Counterdiffusion discussion

[And]

Originally Posted by Mark Chase

If I said on average I saved £50.00 per dive and I do 25 mix dives a year that’s a saving of £1250.00 per year X 2.5 years that’s £3125.00 I paid £3100 for my 3 month old unit. I have also recouped about £1000 in the sale of some of my old OC dive kit.

ATB

Mark Chase

LOL, Now come on, tell the truth, have you really only spent £2100? What about the HUD and the VR3 bits and pieces and the training? I don't look at it in terms of costs, but if you are going to at least be honest.

Andy

[Mdemon]

Now you might run around like a blue arsed fly for a dive. I suggest that if you do that for an OC dive you will do it for a CCR dive, it has nothing to do with the equipment. I definitely don't. Anyone who's seen me dive knows its a generally relaxed affair.

Nooooooooooooooooo! I should point out that I was trying to put together a whole load of borrowed kit, rig stages etc etc - NOT my normal dive config which is pretty much rigged in the car. I should also point out that the guy did have bailout IIRC, so I am guilty of being inaccurate on two points!

Logistically, getting twins + stages + kit onto the boat is a multi-trip affair. And the gear is heavy, let alone the cost of fills and the plan inflexibilty once filled. Compare that with a Box + stage + the flexibility. I agree about the swapping spit bit though - I save that for very special (SWMBO) people only...

Love the idea of a Gavin though...

[Mark Chase]

Originally Posted by And

LOL, Now come on, tell the truth, have you really only spent £2100? What about the HUD and the VR3 bits and pieces and the training? I don't look at it in terms of costs, but if you are going to at least be honest.

Andy

The unit was £3100. The course is £500

The VR3 upgrade is optional as is the HUD but if your interested:

Unit £3100
VR3 Upgrade pin for Trimix CCR and external Po2 £140
HUD including cable and VR3 link £730
Course £500.00

Total cost £4470.00

Extra kit

Apex ATX 40 deco reg DS4 £228
Apex ATX 40 deco reg DS4 £228
Two 7ltr Stages 02 clean £250


OC rig still had a VR3 but we will ignore that

Custom divers wing Harness and back plate £425.00
Twin 12s with manifold and bands £360
Twin 12s with manifold and bands £360
Twin 15s with manifold and bands £395
Four 10ltr stages 02 clean £440
Two 7ltr Stages 02 clean £250

Apex TX50 long hose pressure gauge DST fist stage £320.00
Apex TX40 standard on DST £280
Apex ATX 40 deco reg DS4 £228
Apex ATX 40 deco reg DS4 £228
Apex ATX 40 deco reg DS4 £228

Total cost £3514

All the above is sold or will be sold accept two 7s and two deco regs. I expect to recoup about £1500

Additional equipment...

Second set of twin 15s borrowed for when both dives on the two day trip are past 60m

Yet another set of 12s for when both my sets are full of expensive trimix and the next dive is 30m

If your dive kit doesn’t resemble the above list your not doing the sort of diving I do and possibly don’t need a re-breather.

ATB

Mark Chase










ATX 50 with

[And]

So its really about £3000 then, and therefore at a saving of £50 per dive you need to do 60 UK dives to 60 mtrs to recoup the cost. You also (theoretically) need to take a season or so out to get to the same level you were at which means the saving per dive is less. That is also a secondhand unit, so to buy new would have cost more.

Sorry to hijack the thread MDemon (In my defence Stuart started it )

Isobaric Counterdiffusion. My view is that all the gasses I use, both bottom and deco, have been used by many other divers. I also use the same deco strategy, same suit inflation, same equipment. They have done bottom times of 7 hours or more and deco of 12 hours or more. They don't think of it as a problem, so, applying that to my level of diving, I definitely have absolutely nothing to worry about, regarding that phenomenon. If I recall the article in Diving Physiology or whatever its called was based on experiments on pigs, which gave them skinbends

There was another Georgism regarding this which said that pigs don't make very good divers and decent divers shouldn't really look like pigs

Andy

[Janos]

Hum. Well I was going to post something about how this week I'd got around to reading the Bruce Wienke's paper that Robert kindly emailed me a few months ago, and that had something to say about isobaric counter-diffusion (and I now understand the oxygen window too) although at 167 pages and a lot of formulae it took me a while.

However since we've drifted on to CCRs

I'm currently diving stuff in the 30m to 40m range on a twinset. I'm going to get a 7l stage and learn to use it over the winter. One day I will get mix qualified. Until then, diving below 40m (or even to 40m) scares the bejesus out of me and I'm not comfortable doing it on air (in the UK).

But am I going to go OC trimix? No. Too expensive and too inflexible. I like the independence of a CCR, the idea of turning up for a weekend and not needing to visit a compressor. I also like the idea that I use a weak trimix diluent for all diving, even the 30m to 35m stuff, and not worry about the cost and hassle involved.

I think there are more and more divers who are thinking about helium in a couple of years (I reckon 2007 before I do it!) and choosing to go CCR rather than the hassle and expense of OC.

And of course I guzzle air.

Just my 2p.

Laters,
Janos

[NotDeadYet]

Ere!!! What you doing in my garage, Chasey!!!

Don't forget to factor in the 25% discount on the rebreather cost just for the fact it is damn good fun!!! I've spent maybe £1500 on the current beast and a year of fun filled fettling.

When Kev Gurr was touting Cis Lunars round the country his spiel said it would take 50 trimix dives to recoup the cost of the unit and it wasn't a cheap RB. That was the early 90's when trimix was dearer though. On an Inspiration or KISS at today's prices I think that would still hold true.

I was reluctant to mention cost as what is safety worth (depending on your viewpoint)? But the cost saving is whopping as is the hassle saving. Like Mark says, getting gas fills was a pain for me too, about 60miles of driving and most of the day wasted waiting. And the number of times I've wasted helium on 30-40m dives. Worst was probably a 70m mix on a 8m dive. I was in tears

Sure you can carry another 32% stage. Is it steel or ally, Bob? For me if it is ally I need a hell of a lot more weight. Plus I've either got to re-fettle my regs or have a spare single set with me, lead, adapter plate, etc. If it's steel then it's a bottle I can't use for anything, I don't like steel stages and I never use a single except in the pool.

I can honestly say I will not do a deep trimix dive OC again. I'd rather sit it out than go back to £100 a dive, a gas supply only a few minutes longer than your bottom time, a compromise on deco gas, being cold, narcosis, extra drag, maintenance costs and struggling to get out the water. I plan to continue to do <30m on OC but whether that will happen I don't know.

[Scoff]

Meanwhile back again on thread (rather than how/ why I justify having an RB)),, here is a link to an article that appeared in the Cave Diving Group newsletter some years ago.

http://www.cavedivinggroup.org.uk/Articles/ICGT.html

Rupert did bio-chemistry or somesuch at Uni and understands such things, whereas Fred worked out on the rigs.

The way I understand it is that it's a bad idea to swap from a Trimix/ heliair onto either air or a mix that means you go from a low N2 % to a high N2%. In simple terms means N2 is trying to ongas & get into cells that were busy off-gassing He, and the cells don't like it...

What seems to have happened is that Rob blacked out having swapped from Trimix to air, and could not be pulled through the restriction by his buddy (the way of many caves). Sad whatever the cause (especially as Rob had introduced the CDG to mixes back in Wookey in '85).

Not having too much experience of mix, I still always try to use a travel/ intermediate gas which is compatible with the bottom gas - ideally ensuring that the N2 percent in the bottom mix and the intermediate mix is the same, or that the intermediate mix is less in the N2 %.

But then again, I'm only a cave diver - not a proper diver..


Cheers

Scoff
(Cave Diving Group - Northern Section QD)

[Mark Chase]

Originally Posted by And

So its really about £3000 then, and therefore at a saving of £50 per dive you need to do 60 UK dives to 60 mtrs to recoup the cost. You also (theoretically) need to take a season or so out to get to the same level you were at which means the saving per dive is less. That is also a second hand unit, so to buy new would have cost more.
Andy

I am being conservative in my estimate. In fact I reckon I will get my money back quicker than 2.5 Years.


CCR New with the course is £4250 I paid £3600 with the course.


60 UK dives yes, but not 60 dives to 60m.

60M UK Dive 18/40 Back gas in twin 15ltrs two 10ltr stages 32% & 80%

18/40 twin 15s cost £65.00

10ltr 32% 8.00
10ltr 80% 12.00
Petrol for two trips to Tonbridge from Detling £10.00

Cost of dive £95.00

CCR

Fill of lime 7.00
02 5.00
Mix 10.00
Petrol 2.00

Cost of dive £24.00


Saving over OC £71.00

Last year I did 29 trimix dives. This year I had 27 blown out dives most of which were trimix depth and I managed 21 mix dives over 40m which for me is a Mix dive (Not counting 6 dives over 40m in Egypt on air)

I think 2.5 years is a realistic figure for recouping the cost of the unit IF you’re doing my sort of diving.

As for taking a season out of Mix diving?? My last two CCR dives were 41m and 42m both on Mix. I wouldn’t contemplate doing the sort of diving I was doing on OC for a while but I am using 21/25 for safety reasons and limiting deco to 30mins. We have a weeks CCR diving booked in Egypt for December/Jan and I am pushing for 25 hours on the unit that week.

We have a Trimix livaboard booked for Feb 2005. I have 14 hours logged on the unit since October and I Have booked my Trimix CCR course for Feb 5th. I am planning on getting a min 3 hours a week on the unit between now and then. By June I hope to have around 150-200 hours on the unit and be back to 60M+ diving. I have a weeks UK gas diving booked for July and a weeks UK gas diving booked for August 2005

I seriously expect to get at least 30 trimix dives 40M+ on the unit in 2005 but in reality I will be using trimix for all diving over 30m and therefore I will probably get more like 70-80 mix dives.

ATB

Mark Chase

[Brian Donaghy]

Originally Posted by Scoff

Meanwhile back again on thread

As I understand it ( mostly from my NAUI Trimix course which was written in part by Bruce Weinke) if you:
stick to sensible gases
. ie No deep light (trimix/heliox) to heavy (nitrox) gas switches
and don't surround youself with a gas less dense than you are saturated with
. ie use air or argon for suit inflation
you avoid any issues with ICD.
Deep apparently means >21m (I presume in deference to his DIR fellow travellers)

Originally Posted by Scoff

But then again, I'm only a cave diver - not a proper diver..

Well I'm barely either, so I guess I 'm the most qualified to preach on the internet.

To my mind Mark Ellyat is to the ocean what Laika was to deep space.

[chrisch]

Originally Posted by Janos

I'm currently diving stuff in the 30m to 40m range on a twinset. I'm going to get a 7l stage and learn to use it over the winter. One day I will get mix qualified. Until then, diving below 40m (or even to 40m) scares the bejesus out of me and I'm not comfortable doing it on air (in the UK).

But am I going to go OC trimix? No. Too expensive and too inflexible.

Why not? All you need is the training and you are there. Then you can do 50m in comfort. A 21/25 or similar is all you need and is about 30 quid for a fill.

When you are ready for 60m+ then CCR (if that's the way you want to go).

OC mix is a good stepping point. I cannot comment on the truly deep stuff - I doubt I will ever dive deeper than 60m. However, if RB gets more reliable and cheaper maybe one day......

Chris