Doubles vs Sidemount

[DevonDiver]

I dive predominantly sidemount now. Most of my tech dives are wreck penetration and I dive tropical water and small boat. It lends itself perfectly for my needs and environment. Also, living in a developing country, it's the most convenient way to travel and/or plan logistics for technical diving in remote areas.

For penetration in confined areas, sidemount offers a huge capability increase. That's what attracted me to it in the first place. When I started using sidemount, I found it enabled much easier, more convenient diving in doubles. I feel a lot less strained and worn at the end of a diving day. No heavy weight to carry... it's nice.

I'm getting very comfortable using sidemount with multiple stages/deco now. That was an earlier concern I had...and a reason why I preserved some dives for backmount. I just use sidemount for everything now. I still teach occasionally in backmount, so I make sure to keep diving that configuration regularly enough to retain a high level of comfort and familiarity.

The doubles configuration is long-since standardized;...

By some agencies... by some people... in some areas. Don't drink too much kool-aid.... there are other people out there with their own ideas... and they're not wrong either, just different.

I don't have to explain how to share air to every person on the boat,...

Equip sidemount with long hose right, short necklace hose left... how is the air-share protocol ANY different?!?

I don't have to worry about the DM dropping my bottles to the bottom of the sea....

Nor do I... I use a hang-line. Proper technique... problem has solution. I take my own... I set it up myself. No worries about the crew.

In doubles I have decreased time on the surface as compared to SM (though no SM diver will admit this is true - wait for it), and I can use all the gas available to me in the event of a regulator shutdown.

You admittedly dive primarily in backmount. Don't you think relative familiarity might have a direct correlation with your set-up times?

I agree with you though...no fluent sidemount diver would agree that sidemount took longer to set-up. I do see noobie sidemount divers taking a long time with it though. They get faster....

I can use all the gas available to me in the event of a regulator shutdown.

So can I, on sidemount. Go figure...

 

[HIGHwing]

Now the thread is on track...

 

[Teller]

[/QUOTE]So can I, on sidemount. Go figure... [/QUOTE]

Can you access that gas if the oring on the first stage fails?

 

[DevonDiver]

Can you access that gas if the oring on the first stage fails?

Yes, there's a number of options to access that gas.

 

[vicp]

Can you access that gas if the oring on the first stage fails?

Will probably never happen with DIN valves and regs. Most other reg failures can be handled by feathering the valve which is MUCH EASIER in SM.

 

[chrpai]

I wonder if it clearer at this point to refer to 'backmount doubles' and 'sidemount doubles', rather than 'doubles' and 'sidemount'. [/COLOR]

I would think "manifolded doubles" would be even more clear. Does anyone even dive independent doubles (back mounted, not side mounted) anymore?

 

[PfcAJ]

According to Curt Bowen's article in ADM (great read, btw), an al80 tank can be drained from FULL to EMPTY in something like 2.5mins via a freeflowing reg at 99ft. Average human breathing rate is like 12breaths/min, with an inhale duration of 1.5-2seconds. Lets pretend, for fun, that the ability to modulate flow precisely with 'feathering' the valve is difficult, and this is perhaps amplified while under stress. For the sake of argument.

By feathering the valve ~12 times per min (and that's on the low end, I would bet that a stressed diver's breathing demands are a wee bit higher), how many 1.5-2 seconds valve openings are you going to get? If I did the math right (and it's a bit late here, so I might have goofed, check me), I get 8.33mins. A FULL tank is now reduced to 8mins and change at 99ft. And that's for a 12bpm breathing rate. Up the rate to something a bit more realistic, and its bad news. Count the fact that you probably breathed some of it already, and that tank is hurtin' bad.

By biggest beef with SM is that a real failure effectively makes you lose half your gas. You might be able to get at some of it, but not easily. In BM, you get it all. Everything you have left is yours to use, no games no gimmicks. You can 'look' at your valves all day long, but broke is broke.

And there are more O-rings on a 1st stage than the DIN one. A failure of one of those other ones is gunna be a bad time, too.

 

[vicp]

I personally do not see much reason to back mount (BM) doubles again.

I will backmount singles out of convenience on dive boats and may double up a couple of steel 72s or LP85s if the situation really warrants it (hard to think what that would be - maybe for grins, a historical dive demo, a James Bond type escape with only BM doubles available, or if someone put a gun to my head).

I know the strict DIR folks feel that 99% of all dives can be done in back mounted doubles, but I feel that 99% of all dives (not counting rebreathers) can be done in SM, with BM doubles for special "mission-specific" occasions like those mentioned above.

I have read that many people feel that BM is just as stable as SM, trim is just as easy, and it is important to dive what everybody else in your group dives. My experience is totally different. I had to practice most of a summer in a pool with video to get squared away in BM doubles. Being 6'3" tall, I tended to trim head down, especially in a dry suit. It took a while to learn to get stable (like not turtle-ing) and if I wound up severely head down and/or inverted (like going straight down a chute or looking at something upside down), it was a challenge to get back to normal. It took getting different tanks, smaller wings, moving the tanks and wings around, switching backplates (between AL and SS) to get it to the point where I could keep a good cave trim most of the time.

Accessing your valves behind your head where you can't see what is happening and worrying/checking for valve roll-off is a pain also. It didn't help that my left shoulder is not as flexible as right due to a motorcycle accident.

Carrying and walking cave-filled LP108s out of your car, to the water and out was not much fun either. I did pull muscles in my back several times doing this.

The first time I tried SM, it was like the clouds parted, the sun came out, and the birds started singing. The feeling of freedom and balance was incredible. No more heavy crap on your back. I immediately knew that I would NEVER dive my my LP108s BM doubled again. I kept the LP85s doubled for a while, but finally separated those also. After a few minor adjustments of tank fore-aft position and some trim weights if I was diving wet, I felt like I could soar like Steve Bogaerts in his SM videos (well maybe not quite like Steve - he is incredible). I could roll around sideways, forwards and backwards with minimal effort. You still need body control to remain cave trimmed, but the feeling of needing to keep your tanks balanced was gone. I was then able to concentrate on dry suit air (bubble) management to fine tune my trim.

Anyway, like I said, I don't see much of a reason to BM doubles again and yes, I think that eventually SM doubles will eclipse BM for most people that need to dive doubles, except for maybe a few diehard GUE/DIR types, but I suspect that is changing also.

---------- Post added March 13th, 2013 at 12:53 PM ----------

According to Curt Bowen's article in ADM (great read, btw), an al80 tank can be drained from FULL to EMPTY in something like 2.5mins via a freeflowing reg at 99ft. Average human breathing rate is like 12breaths/min, with an inhale duration of 1.5-2seconds. Lets pretend, for fun, that the ability to modulate flow precisely with 'feathering' the valve is difficult, and this is perhaps amplified while under stress. For the sake of argument.

By feathering the valve ~12 times per min (and that's on the low end, I would bet that a stressed diver's breathing demands are a wee bit higher), how many 1.5-2 seconds valve openings are you going to get? If I did the math right (and it's a bit late here, so I might have goofed, check me), I get 8.33mins. A FULL tank is now reduced to 8mins and change at 99ft. And that's for a 12bpm breathing rate. Up the rate to something a bit more realistic, and its bad news. Count the fact that you probably breathed some of it already, and that tank is hurtin' bad.

By biggest beef with SM is that a real failure effectively makes you lose half your gas. You might be able to get at some of it, but not easily. In BM, you get it all. Everything you have left is yours to use, no games no gimmicks. You can 'look' at your valves all day long, but broke is broke.

And there are more O-rings on a 1st stage than the DIN one. A failure of one of those other ones is gunna be a bad time, too.

Have you even tried this?? I have practiced it, although a simulated failure (holding the purge button open).

The point is that once you start loosing air in BM, you have to be very good and fast to identify what is really happening to take any corrective action before loosing any substantial amount of gas. If for some reason you do have to feather a BM valve (which I admit is not likely) it would be a major pain to do.

In SM, you have TWO separate gas systems (read redundancy), and with proper gas management it should give you the reserves you need to exit. That is why OC solo diving is (or should be) done in SM. In a team, you even have even more options. In BM, if you have a catastrophic gas failure and can not (or do not) handle it properly, you may lose ALL of your gas and then your buddy (or a stage if you are carrying one) is your ONLY option. Solo you are screwed.

Curt Bowen, BTW, dives SM as well as rebreathers (I am sure he also has considerable experience in BM doubles - most people at that level do).

 

[PfcAJ]

"should give you the reserves". Nope.

 

[LiteHedded]

Carrying and walking cave-filled LP108s out of your car, to the water and out was not much fun either. I did pull muscles in my back several times doing this.

harden up.