View Full Version : OC Ascent using Meg BOV



Major Clanger
05-06-12, 05:25 PM
During MOD 1, the OC ascent was without a bov. Using a bov during an OC ascent adds different complexities, eg shared mouthpiece between oc/ccr. Would appreciate tips on venting during ascent using a bov to see if there's anything I've not considered yet. I'm assuming venting involves switching between loop and open circuit to vent but keeping mouthpice in mouth may introduce contaminated gas. Got a seperate reg on the bailout so see myself moving to that soonest if getting a problem, leaving loop free for me to vent at will.

Timw
05-06-12, 05:58 PM
Two ways really - ditch the BOV and switch to the offboard reg before you start ascending and vent it in the same way as the DSV...
Or breath off the BOV for the ascent and vent by turning the knob and just letting the vented gas leak around your lips and the mouthpiece and closing it before the next inhale. If you're worried about contaminated gas in the loop you can exhale at the same time. A flood would have to be quite bad before you got anything caustic to your mouth with a meg but then you'd need to bail off completely.
I'm sure there will be a multitude of methods suggested but this has worked for me albeit only for drills.

windymiller
05-06-12, 06:12 PM
the CL has an opv on it, just lean to the right and let it out of the lung

Gtzav
05-06-12, 06:17 PM
Or just un-clip the left lung ( bottom clip ) and unscrew the OPV all the way.
This way the OPV will float above your head and will vent nicely .

Major Clanger
05-06-12, 06:51 PM
Or just un-clip the left lung ( bottom clip ) and unscrew the OPV all the way.
This way the OPV will float above your head and will vent nicely .

Sometimes the obvious stares you in the face...

Timw
05-06-12, 08:03 PM
I had a go using the opv to dump the lungs a couple of times. I didnt like doing it that way as it was very easy to dump too much gas and knacker your buoyancy. I found using the BOV more controllable for an ascent on a reel.

Twinsetmad
06-06-12, 09:23 AM
On my MOD1 on the KISS.... Simon TW showed us how to dump massive amounts of gas from loosening the top lip. Makes venting and flushing a simple task.

Major Clanger
06-06-12, 12:56 PM
On my MOD1 on the KISS.... Simon TW showed us how to dump massive amounts of gas from loosening the top lip. Makes venting and flushing a simple task.

Did you do this doing an oc ascent on a bov though? You may be venting contaminated loop gas via your mouth in a real incident. I don't see switching the bov between loop and oc to vent on ascent via your mouth as being safe. Venting via the mouth is straight forward but can't see it working well in this scenario without a faff. I like the idea of staying on oc gas and using the open OPV flapping above me to vent. Not thought of that one before. Loosing all loop gas is fine as buoyancy control would then rely on suit or wing.

Garspeed
06-06-12, 02:07 PM
Think trying to swap BOV from o/c to ccr during ascent on bailout to dump loop is just asking for trouble. Keep it simple, breath as normal and vent other way in my opinion. On Inspo this means pulling dump chord on OPV which is easy. Have to admit though, during mod1 I was trying to vent via lips as normal first time round forgetting that all I was doing was wasting o/c gas supplies :-(

Gar

Major Clanger
06-06-12, 02:37 PM
Turn adv and o2 supply off as well, as it'd still be trying to maintain set point, and inject dil during loss of bouyancy?

12480
06-06-12, 02:43 PM
K.I.S.S

This is starting to sound like a bad day out...

Posts 3 & 4 gave straight forward ways of going about it...

Major Clanger
06-06-12, 03:03 PM
They both get my vote, with post 10 to keep it that way.

Iain3
06-06-12, 03:31 PM
Why would anyone ever use the dsv to vent the loop after bailing out? Switching from open to closed, passing bad gas past your lips, etc. In a stressed bail-out situation with a dozen things to think about that just seems like a recipe for disaster. The OPV on the counter lung is designed for the job.

Twinsetmad
06-06-12, 03:58 PM
Just an option for venting gas.... 0)

Major Clanger
06-06-12, 04:27 PM
The OPV on the counter lung is designed for the job.

Completely agree. Before starting this thread was concerned that the opv wouldn't kick in until higher loop volumes, given its relative position, so adversely affecting bouyancy during a bailed ascent if in a less than horizontal posture. However, releasing the exhale cl, so the opv goes uppermost, avoids this. Happy with that answer.

12480
06-06-12, 04:29 PM
My thinking on this as a first year newbie to CCR is that if I am bailing out onto my BOV I am doing so as an intermediate step to going out board completely, I think I am favouring not staying on the BOV only having it as an immediate stepping stone to relative safety. My main reason for this is that it is blatantly obvious to my dive buddy that I am no longer on CC, second reason it keep me separate from any bad gas in the loop....

I can then ascend and dump the loop without all the concerns raised in this thread, with minimal pissing about and with the full attention of my buddy who has a clear picture of what is going on.

Major Clanger
06-06-12, 04:40 PM
Liking the buddy thing. No room for misunderstanding if you're off the loop completely, signalling in the approved manner and thumbing up.

BOV bailout drills aren't something covered on Mod 1 as far as I know, weren't on mine anyway.

Interesting the range of views, but k.i.s.s does it for me.

Major Clanger
06-06-12, 04:48 PM
Another scenario's just popped up. Bailed due to CO2 buildup but unable to bail completely off the bov due to physical response to co2 making it impossible to take the bov out of your mouth as panting hard. Either wait/hope it subsides, then switch to bailout reg and hope there's enough gas left to surface on in the cylinder or immediately start to ascend still on the bov, switch when you can and do your best to vent the loop independantly while still on the bov, assuming your buddy is out the picture for some reason?

Be patient with me, just thinking through bailout responses. Trying to put the learning in to it, before the incident ;)

Twinsetmad
06-06-12, 05:22 PM
Another scenario's just popped up. Bailed due to CO2 buildup but unable to bail completely off the bov due to physical response to co2 making it impossible to take the bov out of your mouth as panting hard. Either wait/hope it subsides, then switch to bailout reg and hope there's enough gas left to surface on in the cylinder or immediately start to ascend still on the bov, switch when you can and do your best to vent the loop independantly while still on the bov, assuming your buddy is out the picture for some reason?

Be patient with me, just thinking through bailout responses. Trying to put the learning in to it, before the incident ;)One thing that is common on Co2 hits is total confusion.....??

With me too... :0)

drews
06-06-12, 07:52 PM
Having just fitted a GG shrimp to my Meg i'm following this one, some great advice already took onboard.
My plan was as BTS suggested, to use it as a stepping stone to get on my bailout.
I could then vent the loop on the ascent, all sounds reasonable until the sh*t hits the fan !

Major Clanger
06-06-12, 08:53 PM
Must be a number of experienced meg divers using bovs that'll see this thread. Would be good to get their views on conducting an OC ascent, or real time examples.

Timw
06-06-12, 09:36 PM
The way you bail out will depend on the problem:
If you have a flood you'll want to get straight onto your off board...
If you have a CO2 hit the last thing you'll want to do is take your BOV out of your mouth...

I'd recommend practicing a few different methods so you can take the best course of action for a particular situation. I don't believe there is any one way you should do it - just react to the circumstances but be well practiced.

Major Clanger
06-06-12, 09:40 PM
Plan to do so this w/e, in particular one ascent staying on the bov and one coming off it to try different ways to vent through the opv. I expect it to be quite difficult when coming up a dsmb line.

ratfish
07-06-12, 02:56 AM
What I was trained to do was to unclip the bottom of the exhale counter lung and let it float up and dump gas through the (open) OP valve during the ascent.

What I would do now after using my meg for a lot of dives, and practising the occasional bail out, is dive with the the OP valve in the open position when away from the surface, and dump gas from the loop on ascent during a bailout by simply rolling to the right so that the OP valve is high enough to dump.

This is a bit like dumping from a drysuit, and assumes I am in a more or less normal swimming position, but is very effective and in a real bailout scenario when task loading might be an issue, it means that you don't have to do extra things like unclip a counter lung or open an OP valve or look around a counter lung floating in your face. If I was stuck in a more vertical position for some reason I might consider unclipping the lung, but think that that would be an unlikely situation.

megangel1
07-06-12, 04:34 AM
My thinking on this as a first year newbie to CCR is that if I am bailing out onto my BOV I am doing so as an intermediate step to going out board completely, I think I am favouring not staying on the BOV only having it as an immediate stepping stone to relative safety. My main reason for this is that it is blatantly obvious to my dive buddy that I am no longer on CC, second reason it keep me separate from any bad gas in the loop....


The bubbles give it away, pretty much immediately! No matter what the reason for bubbles, certainly of the magnitude when on OC, this should alert any buddy that you have a problem.

A better argument for not staying on the BOV is having your bailout gas (off board) totally isolated from your DIL. Even then though, there is no reason why not to run your BOV from isolated bailout/off-board anyway. If you are concerned about breathing 'bad gas from the loop' you can not consider that the first fews breaths from the BOV are not really good sanity breaths either so if this is your major concern, a BOV is not a solution anyway. Just ensure you've switch to OC mode properly and this should not be a concern.

Personally, the only time I go off the BOV is when I switch to a buddy provided bailout cylinder. Personal choice as I still have an OC 2nd stage on my off-board bailout, mainly for a buddy.

No matter where your BOV is ... in your mouth being breathed from, or out of your mouth, it should be OC mode as otherwise your loop could flood. (Shrimp works like this anyway, I have no experience of other BOVs ... do any have a three way mode, ... loop/shut/oc ?)
Having said that, I've found my shrimp sits nicely on my chest when I take it out my mouth, so an OC stage goes over the top and as the BOV mouthpiece is below the T fittings for the CLs, water doesn't actually make it into them when I'm in a vertical position. I don't do this though, ... see below.

If it's in OC mode (or shut mode if one exists for your BOV), you still have the need to vent your loop on ascent.

With some BOVs like the shrimp you can have a kind of half and half situation where the loop is not fully closed yet you can breath from the OC side.
This allows any over-pressure in the loop to exit either into your lungs or out the BOV depending on the part of the breathing cycle.
Obviously you do not want to do this with a flooded system etc and would want to isolate your ADV too. (You may well already dive with the ADV isolated as the norm, as many of us do. With a BOV adding DIL to the loop is simples, take your breath and if you feel the need for more DIL, just switch to OC mode and the rest of your breath in to 'top off' your breath. Switch back to CC mode and breath out)

This is my 'norm' ascent mode if bailed out. I'd never heard or even thought about unclipping the exhale lung and have no intention of practicing it with a flooded loop but if I get a flooded loop and if I remember about it, I'll try it. Which pretty much means I'd end up ascending breathing from my BOV with my OPV open and physically squeezing the lungs if needed to force more air out the OPV, but with a flooded loop I'd guess none of this would be necessary due to the lack of gas in the loop and decreased buoyancy.

Iain3
07-06-12, 07:47 AM
Completely agree. Before starting this thread was concerned that the opv wouldn't kick in until higher loop volumes, given its relative position, so adversely affecting bouyancy during a bailed ascent if in a less than horizontal posture. However, releasing the exhale cl, so the opv goes uppermost, avoids this. Happy with that answer.

I may be missing something as I'm not a meg diver...the Inspo has a toggle to pull to open the dump valve, same with the JJ, does the Meg not have this?

I would never wait for the pressure in the counter lungs to build up enough to dump gas, I'd dump it manually but using the dump toggle, not dumping gas through the mouthpiece.

Timw
07-06-12, 08:06 AM
No. The dump is a variable opv like a dry suit dump.

Iain3
07-06-12, 09:17 AM
No. The dump is a variable opv like a dry suit dump.

I'm not convinced I'd like that. On the plus side it works without needing you to use hands, and I never felt uncomfortable using them on a drysuit. Using a DSV to leak gas would probably be a 2 hand job, especially if not using your mouth to grip the mouthpiece so definately not an option I'd consider.

NotDeadYet
07-06-12, 09:43 AM
I'm not convinced I'd like that. On the plus side it works without needing you to use hands, and I never felt uncomfortable using them on a drysuit. Using a DSV to leak gas would probably be a 2 hand job, especially if not using your mouth to grip the mouthpiece so definately not an option I'd consider.

KISS is like that as well however it's not there for doing ascents with, it's there to stop the lungs going kaboom when users leave the O2 switched on at the surface. You wouldn't want to wait until pressure had built up enough to blow on an ascent. Even if it does blow, the best it is going to do is dump the over-pressure, you've still got the lungs blown full which may make for an interesting ascent rate. I always dumped via the mouthpiece when going up on OC.

windymiller
07-06-12, 09:59 AM
I was always taught to have the opv fully open when diving the meg anyway...it also helps keep the loop volume down...On the Sentinel you have to rely on an opv at the bottom of the stack that you only have a few clicks open from fully closed..The bov is just used to get a few sanity breaths and then you go completely off board..you rely on the opv or crack open the mouthpiece slightly facing downwards to get rid of excess gas.

The inspo is easy; just pull on the dump cord.

In theory, if you had a flood the meg is pretty good at getting rid of water by doing a dil flush and pushing the water out the opv.. If you have a co2 hit and once you had regained some sense of goings on, what is to stop you doing a dil flush a couple times and then coming up on a bov and cracking it to dsv to release any excess gas? You arent breathing off the loop so you arent pushing gas around the system...just a thought?

Iain3
07-06-12, 11:33 AM
KISS is like that as well however it's not there for doing ascents with, it's there to stop the lungs going kaboom when users leave the O2 switched on at the surface. You wouldn't want to wait until pressure had built up enough to blow on an ascent. Even if it does blow, the best it is going to do is dump the over-pressure, you've still got the lungs blown full which may make for an interesting ascent rate. I always dumped via the mouthpiece when going up on OC.

The Inspo certainly wouldn't dump gas out quick enough, that's what the dump cord is there for. Interestingly I never really thought about what to do if doing a bailed out ascent and you snapped the string, now I know.

With no cord on the OPV I'd be tempted to change it. I just think on that occaision when it all goes wrong, you are stressed, clinging onto a reel or a shotline and breathing off a stage like a peado in a playgound the last thing you want to do is try to control the loop through the DSV.

Timw
07-06-12, 01:36 PM
The meg will dump gas very quickly with the opv open fully. You can also press to dump quickly. I think a 2" diameter button is going to be as easier to find than a bit of string when stressed.
I found out how effectively the opv works in my early days when I was per breathing and couldn't work out why the loop volume kept dropping - obvious really - one of my stages was pressing on the opv... Soon sorted that out by moving the d ring a little.

12480
07-06-12, 02:40 PM
I think a 2" diameter button is going to be as easier to find than a bit of string when stressed.
.

A bit of string with a big plastic ball on it might be easier though ;)

Oddly, my inspo trainer has swapped out the standard OPV with the pull cord for a drysuit auto dump.....

Major Clanger
09-06-12, 05:04 PM
Tried an OC ascent today with bov fitted. Up to 8m no problem, then it got interesting due to gas in the hoses. In reality would probably vent this gas using the dsv.

Timw
09-06-12, 05:12 PM
A bit of string with a big plastic ball on it might be easier though ;)
..

...until it gets caught under a stage strap, handset, camera or other paraphernalia hanging off me.

Inspo lungs are tidier than the meg ones as they are a single layer with external seams and dont seem to crumple up when at minimum loop vol like the bottom of the meg ones.

Timw
09-06-12, 05:15 PM
Tried an OC ascent today with bov fitted. Up to 8m no problem, then it got interesting due to gas in the hoses. In reality would probably vent this gas using the dsv.
I'd be off my BOV and onto 50% at 20m so would be dumping the loop through the mouthpiece when the pressure changes are greatest. That's why I advocate being able to use several different methods competently...

Major Clanger
09-06-12, 07:05 PM
I'd be off my BOV and onto 50% at 20m so would be dumping the loop through the mouthpiece when the pressure changes are greatest. That's why I advocate being able to use several different methods competently...

This drill was off the bov and after twisting, turning and everything else I could think of to dump gas through the opv, decided that dumping through the mouthpiece is the only real way to manage the activity with a modicum of control. Worthwhile drill.

djc_offgassing
25-07-12, 12:18 PM
Thanks Gtzav.....

I have a GG SHRIMP BOV & did exactly as you posted below, OC stage bailout ascent from depth during my IANTD Normoxic course, kept loop tucked under my chin, OPV fully open, loop vented unclipped on acsent without intervention.


Or just un-clip the left lung ( bottom clip ) and unscrew the OPV all the way.
This way the OPV will float above your head and will vent nicely .