Why should I bother to dive a rebreather?
It's a question I get quite often from people, especially the old open circuit hold outs. The comments, though different in delivery, often boil down to 5 arguments.
Look, I’m not going to deny that these aren't valid points raised. What I want to do, however, is clear things up so YOU can decide for yourself.
1. "I've been doing these dives on open circuit for years"
And that's great; nobody denies that many closed circuit dives could be done on open circuit as well. Sure, if your plan is to do a single 45 minute lobster dive to 40' once or twice a month then maybe a rebreather is overkill. But lets look at where closed circuit really shines even for the same dives. Logistics.
If you're looking into spending the time and effort to move to closed circuit, chances are you're more than a casual vacation diver. You might travel for the sole purpose of diving. Multiple days, multiple dives, multiple bottles. Now think about all those sets of doubles and stage bottles you plan on wrangling and filling throughout the entire trip. Cut to closed circuit. I fill my bailout bottles before I leave (that is if they're not already filled which they generally are). I fill up 4 sets of small rebreather bottles, Oxygen and Diluent, stick them in a milk crate, and I’m off and covered for the first 4 days. I don't have to step foot in a shop or spend my evenings running around getting fills. I'm done.
I've also cut down on spinal damage from hauling doubles in and out of the car as well as future suspension damage from fitting me and my friend's 8 sets of doubles, plus assorted stage bottles, into a truck whose bumper is now dragging behind us, showering I-95 in a beautiful rainbow of sparks.
These advantages only get better the more remote the dive site, especially on overnighters on boats (see photo below).
2. "It's too much work"
You spend most waking moments thinking about it.
You once selectively heard "narcosis" spoken at a table across a crowded restaurant and spent the rest of the night casually glancing in that direction, secretly hoping that person is accurately portraying said physiological phenomenon to their doe eyed non-diver friends.
You wouldn't think twice about driving 17 hours straight in order to squeeze in one more quick 3 hour cave dive.
You, like me, are a hopeless diver.
You've probably spent countless time driving ludicrous distances at ungodly hours for a chance to get your fix. Maybe it was a wreck, maybe it was a cave, and maybe it was an old car someone rolled into a river back in the 60's. Whatever it was one thing was certain; there was never enough time when you finally got there.
What Closed Circuit can offer you is more time where you want it the most.
When we think about just how much of it we spend to get to the dive (fills, driving, gear prep, driving, flying, driving, boat loading, boat trip, driving, etc. (driving)) why wouldn't we do everything we can to tip the ratio of time we spend getting there in favor of the time we spend actually diving?! It's what rebreathers were made for. Listen, I recognize that there have been some truly amazing and long dives done on open circuit. Let me give an example of a dive that shows you why I'd rather be on a rebreather.
So I’m in Bonaire. I've got my camera, an empty memory card and full batteries. I put on my rebreather, strap on a single aluminum 40 for bailout, and decide I want to do a long shore dive.
I've been down for an hour now when suddenly I spot something. The rare and elusive Jaguar Shark. It's only ever been captured on film once. But wait, what is this? She's giving birth! Hello National Geographic! Thankfully I’m on closed circuit and I spend the next three hours filling up my memory card.
Now lets think about if I were on open circuit...
A 4 hour dive in warm water to 50' can be easily done using my rEvo Rebreather's standard small 23cuft bottles and carrying only a single 40cuft bottle for bailout (a small commonly used tank for bailout). The same dive on open circuit would require 369cuft of gas! That's almost 5 standard aluminum 80cuft bottles. I don't know many people who would agree that a set of double 80's and three 80cuft stage bottles is their common setup for a 50' shore dive. Again, it's about time and flexibility.
Now I realize that this is an extreme example but it illustrates a point. But it doesn't have to be extreme to show the benefits.
For me, most of my dives are spent wreck diving in the North East United States (Long Island, NY specifically) off of our dive charter Tempest. My core dives are mostly in the 100-130' range with deeper dives mixed in throughout the season. One of my favorite dives is the 504' long World War 1 armored cruiser, the USS San Diego (or just Diego as the bearded salts of wreck diving lore call it, ok maybe it's just me).
The Diego sits in 110' with relief up to the 70' range. Towards the warmer part of the season it's not at all uncommon for us to do 2+ hour bottom times on our rebreathers. This is a dive easily done with two comfortably sidemounted bailout cylinders (one with nitrox the other 100% O2). This doesn't even take into account the ability to share bailout gas between team members either; this is a totally self-sufficient rebreather diver carrying enough bailout gas to get them out of the water by themselves.
The same dive on open circuit would require over 400 cuft of nitrox (not even including reserve gas), as well as a deco bottle of O2. If you'd like we can knock that bottom gas requirement down to 380cuft by adding a bottle of 50% nitrox as well.
Not only do we get more time on the bottom, but we also come back to our logistics benefits.
You see, for dives in these ranges with relatively shorter and shallower decompression we have one huge advantage over open circuit divers...
A closed circuit diver only has to carry enough bailout to end the dive and safely get them to the surface.
An open circuit diver must carry this as well as enough open circuit gas to complete the deepest bottom portion of the dive as well as a reserve for their team mate (or themselves if they are solo diving).
It should also be mentioned that the deeper we go the more a rebreather shines as our open circuit gas requirements skyrocket (not to mention our gas fill prices, but we'll get to that).
So with all this in mind what are these people saying is too much work?
It's pre/post dive maintenance.
Oh, that must take hours and hours then for it to not be worth it?!
The prep and breakdown time of a rebreather (maybe 30-60 mins on average) is nothing compared to the benefit of more bottom time that we in turn receive. It's takes me longer to get to the boat than it does to work on my rebreather! When you weight it against how much time we spend doing everything else besides actually diving it's becomes a non-issue.
In Part 2 I’ll address the other common arguments some people make against closed circuit...
Live Here. Dive Here.
-Capt Tom McCarthy
East Coast Wreck Diving
IANTD rEvo Instructor