Closed manifold, most of the time

[Polomelo]

Thank you all!
I may well be overthinking this, sorry, but that's because I'm always thinking about scuba diving when I'm not diving.

Sidemount hadn't really crossed my mind, I've never met SM divers but it is something I should perhaps put more thought into. It is still strongly associated with advanced cave diving in my mind, but I'm a newbie. However, after 10-15 dives with steel twins, I've come to appreciate having two tanks on my back.

It is great to know that there are many options. Fortunately I have a lot of dives ahead of me before solo!

 

[Akimbo]

Both disciplines (SM or doubles) require an investment of time and practice to keep your skill level up to scratch.

That's an advantage of progressive equalization. It is a standard procedure so your skills are always current. You can also operate so you have real-world experience with running out of gas... several times/dive if you choose to operate that way.

 

[chrisch]

That's an advantage of progressive equalization. It is a standard procedure so your skills are always current. You can also operate so you have real-world experience with running out of gas... several times/dive if you choose to operate that way.

Yes, but that is only true if you always dive with that configuration and that method. The point is whatever you choose is OK so long as it becomes your normal. If you dive 90% of the time with a single tank and choose twin configuration and progressive equalisation for your solo dives your skill level is not necessarily current even if you dive 20+ times a year. You might have not closed a manifold underwater for a couple of years even.

Also you need to consider the effects of this procedure and configuration on your buddies when diving in a buddy pair. This is true for someone like myself that dives a primary donate Hogarthian setup all the time. (My buddy is my wife and she is a keen cave diver so no problem [much more keen than I am])

I am not sure what advantage running out of gas confers if you have a massive pressure difference between the tanks. I would be more worried about the excessive stress caused by rebalancing if I'm honest. I think this technique is more a solution in search of a problem. I certainly have no wish to practice running out of gas whilst diving solo. A standard S drill with a manifolded tank can generate the same sensations if required.

 

[Akimbo]

I am not sure what advantage running out of gas confers if you have a massive pressure difference between the tanks.

Not sure I understand this. It is pretty simple, running with the isolation valve shut saves gas that would otherwise be lost during the time it takes you to diagnose the failure and close the isolation. I learned the technique from a ex-British Navy diver. As the story goes, it was developed before SPGs and continued being used because it also works in black water where you can't see and SPG. I like it because it provides a hard reserve and takes full advantage of the options provided by dual regulators on an iso-manifold. In practice, I use equalization "events" as part of my dive profile planning.

 

[beester]

Not sure I understand this. It is pretty simple, running with the isolation valve shut saves gas that would otherwise be lost during the time it takes you to diagnose the failure and close the isolation. I learned the technique from a ex-British Navy diver. As the story goes, it was developed before SPGs and continued being used because it also works in black water where you can't see and SPG. I like it because it provides a hard reserve and takes full advantage of the options provided by dual regulators on an iso-manifold. In practice, I use equalization "events" as part of my dive profile planning.

I'm sorry but how long exactly does it take to close a valve? The GUE procedure takes a bit longer than standard because we first diagnose the side valves and check if that stops the bubbling/noise before closing the manifold valve but even then it takes seconds. If you immediately close the valve it will take less than 10 secs.

Next let's say that you have a failure on your inbalanced set (meaning you haven't equalised in a while and there is like 20 bar difference between the tanks)... if you then have a failure on the fuller tank you are actually losing much more gas than you would ever lose taking your time closing a valve. Next you are complicating a very easy standard procedure.

Not sure I like your procedure.

 

[chrisch]

...I learned the technique from a ex-British Navy diver. As the story goes, it was developed before SPGs and continued being used because it also works in black water where you can't see and SPG.....

OK I see. It has nothing to do with recreational diving. Fair enough.

 

[Michael Guerrero]

You're describing independent twins. Sidemount is the more popular version of this.

But, as others said above, based on the depths you're talking about you're way overthinking it. It's easy to surface from 60ft in an emergency without an issue if you're within recreational limits.

I'd recommend you just practice your emergency ascents with a pony bottle and call it good.

 

[sportxlh]

I haven't done a ton of sidemount diving: only took the course earlier this year, but when I do, I don't carry a third (pony) tank. I think the doubles have probably plenty of redundancy if you are sure you've set them up right. I do carry a heavy duty 50 lb lift bag whenever I dive solo and would use that to get me off the bottom if I had a wing or BCD failure

 

[Akimbo]

If you immediately close the valve it will take less than 10 secs.

How important is 10 seconds when you are near your planned "leave bottom" point and an O-Ring or blow-out plug fails?

 

[lermontov]

How important is 10 seconds when you are near your planned "leave bottom" point and an O-Ring or blow-out plug fails?

yes- ten seconds plus panic! also depends if your in tight spot ie overhead with extra stages etc - it can easily be 20 -30 seconds and if your deep on air its even more difficult