Rebreathers, Partially closed or fully closed?

[landfish]

just a dumb question for you.
Have you dove the dolphin much?
the reason i ask is i dont understand you answer?
below is a program i use.
you can also do the math and figure the same deal out
my metabolic rate is .7 so i plan my dive on .8 in this paticular case 26 percent would be my bag gas.like i posted no you dont get the benifits of the ccr with this unit but i have dove at 150 feet for 60 mins and used 900 pds of gas out of a 65 steal tank.
now do the same dive with doubles on your back and figure out how much gas you would have used and how much extra weight you have carried.
yes my deco time was a little longer then if i was using the optimum mix but the water temp on the hang was close to 70 degrees so it was fine by me.(i would rather be under water then ontop anyday even if it is hanging) exception to that rule is if the hang water temp is below 50 degrees!
anyway the point of all this jibber jabber is the dreager can be used beyond the recreational limit.the only mods. that was done is i use a 65 steal tank with a h valve for redundant air supply and i also have a 13 mounted on the side for suit air and alternative air source.
once again would like to hear all opinions on this
thanks
Flow rate O2 tank gas N2 Depth

5.7 36.00% 64.00% 150


VO2 O2 N2 PPO2

0.5 29.85% 70.15% 1.66
0.6 28.47% 71.53% 1.58
0.7 27.04% 72.96% 1.50
0.8 25.55% 74.45% 1.42
1 22.38% 77.62% 1.24
1.25 18.02% 81.98% 1.00
1.5 13.14% 86.86% 0.73

 

[caveseeker7]

I have a question here.
Why do some say the dreager dolphin can or should only be used for recreational diving?
...you can dive at 100 feet or 200 feet...

Landfish, the Dolphin can certainly be used for extended range diving, the extended being either depth, dive time or both. If you consider recreational diving to 130ft. max and no decompression, the Dolphin can certainly exceed that.

Padiscubapro gave the (I thought quite understandable) technical reason why. The other one being the design as sold.

The Dolphin was designed as a recreational unit, to be used within those limits (certainly as far as depth is concerned). Yes, as the actual mix depends on your metabolism, you can take the unit a bit deeper than the depth/mix rating. Yes, it does extend your gas quite a bit, but in the rebreather realm the least bit. A passive addition SCR is considerably more efficient, with less variation in the loop. A CCR is more efficient yet, with huge variations in the loop to deliver a constant ppO2.

So how do you dive your Dolphin at 200 ft.? With the 26% Nitrox you end up having in the loop your ppO2 would be over 1.8. So that's probably not it. Of course I'm aware some people dive He mixes in their Dolphin, but that is pretty much trial & error until you figurd it out, and you end up needing good and redundant ppO2 monitoring.

Dräger engineers in the past supported dive expeditions that went past 40m, both with parts and know-how. If the company considered the Dolphin a good tool to do so they would either offer the '80m Dolphin' (which was supposedly on the planning board at one point), or sell a kit to convert one. Like they offer kits to add 32% and 100% nozzles and the Oxygauge. If Dräger wanted them, or a civillian SCR, to be used deeper or longer, they could do better than current issue. Such as on the fly adjustment of flow rate, gas switch blocks with multiple flow rates etc. ... .

 

[padiscubapro]

just a dumb question for you.
Have you dove the dolphin much?
the reason i ask is i dont understand you answer?
below is a program i use.
you can also do the math and figure the same deal out
my metabolic rate is .7 so i plan my dive on .8 in this paticular case 26 percent would be my bag gas.like i posted no you dont get the benifits of the ccr with this unit but i have dove at 150 feet for 60 mins and used 900 pds of gas out of a 65 steal tank.
now do the same dive with doubles on your back and figure out how much gas you would have used and how much extra weight you have carried.
yes my deco time was a little longer then if i was using the optimum mix but the water temp on the hang was close to 70 degrees so it was fine by me.(i would rather be under water then ontop anyday even if it is hanging) exception to that rule is if the hang water temp is below 50 degrees!
anyway the point of all this jibber jabber is the dreager can be used beyond the recreational limit.the only mods. that was done is i use a 65 steal tank with a h valve for redundant air supply and i also have a 13 mounted on the side for suit air and alternative air source.
once again would like to hear all opinions on this
thanks
Flow rate O2 tank gas N2 Depth

5.7 36.00% 64.00% 150


VO2 O2 N2 PPO2

0.5 29.85% 70.15% 1.66
0.6 28.47% 71.53% 1.58
0.7 27.04% 72.96% 1.50
0.8 25.55% 74.45% 1.42
1 22.38% 77.62% 1.24
1.25 18.02% 81.98% 1.00
1.5 13.14% 86.86% 0.73

first..
You should NEVER dive deeper than the MOD of the gas PERIOD! Doing so increases risks.. (if you are forced to breath a significant volum of gas right out of the supply gas you now have a very high po2, for example you did a mask clear that used a significant amount of gas - instead of a "bubbleless" mask clear). I agree you can play with all kinds if flow rates to get a target mix but now its Highly dependent on your workload and metabolism.. If you are not consuming oxygen as rapidly as you expect the po2 is higher than you want the converse is true. about the only time you are going to consume a .5 is at rest.. most divers will consume somewhere between .8 and 1.25. Now assuming you get the right mix for depth, the unit becomes hypoxic in the shallows, on top of that if you get into deco you want the richest mix possible not the leanest...
The kind of statement "just hang a little longer" tells me you really don't understand what is going on in your body at this point. You ARE offgassing the compartments that are preventing you from going to the surface BUT you are ONGASING the slower tissure compartments which are the compartments you want to have the least loading. These are the compartments that can withstand the least "bubbling" and cause moost pain type hits. The use of rich oxygen mixes in the sahllows accelerates offgassing but either slows or prevents ongasing of the slower compartments.

Too many people trust various computer program outputs or blindly aplly formulas without reasoning the consequences.
A point for you to think about.. say you have 25% in your tank and you or fighting a nasty current on either ascent or descent (especially 20ft or shallower) work that same mix at these depths with a vo2 or 1.5 to 2.0 (not unreasonable for short runs, can be even higher).. see what your po2 is now... Also you have to complete you ascent to the surface, its still dropping.. What about nasty surface conditions with current?? Your probably not carrying a snorkel (if you did it could be useless if conditions are bas enough) so you have to stay on the loop while swimming hard?? Are you still conscious. You must always plan for the worse case scenario, otherwise one day murphy will come back an bite you in the a**. Not planning for the worse is a stupid habit to get into.

There are many people playing with custom flow rates and tweeking the mix, if you do this you better have some type of PO2 guage.. I know more than one person who has been surprised how off a target can be..

If someone is going to dive a dolphin deep the way to correctly do it is either plan the shallow portion as an open circuit dive and make the proper mix for the deep portion, or have multiple mixes on a manifold.. If you use multiple mixes you do have to flush the loop (exhale the gas through the nose and pull in fresh gas through the demand valve)to get it on target...

 

[Otter]

Now I know why I am reading Mastering Rebreathers FIRST.

 

[landfish]

I have to clear a thing or two up here the statement of hanging a bit longer is just the way i say things.
i left out the part that i carry a 80 percent 02 deco tank with me and during decompression i use that. starting at 30 feet,i believe on that dive the first stop was at 50 feet (sorry for telling the whole story)
the reason for say hang longer is i was comparing if i went to 150 feet like i said with a ccr the pp02 would be much more effiecent then what i am doing with the dreager.
so that is why i would be "hanging longer" then if i was using a ccr
i never said i took that example to 200 feet did i? that was for a 150 foot dive which i remained at 145 to 150 during the dive nad yes i use a has explorer to track my pp02.
i plan my deco on .8 i stated that i am a .7 actualy i am between the .6 and .7.
yes figthing a currect or working hard on a dive i have seen a .9 out of me.
I carry on a slate back up plans just for that reason.my niteck is and was set for that gas on the dive. if it was a hard working dive where i went over my planed po2 at any given time, i would ignore my computer and go to my slate and hang longer then planned.
i hope this explains?

 

[padiscubapro]

Flow rate O2 tank gas N2 Depth

5.7 36.00% 64.00% 150

SOMETHING ELSE i FORGOT TO MENTION IN THE PREVIOUS RESPONSE..

At 36% I hope not just for covering a gas loss but for PO2 concerns you are carrying some type of bailout bottle other than your primary gas.. 36% at 150 is almost a 2.0 po2.. this is ok as long as you can IMMEDIATELY start an ascent as soon as you get on it as open circuit. You now have to get up about 50 feet for it to be a reasonable mix to breath.. If an immediate ascent cant be done (like having to swim to an upline or out of an ovehead)You MUST have another bottle with a truely breathable mix.

 

[landfish]

yes i do carry a redundant air supply like i posted in the first post on this thread.
2 to be exact plus my deco bottle
i have a 13 bottle on the side of the dreager (.21) that i use to fill my suit and in the event my 65 tank that has a h valve on it with another first and second stage for my bail out fail or i am to deep to go on the gas that is in the 65 i would use the 13 till i got to the depth i could use the 36 (that was in the tank for that dive)
if something happens to the rebreather i can go to bail out on my 65 and shut the valve off to the rebreather and use the reaming gas to get me to surface
and yes if i have deco i would do the deco!
now if i hope i cleared this up if not i will try to explain
but like i posted i dont understand why anyone would think you could not use the scr for diving like this?
remember they say oc should never be used for anymore then 130 feet to!
what does inspiration tell you?

 

[padiscubapro]

yes i do carry a redundant air supply like i posted in the first post on this thread.
2 to be exact plus my deco bottle
i have a 13 bottle on the side of the dreager (.21) that i use to fill my suit and in the event my 65 tank that has a h valve on it with another first and second stage for my bail out fail or i am to deep to go on the gas that is in the 65 i would use the 13 till i got to the depth i could use the 36 (that was in the tank for that dive)
if something happens to the rebreather i can go to bail out on my 65 and shut the valve off to the rebreather and use the reaming gas to get me to surface
and yes if i have deco i would do the deco!
now if i hope i cleared this up if not i will try to explain
but like i posted i dont understand why anyone would think you could not use the scr for diving like this?
remember they say oc should never be used for anymore then 130 feet to!
what does inspiration tell you?

I must have been editing my message while you posed the previous response..

You are diving the drager outside its "normal" mode of operation. You are using multiple gases not s single gas that is normally used. This is the proper way to extend the depth use of the drager. There is another caution I must state.. when diving with very low flow rates the chance of a hypoxic mix is increased due to a blocked jet.. Higher flow rates tend not to block as easily and offer more room for error.

The 80% gives you a breathable gas shallow and helps the deco.. Without these changes it would be unsafe to use the drager in the conventional way, without a po2 guage its an accident waiting to happen.

On reasonable length dives there is more than a few minutes differance between a CCR and SCR especially if deep stops are employed. I have nothing against CMF SCRs but I still stand by my opinion they are best when they are used shallow. Passive addition SCRs are better for deeper depth but then again they require more than one mix.

If you are doing these type of dives (and have as much experience as you say) you should definately look into getting some CCR training and turn the drager into a CCR like Ron M. (www.tmishop.com) did or move onto a commercial CCR. I know its the best decision I have ever made...
If you do a CCR mod you could easily switch back and forth between CCR and SCR modes.

If you start going deeper still you'll have to account for the fact that the flow rate shown on your flowmeter will be wrong(actually its already wrong for most mixes (flow meters are typically calibrated for AIR or Oxygen but the error is acceptable) once you put helium in it and will have to use corrective factors to get the actual flow..

 

[landfish]

i have to tell you that you are correct about the low flow rate.
just recently i check the flow getting ready to go diving the night before.while on the dive on noticed my pp02 guage reading was off big time about 20 mins into the dive.
After aborting the dive and when back on the surface i found the 5.7 flow was partialy pluged.I did take it part to cean out but it was not right so i just purchased a new one.
that is a very good point you brought up

 

[padiscubapro]

i have to tell you that you are correct about the low flow rate.
just recently i check the flow getting ready to go diving the night before.while on the dive on noticed my pp02 guage reading was off big time about 20 mins into the dive.
After aborting the dive and when back on the surface i found the 5.7 flow was partialy pluged.I did take it part to cean out but it was not right so i just purchased a new one.
that is a very good point you brought up

The blocked jets are all too much of an occurrance. That why there is now way in hell that I would dive ANY rebreather without some form of loop monitoring. Every RB has some failure mode that can cause the loop to be other than whats planned.. I want to know at all times, so are just more likely than others...

Diluted Vinegar works well to remove all sorts of corrosion, just don't let it sit overnight!