Considering a Rebreather....

[doctormike]

I understand that. I asked questions about such limitations to Leon Scamahorn when he presented at a local dive club. Note, I am not a rebreather diver/owner. Ultimately, there are always limitations due to physics and engineering. Engineering/design sometimes makes a noticeable difference.

OK, maybe it's just a semantic thing, but since non-rebreather divers read these threads, I just wouldn't phrase it like this:

"[my rebreather buddy] also has to ascend/descend slowly. My understand (and I am not a rebreather yet), is that the Meg doesn't have such limitations."

All rebreathers have the same limitations, and while of course engineering makes a difference, some things can't be engineered away. I'm not certified on a Meg, but I'm pretty sure that you can spike your PO2 or become hypoxic on this unit like any other CCR.

Didn't mean to sound snarky, I'm a VERY new rebreather diver!

 

[rjack321]

Rapid ascents and descents are avoided on CCR to prevent hyperoxic spikes or hypoxia on ascent, even on a Meg. Also, overbreathing can result in CO2 breakthrough and hypercapnia (CO2 buildup) if you are moving gas faster than the scrubber can clean it.

Each rebreather has a certain work of breathing, which is usually available both as resistive WOB and hydrodynamic WOB. The Meg has a great reputation, but its a CCR just like all the others, and physics and physiology isn't something that can be changed by design. Also, different units have different breathing characteristics in different orientations.

WOB depends on the CL design relative to lung centroid as well as gas flow dynamics. The Meg only uses front mounted or TOS counterlungs and larger bore loop hoses that can't collapse. (larger than the hammerhead or kiss for instance). So some of the poor characteristics of say a backmounted counterlung and small bore hoses are thus either avoided or designed around. But its large and the counterlungs add bulk in impractical places. Great WOB but trade offs.

 

[rjack321]

For the OP you might want to first develop a list of which units are actually practical for your area. Usually that means at least one other diver has one locally already.

Then decide on the next issues:
mCC, hCCR, or eCCR
front, top of shoulder, or backmounted counterlung
axial or radial scrubber
overall WOB
flood tolerance/acceptance
what can you afford.

Usually these factors (some probably more important that others) are going to drive your choices down to 1 or 2 units. Try those units and pick one. Get trained and start diving it. You will learn what you really like or dislike over time and hours. If something is truly an insurmountable hurdle (unlikely) then sell it and get something else.

 

[doctormike]

The standard business model for getting one's first rebreather seems to be (1) buy a unit after doing some research, and (2) get training on it. An alternative model is to train on a rental unit and then buy one. I opted for the latter.

It's certainly a bit more expensive, but I feel so much better able to consider all of these issues now. No matter how much research you do, it's much harder to understand the tradeoffs if you aren't certified, IMHO.

 

[rjack321]

The standard business model for getting one's first rebreather seems to be (1) buy a unit after doing some research, and (2) get training on it. An alternative model is to train on a rental unit and then buy one. I opted for the latter.

It's certainly a bit more expensive, but I feel so much better able to consider all of these issues now. No matter how much research you do, it's much harder to understand the tradeoffs if you aren't certified, IMHO.

And how would you know about a unit you didn't rent? I very much doubt many people ever rent a unit for a course, decide they hate it, and end up doing a cross-over to a completely different unit without ever buying the original.

 

[doctormike]

And how would you know about a unit you didn't rent? I very much doubt many people ever rent a unit for a course, decide they hate it, and end up doing a cross-over to a completely different unit without ever buying the original.

You wouldn't, but the point is that you would be far more equipped to even ask the appropriate questions about different rebreathers with training. Are you saying that it's better to just buy a unit without being a rebreather diver at all? I mean, that's what most people probably do, and it's certainly cheaper, but the point of my post is that training on a rental unit has value.

I'm about to pull the trigger on buying the JJ because I really did like a lot of things about it, but I considered doing a couple of test flights on other units after training. Those test flights would be worth a lot more than the ones I did before training.

Also, some people might do the training and decide that it isn't for them, which is easier when you haven't already put 10K into the project.

 

[CptTightPants21]

And how would you know about a unit you didn't rent? I very much doubt many people ever rent a unit for a course, decide they hate it, and end up doing a cross-over to a completely different unit without ever buying the original.

I am pretty sure Net Doc was certified on at least one unit before buying his first rebreather (and SF2). Someone can search, there was a very long thread on his experience and reasoning.

 

[JohnnyC]

Read Jeff Bozanic's book "Mastering Rebreathers." Then read it again.

Decide what dives you plan on using it for. If you're already limiting yourself to 40m and light deco, a CCR is not really the best choice. It's expensive for piddling around on a shallow reef or wreck, even an inexpensive used unit like a KISS Classic is gonna be 3 grand. Plus fills, plus sorb, plus training. That's a lot of nitrox and boat rides before you even break even for the cost of the unit and training. Hell, even an SCR is probably overkill, but at least you can get into one for 500 bucks.

Trying to buy a unit before knowing why you want or need a rebreather is gonna get you into an expensive unit that doesn't serve your needs. There's something to be said for buying the unit your friends use, but if that unit isn't the best for your type of diving, it offers no gain. Why do you need a X-CCR with an 8 hour scrubber and 4L tanks when you're going to spend an hour on a reef at 15m? Because your dive buddies have them isn't a good answer.

mCCR vs eCCR vs hCCR is a personal choice, as is ADV, BOV, CL location, and aftermarket electronics. You have to understand what all of these are and the pros and cons to each before you can make a decision on a unit, and you're not going to find that information out without a bunch of forum bias. You need to have an underlying understanding of the physiology, design, and purpose behind all of them before soliciting opinions.

 

[ScubaInChicago]

You should check out the Hollis Explorer, you are the target candidate and the reason it has dominated that market. It fits the bill perfectly, comes turnkey, and is priced accordingly. When you've gotten some hours under your belt, you can easily trade up, or be happy about the benefits your Explorer will give you at a fraction of the cost of an exploration grade rebreather unit. Safe diving

 

[RainPilot]

Divers Down is setting up to be a big rebreather centre here in the UAE, they are focusing on the Optima. Coastal Technical Divers are the go-to for the others, Simon Nadim is an instructor on rEvo, JJ and several other units which he has available for try dives. If you feel like a coffee and a natter about rebreathers and some options here in the UAE, drop me a line and we can chat.