Dolphin Limiting Factors

[WartedEmperor]

Drager Dolphin

0 to 17 msw 125 min with 60% O2 and 40% N2
• 0 to 22 msw 95 min with 50% O2 and 50% N2
• 0 to 30 msw 67 min with 40% O2 and 60% N2
• 0 to 40 msw 47 min with 32% O2 and 68% N2

What is limiting the bottom time for these times? Is it the scrubber or the tank size?

If it is the tank size and I put a bigger tank on it what is the biggest size i could put on?

What is the scrubber duration?

 

[Thalassamania]

I only used it for a weekend and that must have been 10 years ago, but if memory serves: the Dolphin scrubber is rated for 3 hrs.

 

[DA Aquamaster]

It has also been several years since I took a dolphin course, but the limiting factor is the tank size and the higher flow of gas through the lower nitrox orifices at depth. Its one of the downsides of an SCR.

Back then many divers converted them to CCR operation and at the same time used larger tanks.

 

[Thalassamania]

You got a course? I'm jealous ... I got a manual.

 

[WartedEmperor]

No not yet.
Does the scrubber duration change with depth?

Also If I put a bigger tank on the Dolphin what is the max time I could get out of this unit? Also what is the size tank I would need to do this?

 

[Thalassamania]

Scrubbers are independent of depth, their duration is a function of CO2 production and temperature. The Dolphin scrubber is rated at 3 hours, that's depth independent. If you're willing to push it to the limit and have found a way to carry enough gas ... you can get 3 hours.

 

[WartedEmperor]

How much gas would i need to push the duration to 3 hours using the 32 flow?

I just found this site and they say the scrubber is good for 4 hours.
http://www.sidneydivensurf.com/articles/archive/rebreather.htm

 

[Thalassamania]

The Dolphin has 27 cubic ft of gas, if you use 32%, that should last 47 minutes. So to have enough gas that the scruber becomes the limiting factor (and I should note that this is not a good idea) you'd need about 88 cubic feet of gas. I've seen folks with Dolphins using old Aluminum 50s and even 65s mounted under the fairing. Other cylinders are too long and have to mounted vertically.

But remember ... you ain't got the OTUs for a 3 hour dive to 130FSW!!!!!

 

[WartedEmperor]

So do you think the best size tank is the one that comes with it then?

 

[scubanimal]

This questions causes me a bit of concern. Your dolphin course should have given you the formula's to figure this out.

But to answer your question, I used an alum 50 cu in tank when getting fills was tough, or if able just changed out the 27/28 cu ft tanks between dives. The oriffice size determines how long a tank will last. Your NDL and OTU loading will factor in when determining your bottom time. These units are great for the 60-100 ft range dives, depths beyond that a CCR is generally considered a better tool.

Please do get training before using your unit. While they appear easy to use (and they are) there are areas that you need to have good procedures and a fair amount of knowledge. There are several good instructors there on the east coast.