why did GUE , DIR take so long to adopt sidemount.

[Dhboner]

I can accept the notion that sidemount isn't "better" than back mount but I get frustrated with the suggestion that it is "inappropriate". Switching regs becomes second nature quickly and actually ensures that you are completely comfortable removing a reg from your mouth...even in REALLY cold water! Feathering a valve is very easy and a skill that I practice almost every dive (along with other more conventional skills). I would never try to convert someone to sidemount but it gets a little tiresome defending it to legions of backmount divers who look at my kit like a recipe for disaster.

 

[Bennno]

I think there are distinct downsides to SM. The reg switching does add complication (however slight it may be), certain failures result in loss of half your gas, and donating gas means the receiver only has access to half the remaining gas volume. Fixing that requires switching to the other bottle at some point during exit/ascent and stowing the other hose. Ain't nobody got time for that.

Switching is a super tiny downside.
If you lose the one whole tank due to some valve failure you would also lose the same amount of gas is BM. If it's a problem with the reg/hose you would still be able use a portion of the gas in many cases and there should be enough gas in the other tank to get you out.
If I had to feather, I'd feather as long I'm not busy, in that case I'd switch to the good reg.
I think SM is just fine for most dives and so is BM.

I do not buy for a second the idea of swapping regs underwater, and I barely accept feathering. Those are both great pool techniques, but in real life? Naw dawg.

Of course not. Does anyone teach this?

 

[PfcAJ]

If you lose the one whole tank due to some valve failure you would also lose the same amount of gas is BM. If it's a problem with the reg/hose you would still be able use a portion of the gas in many cases and there should be enough gas in the

Nope, BM tanks are connected with a manifold. Closure of 1 valve till leaves the gas accessible.

 

[Bennno]

Nope, BM tanks are connected with a manifold. Closure of 1 valve till leaves the gas accessible.

If you can still open an close the valve, yes. In that case you would likely be able to access the gas in SM too though. If you somehow rip the reg of the valve or the turrent (if you have one) of the reg, sure, you'd be better off in BM... but is it that much more likely to happen than having the manifold fail?
You should try SM diving (some more), all the kids are doing it.

Have you heard of an accident were someone would have been better off in BM?

 

[PfcAJ]

it doesnt have to be some big dramatic thing. I can be as simple as a stick punctures the 2nd stage diaphragm or a stupid oring extrudes.

 

[DA Aquamaster]

Nope, BM tanks are connected with a manifold. Closure of 1 valve till leaves the gas accessible.

I think what he is suggesting is that if you have a failure like an extruded neck o-ring, where you have to isolate to save the gas, you're losing just as much gas in BM as SM.

In fact, you're actually losing a little more in BM as the manifold will be moving gas from the high pressure side to the side losing gas, and it will keep doing that until the isolator valve is closed. In SM, you don't have that same gas exchange.

 

[PfcAJ]

I think what he is suggesting is that if you have a failure like an extruded neck o-ring, where you have to isolate to save the gas, you're losing just as much gas in BM as SM.

In fact, you're actually losing a little more in BM as the manifold will be moving gas from the high pressure side to the side losing gas, and it will keep doing that until the isolator valve is closed. In SM, you don't have that same gas exchange.

I will concede that, however rare it might be. I've seen a plenty of scuba stuff break between the valve (bonnet oring is my fav) all the way to the 2nd stage, but never once tank oring. I've heard (but never witnessed) of burst plugs leaking a bit, too.

 

[DA Aquamaster]

Have you heard of an accident were someone would have been better off in BM?

it doesn't have to be some big dramatic thing. I can be as simple as a stick punctures the 2nd stage diaphragm or a stupid o-ring extrudes.

I agree that some circumstances can leave you with more accessible gas in back mount - but it's rare, and it's a non issue.

For example, I made my first gas switch and noticed I had picked up a rock in the exhaust valve that left the reg breath very wet and anything more than a very slow inhale would bring water with it. It would not shake out and couldn't be purged out. In back mount all of the gas would have still been available through the remaining regulator. However in side mount, it left half the gas inaccessible for any practical breathing purpose (although the inflator still operated).

The default option in back mount is to switch to the other second stage and abort the dive - as you won't continue the dive with an inoperative second stage anyway.

That's also the same option in side mount, and with proper gas management you'll have adequate gas in either tank to exit the cave - even at max penetration, plus you've got a third in reserve in your team mate's tanks.

It's true you potentially have more gas in reserve in back mount, but it's in excess of what you need.

-----

In this instance, the problem was fixable and since the bottom was rock and the flow was low, I switched back to the first tank, turned off the leaky reg, screwed off the cover, removed the friction ring and diaphragm, shook out the pebble, put it back together, tested it and continued the dive, with a total interruption in the dive of about 90 seconds. The same thing could be done in back mount, but it's much easier when the second stage is on a 5' hose rather than an 18" to 22" hose.

 

[Kevrumbo]

The problem with Classic Independent Doubles technique with Sidemount is that after prescribed amount of psi/bar consumed, you have to continually alternate breathing & switching out 2nd stage regs between the two independent tanks with both cylinder valves remaining open in order to balance the tanks' trim. The real problem that arises is if you're scootering in open water into a strong current, there is the potential for the un-used 2nd stage reg to start free-flowing and losing gas without you noticing it (a practical solution for this is to clip the unused reg to a bungee necklace right underneath your chin -and then you would more easily recognize/sense a free flow condition)...

Also, inside of a wreck there can be a lot of "Toxic Brew" in the machine spaces/engine rooms/cargo holds -especially on the 70 year-old WWII Truk Lagoon Wrecks (fuel oil, caustic aviation gasoline, chemical leakage etc)- you want to minimize taking out switching regs if at all lest you inadvertently take a mouthful of this foul soup. . .

UTD's Z-system sidemount always has you breathing the long hose at working operational depth, no switching regs to balance out cylinders as in Independent Doubles technique. To balance the cylinders' trim as you consume gas from each tank, Z-system technique calls for alternately turning one side tank on and then turning the other side tank off, each connected via Swagelock QC6's through the common Distribution-Block or Iso-Fold Manifold.

 

[kensuf]

Why not? Going into a place that you shouldn't be in is really not a gear issue but a poor judgement issue imho. BM divers can get themselves in trouble too.
How many dives are really being done these days that you can only safely do in SM or BM? Hardly any.
I don't get why people like you and AJ think that SM diving is not as safe as BM. For most dives, I don't think it makes much difference as long as you are properly trained and have the right mindset. I would love to see GUE getting into SM training... It'll be good for the industry, all these rinky dink agencies out there need more competition.

Now, as for your rebreather point. I don’t think you can compare them to SM at all. Breathers are dangerous and all this 'rec' rebreather stuff is bs but sidemount is not more dangerous than BM.

I would like to do a GUE workshop or course and learn more about ratio deco and project stuff but I don't what to buy a bunch of extra gear that would never use.

I appreciate your ability to read my mind.

I don't think sidemount is inherently more dangerous, and I don't have any issue with someone diving sidemount. Heck, I have a sidemount rig and I sidemount my bailout bottles from my rebreather.

The only real risk that I see in sidemount configuration is losing a reg, you will lose 1/2 of your gas in that situation. The idea of switching regs while holding your breath in a stressful situation is right up there with unicorns and rainbows. But, if you lose a reg you should call the dive and head home anyway, so it's a manageable risk.

However, here are some cons I see in sidemount:

1. increases task loading the first few times you dive it with the constant gas switching. Someone learning how to cave dive is already tasked loaded enough, and really doesn't need the extra bit of task loading involved with learning sidemount at the same time. IMHO, beginning technical / cave divers are better served diving backmount, OR mastering sidemount before undertaking technical training.

2. Is less efficient. When I dive backmount I can be suited up and in the water in a fraction of the time it takes when diving sidemount (how many trips do you make to the water?). Ditto for breaking gear down.

3. Is frequently taught in a sloppy style that leads to damage to caves. Ever notice those twin furrow trails in clay floors? Look at the antenna that are sticking out from under your armpits to understand how they happened.

But these are just my opinion, and while I think newer technical / cave divers will be better served by learning backmount first, as long as someone isn't hurting themselves or others, and their config is safe, then knock yourselves out.