A different kind of modern double hose

[luis]

A different kind of modern double hose.

Below are some pictures from last weekends Boston Sea Rovers rebreather demo.

We got to try 4 different rebreathers, the rEvo, the Dive Rite O2ptima, the Silent Diving Evolution, and the Hollis Prism.

It was a great experience, in particular to be able to try different rebreathers side by side. I have demo/ tried a couple of other different rebreathers, but having the opportunity to try them together was great.

The short class was also very good.


rEvo












Dive Rite O2ptima






Hollis Prism





Silent Diving Evolution



All of the rebreathers underwater:








Note: These are all modern, but I am sure everyone knows that rebreathers do predate open circuit scuba.

[Herman]

Somehow, I don't think the scull on the rebreather was a good idea if you are trying to get people to dive them.
I had an oppertunity to dive one years ago, they are really differnt and well worth the effort if you get a chance to dive one. That said, I just don't feel the hassle and expense is worth the effort for the diving I do.

[Gilldiver]

How was the work of breathing between the models and how was it compared to say a well tuned Mistral or RAM?

[luis]

Three of the rebreathers had over the shoulder counter-lungs. In the rEvo they were back-mounted. The WOB on all four was comparable, except that on the rEvo was not quite as good when I turn over on my back, but it wasn’t bad.

I did like the rEvo for a number of reasons and it performed great in the normal swimming position.

Because of the size of the group, we were not able to spend a lot of time on any of them, to really tell minor differences. But, nothing stood out as a substantial difference in WOB.

As compared to a RAM, it is hard to tell since I did not dive a RAM side by side with them, but my impression is that they were comparable, but in a different way. I do believe that one of my better tuned PRAM or the new Argonaut (placed in the right location) does breathe better, but it would not be a huge difference.

Rebreathers use large hoses, very low resistance mushroom valves, and everything is optimized in the breathing loop, but they don’t have any pneumatic assistance or venturi flow assistance. Therefore, the feeling is not the same. The WOB (or the perceived WOB), I don’t think is substantially different, but the sensations are a bit different.

I would really like to test them side by side against a DH and I may have an opportunity this summer.

[8dust]

Very interesting, thanks for sharing, Luis.

I'd like to try one some day, but I'll confess to being a bit afraid of them and would really need to trust whoever it was that set it up.... esp. if it was off-shore. With any luck there will be a pool-day in my future sometime.

[Gilldiver]

I think I can help do that, want to try it on the U-boat?

Three of the rebreathers had over the shoulder counter-lungs. In the rEvo they were back-mounted. The WOB on all four was comparable, except that on the rEvo was not quite as good when I turn over on my back, but it wasn’t bad.

I did like the rEvo for a number of reasons and it performed great in the normal swimming position.

Because of the size of the group, we were not able to spend a lot of time on any of them, to really tell minor differences. But, nothing stood out as a substantial difference in WOB.

As compared to a RAM, it is hard to tell since I did not dive a RAM side by side with them, but my impression is that they were comparable, but in a different way. I do believe that one of my better tuned PRAM or the new Argonaut (placed in the right location) does breathe better, but it would not be a huge difference.

Rebreathers use large hoses, very low resistance mushroom valves, and everything is optimized in the breathing loop, but they don’t have any pneumatic assistance or venturi flow assistance. Therefore, the feeling is not the same. The WOB (or the perceived WOB), I don’t think is substantially different, but the sensations are a bit different.

I would really like to test them side by side against a DH and I may have an opportunity this summer.

[SurfLung]

- At the Midwest Shipwreck Society show a few weeks ago, there was a fellow who had been diving rebreathers for quite awhile. He was actually on his second one, an "Evo" and spent some time explaining some things:
- For one thing, CO2 and oxygen poisoning are not the only problems you can encounter. He said you have to watch your O2 partial pressure as you come up because if you leave it low as it would be at depth, you will encounter hypoxia and pass out without any warning.
- He said Rebreathers are totally safe, however. And, he explained the redundancy of his multiple sensors and read-outs. He sounded like he was very skilled in everything that can happen as well as what to do if trouble happens. I suppose, like Scuba, know what you are doing and don't panic. But the thing that's different about rebreathers is this problem of passing out without any warning. There's not even a chance for panic to be a problem there... You're just... Gone!?

[Nemrod]

I took a similar class some years back when I was still in Phoenix. Obviously rebreathers have evolved some since then. I also used one about two years ago in the WSU dive pool. But, I just do not think they are at a level of development yet that I would be trusting of. Sure, if I was a twenty something I could see myself working into one because you can go really deep and stay with the things. But, now, I would just kill myself or worse. A steady string of them on scubieboard that are now deceased.

When they get a little more development and a purely recreational unit for scuba depths to say, 150 feet is on the market with cartridge replacement of the chemicals, I may take another look.

Nem

[Gilldiver]

With open gear the question is always "How much gas do I have?" and on deep dives you reach a point where you just can't bring enough. I usually put that point at around 230-250 feet

With rebreathers the question is "What gas do I have?"

Rebreather have their place in deep sub 230 foot diving where the amount of gas you can bring is size limited.

Where time in the water is getting you to the same place (which may or may not mean depth is a factor, I know many cave divers in Mexico who do 2 to 6+ hour dives in only 30-40 feet of water.

Where logistics of the dive favor the compactness of a rebreather over open gear. Take 6 to 8 divers for a 2-3 day deep trip on a boat and the number of tanks needed to support them becomes incredible and very heavy. A rebreather with 2 spare canisters and a max total of 3x30 or 40 O2 bottle and 3x30 or 40 dill bottles (6x40's is way more compact than 3 to 6 sets of 120/130's, 3x 80 of 32% + 3x40 of 100% per diver (12 tanks if you are counting),