Hello from SoCal / Dolphin, PO2-Mon, Oxygauge

cepheus

Hey Guys,

New to Rebreather's Worls and Rebreather in General and somewhat playing with the thought of getting a Dolphin.

I've read a lot of articles in here about the Drager Dolphin and Rebreather in general, have a couple of unanswered questions though..

1. What's the deal with the Oxygauge?
I read a lot it's bad and evil but what exactly is wrong with it. Would you remove it if existing on a used dolphin?

2. How important is PO2 monitoring on a SCR like the dolphin?
Have there been actual incidents or even fatalities? Or is it just good rebreather diving practice? I mean what are you gonna do if the PO2 Monitor shows you bad numbers? There is not much to set or do other than flee to the surface...

3. In recreational diving, what's the main disadvantage of a dolphin compared to a CCR? Dive Time? Is the dive time not gonna be limited through NDL anyway over the scrubber / air times? What does one realisticly get out of a dolphin in a safe manner?

Thomas



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Many people would sooner die than think; In fact, they do so.
- Bertrand Russell

Dsix36

Sooooo many questions. I will give this a crack though.

1. The Oxyguage is not bad or evil. It just is not reliable enough since it only reads PO2 from one sensor. What happens if the sensor is bad and giving a false reading? There are no other sensors to compare the readings to and your PO2 can be anywhere (death comes to mind - if an orifice is plugged and the loop goes hypoxic on you). It is still better than having no means of monitoring you PO2 at all though.

2. PO2 monitoring is the difference between life and death - even on a SCR like the dolphin. Yes there have been incidents (some by me even) but that still does not change the golden rule of Rebreather diving "Know Thine PO2".If your monitor show bad PO2, simply bailout to OC and ascend normally. Do not bum rush the surface.

3. In recreational limits diving the only concernable disadvantage of an SCR vs. a CCR is the bubbles from the Over Pressure Valve venting the loop. The Dolphin will extend your NDL bottom times, but it will depth limit you according to the mix in your tank. The interaction with marine life is more abundant and easier to achieve. Big improvement for photography, obviously not as great as with CCR though.

I hope this helps and has answered a few of your questions.

__________________
THE MORE THAT I LEARN, THE MORE THAT I STILL NEED TO LEARN!!!!!!

firemandiver

Hey Guys,

New to Rebreather's Worls and Rebreather in General and somewhat playing with the thought of getting a Dolphin.

I've read a lot of articles in here about the Drager Dolphin and Rebreather in general, have a couple of unanswered questions though..

1. What's the deal with the Oxygauge?
I read a lot it's bad and evil but what exactly is wrong with it. Would you remove it if existing on a used dolphin?

2. How important is PO2 monitoring on a SCR like the dolphin?
Have there been actual incidents or even fatalities? Or is it just good rebreather diving practice? I mean what are you gonna do if the PO2 Monitor shows you bad numbers? There is not much to set or do other than flee to the surface...

3. In recreational diving, what's the main disadvantage of a dolphin compared to a CCR? Dive Time? Is the dive time not gonna be limited through NDL anyway over the scrubber / air times? What does one realisticly get out of a dolphin in a safe manner?

Thomas



OK, I'll give it a go too.

1) The Oxyguage is prone to leaking around the p-port seal. This floods the bag and also ruins the sensor in most cases. It can get very expensive to keep replacing sensors. Also the Oxyguage only monitors with a single sensor in the mix bag. This isn't as accurate a reading as a system that monitors the loop. It is better than no monitoring, but definitely has it's drawbacks.

2) Absolutely have some type of monitoring. You can dive the unit with no electronics, but you must dive it exactly as it was designed. The mix for depth must be followed correctly. Even so, eveyone is different, and the metabolic rate varies from diver to diver. A young, small, fit diver will likely have a better metabolism than a older, large, pudgy diver. Therefore the consumption rates will be at opposite ends of the spectrum. If you fall in the middle, you could probably dive it all day without issue, as long as you follow the rules. The issue is, that it will only be a matter of time before you start pushing the limits. You may want to go a little bit deeper than the particular jet is designed for, or go a little leaner on the mix for a lower PO2. Without monitoring, you have no accurate way to know your true numbers. With monitoring you can see what your actual mix, VO2, and consumption is and tweak your profile to get the most out of the unit. That being said, you still must have a very good understanding of nitrox, the unit itself, and how the changes will affect the whole thing. Although they're reasonably safe when used properly, a rebreather can and will kill you if you dont do it right. Yes there have been poeple killed from doing it wrong.

As for you concern about what would you do if you get bad numbers? There are several corrective actions you can take while underwater. If, for example, you see that your PO2 is rising, or getting close to the limit, you would ascend a bit to counter the increase in PO2. You can also use the information from your monitoring system to see what your actual rates are. If you see that you are exerting too much effort, you can relax and get your numbers back in line. Without some type of monitoring, you can't do this.

3)Advantage/Disadvantages:

There are many pages on the site about this very issue. I'll leave that up to you to dig up. I will give you my personal experience. Keep in mind that this is my personal opinion, not Drager's reccommendations.

Accoriding to the "rules", all recreational and standard nitrox limits apply. However, anyone who has been using the Dolphin for any time will tell you that you can fudge a lilttle. ( that's why you need electronics! ) Exactly how much you are willing to push it is a personal choice. I don't do anything I'm not 100% comfortable with.

The scrubber time for a properly packed canister is 180 minutes. I use AL27's for my supply gas. I get two 30-40 minute dives from each tank. A little less time if I go real deep, more if I stay shallow, but that's a good average. That leaves a little in reserve in case of heavy work load. I always carrry three tanks when I go diving, and only use two. I normally dive in the 50-150 range. I have bounced to 170ft or so for a shot on a fish, but I never stay very long at that depth. I never go beyond 2.5 hrs on the scrubber. This, in my mind, is a little safety net. Basically I can dive all day, 4-5 dives, with one scrubber fill and two tanks. That's usually about all I can get in with surface intervals and travel time.

I couldn't maximize my dive time without the monitoring. But as I said, you must know without a doubt how the changes you make are going to play out on the dive(s). If you choose to bend the rules a little, you have to be very careful how far, cause it can be a bit risky. I'm sure others will have similar thoughts on the subject.

I hope I was able to provide a little insight on your questions. If you'd like, check my previous posts for some info on monitoring choices and the pros and cons.

Dive safe! FD

cepheus

Hey Guys,


Thanks for your replies.
Helped me a lot.


Thomas


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