BOV with MAV and/or ADV - thoughts?

[joshk]

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)

Curious on this point, can you elaborate?

If this is too far off topic, feel free to PM

 

[stuartv]

Curious on this point, can you elaborate?

If this is too far off topic, feel free to PM

I'm curious, too. I reckon the answer is "because then you can't breathe it on the surface." But, I don't understand that. It seems no different than diving OC and having a hypoxic mix for back gas.

 

[tbone1004]

@stuartv and @joshk when you have a BOV, the BOV is your first source of bailout. It's in your training and the muscle memory that you developed where when something is identified as a problem, you switch to it. You can't switch to 10% fO2 much shallower than 20ft. If it's plugged into offboard, you can have a travel gas plugged in for the start of the dive, then as part of your 20ft ppO2 checks you switch over to the bottom gas. You don't want to hop in at the surface without a scrubber, bad mushroom valve, etc. take a CO2 hit, then pass out because you had hypoxic dil plugged in.

@rjack321 I'd argue that hypercapnia is the one thing that is most likely to cause a problem on the CCR in addition to being the one thing that the BOV is really good at helping. Hyperoxia, hypoxia, those are all usually diver error and don't usually hit you like a truck. Hypercapnia can be caused by a myriad of reasons and comes on rather quickly....

 

[PfcAJ]

@stuartv and @joshk when you have a BOV, the BOV is your first source of bailout. It's in your training and the muscle memory that you developed where when something is identified as a problem, you switch to it. You can't switch to 10% fO2 much shallower than 20ft. If it's plugged into offboard, you can have a travel gas plugged in for the start of the dive, then as part of your 20ft ppO2 checks you switch over to the bottom gas. You don't want to hop in at the surface without a scrubber, bad mushroom valve, etc. take a CO2 hit, then pass out because you had hypoxic dil plugged in.

@rjack321 I'd argue that hypercapnia is the one thing that is most likely to cause a problem on the CCR in addition to being the one thing that the BOV is really good at helping. Hyperoxia, hypoxia, those are all usually diver error and don't usually hit you like a truck. Hypercapnia can be caused by a myriad of reasons and comes on rather quickly....

Hyperoxia can certainly hit you like a truck.

 

[tbone1004]

Hyperoxia can certainly hit you like a truck.

I meant more like your loop doesn't magically go from 1.0 to .10 in 30 seconds. It obviously goes from "I'm fine" to "blacked out" almost instantly, just takes a few minutes to get there. That did come out poorly though
Dead in 7 Minutes - The importance of a constant flow oxygen orifice • ADVANCED DIVER MAGAZINE • By Curt Bowen

 

[rjack321]

Curious on this point, can you elaborate?

If this is too far off topic, feel free to PM

I know lots of divers who use 10/50 dil for everything. Even on a recreational dive, its cheap enough and covers pretty much all their local diving and they don't have to worry about a dil bottle having the wrong mix in it. They add air, nitrox or trimix BOs depending on what their plan is. But they don't plumb their BOV to it - if you do, now you have a hypoxic BO on every dive too. Why? There's zero reason to plumb this way.

This discussion feels like something out of the 1990s...

 

[Superlyte27]

I used to pump 10/70 for DIL for everything. Mostly that was because I was diving a REVO and it needed all the help it could get for WoB. Later I realized just how easy it is to manage PPO2 with the proper DIL in the mix, especially on really sawtooth dives like Manatee on a scooter.

I am interested in these chin rests a few of you speak of.

 

[joshk]

I know lots of divers who use 10/50 dil for everything. Even on a recreational dive, its cheap enough and covers pretty much all their local diving and they don't have to worry about a dil bottle having the wrong mix in it. They add air, nitrox or trimix BOs depending on what their plan is. But they don't plumb their BOV to it - if you do, now you have a hypoxic BO on every dive too. Why? There's zero reason to plumb this way.

I'm wondering how you would do a deeper dive if you can't allow the BOV plugged into a hypoxic mix. Switch block? Seems annoying and risky.

Or do you change how this works with on a hypoxic dive and then you have to remember “oh I'm on a hypoxic BOV I need to make sure that I don't use it above 20'”

Seems like you could consolidate to “don't use the BOV above 20'” as a general rule.

 

[Superlyte27]

Well, I’m just guessing, because I’ve never done a big dive on a BOV...

Let’s say I’m going to 300’ on CCR with a BOV that is plumbed into a bailout bottle of 10/70. I’ve dropped bailout for 20’ 70’ and 120’. Here’s a few scenarios and what I think I would do.
Likely, my DIL is plumbed from that left Bailout Bottle. My 3l bottle is air (for inflation and later it’ll clear the helium out of my loop faster)

If I notice breakthru or flood shallower than 20’ at the beginning of the dive, I’m not going to BOV. I’ll simply inflate and establish positive buoyancy. I’m assuming I can grab my necklace that has a 200’ mix that can be breathed on the surface.

But, let’s say something more sinister...
Breakthru two hours into the dive at 300’. I go to BOV. But I’m only going to be on that until I get to a proper bailout bottle. Perhaps that BOV is the best mix for a while (until I ascend to a point where something staged is better) or my necklace has less helium and more oxygen in it being a 200’ mix. Until I get to a 100’ mix, and then a 70’ mix, then a 20’ bottle of O2. I’m only on the BOV until I get to my 200’ OC mix, then never going back on it.

At least this is how I think I would do it if you forced me to use a BoV. Hahaha.

 

[rjack321]

On hypoxic BO I just inflate and go up (<20ft), by the same token I have never used a travel gas to go down on OC. I put the reg in my mouth and drop.

I would never use a switch block, but if it were warm water (no gloves) and some shallow horizontal distance - I would plug in a deco gas to the BOV's QC6. Never had such a site or circumstance so that's academic for me.