BOV with MAV and/or ADV - thoughts?

[tbone1004]

@stuartv what's the point of having the bov if all it is doing is getting you a second to get to another regulator?

If you're going to use one, don't be an idiot. Use the pre-dive checklists. You should have 2. A build checklist, and a pre-jump checklist.

Bailout bottles for primary bailout should look identical to sidemount regulators, since they are sidemount bottles. If you have a BOV, the BC inflators can get replaced with QC6's to plug into the manifold. I would recommend keeping a QC6-BC inflator adapter attached to the right side bottle so you can plug that into a wing or suit inflator in a pinch

If you have a bov, you need it plugged into something you can breathe from. A 3l is not something you can breathe from for any length of time, so there is no point in having the bov there. You use it for sanity breaths, dil flushes, etc. but if it's on a 3l it may not be enough depending on the depth/duration of the dive and frequency that you choose to do dil flushes.
On the subject of why it matters what it plugs into, it comes back to bringing unnecessary stuff on the dive. If like @Superlyte27 you believe they aren't necessary, don't take it and you don't have to worry about it. If you choose to use one, it's because you think they are beneficial, and if you believe they are beneficial you should have it plugged into something useful.
If/when you go to hypoxic dil mixes, you also want to make sure you can plug it into something else if you need it at the surface....

Pre-jump checks that I use from IANTD
#1 "Check Bailout"-literally the first thing you check
#2 Recheck all gas gauges and valves
#3 Recheck MAV's-your BOV ideally is on a manifold with your MAV and ADV so if you aren't plugged in, you fail #1 and #3
#4 BCD working & inflator inhand?-Your BCD inflator is on this same manifold unless you have the suit and wing inflator from onboard so it may fail #4 if not connected as well. In your situation I'd probably use that for wing+suit inflator so it wouldn't matter on this one
#5 check ADV, if applicable-it applies to your Revo so it would fail this one as well
#6 Check Handset & HUD are on
#7 Confirm safe ppO2 & O2 system on

So, of the 7 things you check before jumping in, if you route your BOV properly from offboard, you will fail #1,3,5 and potentially #4 on that list. If you follow that checklist, you won't forget to plug it in. Image of the cards below

 

[joshk]

"you should be able to deploy your deep OC reg in seconds..........that is what having the BOV on your dil is allowing you to do. There are lots of divers comfortable with diving without a BOV of course, who are bailing straight to OC"

So don't dive with a BOV then.

The point here is you can very quickly run out of gas in the BOV even if you're actively trying to switch off it to a larger gas supply.

One part of the appeal, to me, is that plumbing to onboard dil means one less thing you have to do during the final pre-splash gear-up. Which I take as an improvement in safety.

Based on the number of times I have splashed with my drysuit inflator not connected to my suit, I could easily imagine myself forgetting to connect offboard gas to my BOV.

Put it on your checklist. Now you can't forget.

From that perspective, having offboard BO that is always configured with a hose on the 1st stage that can be plugged into the loop somewhere seems like a good idea. I believe you'd have that whether you have a BOV or a DSV.
...
If you believe that a BOV is unnecessary and that you will always be able to switch to OC when needed (whether that's because you will always detect the issue before it becomes too big of a problem, or otherwise), then what does it really matter what your BOV is plugged into?
...
If you believe that a BOV is a good idea, well, in that case, I can definitely see your arguments in favor of just having it plugged directly into your big BO cylinder. In which case, what do you think about the possibility that you might splash and forget to plug your BO into your BOV?

Yes, you still need a stand-alone second stage. The BOV does not replace that.

If you believe the BOV is unnecessary why add that complexity? Ignore plugging it into your onboard diluent, just leave it off entirely.

I prebreath my BOV and it's part of how I gear up, so no I haven't thought about the possibility where I jump and it's not plugged in. Even if that were to be the case (or it becomes disconnected somehow) there's another second stage to grab quite easily.

 

[Superlyte27]

I do the same thing every single time. One of those things is breathing off of all of my bailout underwater before the start of the dive.

I cave dive almost exclusively, so it’s a bit different for me than others who might be diving from a boat maybe.

I get to the park and unload all the bottles and all the scooters and the rebreather. I do my checks on the rebreather. If it is good to go, I put bottles and scooters at waters edge and put on undergarments and suit. I am probably hot by now, so I carry a scooter in the water with me to cool off, checking for bubbles and floatyness. I tie it to land. I carry each bottle down breathing off of them underwater to make sure no bugs, holes in diaphragms, holes in mouthpieces and the ability to supply gas. I tie them to land. Then, I go get the rebreather on, get in the water, plumb in all of my bailout and in its configured state, make sure it is all routed properly and breathing properly.

I’ll admit that I have forgotten to hook up the inflator to my dry suit (which isn’t really crucial life support) finding out when I hit that inflator the first time at 20’. But so far, I’ve never not had working bailout.

If I were to start using a BOV, it would be for coolness factor or marketing (to sell more), in which case, I doubt very much that I would miss plumbing it in, as pre-breathing all of my bailout options is probably more important to me than any other part of my pre-dive process.

 

[rjack321]

For both boat (I have a RIB) and cave dives my BOs are staged in the water before I splash. Plugging in the BOV is not part of the build list. Plugging it in and doing a test breath is a key part of the pre-dive checks. Just like doing a pre-breath on any OC reg should be. If you ever had a torn or compromised 2nd stage diaphragm you'll know why this a critical part of any technical dive - and all CCR dives (even no deco dives) are technical dives because you are mixing gas on the fly-among other reasons. If you can't remember to test a reg (and a BOV is a reg) before diving, CCRs are not going to be kind to you.

 

[stuartv]

Thank you all for taking my questions, dumb as they may, with some seriousness and not just telling me to forget about diving a CCR. The conversation is definitely helpful to me. It will be a while before "do I go ahead and buy a BOV" is a question at the top of my priority list, but I am glad to have all this to think about, ask my instructor about, etc., as I go through the training.

One of the things that I especially liked was the commentary about breathing all your BO regs during pre-dive and/or at the start of the actual dive. I have dived with people on CCR a number of times and maybe I just didn't notice it happening, but I don't recall ever seeing any of them do that. It seems like BO bottles kind of get treated like most other dive accessories. They are there. Once assembled and checked, they are presumed to work. So, a BO bottle might be put together at the start of a week of diving and then just moved around and dived with but never checked again during the week. I KNOW that I've never dived with someone on CCR that paused at the start of a dive, in the water, and went through breathing all BO bottles. Yet, it does seem like a good idea...

 

[tbone1004]

@stuartv
this may shed some light

Me-cave diver
Superlyte27 -cave instructor
kensuf -cave instructor
rddvet -cave diver
rjack321 -cave diver
lv2dive -cave diver
JohnnyC -cave diver

doctormike I don't think is, but he's been doing some seriously cold/deep stuff for a long time, especially since the currents up there mean you still have to get back from whence you came before you can come up.

The direction that we approach things are going to be different because of the need to get home first. Pre-dive checks matter a whole lot more when that is your paradigm. Those that have advocated bov's on the onboard 3l clearly don't have that concern so to them the 3l may well be enough to actually get you up to your deco bottles or even to the surface. IMO it's wrong to even consider that, but people obviously do.
If I take a bailout/deco/stage bottle into a cave and it's going to be there for a few days, I check it each time I swim past it. Had them in this past weekend. Each time I swam into the cave I reopened the valve, checked second stage function and fill pressure then turned it back off and kept going because I needed that bottle to continue that dive as it was part of my gas plan.
If I'm doing it on the surface, obviously being in a cave the surface is usually easier than the ocean, but I breathe them before I submerge since it's easier to check them as I'm clipping them off.
When I was in NC ocean diving in June I was hurling over the side of the boat and it was everything I could do to stop hurling long enough to jump in. I jumped in on OC just in case, but when I did my 20ft stop and doffed the safety bottle I checked it and both of my onboard second stages before I continued descent. In that case it's safer to get in and get down to 20ft to finish those checks, but before I stood up from the bench I checked the bailout regulator around my neck since it is my "primary" bailout regulator. I'll check the rest before I continue the dive but at least that one needs to be working before my face goes in the water

 

[rjack321]

Hey now I have a boat! I dive CCR in OW!

The cave vs RIB thing can be critical but not really with the BOV. Where its critical is with the wing. I am fine waddling into a cave entrance with my power inflator not connected to anything. For cave diving my BOV, wing and ADV are all fed from offboard gas. The onboard (normally dil) bottle is suit gas.

For ocean diving there is no no no way I am even sitting on the tube of a RIB without gas connected during the build process to an onboard bottle (dil). Its too dangerous to even think about rolling off without primary buoyancy control. Which is why I think the idea of using a 2 or 3L onboard dil bottle as a BOV source is ridiculous. Its very difficult to orally inflate a wing while on closed circuit, you don't want to be losing wing gas by squandering it for 90-120 seconds on a BOV ever.

 

[Superlyte27]

So wing plugged I to 3l
Suit plugged into right bailout
Pigtails on all bailout in case I loose anything
Right Sidemount/Bailout has long hose
Left has necklace

This changes a bit if I go deep

 

[rddvet]

One of the things that I especially liked was the commentary about breathing all your BO regs during pre-dive and/or at the start of the actual dive. I have dived with people on CCR a number of times and maybe I just didn't notice it happening, but I don't recall ever seeing any of them do that. It seems like BO bottles kind of get treated like most other dive accessories. They are there. Once assembled and checked, they are presumed to work. So, a BO bottle might be put together at the start of a week of diving and then just moved around and dived with but never checked again during the week. I KNOW that I've never dived with someone on CCR that paused at the start of a dive, in the water, and went through breathing all BO bottles. Yet, it does seem like a good idea...

That's why stupid or lazy people kill themselves on rebreathers. No excuse.

 

[rjack321]

If you actually read CO2 hit reports, which pretty much the ONE thing that a BOV excels at (at the expense of several others) you'll see that it took victims a good 5-10 mins of huffing before their breathing stabilized enough to be able to even remove a reg from their lips. In a full on CO2 hit you just can't stop the 0.5 second needed to switch. By hooking up your BOV to onboard dil you:
1) Have an inadequate supply for really the one thing BOVs are best at
2) Can't use hypoxic dil (10/50 is a really common "versatile" dil for many divers and the depths the vast majority of CCR dives happen at 10-220ft)
3) You will run out of dil more often
4) 2L tanks are a joy to dive and even more ridiculous to think about using
5) You lose primary buoyancy when you run out

If you don't think CO2 is THE reason to have a BOV then you might as well not have one at all.