How Many Off Board DIL's to allow for?

[Janos]

I'd be interested to know what your CNS clock ends up on at the end of the dive with a 90m start on PPO2@1.5? Not sure I'd be too keen to run it that high that early.

I wrote down a few numbers, and, from a deco perspective, doing a 90m dive on a set point of 1.2 is like doing a 93m dive on a setpoint of 1.5.

Ie you can swap a 0.3 change in ppO2 for an extra 3m depth of inerts.

So for me, it really makes sense to lower the ppO2 at depth, (90m vs 93m is not much) and boost it in the mid-range and shallows. (9m vs 6m is a big difference).

Janos

 

[Dave Sutton]

True, diving physiology and physics are not important. Important as it is written in the manual.


greet rc

The manual is one describing the onboard implementation of DCAP, written by my late friend Dr. Bill Hamilton, at that time the worlds leading decompression table generation expert and the man who "gave us the keys" to allow the earliest Trimix diving. You might wish to do a little reading on both he and the Cis lunar.

It's noteworthy that when we did saturation compressions we did essentially the same thing: blew the entire complex down to a fairly shallow depth with air to set PP02 (and END, although that was not the goal) and then the balance of the descent was on pure helium. No further PP02 increase at all. Seems to me that we went to about 10 meters on air then to depth with pure helium. Typical saturation stow depth was about 150 meters. Dr Hamilton had done our tables for this as well.

Dave

.

N

 

[anarchista]

You might wish to do a little reading on both he and the Cis lunar.
...
and then the balance of the descent was on pure helium. No further PP02 increase at all. Seems to me that we went to about 10 meters on air then to depth with pure helium.

Of course, I'm always interested in scientific information.

Recently I wrote about the technique of pure gases, I spoke about the fact that in the pure gases, ppO2 remains constant with immersion.
Were the enemy, reminded the statement. Then you reminded yourself of compression in saturated systems.
Now you're talking about pure helium.
Thank you for confirming that this, well-known piece of history.

greet rc

 

[divelermontov]

i second what dave said

always have normoxic gas in my inboard. In fact more often than not I have air in my onboard as this will run inflation as well.

Than at 10 meters I plug the onboard with quick connector into the dil manifold and unplug the inboard form the manyfold. On the way up the reverse, unplug go board and plug in onboard


inflators are fed form onboard directly and not form the dil manifold

but only my .02
christian

^^^^

What he said.

One offboard manual add valve on the rig and a quick disconnect hose on every bottle and you'll be golden.

NEVER have a gas on a BOV that you cannot breathe from at the depth where you are. That means normoxic gas at the surface. And unless you like to climb ladders with a stage bottle attached that means normoxic inboard and a system to switch BOV gas.

Should I post yet another link to the YouTube video of my symposium presentation? It may not be all correct and there's plenty of room for other ideas but it will raise a lot of discussion for you to consider.




Dave


.

 

[matt]

No worries Matt, better late than never.

So they tell me. ;-)

Post this whole thread, I've pretty much decided that I'm going to run with normoxic in my onboard DIL

Take care, 0.2x14=2.8. For me, I'd rather dive hypoxic and KISS. I accept there are other ways though. However most people, after experimenting, seem to come back to simple method.

I'd be interested to know what your CNS clock ends up on at the end of the dive with a 90m start on PPO2@1.5? Not sure I'd be too keen to run it that high that early.

When I dived the Britannic we had to make air-breaks. It was the team plan. I did that, and also took the chance to drink. If you believe in breaks this keeps your CNS down - for me it just meant humping another cylinder. That was the last time I did breaks (2008). Since then I run the clock to 200% and if I want to have it lower would do a dil flush and keep SP at 0.4 for 5 mins.

25 mins, 130m, GF15/85, 6/72 1.3->1.5 last stop 6m: 220%. There's no utopia below 100mm just risk management.

Cheers
Matt.

 

[JONT]

^^^^

What he said.

One offboard manual add valve on the rig and a quick disconnect hose on every bottle and you'll be golden.

NEVER have a gas on a BOV that you cannot breathe from at the depth where you are. That means normoxic gas at the surface. And unless you like to climb ladders with a stage bottle attached that means normoxic inboard and a system to switch BOV gas.

Should I post yet another link to the YouTube video of my symposium presentation? It may not be all correct and there's plenty of room for other ideas but it will raise a lot of discussion for you to consider.




Dave


.

What John Katerenchuk and Dave S. said, here's what you do:

put M&J's on every bail out second stage you have and an M&J male on the pipe in to your RB, use a lower 02 mix for the deep stuff and plumb in, you don't want to pipe in 100% 02 at depth.

The benefit of the M&J's is that is a second stage fails you can switch seconds under water between cylinders.

I've had to do this just once and its nice to have options.

Jon

 

[DeepUnderground]

That's a lot of extra connectors and failure points IMO

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[matt]

That's a lot of extra connectors and failure points IMO

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That's my view too. Makes everything complicated IMHO. But if it works and your happy, then that's OK!

Matt.

 

[JONT]

That's a lot of extra connectors and failure points IMO

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Thats what I thought until I did it, what it actually does is give you options that are simple and affective:

You have your RB with ONE way to pipe in off board to the loop (M&J), 2 ways are not needed.

Now all stages and drop cylinders have M&J's at the seconds, so every bottle you have can be plumbed into the RB and every second can be swapped if one fails and you can remove EVERY second for every bottle you leave in a cave so no one will F*** with it.......lots of options.

Last week one second on a 80 popped while I was scootering into devils eye, with one hand I popped it off and didnt let off the trigger, went to the sign, looked at it, made an adjustment and it was fixed, swapped both seconds for good measure and continued to dive.

Options are nice but yes you do need to check the connections and that takes 5 minutes for 4 stages......time well spent.

 

[GaryL]

...

 

[dwaynej]

If I can ever *ever* get another Cis Lunar switch block to put on my Meg, I'd have the perfect rebreather. After I stuck the Cis waterproof scrubber into it...

How many positions does the Cis Lunar gas block have? From your picture it looks like it was built for a space suit. Are they hard to find???

Just putting it out there, what do you think about using a double or triple block on your left shoulder dedicated to dil with the "O2" position dedicated to rich dil?

 

[gallathan]

thought.s

Perhaps it depends on ccr you're using (MCCR / ECCR / ADV flow rate). Using dil like 6/70, with an inspo vison and/or golem gear ADV's, the solenoid will EASILY keep the PPO2 at a reasonable level @ the surface...
If you get that much of an ADV leak, then the buoyancy means you're not going anywhere except staying on the surface, and dive should be abandoned...

Perhaps LONG / difficult surface swims / long initially shallow cave entrance(s), followed by deep / hypoxic dil dives might make me consider switching dils, but thats a pretty rare combo...
Even then I'd probably just use an OC stage of Air/EAN32 and leave RB unaltered...

I have an O2 rig with 2 cells and revodream, which lets me more easily see how effective flushes really are... NO single flush will evacuate ALL the loop gas, not even 3+ flushes, let alone just switching dil with minimal flushing @ some depth - so you're basically doing a dive with best guess loop content, and therefore best guess deco calcs, and/or increasing risk of narcosis @ depth, not good risk management...

I dont like BOV's deep, WOB concerns, multiple gas mix switches a pain, single point of failure etc.
I get the concern about unbreathable gas in BOV - why not loose the BOV?
I don't like flow stop(s) either (look at number of O rings/joints), and I've seen too many user error(s)... Simpler to have dil hose pluggable...

Personally, I'd wager that odds of ADV leak, etc are (much less) likely than diver/operator error.

If the dives aim is to minimise risk, and the biggest risk is probably the operator, surely KISS / eliminating manual / potential mistake points is the way to go...
So, single dil, NO switching at all for me.
Also minimises IBCD risk on bigger dives - type III / vestibular hits would be nasty to manage in water - not worth the risk in my book for a little less deco...
For high CNS clock dives, I do OC air breaks (risk minimisation), my experience was that switching loop to lower set point wasted a lot of gas on flushing/evacuating loop, and you can't switch to as low a ppo2 on the break as you can OC...

YMMV / personal thoughts / interesting discussion