubble models are accurate in 99% of all dives - including any gas mixes, all diver types.. etc, how could you suggest otherwise??

Andy.. you still have NOT presented anything to counter the view expressed in the article ... nothing at all... still waiting?

[And]

Originally Posted by rossh

Andy.. you still have NOT presented anything to counter the view expressed in the article ... nothing at all... still waiting?

[sigh] I had ignored the 'fluff and extra's ' bit but now its 'bent and twisted' LOL.

Firstly, I did not add any fluff and extras to the plan. That is the plan, the way it was meant to be dived. To try and make your computer program fit is adding the fluff and extras. Anyone who spends any time reading up on the WKPP deco stuff will know that it is not 'justified' against any model. The only reason that GUE say it is roughly equivalent to a 30/90 profile is to give students a point of reference. You only need to run a 6 hour dive at 90 mtrs on decoplanner to know that WKPP deco has nothing to do with models.

Anyway, I digress. Back to your article.

The 80% rule

To justify the 80% of the ATA's is extremely easy, especially when compared with your 2 ATA rule. Its called Boyles Law. You may have heard of it.

For a 45 mtr dive the ATA's are 5.5. Using the 80% rule the first stop (or ascent is slowed) is at 34 mtrs or 4.4 ATA. Using your 2ATA rule the first stop is at 25mtrs or 3.5 ATA. It is obvious to see that the pressure differential is hugely different. When you consider that some divers will use plenty of helium in their gas and consider that Erik Maiken himself says that the way the model treats helium is dubious then it seems to me that your 'rule' has two possible effects.

One, that it has a higher probability (remember, we know nothing for sure )of promoting bubbles to be formed which need to be treated later in longer shallow stops.
Two, that it may also promote bubbles to be formed which may hamper the offgassing process throughout the deco, making it less efficient.

It is obvious why the deep stop gets 'deeper' on shallower dives, as the pressure differential between stops becomes greater the shallower you get.

All the others stem from this one so we can deal with this one first can't we?

Andy

[rossh]

Originally Posted by And

It is obvious why the deep stop gets 'deeper' on shallower dives, as the pressure differential between stops becomes greater the shallower you get.
Andy

Andy, Thank you for the response.

The pressure change between levels is same for the same distance - regardless of depth....

Before any of the deep stop models and methods (WKPP, Pyle, and bubble models,etc) divers would often ascend 4+ ATA to the first stop on a Haldanian style plan. We all know better now, however it appears in some planning methods and depths (re: the 80%), the stops are being applied too deep. Has the race to add deep stops, overshot the mark? I think so.

There is a practical limit to the amount of extra time that can be added to the bottom without penalty. Extra deep time requires extra deco. If the diver does the extra deco - thats all OK. But the mistake is to think the extra time can be added without penalty.

[simonn]

Originally Posted by rossh

The pressure change between levels is same for the same distance - regardless of depth....

You have an empty balloon at 40M. Add 1L of gas. Ascend to 30M. What is the volume of the gas in the balloon.

You have an empty balloon at 10M. Add 1L of gas. Ascend to the surface. What is the volume of the gas in the balloon.

Would this have an effect on bubble size?

[Janos]

Originally Posted by simonn

You have an empty balloon at 40M. Add 1L of gas. Ascend to 30M. What is the volume of the gas in the balloon.

You have an empty balloon at 10M. Add 1L of gas. Ascend to the surface. What is the volume of the gas in the balloon.

Would this have an effect on bubble size?

I think the 2 atm thing isn't so much about bubble size as the likelihood of a bubble forming, which is to do with differences in pressure. If the surface tension of the bubble is greater than (PP of inert - ambient) then the bubble collapses into nothingness (ie it doesn't form)

If (Partial pressure of inert - ambient) is greater the the potential surface tension, then there is chance a bubble will form. Thus it's all about differences in presure rather than ratios.

Of course, once a bubble has formed, then your post becomes very relevant.

Incidentally Surface tension depends on bubble size (smaller bubbles have more surface tension, which explains 'seeding' - the same amount of gas forms a large bubble.

Laters,
Janos

[simonn]

Originally Posted by Janos

I think the 2 atm thing isn't so much about bubble size as the likelihood of a bubble forming, which is to do with differences in pressure.

If the surface tension of the bubble is greater than (PP of inert - ambient) then the bubble collapses into nothingness (ie it doesn't form)


If (Partial pressure of inert - ambient) is greater the the potential surface tension, then there is chance a bubble will form. Thus it's all about differences in presure rather than ratios.

Of course, once a bubble has formed, then your post becomes very relevant.

Incidentally Surface tension depends on bubble size (smaller bubbles have more surface tension, which explains 'seeding' - the same amount of gas forms a large bubble.

But don't the bubble models (i.e. VPM and RGBM) assume that there are already bubbles and you need to control the size? Haldane/Buhlmann assume that there are no bubbles.

[Janos]

Originally Posted by simonn

But don't the bubble models (i.e. VPM and RGBM) assume that there are already bubbles and you need to control the size? Haldane/Buhlmann assume that there are no bubbles.

To be honest I'm not sure, but I think the idea behind RGBM is to prevent bubbles forming as much as possible, rather than controlling them once they have been formed. Therefore RGBM etc brings in deep stops, hence the 2 atm thing rather than a ratio.

Once you have bubbles in your system then other factors come into play, but then you're not talking about microbubble formation anymore, but more 'traditional' (can't think of a better word) deco theory.

Laters,
Janos