Sidemount Rebreather

[kensuf]

So...

If you're just getting into cave diving, I would suggest starting that with open circuit before moving to rebreather. You should also be aware that you'll be required to have at least 50 hours on the rebreather before you can do any cave training with it.

Now in terms of the CCR for research diving. While I understand your concerns about the travel friendly part, I would first check with the DSO at your future destination as to what units are acceptable and the support you can get. You probably don't want to show up at a research facility with a CCR that is not approved for use.

Generally speaking, most DSO's will probably want you on one of three or four different backmount units - AP Inspiration, Hollis Prism, ISC Meg/Tiburon and DiveRite Optima. AP is going to be the most common, but I've worked with scientific divers utilizing the other three units as well. Jason Gulley at USF has been using a sidewinder the past year or two, but he's the minority.

Also, local availability of spares kits, etc should be something you also take into account. If you puncture a counterlung, tear a loop hose, have a cell failure, or have an electronics failure are you staying dry while waiting for parts to arrive from abroad, or do they have spares that can help get you back in the water quickly? If your choice of unit means you're 100% on your own, you'll want to be well stocked on spare parts. I personally bought an AP last summer because I'm going to the far side of the world this summer and everyone else on the trip is bringing an AP, we'll be able to pool our spares this way.

 

[tbone1004]

Question for the more experienced CCR divers: do chestmount rebreathers (Triton, ChOptima) work well in caves, better than backmount and comparible to sidemount rebreathers?s

Some people prefer them. You are actually a taller profile than in backmount when you are moving around but that is rarely an issue in most caves. It has the advantage of being able to unclip it extremely easily to push forward and then you are in a "normal" sidemount profile at least height/width wise. Pros and cons. I don't personally love it, but I have a strong aversion to things on my chest when diving. There are quite a few on the KUR right now and guys are loving them.
The biggest downside to the true sidemounted rebreathers is how limiting they are with how much bailout you can carry. When I sidemount my Kisskat I have a LP121 on the right side, unit on the left with a small dil bottle on it and carrying stages on the CCR side is not the easiest of things. It also requires a major departure from your OC configuration and you can't shed the CCR in the water without going off-balance. Most of my diving with the Kisskat is actually with backmount doubels as dilout because my main partner is diving is GUE configured JJ.
Other sidemount issues specific to long-range cave diving
SF2 is too long for a sphere for the vast majority of people so you have to mount O2 to the side which makes carrying stage bottles really difficult.
Sidekick basically requires a sphere which are extremely expensive and hard to come by, same with the sphere holders. If you want dil on it, which most do then you have to strap a bottle to the side which gives it the same issues as above.
Liberty is REALLY big and while it is self contained, it's about the size of @grantctobin which can make it difficult for a lot of divers.

Backmount O2ptimas are super cheap used and you can get the conversion kit for them to the CM pretty cheap so keep that in mind. I actually kind of like the O2ptima as a backmount unit even though it can't fit in a rack.
O2ptima CM solves the bailout problem by letting you use whatever you want for bailout without modification to your bailout paradigm and you can also easily "park" it by unclipping it and then moving around on standard OC equipment. It's probablyNow, this is a nice party trick but if we are being honest it matters for like a dozen of us that are doing long range cave diving in tight spaces, it is certainly not a variable that I would bother with for the vast majority of divers. All of these rigs in their sidemount configuration can easily be clipped in like a left-side sidemount bottle to a standard backmount single tank or doubles for ocean diving, O2ptima CM can be clipped off to the front and off you go. I don't think it's nearly as nice of a configuration as a rack mounted unit like the Fathom, Liberty Heavy, etc. and it has some very real downsides in terms of the rebreather itself which is why you're seeing so many recommendations to start on a backmount unit, but if sidemount is a requirement for where you are going then it is what it is.

 

[Wibble]

(Sorry for the loads of questions!)

How come you ended up with the SM CCR on LHS with bailout on RHS? Any reason or just that's how you dive?

 

[tbone1004]

(Sorry for the loads of questions!)

How come you ended up with the SM CCR on LHS with bailout on RHS? Any reason or just that's how you dive?

CCR on the right when using backmount dilout doesn't allow for donation of long hose since it would trap the loop. Keeping it on the left basically makes it a stage bottle and while you do have to remove the DSV to donate a long hose, once you remove the loop you have a normal backmount configuration. In sidemount the paradigm most of us subscribe to is left bottle is "mine" with the short hose, etc. and right bottle is "yours" and is where the donation gas comes from, this obviously correlates to backmount doubles. I use a small manifold block where a whip connects to the CCR which has a regulator on a necklace and wing inflator so any bottle that is plugged into the CCR for diluent gives me access to my short hose around my neck and wing inflation. If it was on the right then I would have to deal with the long hose being on the wrong side which makes the hose cross under a diver which is not only irritating because they float but also severely reduces the effective length of the hose *I dive a 9ft hose in sidemount because I am quite tall and the 7ft hose doesn't allow a lot of space between divers* and it would also put a lot of rotational torque on the mouthpiece since the hose comes into the mouthpiece at 3 o'clock but is being pulled by the hose at 7 o'clock so it's really uncomfortable to share gas when the long hose comes from the left. Left handed/reversible regulators obviously solves this but it makes everything "backwards" from normal and requires specific second stages to handle it. When compounded with the backmount bailout issues with the long hose I've found it best to just put it on the left. It does obviously limit standard mounting of stage bottles but you can get one bottle under the breather in a standard DIR type configuration and you do have full access to using leashes and if I have trimix in the bottles I much prefer to butt mount them anyway.

I know the standard is to put them on the right but none of the manufacturers have ever actually given any solid reasons as to why they put them on the right and until I hear a compelling reason to switch, it stays on the left.

 

[billgraham]

My friend Edd Sorenson teaches CCR and CCR cave on all of these units, why not give him a call and ask his advice?

Cave Adventurers -- 850-482-6016.

Good luck!

 

[Wibble]

Good logic @tbone1004 .

Never thought of the Left=mine, Right=yours in sidemount, even though I dive (sidemount) in that configuration (longhose on RHS).

Thanks.

 

[Tracy]

Question for the more experienced CCR divers: do chestmount rebreathers (Triton, ChOptima) work well in caves, better than backmount and comparible to sidemount rebreathers?

Loaded question that is mostly covered up with people who have only dove one unit.
The Choptima travels better than anything else I have seen. I carry it directly on the plane as a personal item. You can wear it as a purse and walk on. It is extremely versatile as you can use it with any configuration you can get anywhere.
Outside of that, I consider it like a leatherman. If you are only going to have one tool, it does a lot of things pretty well. But outside of travel, I don't think it is better at anything than a purpose designed unit.
I would prefer it over any of the sidemount rebreathers, but it isn't a sidemount rebreather. Unless I need sidemount for incredibly small passage, I prefer a full sized backmount unit for just about everything.

 

[sea_ledford]

I'll respond as a DSO that oversees cave dives and is a CCR research diver, certified on the Inspo, SF2 back and sidemount, and Prism 2.

First off, skip the side mount CCR. They seem like awesome do-anything machines, but realistically they are only worth the complexity tradeoff if you are doing dives that really need them. If you are doing mesophotic coral work, a sidemounted CCR will be a strong disadvantage. They call it widemount when you are diving off a boat. If you came to me with a dive plan that needed a sidemount CCR, I would be expecting to see your experience in the range of 500+ dives, 100 hours on CCR, and 50-100 cave dives. Minimum.

The units I know of that Organizations are using are Hollis Prism 2, AP inspiration, Megs, and Xccr.
The Megs and Inspirations are generally used by individuals that have been diving them for 10+ years and their associated dive programs. Prism 2 is the big up and comer these days, especially if you are doing coral work. I'm part of a big mesophotic project starting this summer, and we are all on Prisms. Their huge advantage is the dive programs can get certified and authorized to service them in-house. I don't know of any other unit where that is an option. People write them off as plastic pieces of junk, but the Cal Academy team has been doing working dives to 500-ish feet on them, so they work.

Xccr is mostly National Park Service, and maybe U Miami at this point? I know the former DSO used the Inspo, but the current DSO dives an X because she is a former NPS diver. Not sure what they are running as a program at this point.

These are the units I know of that programs are running. There are certainly people within programs that are diving their own units (I own an SF2, and not a Prism), and I'm sure there are people all over cave country using side mounted CCRs as part of research diving. One of our former researchers, that pretty much exclusively does cave research is moving to a Sidewinder for his post-doc work.

I would get a back mounted unit that has support where you are going. And buy used because you'll probably end up swapping it out for something else anyway.

 

[Jlukescuba]

I'll respond as a DSO that oversees cave dives and is a CCR research diver, certified on the Inspo, SF2 back and sidemount, and Prism 2.

First off, skip the side mount CCR. They seem like awesome do-anything machines, but realistically they are only worth the complexity tradeoff if you are doing dives that really need them. If you are doing mesophotic coral work, a sidemounted CCR will be a strong disadvantage. They call it widemount when you are diving off a boat. If you came to me with a dive plan that needed a sidemount CCR, I would be expecting to see your experience in the range of 500+ dives, 100 hours on CCR, and 50-100 cave dives. Minimum.

The units I know of that Organizations are using are Hollis Prism 2, AP inspiration, Megs, and Xccr.
The Megs and Inspirations are generally used by individuals that have been diving them for 10+ years and their associated dive programs. Prism 2 is the big up and comer these days, especially if you are doing coral work. I'm part of a big mesophotic project starting this summer, and we are all on Prisms. Their huge advantage is the dive programs can get certified and authorized to service them in-house. I don't know of any other unit where that is an option. People write them off as plastic pieces of junk, but the Cal Academy team has been doing working dives to 500-ish feet on them, so they work.

Xccr is mostly National Park Service, and maybe U Miami at this point? I know the former DSO used the Inspo, but the current DSO dives an X because she is a former NPS diver. Not sure what they are running as a program at this point.

These are the units I know of that programs are running. There are certainly people within programs that are diving their own units (I own an SF2, and not a Prism), and I'm sure there are people all over cave country using side mounted CCRs as part of research diving. One of our former researchers, that pretty much exclusively does cave research is moving to a Sidewinder for his post-doc work.

I would get a back mounted unit that has support where you are going. And buy used because you'll probably end up swapping it out for something else anyway.

Thank you for your insight! I will definitely keep your points in mind.

 

[tbone1004]

@sea_ledford the Poseidon Se7en is being used by some of the AZA programs and any diver can be factory certified to service them. It's actually much more open than the Prism since it is open to any diver not just someone with a Huish dealer account. I'm 99% sure that Dive Rite will still do factory training for institution programs but don't quote me on that.