Hey Rebreather folks

[Hoosier]

I finally tired the a semi closed Drager Dolphin one yesterady. I can say it provided very silent dive, but it was a harder to breath than the ordinary regulator. Is it a normal symtom on every rebreather or only in this particular brand? I never tried CCR so that I can't comapre it though.

In addition, it was a kind of heavy to me.like the double set up. I am not sure how much weight it used to be..

Thanks in advance,

[wedivebc]

I finally tired the a semi closed Drager Dolphin one yesterady. I can say it provided very silent dive, but it was a harder to breathe than the ordinary regulator. Is it a normal symtom on every rebreather or only in this particular brand? I never tried CCR so that I can't comapre it though.

In addition, it was a kind of heavy to me.like the double set up. I am not sure how much weight it used to be..

Thanks in advance,

Rebreather diving takes some getting used to. You will find your respiration rate is more like when breathing on land. When breathing normally we take in about 10-16 breaths per minute yet when diving OC we breath slower, like 5-8 breaths per minute. Well rebreather divers usually breath at the higher rate because it does not matter how often we breath. Gas consumption does not change.
The dolphin has a pretty good WOB compared to some units although I am told over-shoulder CLs like the inspiration or the megaladon are better suited to different positions.

[caveseeker7]

... Drager Dolphin ... was a harder to breathe than the ordinary regulator.
Is it a normal symtom on every rebreather or only in this particular brand?

Hoosier,

the WOB on rebreather varies as it does on OC regulators.
There are a variety of factors that influence the WOB such as diameter of the gas path, design of the scrubber, scrubbing media (mesh size) etc. Among them are hydrostatic differences due to the distance/difference of the diver's lung and the counterlung in the water columm.

On RBs with back mounted counterlungs inhalation effort tends to be higher, exhalation effort lower, given all else being the same. On front mounted CL rigs like many O2 CCRs it's the opposite. The least difference is in over-the-shoulder mounted CL like the Inspiration, PRISM, Meg etc. Front and back mounted CL rigs usually have a sweet spot where the lungs of the diver and rig are on the same level and hydrostatics don't cause increased resistance.

Another factor on cmf-SCRs like the Dolphin is that the CL frequently are full in order to purge gas, which means you have to overcome the OPV's cracking pressure, too.
That's quite different with mixed gas CCR where you try to achieve minimal CL volume.

Having spend some time on an Atlantis, having had the Dophin, Inspiration and MK16 in the pool and having deceided on the PRISM I can tell you either of the o-t-s configured CL breathes considerably better than either of the back mounted ones.

As for the weight, Dolphins are fairly light but require a second tank for bailout and inflation, and the before mentioned full loop tends to add some extra bouyancy compared to CCRs. Depending on the size of the twins you used to dive it should still save you some weight unless you count the lead.

[gkndivebum]

I find the WOB on the Dolphin pretty high. The Ray, with OTS counterlungs has much better
WOB. Same goes for the PRISM ... (and I assume the Meg and Inspiration, though I've not had
the opportunity to dive either one)

[BigJetDriver]

GKN, et al,

Work of breathing is, in most cases, just that of normal breathing effort with modern over-the-shoulder (OTS) counter-lungs (CL's); i.e. Prism, Inspiration, Megalodon, and so on.

The older back-mounted counter-lungs, depending upon body position in the water column, will have issues with hydrostatic loading; i.e. chipmunk cheeks, or sucking for air.

From Caveseeker7's post:
"On RBs with back mounted counterlungs inhalation effort tends to be higher, exhalation effort lower, given all else being the same. On front mounted CL rigs like many O2 CCRs it's the opposite. The least difference is in over-the-shoulder mounted CL like the Inspiration, PRISM, Meg etc. Front and back mounted CL rigs usually have a sweet spot where the lungs of the diver and rig are on the same level and hydrostatics don't cause increased resistance."


Cheers!

[scubanimal]

My first dives with the dolphin were similar, enough that it took me a long time to take the plunge. I can say that since purchasing my unit last month I've done 11 dives and I find it now to be very natural and I don't feel like I'm working harder than I did on my Atomic reg. As mentioned above, your position in the water will significantly affect the work of breathing (WOB). It is lousy when your face up, and I don't care for it when heads up vertical. 15-20 degrees heads up or down works best for me, and straight down which I use a lot for photo is now easier than I when I was using OC. Also how high the unit is on your back will affect WOB as well.

I can say that I really like it now. I too was disappointed in the weight, but when I added it up, it is actually less than my normal rig. I think it feels heavier because BC on the Dolphin does not distribute the weight as well as others.

[Pawel]

Stefan pretty much covered it. All I wanted to add is that inhale resistance is generally more important than exhale. Our lung muscles are built to blow rather than suck for some reason :eyebrow: This is why front and o-t-s counterlungs usually work better than back mounted, all other things being equal. In a back mounted SCR you need an exact amount of positive pressure for hydrostatic inhale resistance to be at the minimum.
I have never dived a Dolphin, but from my Azimuth (back clounterlung SCR) experience I know it can be adjusted to work effortlesly in vertical, face down position and anything in between. On that unit I found that about 12mBar OPV cracking pressure works best for me. This is equivalent to about 12cm of water column, which is about the depth difference between the OPV valve and the lungs. In belly up position it is obviously not much good because it has an opposite effect (positive pressure in your mouth). I am not sure if Drager supplies a calibration manometer, but it is worth tunning it up correctly (if it is hard to inhale, tighten up the OPV spring).

Cheers,

Pawel

[caveseeker7]

No such niceties from Dräger. ;)

Cool pics in the gallery, the Caimano looks like a sleek little unit.
Are the Castoro CCRs about the same size (plus O2 tank in the back)?

Lots of camera you're pushing there. Another cool shot.
Thannks for posting those.

Stefan

[Pawel]

No such niceties from Dräger. ;)

Cool pics in the gallery, the Caimano looks like a sleek little unit.
Are the Castoro CCRs about the same size (plus O2 tank in the back)?

Lots of camera you're pushing there. Another cool shot.
Thannks for posting those.

Stefan
Greetings Stefan,

You are correct, Castoro is exactly the same size and most of the parts are interchangable. Yes, I love Caimano MK4, it just costs as much as good car, but don't mention this to the misses.
The shot with camera was taken by Errol in January this year. He was testing his latest'n'gratest Abyss on this dive and I was trying not to lose the seadragon from my sight. I guess the worst rb buddy combination I can think of ;) It was fun.
Re HD Camera, now you know why I want a small and capable breather.

Cheers,

Pawel

[caveseeker7]

Re HD Camera, now you know why I want a small and capable breather.

Small? Small is for sissies!
You need bigger (http://www.howardhall.com/stories/coralreef.html) ! ;)
Just kidding, good to read your feedback on TDS.
Cheers
Stefan

[Pawel]

Small? Small is for sissies!

:D

[Hoosier]

Thanks for many inputs.

Of course, after getting used to the new unit, I am sure that it will be much easier to breath. Otherwise, who is using this brand rebreather out there J It was just my first impression after trying it out. But, it was a good try to have some sense of the new equipment.

Regarding the weight, the tank that is mounted on the left side for the inflation was kind of weird.

I think it caused me to feel the some unbalanced problem underwater. I also felt some drags while I was swimming in the pool.

Like you see, I am totally newbie in the rebreather world. But, I will definitely be in this area in future.