left post vs right post

[Green_Manelishi]

inquiry:

why not drive primary off of LEFT post and backup off of RIGHT?

Advantages:

1) immediately aware primary has shut down. switch to backup
and re-open
2) if you have to hand off your primary there is no chance of
you placing a rolled-off backup in your mouth

Disadvantages?

One final question: does anyone know anyone that does this?

Ps. if you feel that I must be flamed .. be clever ,.,, don't simply
scream "you heretic stroke"

[Jonathan]

I'm not quite sure that I follow your pros and cons but I tend to dive primary on left, backup on right - mainly because I find the routing of the long hose easier and to keep things more out of the way.

It is one of the more bizarre sections of the DIRF book that and I really do not buy their arguament.

As long as you are aware which is where, surely that is the important thing.

Jonathan

[D.I.R.Lizard]

Your primary concern when handing off your primary in an OOA emergency is not whether your back up has rolled off, it is assuring that your buddy has one that works.

He will be possibly a little freaked out and you should be calm enough to fix it if your back up has rolled off.

And if you use the long hose(primary) on the right post it can only be rolled off in the on position, thus insuring that your buddy is getting a good working regulator. That is asumming you are breathing the long hose and not stuffing it.

As far as routing to the left post with the long hose, I don't see how it would be better for routing since there is more distance to cover and off the right post it drops straight down between the tanks and wing and up under the cannister light and wrapped around your neck, pretty simple and easy to route.

Just my opinion.

[roakey]

It revolves around an OOA scenario.

By routing the long hose off the right post, it will NEVER roll off, so the OOA diver has one less thing to worry about. You on the other hand are breathing off a post that can roll off, but if it starts breathing hard you have immediate feedback AND the ability to turn it back on.

This is probably one of the few places where a double failure is actively considered. If you’re donating and your exit involves a tight passage, there’s a real possibility of a roll-off in a place where your buddy may not be able to turn around and communicate that their air has been turned off.

A during-the-dive roll off of the left post should be discovered on one of your SPG checks.

Roak

Ps. You're a heretic stroke :)

[Jonathan]

I must be missing something here? Please define "roll off". Just trying to get a handle on what you are saying.

The reason for putting the long hose on the left post for me is that I am using the port on the bottom of a Scubapro Mk20. This way I can turn the primary at an angle and I can get to the tank knob easier with no hoses in the way.

Jonathan

[Green_Manelishi]

If (you hand off the right-post-driven primary)
and (you are passing through a restriction
and (your left post rolls off)
and (you can't get to it because you are too restricted) THEN
you drown
your buddy drowns
End if

or is that a time to breathe FROM (not re-breathe) your wing
inflator?

G_M

[Campana]

My buddy and I did a dive a couple of weeks ago that we knew would involve a major restriction or two. Before the dive, since I had not dived with this guy very much, I mentioned checking for a roll off after we negotiated the restriction. After the dive, he mentioned that he was somewhat suprised to find that we both had a major roll off after the restrictions. Like, a total roll off. Of course, it was easy to turn our valves back on.

So, as dumb as it is to say it, if you think you might be in roll off conditions, check before you have an out of air emergency. If you get in an out of air emergency and hand off your primary, and find that your secondary is rolled off, you have already made two mistakes. First, not checking for a roll off after "bumping" your valve, and second, not noticing that your SPG isn't changing as your dive progresses.

[Green_Manelishi]

FWIW .. I am currently running the primary off of the RIGHT
post.

I agree that you should periodically and methodically "check your
instruments".

I am merely presenting the question of "why not on left" to
promote discussion.

Has anyone ever been in such a tight restriction they could
NOT access the left post?

[Wendy]

I agree with Campana, if you think you made contact with something that would cause a roll-off then check your valves. They aren't going to roll off on their own. Also you aren't going to get a roll-off on your right post unless you are swimming backwards. And even if you don't check your valves for a roll off, you would know if you have accidently rolled off your left valve because your SPG would either be at zero or not move at all. I check my gauges enough to know when I'm using air or not.

Green-M you wrote that in an OOA situation that if you put your primary on your left post then you don't ever have to worry about putting a rolled off reg in your mouth. Well are you saying that it is better to give someone that is already OOA a reg that is rolled off? They are already probably pretty freaked, and when they stick that reg in their mouth they are wanting some air in the worst way. Don't you think that your stress level would be a little lower than theirs were you couls reach back and make sure that your backup is fully open?

[Ontario Diver]

I was taught the same thing. Keep your alternate on the left post so that it will get "rolled on" rather than "rolled off" . That way you know that it "should" work if you switch to it. If your primary gets rolled off - you'll figure it out pretty quickly and can fix that (giving a reason for those 398 shutdown drills that the instructor made us do!) and you can still breath off of your alternate.

I like the tip to keep checking it tho' - thanks

[Ontario Diver]

Originally posted by Jonathan
I must be missing something here? Please define "roll off". Just trying to get a handle on what you are saying.

...

Jonathan
In an overhead environment, it is possible/common to rub against the roof through non-perfect boyancy control (me - ;-0) or encoutering a restrictive passageway (everyone else :D). In this situation, it is not uncommon for the valve knobs to be rubbed along the roof. This can have the effect of "Rolling" the knobs across the roof.

On a set of doubles, the action that the left hand valve post knob takes when it is rolling along the roof is the same as the action that you take when you turn off your valve. When this happens, it is refered to as "Rolling Off". The opposite takes place on your right valve post (the same as a single tank) - the action tends to open up the valve - hence "Rolling On".

Hope that this helps....

[Green_Manelishi]

I agree that monitoring gauges, etc. should be part of
your dive.

Perhaps I am not clearly stating the question.

Per "DIR" the PRIMARY is off the RIGHT post (as in wearing the
rig the RIGHT post is behind your RIGHT shoulder) and the
BACKUP is on your LEFT post (behind left shoulder). The rational
is the RIGHT post will never be rolled off and you KNOW the
reg works should you ever have to donate gas. You then switch
to your BACKUP on the left post (which MIGHT have rolled off
and you don't know it ... assuming you are NOT monitoring ...
but if it is you just roll it back on)

It seems to be a common statement that you should at all
times be able to reach the valves and re-open anything that
is closed so ...

The question:

If you run the PRIMARY from the LEFT post and breathe it
you will know IMMEDIATELY if it is compromised and you can
re-open it. Therefore it is working (and you know it) and you can confidently hand it off then switch to your backup (on the
right post which cannot roll off) ...

So far the *most logical reasons* AGAINST what I am "proposing"
are:

1) the backup driven from the right post would necessitate
a VERY short hose or it would be a major PITA.

2) the long hose on the left would lose some of its useful length
as it passed behind over your shoulders then down and around

[roakey]

Originally posted by Green_Manelishi
If (you hand off the right-post-driven primary)
and (you are passing through a restriction
and (your left post rolls off)
and (you can't get to it because you are too restricted) THEN
you drown
your buddy drowns
End if

or is that a time to breathe FROM (not re-breathe) your wing
inflator?
Yes, which is why your inflator comes off your right post too.

Note that your middle two “ANDs”: (you are passing through a restriction) and (your left post rolls off) have a high correlation, so though you list them as independent variables, they aren’t. Especially if you’re task loaded because of the OOA situation and your buoyancy isn’t spot on.

And your last AND: (you can't get to it [left post knob] because you are too restricted). This is far less likely than the restriction simply being too small for your buddy to turn around and effectively signal that their gas supply had been turned off (if you ran the long hose from the left post).

That’s why I only count it as only a double failure: OOA and a roll off, because a tight restriction makes a roll off not only probable, but likely. And because it’ll be likely in a restriction, your buddy may not be able to turn around (the buddy always leads in an OOA situation). All related, not independent situations. And lastly, a second OOA situation might push your buddy over the edge and they may respond in a not-so-calm manner.

Roak

[roakey]

Originally posted by Ontario Diver
On a set of doubles, the action that the left hand valve post knob...
Careful of your terminology, OD. What we call the “right post” the SCUBA industry calls the “left valve” and visa-versa. So saying “left hand valve post” is precisely ambiguous (I can never resist a good oxymoron :)).

Left and right posts are sides the valves are on when wearing the cylinder. Left and right valves are what side the knob is on when the valve outlet is facing you. Most simple K valves are left valves. But they correspond to right posts.

Go figure.

Roak

Ps. Please don’t shoot the messenger :)

[Green_Manelishi]

Roakey,

Me thinks you just provided *the* best argument against
my "proposal":

"If the LEFT post primary rolls off while I am donating in a restriction and my buddy cannot signal that he is f***ed ..."

Add to that EVEN if he can signal me do I really want to risk
aggravating the situation by giving him a reg that might roll
off? I think not. We will both have enough to handle.

Thanks my friend.

[roakey]

Originally posted by Green_Manelishi
So far the *most logical reasons* AGAINST what I am "proposing"
are:

1) the backup driven from the right post would necessitate
a VERY short hose or it would be a major PITA.

2) the long hose on the left would lose some of its useful length
as it passed behind over your shoulders then down and around
No, the most logical reason against what you're proposing is that it increases task loading in an OOA situation which already is at a level of increased task loading in exchange for a decrease in task loading when your task loading is already a minimum (normal dive).

To reach back and check that your left post hasn't rolled off after bumping the ceiling is a non-issue during a normal dive, as is making sure the gas supply as shown on your SPG is slowly going down. And it’s a non-issue to check your left post during an OOA situation as well.

What you’re proposing is streamlining those simple, no-brainer procedures (like they need it?) and increasing the complexity and task loading in an emergency situation.

It’s not worth it.

Roak

[Green_Manelishi]

Roakey,

We "crossed posts" (no pun intended) ... while you were
replying to my "the most logical ..." post I was replying to your
"if your buddy cannot signal .." post.

I agree that it is bad juju to hand off a reg that might roll
off and at best cause your dive buddy to hate you.

But i reserve my right to experiment and do what's best for
ME :-)

NOW you may refer to me as a heretic stroke.

[roakey]

Gost durnit, that last post was a complete waste of time! :)

Roak

[Divesherpa]

There is a group of 6 of us in Fl who dive opposite the popular view. It works for us, but that's just us. We ALWAYS drop stages past major restrictions so OOA through restriction isn't a problem(except no mount).
Hose routing is easier for us as I mount my light to my backplate.
Cheers

[caverkevin]

I am merely presenting the question of "why not on left"

Because some people(like me) will not dive with folks that do this type of stuff. That long hose is MY regulator and mine is yours. Why put some on in a position that the reg they are breathing could be turn off and have no control or ability to turn it back on. Be the best diver you can be and use the best equipment so no one can have a problem you. Then it is you have fun and go dive.

KLJ

[Jonathan]

Thanks Ontario - I wasn't sure. Surely if you do "rub" against something it is good practice afterwards to check everything is hunky dory? Also on my twins I have valve protectors so the chances of a "roll off" are pretty slim - much more likely I ****** up and did not turn one side on.....

I still stick by my earlier statement that as long as you know what is where what does it matter? As to inflation I usually dive a dry suit so the dry suit inflator comes from the right post and the wing inflator from the left post so I am covered there.

Cheers
Jonathan